Fundamentals of 3D food printing and applications 9780128145647, 0128145641

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Fundamentals of 3D Food Printing and Applications

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Fundamentals of 3D Food Printing and Applications

Edited by Fernanda C. Godoi Bhesh R. Bhandari Sangeeta Prakash Min Zhang

Academic Press is an imprint of Elsevier 125 London Wall, London EC2Y 5AS, United Kingdom 525 B Street, Suite 1650, San Diego, CA 92101, United States 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom Copyright Ó 2019 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein).

Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN: 978-0-12-814564-7 For information on all Academic Press publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Andre Gerhard Wolff Acquisition Editor: Nina Rosa de Araujo Bandeira Editorial Project Manager: Susan Ikeda Production Project Manager: Divya Krishna Kumar Cover Designer: Miles Hitchen Typeset by TNQ Technologies

Contents List of Contributors Preface

1. An Introduction to the Principles of 3D Food Printing

xi xiii

1

Fernanda C. Godoi, Bhesh R. Bhandari, Sangeeta Prakash and Min Zhang 1.1 Introduction 1.2 3D Printing Techniques 1.2.1 Inkjet Printing 1.2.2 Extrusion-Based 3D Printing 1.2.3 Assessment of Printing Quality 1.3 Heating Mode: Powder Layer Binding 1.4 Summary and Future Directions References

2. 3D Food Printing Technologies and Factors Affecting Printing Precision

1 3 3 6 11 14 15 16

19

Zhenbin Liu and Min Zhang 2.1 Introduction 2.2 3D Food Printing Technologies and Factors Affecting Printing Precision 2.2.1 Extrusion-Based Printing 2.2.2 Selective Laser Sintering 2.2.3 Binder Jetting 2.2.4 Inkjet Printing 2.3 Summary and Future Directions References

3. Critical Variables in 3D Food Printing

20 20 23 30 32 34 35 37 41

Antonio Derossi, Rossella Caporizzi, Ilde Ricci and Carla Severini 3.1 3D Printing Technology Applied to the Food Sector 3.2 Structural Configuration of 3D Printers 3.2.1 Stepper Motors Drive the Movements of a 3D Printer in Four Axes: Basic Features and Their Effects

41 47 51 v

vi Contents 3.3 Computer-Aided Design Systems to Create 3D Virtual Models of Food 3.4 Process Planning of 3D Food Printing 3.4.1 Basic Principles of the Slicing Software to Prepare 3D Food Printing 3.4.2 Printing Variables and Their Effects on the Quality of 3D Edible Objects 3.5 The Firmware of the 3D Printer: Basic Principles and Settings That Affect the Printing Quality 3.6 G-Code: The Language To Drive Printers and To Optimise Printing Quality 3.7 Conclusions References

4. Cereal-Based and Insect-Enriched Printable Food: From Formulation to Postprocessing Treatments. Status and Perspectives

54 60 62 63 80 83 87 88

93

Rossella Caporizzi, Antonio Derossi and Carla Severini 4.1 Introduction 4.2 3D Printing Technologies for Cereal-Based Formulations 4.3 Factors Affecting the Printability of a Dough 4.3.1 Effect of Ingredients and Nutritional Compounds in the 3D Printing Process 4.3.2 The Use of Binding Agents to Improve the Printability of Dough 4.4 Postprocessing Technologies 4.5 Textural Properties of 3D-Printed Cereal-Based Products 4.6 Printing Variables Affecting the Quality of Cereal-Based Products 4.7 Innovative Food Formulations in 3D Printing: The Case of Cereal-Based Products Enriched With Edible Insects 4.7.1 Nutritional Properties of Edible Insects 4.7.2 Current Research in 3D Printing for Obtaining Insect-Enriched Products 4.8 Conclusions References

5. 3D Printed Food From Fruits and Vegetables

93 94 97 98 100 102 104 107 108 108 110 113 113 117

Ilde Ricci, Antonio Derossi and Carla Severini 5.1 Introduction 5.2 Potential Application of 3D Printing Technology for Vegetable-Based Products 5.2.1 Potential Nutritional and Healthy Properties of 3D Printed Fruit and Vegetables Used for 3D Printing

117 118 119

Contents vii

5.3 Processing Steps for Fruit and Vegetable Printing 5.3.1 Selection of Raw Fruits and Vegetables and Designing of Personalised Food Formulas 5.3.2 Processing Steps for Preparing Fruits and Vegetables for 3D Printing 5.4 Settings of Conditions for Fruit and Vegetable 3D Printing 5.5 Methods to Improve the Shelf-Life of Vegetable 3D Printed Foods 5.6 The Use of Fruit and Vegetable Waste for 3D Food Printing as Future Perspectives 5.7 Conclusion References Further Reading

6. 3D Printing Chocolate: Properties of Formulations for Extrusion, Sintering, Binding and Ink Jetting

123 126 129 134 139 141 143 144 148

151

Matthew Lanaro, Mathilde R. Desselle and Maria A. Woodruff 6.1 Introduction 6.2 Properties of Chocolate 6.2.1 Chocolate Structure 6.2.2 Chocolate Rheology 6.3 Chocolate Formulations 6.3.1 Common Chocolate Products 6.3.2 Specialty Chocolate Products 6.4 3D Printing Platform 6.5 3D Printing Chocolate: Extrusion 6.5.1 Process Optimisation 6.6 3D Printing Chocolate: Sintering and Binding 6.7 3D Printing Chocolate: Inkjet 6.8 Future Trends References

151 152 155 157 158 158 160 161 163 166 168 169 171 171

7. Potential Applications of Dairy Products, Ingredients and Formulations in 3D Printing

175

Megan M. Ross, Alan L. Kelly and Shane V. Crowley 7.1 Introduction 7.2 Overview of Relevant 3D Printing Technologies 7.3 Structure-Forming Mechanisms Involving Milk Components 7.3.1 Milk Proteins 7.3.2 Milk Fat 7.3.3 Lactose 7.4 Studies of Printable Dairy Structures 7.5 Analytical Tools for 3D-Printed Dairy Applications

175 177 181 181 184 185 186 188

viii Contents 7.6 Case Study: 3D Printing of Processed Cheese 7.7 Research Needs, Challenges and Opportunities 7.7.1 Safety and Acceptance 7.7.2 Research Challenges 7.7.3 Industrial Advantages and Disadvantages References Further Reading

8. Material, Process and Business Development for 3D Chocolate Printing

193 197 197 197 199 200 206

207

Liang Hao, Yan Li, Ping Gong and Weil Xiong 8.1 Introduction 8.2 Commercial Feasibility Study 8.2.1 Chocolate Background 8.2.2 Chocolate Status Quo 8.2.3 Research on the 3D Chocolate Printing Business Model 8.3 Development of Chocolate 3D Printing Technology 8.3.1 Chocolate Features 8.3.2 Chocolate Additive Layer Manufacturing 8.3.3 Experimental 8.3.4 Results and Discussion 8.3.5 Conclusions 8.4 Optimisation of Chocolate 3D Printing Technology 8.4.1 Adaptive Extrusion Layer Thickness Optimisation Based on Area Change Rate 8.4.2 Layer Scanning Speed Optimisation Based on Perimeter Change Rate 8.4.3 Conclusions 8.5 Extension of Chocolate 3D Printing Application Technology 8.5.1 Healthcare Products and Chocolate 3D Printing 8.5.2 Feasibility Experiment of Adding Healthcare Products 8.6 Summary and Outlook References Further Reading

9. Creation of Food Structures Through Binder Jetting

208 210 210 210 211 216 216 219 221 223 229 230 230 233 236 237 238 240 251 252 254

257

Sonia Holland, Tim Foster and Chris Tuck 9.1 9.2 9.3 9.4

Introduction to Binder Jetting Powder Characteristics and Interlayer Cohesion Powder Binding Mechanisms Suggested Analysis

257 260 262 265

Contents

9.5 Formulating a Functional Printing Ink 9.5.1 Ink Jetting Theory 9.5.2 Viscosity Considerations for Ink Jetting 9.5.3 The Effects of Additives to Enhance Viscosity 9.5.4 Surface Tension and Density 9.6 Controls and Considerations During and Postprinting 9.6.1 Printer Settings 9.6.2 Combining Powder and Ink During Print 9.7 Postprocessing 9.8 Application and Outlook for Food Materials References

10. 3D Food Printing Technology at Home, Domestic Application

ix 267 267 269 271 273 274 274 276 278 278 283

289

Estefanı´a Rubio and So`nia Hurtado 10.1 Global Scope 10.2 3D Food Printing Technology 10.2.1 How Does 3D Food Printing Work? 10.2.2 3D Food Printers 10.3 Food Preparations for Extruder-Based 3D Food Printing 10.3.1 Food Preparation Examples Related to Print Purpose 10.3.2 Rheological Limitations and Technical Considerations 10.3.3 3D Printer Device-Related Technical Considerations 10.4 3D Food Printing at Home 10.4.1 A 3D Food Printer Conceived as a ‘Mini Food Factory’ 10.4.2 Versatility: Everyday Cooking and Fine Cuisine, at Home and Hospitality 10.4.3 Traditional Recipes and Adapted Formulations 10.4.4 Reduce, Reuse, Recycle. Environment Friendly and a Potential Contributor to Circular Economy 10.4.5 Domestic Applications with Dietetic Purposes 10.5 Limitations, General Considerations and Conclusions References

11. Prosumer-Driven 3D Food Printing: Role of Digital Platforms in Future 3D Food Printing Systems

290 291 291 292 300 301 302 307 308 308 310 311 314 315 322 324

331

Siddharth Jayaprakash, In˜igo Flores Ituarte and Jouni Partanen 11.1 11.2 11.3 11.4

Introduction What Is Prosumption? Evolution of Prosumption Current State of 3D Food Printing 11.4.1 Market Segmentation 11.4.2 3D Food Printing Ecosystem and Associated Value Chains

331 333 334 335 335 337

x Contents 11.4.3 Ingredient Portfolio 11.4.4 Machine Concepts 11.5 Food Prosumption With 3D Food Printing 11.5.1 Change Drivers 11.5.2 Future of Food 11.5.3 Digital Platform for 3D Food Printing 11.5.4 Futuristic Application Areas 11.5.5 Example Use Cases 11.5.6 The Impact 11.6 Conclusions References

12. Safety and Labelling of 3D Printed Food

340 341 342 342 343 345 345 348 350 351 352 355

Jasper L. Tran 12.1 Introduction 12.2 3D Printed Food’s Possibilities and Implications 12.2.1 3D Printed Food’s Endless Possibilities 12.2.2 Implications of 3D Printed Food 12.3 3D Printed Food’s Safety and Labelling Issues 12.3.1 Safety Issues 12.3.2 Labelling Issues 12.4 Conclusion References

13. Future Outlook of 3D Food Printing

356 356 356 358 361 362 365 368 369 373

Sangeeta Prakash, Bhesh R. Bhandari, Fernanda C. Godoi and Min Zhang 13.1 Introduction 13.2 Future of 3D Printing 13.2.1 Constructs with Varying Microstructure Leading to Novel Food Textures 13.2.2 Improved Texture-Modified Food for People with Swallowing and Chewing Difficulties 13.2.3 Increased Fruit and Vegetable Intake Among Children 13.2.4 Healthy Foods With Reduced Fat, Sugar and Salt 13.2.5 Preventing Wastage of Perishables and Sustainability 13.3 What to Expect in the Next 5 Years? References

Index

373 374 375 375 377 378 379 380 381

383

List of Contributors Bhesh R. Bhandari, School of Agriculture and Food Sciences, The University of Queensland, Brisbane, QLD, Australia Rossella Caporizzi, Department of Science of Agriculture, Food and Environment (SAFE) e University of Foggia, Foggia, Italy Shane V. Crowley, School of Food and Nutritional Sciences, University College Cork, Cork, Ireland Antonio Derossi, Department of Science of Agriculture, Food and Environment (SAFE) e University of Foggia, Foggia, Italy Mathilde R. Desselle, Queensland University of Technology (QUT), Science and Engineering Faculty, Brisbane, QLD, Australia Tim Foster, Division of Food Science, Sutton Bonington Campus, University of Nottingham, Loughborough, United Kingdom Fernanda C. Godoi, Tessenderlo Innovation Center e Tessenderlo Group, Tessenderlo, Belgium Ping Gong, Advanced Manufacturing Research Centre for Jewellery, Gemmological Institute, China University of Geosciences, Wuhan, China Liang Hao, Advanced Manufacturing Research Centre for Jewellery, Gemmological Institute, China University of Geosciences, Wuhan, China Sonia Holland, Division of Food Science, Sutton Bonington Campus, University of Nottingham, Loughborough, United Kingdom; 3D Printing and Additive Manufacturing Research Group, University Park, University of Nottingham, Nottingham, United Kingdom So`nia Hurtado, Former Lead Food Technologist at Natural Machines SL In˜igo Flores Ituarte, Department of Mechanical Engineering, Aalto University, Espoo, Finland Siddharth Jayaprakash, Department of Mechanical Engineering, Aalto University, Espoo, Finland Alan L. Kelly, School of Food and Nutritional Sciences, University College Cork, Cork, Ireland Matthew Lanaro, Queensland University of Technology (QUT), Science and Engineering Faculty, Brisbane, QLD, Australia Yan Li, Advanced Manufacturing Research Centre for Jewellery, Gemmological Institute, China University of Geosciences, Wuhan, China

xi

xii List of Contributors Zhenbin Liu, State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, China Jouni Partanen, Department of Mechanical Engineering, Aalto University, Espoo, Finland Sangeeta Prakash, School of Agriculture and Food Sciences, The University of Queensland, Brisbane, QLD, Australia Ilde Ricci, Department of Science of Agriculture, Food and Environment (SAFE) e University of Foggia, Foggia, Italy Megan M. Ross, School of Food and Nutritional Sciences, University College Cork, Cork, Ireland Estefanı´a Rubio, Former Researcher in Food Science and Technology at Natural Machines SL Carla Severini, Department of Science of Agriculture, Food and Environment (SAFE) e University of Foggia, Foggia, Italy Jasper L. Tran, University of Minnesota, San Francisco, United States Chris Tuck, 3D Printing and Additive Manufacturing Research Group, University Park, University of Nottingham, Nottingham, United Kingdom Maria A. Woodruff, Queensland University of Technology (QUT), Science and Engineering Faculty, Brisbane, QLD, Australia Weil Xiong, Advanced Manufacturing Research Centre for Jewellery, Gemmological Institute, China University of Geosciences, Wuhan, China Min Zhang, State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, China

Preface The increasing demand for personalised food has encouraged a period of innovation and experimentation with emerging techniques to customise texture, flavour and nutritional contents of foods. In this scenario, three-dimensional (3D) printing technology is an emerging technology that occupies a high rank because of its ability to create complex edible shapes and, at the same time, enable alteration of food texture and nutritional content required by specific diets. Although the first reports about 3D food printing are completing nearly a decade, most the existing literature is composed of research articles, patents, review papers and interviews in nonscientific magazines. This book provides a broad picture of 3D food printing technologies, including their working mechanisms within a broad spectrum of application areas, including but not limited to the development of soft foods and confectionary designs. Efforts have been devoted to provide a unique and contemporary guide to assist the correlation between the supply materials (edible formulations) and technologies (e.g., extrusion and inkjet into a powder bed) used during the construction of computer-aided 3D shapes. The book presents several chapters contributed by leading scientists working on 3D food printing technology. Chapter 1 presents an introduction to the principles of 3D food printing, emphasising the correlation within rheology behaviour and 3D printing techniques (inkjet and extrusion based). Chapter 2 highlights the importance of self-supporting mechanisms, process parameters, materials’ properties and pretreatment and postprocessing methods in achieving an accurate and precise printing in the printing process. A very interesting approach is presented in Chapter 3, which correlates each phase of the development of a 3D printed food with the algorithms used by a computer-aided design (CAD) and printability features of food-related products. The authors of Chapter 3 aimed to give the basic information to control printing movements, making possible the match between 3D food and virtual models as much as possible. The printability of several materials is described from Chapters 4 to 8. Chapters 4 and 5 present, respectively, information on the printing behaviour of cereal-based/insect-enriched and fruit/vegetable printed foods. Threedimensional printing of chocolate is explored in Chapters 6 and 8. Chapter 6 reviews the structural and rheological properties of chocolate formulations used to create these 3D printed products. Chapter 8 introduces a background of the

xiii

xiv Preface

development of the 3D chocolate printing and investigates the commercial feasibility of the chocolate supply chain-centric business models by computer modelling and simulation. Chapter 7 focusses on the structure-forming potential of dairy-sourced materials and gives an overview of the latest research in printable dairy structures. Chapter 9 describes the mechanisms involved in the creation of 3D printed food by means of binder jetting technology. Chapter 9 takes into consideration both powder and ink development, interactions during and after printing as well as the current status and outlook of binder jetting technology. In Chapter 10, the concept of 3D food printing technology being used as a mini-food manufacturing plant at home is introduced. To emphasise this trend, Chapter 11 creates an understanding on how digital platforms could work together with future 3D food printing systems to foster food prosumption. Chapter 12 covers the issues of safety and labelling in 3D printed food by utilising hypothetical scenarios. To finalise, a future outlook of 3D food printing is presented in Chapter 13. We believe that the compilation of data about the 3D printing behaviour of various edible formulations and knowledge on consumption trends (aligned to safety concerns) will help students, researchers and professionals in the food sector by guiding them to make a rational choice about the 3D printing technology for a given material that can be presented in liquid or powder form. We would like to thank all the contributors to the book, the scientific community, our publisher and family and friends who encouraged us to bring forward the first book on 3D food printing. Fernanda C. Godoi Bhesh R. Bhandari Sangeeta Prakash Min Zhang Editors

Chapter 1

An Introduction to the Principles of 3D Food Printing Fernanda C. Godoi1, Bhesh R. Bhandari2, Sangeeta Prakash2, Min Zhang3 Tessenderlo Innovation Center e Tessenderlo Group, Tessenderlo, Belgium; 2School of Agriculture and Food Sciences, The University of Queensland, Brisbane, QLD, Australia; 3 State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, China 1

Chapter Outline

1.1 Introduction 1.2 3D Printing Techniques 1.2.1 Inkjet Printing 1.2.1.1 Applicability of Inkjet Printing 1.2.2 Extrusion-Based 3D Printing 1.2.2.1 Melting Extrusion 1.2.2.2 Gel-Forming Extrusion

1 3 3 4 6 7 9

1.2.3 Assessment of Printing Quality 1.2.3.1 Shape Fidelity 1.2.3.2 Mechanical Properties of the 3D Printed Construct 1.3 Heating Mode: Powder Layer Binding 1.4 Summary and Future Directions References

11 11

13 14 15 16

1.1 INTRODUCTION Food products are rapidly evolving; therefore, all professionals in the food manufacturing field need to follow up the latest trends, best practices and tools to work effectively. Personalisation has been pointed as the driving force to disrupt traditional ways to produce and deliver food. Threedimensional food printing (3DFP) is constantly associated as a potential alternative to achieve personalisation and enchant a variety of customers. It should be minded, however, what is the type of personalisation required by each population. And, most importantly, the research in 3DFP is not meant to change the way food is consumed. In extrusion-based 3DFP, for example, the printable food should present paste-like consistency, and it is recommended

Fundamentals of 3D Food Printing and Applications. https://doi.org/10.1016/B978-0-12-814564-7.00001-8 Copyright © 2019 Elsevier Inc. All rights reserved.

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2 Fundamentals of 3D Food Printing and Applications

for printing doughs, vegetable or meat purees and confectionary. In powderbased 3DFP, powdered food such as sugar and chocolate can be used. Therefore, the driven force to develop expertise in 3DFP relies on finding the ideal application which, in turn, is dependent on the properties of food materials. Considering, for example, fused deposition modelling (FDM; the most common 3DFP technique) which is constantly used as an alternative to replace moulding processes of paste materials. The effective substitution of casting methods by FDM will only happen in applications where the set of fluid and/or semisolid foods into a mould does not attend the essential needs of the consumers, such as: l

l

l

the design of internal structures: this feature cannot be achieved by conventional casting methods used to shape food. By 3DFP, however, the internal structure of the food object can be tailored by means of infill percentages (in single-nozzle extrusion) and variations of the nutritional profile in the core structure (more than one nozzle is necessary); encapsulation of probiotics, vitamins and nutrients by means of coextrusion 3DF; and freshly mixing of ingredients to ensure the ideal texture.

Once one or more of the examples listed above fulfils the need of a population, the implementation of 3DP technology for food materials rely on the following points: l

l

l

l

Material: Material choice and deep understanding of its physicale chemical and rheological properties. 3DP technique: The choice of the 3DP technique is based on the material properties, applicability and postprocessing requirements. 3D design and path planning: 3D content is necessary to be generated as a first step of implementing 3DP. A wide variety of software is available, from beginners to advanced, to design the construct to be printed (e.g., SketchUp, Tinkercad and OnShape). The design is then converted to an .stl file and ‘sliced’ by a slicing software (e.g., Cura, Repetier and Simplify3D). A G-code is generated with the commands necessary to guide the printhead at predetermined conditions of speed, flow and temperature, for example. This is an important step once successful printing is closely related to the path-planning choice for the design. Assessment of printing parameters and printed object quality: Printing parameters and printed material quality can be assessed regarding shape fidelity (in comparison with the original design) and mechanical properties.

This chapter focuses on reporting the different types of 3D printing techniques and assessment of printing quality. An entire chapter of this book (Chapter 3) is dedicated to the practicable aspects of path planning that can enhance printability of various food materials.

An Introduction to the Principles of 3D Food Printing Chapter | 1

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1.2 3D PRINTING TECHNIQUES In this chapter, we describe the current 3D printing techniques applied to design food materials. They are classified according to the driving mechanisms of printing: inkjet, extrusion and heat source (powder layer binding). The deposition of liquid-based materials can be performed via extrusion and inkjet processes. Powder-based structures are printed by deposition followed by application of a heating mode (laser or hot air) or binder jetting (inkjet technology). Our discussions, however, are especially devoted on how the food constituents would behave during 3DP processes. Fig. 1.1 illustrates the schematic classification of 3DFP technologies as per the type of driven mechanism.

1.2.1 Inkjet Printing Inkjet printing (IJP) can be applied to the formation of 2D and 3D patterns upon deposition of liquid droplet onto a substrate guided by computer-aided design systems. Usually a printhead of IJP, the ink is jetted through channels of typically 20e50 mm. A 1-pL (picolitre) ink droplet is typically 13 mm across (Xaar, 2012). Inkjet printing (IJP) can be carried out continuously (C-IJP) or through drop-on-demand (DoD-IJP). Both methods occur by forcing a fluid through an orifice, which subsequently breaks up into a stream of droplets with the same volume but less surface area instability (Rayleighe Plateau instability phenomenon). In C-IJP, a high-pressure pump directs the liquid ink through an orifice between 50 and 80 mm in diameter, creating a continuous ink flow. C-IJP

FIGURE 1.1 Schematic diagram of various 3D food printing techniques.

4 Fundamentals of 3D Food Printing and Applications

operates at faster droplet generation rates than DoD-IJP; however, it requires the use an electrically conducting fluid which limits the application in food customisation. The DoD-IJP presents multiple heads (100e1000) and generally operates using thermal or piezoelectric heads. In a thermal inkjet printer, the printhead is electrically heated to generate pulses of pressure that push droplets from the nozzle. Piezoelectric inkjet printers contain a piezoelectric crystal inside the printhead which creates an acoustic wave to separate the liquid into droplets at even intervals. Employing a voltage to a piezoelectric material arouses a prompt change in shape, which in succession produces the pressure necessary to eject droplets from the nozzle. The fluid dynamics behaviour of the droplet ejected from a small opening was previously obtained from an approximate solution to the NaviereStokes equation. Three main parameters are adopted to predict the droplet jetting behaviour (Seerden et al., 2001): l

l

l

Re/We: Ratio between the Reynolds number (Re) and the Weber number (We) which is representative of trends observed on the viscous, inertial and surface tension forces on fluid flow. In Eq. 1.1, a, r, g and h stand for the characteristic length, density, surface tension, and viscosity of the fluid, respectively. Droplet spreading in absence of solidification (ε): Eq. 1.2, derived by Bhola and Chandra, where rmax and r are the maximum splat radius and initial drop radius, respectively, and q is the equilibrium contact angle that the droplet makes with the substrate. Splashing of liquid drops (K): splashing of the droplet upon jetting results in dimensional instability and lack of uniformity. Splashing occurs when the parameter K exceeds a critical value, Kc (Eq. 1.3).

rmax ε¼ ¼ r

Re ðgraÞ1=2 ¼ We h " We2 þ 12 3ð1  cosqÞ þ 4 K ¼ WeRe1=4

(1.1) #1=2 We2 Re1=2

(1.2)

(1.3)

1.2.1.1 Applicability of Inkjet Printing Inkjet printers generally handle low-viscosity materials; therefore, IJP does not find application on the construction of complex food structure. The technology is normally used in graphical decoration, fillings, microencapsulation and, at much lower extension, nanoprinted 3D constructs (usually bioprinting applications).

An Introduction to the Principles of 3D Food Printing Chapter | 1

l

l

5

Graphical decoration, fillings: The technology developed by Grood and Grood (2011) for dispensing a liquid onto layers can be classified as DoD deposition (US8556392B2, 2013). This technology was commercialised by the name of FoodJet printing and uses an array of pneumatic membrane nozzle jets which layers tiny drops onto a moving object. Several patents report the development of inks on edible substrates (US7029112B2, 2002) (US20160021907A1, 2013). The patent deposited by Mars Inc., for example, reports the use of piezoelectric printhead to print high resolutions of images that might be composed of fat or edible. The substrate, in this case, can include confectionary pieces with nonplanar and hydrophobic surfaces. The image reaches resolution greater than 100 dpi, preferably greater than 300 dpi (US7597752B2, 2012). The inkjet technology can also be used for flavour application on edible substrates, as described in US20080075830A1, assigned by Procter and Gamble Co (US20080075830A1, n.d.). Microencapsulation: Inkjet technology finds application on microencapsulation processes such as the one developed by Netherlands Organisation for Applied Scientific Research (TNO). Their invention reports a printhead that produces highly monodisperse droplets converted into highly monodisperse powders after drying. The printhead has 500 nozzles with capacity of 100 L/h. Fig. 1.2 illustrates examples of coreeshell particles made with

FIGURE 1.2 Netherlands Organisation for Applied Scientific Research (TNO)’s encapsulation printer and examples of coreeshell structures: mint syrupewax and linseed oilecarrageenan (TNO, 2017).

6 Fundamentals of 3D Food Printing and Applications

l

TNO’s encapsulation printer, mint syrup core with wax shell (left, bottom) and linseed oil with carrageenan shell (right, bottom) (TNO, 2017). 3D constructs: In 3DFP applications, the inkjet technology classified as drop-on-powder has been used to eject binder solution onto a thin layer of powder following a sliced 2D profile generated by a computer 3D model. The technique is generally named binder jetting and will be detailed in Chapter 9. The binder plays an important role of joining adjacent particles together, creating, therefore, a 3D construct. This can occur due to the dissolutionefusion or cross-linking of the particle surfaces (Peltola et al., 2008). An example of this technology applied for food design is the 3D System’s ChefJet printer which uses the Z-Corp inkjet process to produce a broad range of confectionary recipes including sugar, fondant and sweet and sour candy in a variety of shapes and flavours. TNO researchers described a liquid binding-based method called powder bed printing. In this method, edible 3D objects are produced by spatial jetting of food fluid (binder) onto a powder bed containing formulated food powder composed of a water-soluble protein and/or a hydrocolloid (Diaz et al., 2014). Inkjet printing technology has been also used to build 3D constructs in a nanoscale, such as printing of conductive inks with metal nanoparticles for electronics (Vaithilingam et al., 2018) or cell-laden hydrogels for bioprinting applications (Gudapati et al., 2016).

1.2.2 Extrusion-Based 3D Printing Unlike DoD-IJP methods, extrusion-based techniques rely on the flow of a continuous ink in a layer-by-layer fashion, generally highly concentrated colloidal inks. The concentration in total solids can range from 5% to 50%, depending on the capability of the material on forming gel or achieving paste consistency. The ink flows through the nozzle upon the application of a pressure gradient DP along with the length (l). Therefore, a radially varying shear stress (zr) develops as per Eq. 1.4, where r is the radial position within the nozzle. At the nozzle wall centre (r ¼ R), there is zero velocity, and in the centre (r ¼ 0), the velocity is at a maximum (Lewis, 2002). zr ¼

rDP 2l

(1.4)

Ideally, the extruding material should show fast, solid-like response throughout the deposition process. This feature can be evaluated regarding the yield stress (YS) which, in turn, is classified in two types for some fluids: (1) static YS: stress required to flow from a rest state; and (2) dynamic YS: stress required for a fluid in motion to continue flowing. Both YSs are important to ensure printability because the material must flow through the nozzle, overcoming the static YS. However, sufficient dynamic YS is required to resist

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high shear rates and still form objects with minimum deformation after printing (Lewis, 2002; Smay et al., 2002). Pneumatic and mechanical (piston or screw) methods are usually used to extrude food materials for 3DFP applications. The piston-driven configuration generally provides more direct control over the flow of viscous materials through the nozzle, while the screw-driven system might favour the spatial control and can be beneficial for dispensing and mixing materials with higher viscosities. As an example, the screw-driven system used by Mantihal et al. (2017) helped to ensure the homogeneity is melted grated chocolate while printing (Mantihal et al., 2017). Pneumatic configurations can sometimes be disadvantageous due to delays of the compressed gas volume in pneumatic systems, although pneumatic systems can also be suited to dispense highviscosity materials and have the advantage of being driven by simpler components, with the force limited only by the air pressure capabilities of the system (Murphy and Atala, 2014). Depending on the materials used in extrusion processes, the binding mechanisms may happen by the accommodation of layers controlled by the rheological properties of the materials (nonphase change extrusion), solidification upon cooling (melting extrusion) or gel-forming extrusion. Nonphase change 3DP extrusion is usually performed without temperature control and has been applied to print 3D constructs made of materials such as dough (Yang et al., 2018b) and meat paste. The viscosity of the material is critical to be both low enough to allow extrusion through a fine nozzle and high enough to support the structure postdeposition. Thickener agents, or additives, can be used to achieve the desired rheological properties but must comply with food safety standards. In a multicomponent food system, the synergism within ingredients impart homogeneous distribution of the printing paste on the printer reservoir, uniform flow throughout the nozzle opening and instant recovery after extrusion. Rheological properties are also relevant in melting extrusion and gel-forming extrusion; however, the phase transitions taking place during extrusion will determine the quality of the final printed construct. The following topics describe the key characteristic of melting extrusion and gel-forming extrusion types of 3DFP technologies.

1.2.2.1 Melting Extrusion Materials suitable for melting extrusion can be presented in three forms: pastelike, powder (or solid pieces) and filament (rare in food applications). The temperature control during extrusion-based 3D printing of pastes rich in fat or sugar (mostly amorphous) is essential to ensure printability. As an example, fatty acids with larger numbers of carbon atoms depict higher melting point. In an opposite way, a larger number of double bonds result in lower melting point. Lipton et al. (2010) optimised the content of butter fat in traditional dough recipes to avoid liquefaction of the printed structure when baked

8 Fundamentals of 3D Food Printing and Applications

(Lipton et al., 2010). The same researchers have used bacon fat as flavour enhancer to print turkey meat puree in combination with transglutaminase additive. Chocolate is the most common edible ink due to its melting behaviour. It can be fed into the printer reservoir in melted state (paste-like) or in powder form. A recent study conducted by Mantihal et al. (2017) used grated chocolate to print intricate shapes. The dimensions (wall thickness, height and diameter), weight as well as physical properties (melting properties, flow behaviour, snap ability) of the 3D printed chocolate were evaluated. The nozzle temperature before deposition was maintained at 32 C to extrude the melted state of the sample, as the flow behaviour curves indicated that the melting of chocolate started between 28 and 30 C. The operating temperature adopted by Mantihal et al. (2017) was within the range observed in previous studies in which temperatures from 28 to 40 C were employed (Hao et al., 2010; Sewell et al., 2009). The formulation of chocolate self-supporting layers is challenging due to the complex crystallisation behaviour exhibited by cocoa butter, the main structuring material in chocolate and confections. Six different crystal polymorphs have been identified for cocoa butter (Marangoni and McGauley, 2003). The correct polymorph should be produced in the chocolate for its best melting, textural and shelf-life properties. The chocolate deposition directly into a 3D object by means of extrusion was introduced by researchers from Cornell University using a Fab@home fabrication system (Schaal, 2007). Their studies, however, did not look at the materials’ properties and geometrical accuracy of the extrudate. Hao et al. (2010) revealed the factors influencing the geometrical precision of the chocolate deposition: (1) nozzle aperture diameter, (2) optimum nozzle height from the forming bed, and (3) the extrusioneaxis movement. The expertise of the research group led by Hao enabled the foundation of ChocEdge Ltd, a spin-off company from the University of Exeter, which pioneered the commercialisation of 3D chocolate printers. Production and printing of edible filaments are rare. Only a patent was found on the incorporation of an active ingredient such as an oil extract for taste, odour or medicinal benefit, into a filament made of polyvinylpyrrolidone, starch and thickening (or binding) agents. The hot melt extruded presented by the invention shows a 1.75 or 3 mm. When printed, the thermoplastic has good strength, stiffness and physical properties, and can be 3D printed in any shape (US20160066601A1, 2014). In pharma applications, however, it is possible to find few works on the loading of medicines into thermoplastic filaments. Goyanes et al. (2015) produced different filaments containing paracetamol or caffeine in a water-soluble polymer (polyvinyl alcohol) suitable for printing into pharmaceutical dosage forms. They used a dual FDM 3D printer to print a diverse range of multilayer capsule-shaped devices with modified drug release profiles to meet the needs of specific therapies. Sadia et al. (2016) developed pharmaceutical filament composed of

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methacrylic polymer (Eudragit EPO) and thermally stable filler, tribasic calcium phosphate. They tested four model drugs with different physicochemical properties: 5-ASA (5-aminosalicylic acid), captopril, theophylline and prednisolone. The production of filaments followed by FDM can be advantageous to avoid postprocessing steps usually required for 3DP using semisolid starting materials through a syringe-based tool head. For food applications, within a limited range of ingredients, it is believed that edible or food-grade filaments will find application in the confection of food packaging.

1.2.2.2 Gel-Forming Extrusion The rheology of gels can be tailored based on the fraction and/or colloidal forces. When stressed beyond their gel yield point (s), they exhibit shearthinning flow behaviour y due to the attrition of particleeparticle bonds within the gel, as described by Eq. 1.5. s ¼ sy þ Kgn

(1.5)

where s is the shear stress, n is the shear thinning exponent ( 1 (also related to the gelation visual aspects). Illustration based on Ouyang et al., 2016.

of droplet at the nozzle end will be observed. When the ink is too concentrated or overgelation takes place, a stiff filament with fractures throughout its length will be observed. Ouyang et al. (2016) demonstrated that the printability can be correlated with level of circularity of the internal square areas in a lattice structure. Their work reports the use of Eqs. 1.8 and 1.9 to evaluate printing quality of gel-like inks. It has been stated that when the ideal gelation is

An Introduction to the Principles of 3D Food Printing Chapter | 1

13

achieved, Pr ¼ 1. At conditions of undergelation and overgelation, Pr < 1 and Pr > 1, respectively (Ouyang et al., 2016). Circularity ¼ C ¼

4pA L2

p 1 L2 Pr ¼ $ ¼ 4 C 16A

(1.8) (1.9)

1.2.3.2 Mechanical Properties of the 3D Printed Construct Texture profile analysis (TPA) for the semihard materials and hardness test of solid food constructs is measured by using a texture analyser. TPA as a large deformation test has been applied in many works to evaluate the mechanical properties of 3D food printed constructs made of soft materials (e.g., gels or purees). The results obtained can be correlated with texture attributes that can be manifested in macro- or microstructure. The applied force, force working distance and time of deformation can be measured to get textural properties such as chewiness and gumminess which are important in gummy candy, for example, due to the ductile characteristics. Two-peak force curve can be obtained from TPA from the twice penetrating method commonly applied to food products. Hardness, adhesiveness, springiness, gumminess and chewiness are relevant attributes to be determined for gel-like systems (Rosenthal, 2010). Kim et al. (2017) analysed the mechanical properties of a range of gels for 3D printing applications, including gellan gum, methylcellulose, guar gum, locus bean gum, hydroxypropyl methylcellulose, xanthan gum and gelatin. They observed that the hardness of all samples increased significantly with by augmenting the concentration. Interestingly, gellan gum and gelatin depicted stiffer behaviour (high gel strength; however, no information was provided regarding the bloom of the gelatin used). High hardness was accompanied by high levels of fracturability in these gels which is prejudicial during extrusion (Kim et al., 2017). Springiness attribute in gels can be associated to the behaviour presented by certain polymers of ‘remembering’ its previous shape. Kim et al. (2017) classified as printable the gels with low springiness and wide gel strength. The springiness of methylcellulose (0.85  0.0064) and xanthan gum (0.87  0.0026), at concentration of 8% w/w, was lower than springiness obtained by the other hydrocolloids tested. The values were comparable to the springiness of cheese (0.88) which is considered as natively printable material (Kim et al., 2017). Yang et al. (2018a,b) observed the effect of starch addition in the mechanical properties of lemon juice 3D-built gels. The increase of starch resulted in more significant increase of hardness and gumminess as a consequence of the more compacted network afforded by the starch molecules (Yang et al., 2018a). A similar trend was observed by Azam et al. (2018) on

14 Fundamentals of 3D Food Printing and Applications

their investigation of the starch addition in orange concentrates. The highest hardness, adhesiveness and gumminess values were observed for the highest concentration of starch (30% w/w) which was related to the crystallinity augment with the presence of sugar and acid in combination with starch granules (Azam et al., 2018). Recently, Wang et al. (2018) correlated gel strength (force required to break the gel, measured by TPA) with the increasing concentration of NaCl in surimi gels. The authors observed an upward trend of gel strength with the increasing concentration of salt in the system (max of 7.2 N; 2 higher than the sample prepared without NaCl). The behaviour was associated with the swelling of myofibrillar protein caused by the increment on the ionic strength which, in turn, promoted an increased proteineprotein interaction (Wang et al., 2018). The mechanical strength of hard materials (solids) cannot be measured by means of TPA analysis. Lille et al. (2018) used a texture analyser to measure hardness (cutting test) of oven-dried and freeze-dried protein-rich 3D printed shapes. Briefly, the samples were placed on a slotted insert and cut in the middle over their whole width (w2.5 cm) with a knife blade (model HDP/BS) at a speed of 1 mm/s. Hardness was obtained by recording the maximum force of the first peak. In both drying conditions, lower hardness values were observed by replacing part of semiskimmed milk powder by cellulose nanofiber (Lille et al., 2018). Mantihal et al. (2017) have studied the snap quality of 3D printed chocolate structures. Their work reported the influence of supports on the snap force, using a texture analyser. It was observed that the constructs with the crosssupport required a higher force to break the sample with >56.00 N and had a high snap quality and firmer texture as compared to other sample designs. Samples built without internal support required less force to break (snap force < 16.0 N). Cross-support structure enabled holding the main angle of the chocolate geometry (Fig. 1.6), keeping it firm and stable as compared to sample with parallel support and without support (Mantihal et al., 2017).

1.3 HEATING MODE: POWDER LAYER BINDING CandyFab machines, a project by Evil Mad Scientist Laboratories (California, United States), use selective hot air sintering and melting (SHASAM)

Break probe Cross support

Force (N)

Break probe Parallel support

Force (N)

Break probe

Force (N)

No support

FIGURE 1.6 Illustration of positioning of three different designs of printed chocolates for snap properties analysis by the texture analyser (Mantihal et al., 2017).

An Introduction to the Principles of 3D Food Printing Chapter | 1

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technology to print sugar-based 3D objects. SHASAM technology uses a narrow, directed, low-velocity beam of hot air to selectively fuse together sugar powder, building a 2D picture out of fused powder. At first, the powder bed is slightly lowered; then a thin flat layer of particles is spread to the top of the bed, and hot air is directed by the software at localised areas to selectively fuse the media in the new layer. The freshly printed 2D object is indeed fused to any overlapping connected areas in the previous layer. By performing this step again, a 3D object is gradually built up. Upon finishing the 3D object, the bed is brought to its initial position, disinterring the manufactured model, while the unused powder is kept for use in the construction of the next object (CandyFab, 2006).

1.4 SUMMARY AND FUTURE DIRECTIONS Three-dimensional food printing is strongly dependent on the material properties and binding mechanisms. In recent years, great efforts have been made aiming to achieve end properties of 3D constructs having end-use properties aligned with or more advantageous than those obtained through traditional manufacturing method. However, there are still many barriers to overcome for 3DFP to be incorporated in niche markets requiring personalisation. Due to the lack of an ideal software to set up the printing parameters of multicomponent systems of viscous materials. Currently, researchers all over the world adapt the variables normally controlled in the fusion deposition of plastic filaments to achieve the ideal pressure in extrusion processes, for example. In our opinion, hardware and software will be developed as soon as the applicability of 3DFP is imbedded in a profitable business model. Researchers and the industrial community related to food production should be aware of exiting industrial trends that affect the habits of the consumers and, at the same time, pay attention to the evolution of 3DP towards the creation of novel 3D constructs. l

l

Industrial trend: 3DFP will not replace completely the conventional methods adopted for food production. Conversely, this versatile technology fits in specific markets with special needs and shows potential of creating new needs for groups of population of which the size is unpredictable at this stage. Many reports reveal that 3DP technology is part of the 4.0 industry revolution (Boutouchent, 2016; Subic and Gallagher, 2017). More and more production will be closer to the end consumer in decentralised production and distribution structures. Another key aspect of the 4.0 industry is that everyone can be a developer and producer at once (prosumer trend). Therefore, 3DP printing fits perfectly to the future ways of production in a variety of fields, including food manufacturing (Kocovic, 2017). Evolution of 3DP technology: 3DP technology is fast evolving regarding (1) material, and (2) machinery. The material evolution towards 3DP gave

16 Fundamentals of 3D Food Printing and Applications

rise to the development of 4D printing. The term 4DP was recently coined as the integration of 3D printing and active material technologies to generate novel components that can be switched between multiple configurations via an environmental stimulus, for example, heat or moisture (Ding et al., 2017; Ge et al., 2013). An example is the sheets of gelatin developed by Massachusetts Institute of Technology researchers that transform into 3D shapes when dunked in water (Chu, 2017). Food 3D printing can be considered as 4D printing, as the finished product may have to be cooked or treated prior to consumption, and the shape and size changes during postprinting will need to be considered while designing the product. The term 5D printing, however, emerged from machinery development. Five-dimensional printing development was driven by the convenience of not being necessary to print support structures in complex designs. Five-dimensional printing can be defined as a five-axis 3D printer instead of the three-axis printer used in conventional 3D printing. A fiveaxis 3D printer essentially builds the object from multiple directions (X, Y, Z with rotational and translational movements), thus producing stronger parts than regular 3D printing (Ethereal-Halo, 2018).

REFERENCES Azam, R.S.M., Zhang, M., Mujumdar, A.S., Yang, C., 2018. Study on 3D printing of orange concentrate and material characteristics. Journal of Food Process Engineering e12689. Bokkhim, H., Bansal, N., Grøndahl, L., Bhandari, B., 2016. Characterization of alginate-lactoferrin beads prepared by extrusion gelation method. Food Hydrocolloids. https://doi.org/10.1016/j. foodhyd.2014.12.002. Boutouchent, A., 2016. Industry 4.0: The 4 Technologies Behind It. Bridge Insights. Retrieved from: http://insights.bridgr.co/manufacturing-trends-industry-4-technologies/. CandyFab, 2006. The CandyFab Project. https://candyfab.org/. Cavin, S., Pipe, C., Michel, M., 2013. US20160021907A1. US. Ching, S.H., Bhandari, B., Webb, R., Bansal, N., 2015. Visualizing the interaction between sodium caseinate and calcium alginate microgel particles. Food Hydrocolloids. https://doi.org/10. 1016/j.foodhyd.2014.05.013. Chu, J., 2017. Researchers Engineer Shape-Shifting Noodles. MIT News Office. Retrieved from: http://news.mit.edu/2017/researchers-engineer-shape-shifting-noodles-0525. Cohen, D.L., Lipton, J.I., Cutler, M., Coulter, D., Vesco, A., Lipson, H., 2009. Hydrocolloid printing: a novel platform for customized food production. In: Twentieth Annual International Solid Freeform Fabrication Symposium. https://doi.org/10.1017/CBO9781107415324.004. Diaz, J.V., Van Bommel, K.J.C., Noort, M.W., Henket, J., Brier, P., 2014. Preparing Edible Product, Preferably Food Product Including Bakery Product, and Confectionary Product, Involves Providing Edible Powder Composition, and Subjecting Composition to Selective Laser Sintering. The Netherlands. Ding, Z., Yuan, C., Peng, X., Wang, T., Qi, H.J., Dunn, M.L., 2017. Direct 4D printing via active composite materials. Science Advances. https://doi.org/10.1126/sciadv.1602890. Ethereal-Halo, 2018. The Ethereal Halo. Retrieved from: https://etherealmachines.com/products/ halo.

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Ge, Q., Qi, H.J., Dunn, M.L., 2013. Active materials by four-dimension printing. Applied Physics Letters. https://doi.org/10.1063/1.4819837. Goyanes, A., Wang, J., Buanz, A., Martı´nez-Pacheco, R., Telford, R., Gaisford, S., Basit, A.W., 2015. 3D printing of medicines: engineering novel oral devices with unique design and drug release characteristics. Molecular Pharmaceutics. https://doi.org/10.1021/acs.molpharmaceut. 5b00510. Grood, J.P.W., Grood, P.J., 2011. Method and device for dispensing a liquid. Google Patents. Grood, J.P.W., Grood, P.J. De, 2013. US8556392B2. Gudapati, H., Dey, M., Ozbolat, I., 2016. A comprehensive review on droplet-based bioprinting: past, present and future. Biomaterials 102, 20e42. https://doi.org/10.1016/J.BIOMATERIALS. 2016.06.012. Hao, L., Mellor, S., Seaman, O., Henderson, J., Sewell, N., Sloan, M., 2010. Material characterisation and process development for chocolate additive layer manufacturing. Virtual and Physical Prototyping. https://doi.org/10.1080/17452751003753212. He, Y., Yang, F., Zhao, H., Gao, Q., Xia, B., Fu, J., 2016. Research on the printability of hydrogels in 3D bioprinting. Scientific Reports. https://doi.org/10.1038/srep29977. Herr, A.G., Colen, P.E., 2014. US20160066601A1. US. Kim, H.W., Bae, H., Park, H.J., 2017. Classification of the printability of selected food for 3D printing: development of an assessment method using hydrocolloids as reference material. Journal of Food Engineering 215, 23e32. https://doi.org/10.1016/J.JFOODENG.2017.07.017. Kocovic, P., 2017. 3D printing and supply chain management. In: 3D Printing and Its Impact on the Production of Fully Functional Components: Emerging Research and Opportunities. IGI Global. Lewis, J.A., 2002. Direct-write assembly of ceramics from colloidal inks. Current Opinion in Solid State and Materials Science. https://doi.org/10.1016/S1359-0286(02) 00031e1. Lille, M., Nurmela, A., Nordlund, E., Metsa¨-Kortelainen, S., Sozer, N., 2018. Applicability of protein and fiber-rich food materials in extrusion-based 3D printing. Journal of Food Engineering. https://doi.org/10.1016/j.jfoodeng.2017.04.034. Lipton, J., Arnold, D., Nigl, F., Lopez, N., Cohen, D., Nore´n, N., Lipson, H., 2010. Mutli-material food printing with complex internal structure suitable for conventional post-processing. In: 21st Annual International Solid Freeform Fabrication Symposium - An Additive Manufacturing Conference. SFF, pp. 809e815. Mantihal, S., Prakash, S., Godoi, F.C., Bhandari, B., 2017. Optimization of chocolate 3D printing by correlating thermal and flow properties with 3D structure modeling. Innovative Food Science and Emerging Technologies. https://doi.org/10.1016/j.ifset.2017.09.012. Marangoni, A.G., McGauley, S.E., 2003. Relationship between crystallization behavior and structure in cocoa butter. Crystal Growth and Design. https://doi.org/10.1021/cg025580l. Murphy, S.V., Atala, A., 2014. 3D bioprinting of tissues and organs. Nature Biotechnology. https:// doi.org/10.1038/nbt.2958. Ouyang, L., Yao, R., Zhao, Y., Sun, W., 2016. Effect of bioink properties on printability and cell viability for 3D bioplotting of embryonic stem cells. Biofabrication. https://doi.org/10.1088/ 1758-5090/8/3/035020. Peltola, S.M., Melchels, F.P.W., Grijpma, D.W., Kelloma¨ki, M., 2008. A review of rapid prototyping techniques for tissue engineering purposes. Annals of Medicine. https://doi.org/10. 1080/07853890701881788. Rosenthal, A.J., 2010. Texture profile analysis - how important are the parameters? Journal of Texture Studies. https://doi.org/10.1111/j.1745-4603.2010.00248.x.

18 Fundamentals of 3D Food Printing and Applications Sadia, M., Sosnicka, A., Arafat, B., Isreb, A., Ahmed, W., Kelarakis, A., Alhnan, M.A., 2016. Adaptation of pharmaceutical excipients to FDM 3D printing for the fabrication of patienttailored immediate release tablets. International Journal of Pharmaceutics. https://doi.org/10. 1016/j.ijpharm.2016.09.050. Schaal, N., 2007. Printing Chocolate. DuPont Manual High School. Schutyser, M.A.I., Houlder, S., de Wit, M., Buijsse, C.A.P., Alting, A.C., 2018. Fused deposition modelling of sodium caseinate dispersions. Journal of Food Engineering. https://doi.org/10. 1016/j.jfoodeng.2017.02.004. Seerden, K.A.M., Reis, N., Evans, J.R.G., Grant, P.S., Halloran, J.W., Derby, B., 2001. Ink-jet printing of wax-based alumina suspensions. Journal of the American Ceramic Society. https://doi.org/10.1111/j.1151-2916.2001.tb01045.x. Sewell, N., Henderson, J., Sloan, M., Hao, L., Mellor, S., Seaman, O., 2009. Extrusion behavior of chocolate for additive layer manufacturing. Innovative Developments in Design and Manufacturing. https://doi.org/10.1201/9780203859476.ch37. Shastry, A., Ben-Yoseph, E., Collins, T., 2002. US7029112B2. Shastry, A., Collins, T., Suttle, J., Willcocks, N., Ben-Yoseph, E., Walters, M., 2012. US7597752B2. Smay, J.E., Cesarano, J., Lewis, J.A., 2002. Colloidal inks for directed assembly of 3-D periodic structures. Langmuir. https://doi.org/10.1021/la0257135. Subic, A., Gallagher, S., 2017. Industry 4.0 Testlabs in Australia - Preparing for the Future. Swinburne University of Technology, Hawthorn. TNO, 2017. The Future of Food. Retrieved from: https://www.tno.nl/media/2216/future_of_ food.pdf. Vaithilingam, J., Saleh, E., Ko¨rner, L., Wildman, R.D., Hague, R.J.M., Leach, R.K., Tuck, C.J., 2018. 3-Dimensional inkjet printing of macro structures from silver nanoparticles. Materials and Design 139, 81e88. https://doi.org/10.1016/J.MATDES.2017.10.070. Vancauwenberghe, V., Katalagarianakis, L., Wang, Z., Meerts, M., Hertog, M., Verboven, P., et al., 2017. Pectin based food-ink formulations for 3-D printing of customizable porous food simulants. Innovative Food Science and Emerging Technologies. https://doi.org/10.1016/j. ifset.2017.06.011. Vancauwenberghe, V., Verboven, P., Lammertyn, J., Nicolaı¨, B., 2018. Development of a coaxial extrusion deposition for 3D printing of customizable pectin-based food simulant. Journal of Food Engineering. https://doi.org/10.1016/j.jfoodeng.2018.01.008. Wang, L., Zhang, M., Bhandari, B., Yang, C., 2018. Investigation on fish surimi gel as promising food material for 3D printing. Journal of Food Engineering. https://doi.org/10.1016/j.jfoodeng. 2017.02.029. Wang, X., Ao, Q., Tian, X., Fan, J., Tong, H., Hou, W., Bai, S., 2017. Gelatin-based hydrogels for organ 3D bioprinting. Polymers. https://doi.org/10.3390/polym9090401. Wen, L., Swaine, R., Henry, W., n.d. US20080075830A1. US. Xaar, December 2012. A Guide to Industrial Inkjet. Retrieved from: https://www.xaar.com/media/ 1312/xaar-guide-to-inkjet.pdf. Yang, F., Zhang, M., Bhandari, B., Liu, Y., 2018a. Investigation on lemon juice gel as food material for 3D printing and optimization of printing parameters. LWT - Food Science and Technology. https://doi.org/10.1016/j.lwt.2017.08.054. Yang, F., Zhang, M., Prakash, S., Liu, Y., 2018b. Physical properties of 3D printed baking dough as affected by different compositions. Innovative Food Science and Emerging Technologies. https://doi.org/10.1016/j.ifset.2018.01.001.

Chapter 2

3D Food Printing Technologies and Factors Affecting Printing Precision Zhenbin Liu, Min Zhang State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, China

Chapter Outline

2.1 Introduction 2.2 3D Food Printing Technologies and Factors Affecting Printing Precision 2.2.1 Extrusion-Based Printing 2.2.1.1 Melting ExtrusionBased Printing 2.2.1.2 Soft Materials Extrusion-Based Printing 2.2.1.3 Pre- and Posttreatment Methods 2.2.1.4 Application of Soft Materials Extrusion-Based Printing in Food Creation 2.2.2 Selective Laser Sintering 2.2.2.1 Effect of Printing Parameters on Printing Behaviour 2.2.2.2 Implications of Materials’ Properties on Laser-Based Printing 2.2.2.3 Application of Laser-Based Printing in Food Creation

20 20 23 23

24 29

30 30

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2.2.3 Binder Jetting 2.2.3.1 Effect of Printing Parameters on Printing Behaviour 2.2.3.2 Implications of Materials’ Properties on Binder Jetting 2.2.3.3 Application of Binder Jetting in Food Creation 2.2.4 Inkjet Printing 2.2.4.1 Effect of Printing Parameters on Printing Behaviour 2.2.4.2 Implications of Materials’ Properties on Binder Jetting 2.2.4.3 Application of Inkjet Printing Food Creation 2.3 Summary and Future Directions References

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Fundamentals of 3D Food Printing and Applications. https://doi.org/10.1016/B978-0-12-814564-7.00002-X Copyright © 2019 Elsevier Inc. All rights reserved.

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20 Fundamentals of 3D Food Printing and Applications

2.1 INTRODUCTION Three-dimensional (3D) printing, also known as additive manufacturing solid free-form fabrication, was first introduced in the food sector by researchers from Cornell University using an extrusion-based printer (Fab@home) (Periard et al., 2007). This technology is characterized by a layer-by-layer material deposition mode based directly from a predesigned file (Pinna et al., 2016; Rayna and Striukova, 2016). There are many potential advantages of 3D printing technology applied to the food sector, such as customized food designs, personalized and digitalized nutrition, simplifying the supply chain and broadening the source of available food material. Using this technology, some complex and fantastic food designs which cannot be achieved by manual labour or conventional mould can be produced by ordinary people based on predetermined data files that comprise culinary knowledge and artistic skills from chefs, nutrition experts and food designers (Sun et al., 2015c, 2018). It also can be used to customize confectionery shapes and colourful images onto surfaces of solid edible substrates (Young, 2000; Zoran and Coelho, 2011). In addition, 3D food printing permits digitisation and personalisation of the nutrition and energy requirements of an individual person according to their physical and nutrition status (Severini and Derossi, 2016; Sun et al., 2015c; Wegrzyn et al., 2012; Yang et al., 2015). The conventional food supply chain can be simplified by 3D food printing. The universal application of this technique will make the manufacturing activities slowly move to places closer to the customers and will lead to reduced transport volume, thus reducing the packaging, distribution and overriding costs (Chen, 2016; Jia et al., 2016; Sun et al., 2015a,b,c). Food printing technology will also broaden the source of available food material by using nontraditional food materials such as insects, high-fibre plant-based materials and plant- and animal-based by-products (Payne et al., 2016; Severini and Derossi, 2016; Tran, 2016). Currently, 3D printing techniques available in the food sector generally include four types: extrusion-based printing, selective sintering printing (SLS), binder jetting and inkjet printing. This will be discussed in the chapter.

2.2 3D FOOD PRINTING TECHNOLOGIES AND FACTORS AFFECTING PRINTING PRECISION As mentioned earlier, the quality and precision of printed objects depend on the materials’ properties, processing factors and postprocessing treatments. Each 3D food printing technique has its own advantages and limitations. Table 2.1 shows the comparison of different 3D printing techniques and factors affecting the printing precision and accuracy. This is discussed in detail in the following.

TABLE 2.1 Comparison of Different 3D Food Technologies Selective Laser Sintering

Binder Jetting

Inkjet Printing

Available material

Chocolate, soft material such as dough, cheese, meat puree

Powdered materials such as sugar, chocolate, fat

Liquid binder and powdered materials such as starch, sugar, protein

Low-viscosity material such as pizza sauce

Material properties

Rheological properties, mechanical strength, Tg

Melting temperature, flowability, particle size, wettability, Tg

Flowability, particle size, wettability and binder’s viscosity and surface tension

Compatibility, ink rheological properties, surface properties

Processing factors

Printing height, nozzle diameter, printing rate, nozzle movement rate

Laser types, laser power, laser energy density, scanning speed, laser spot diameter, laser thickness

Head types, printing rate, nozzle diameter, layer thickness

Temperature, printing rate, nozzle diameter, printing height

Postprocessing

Additive, recipe control

Removal of excess parts

Heating, baking, surface coating, removal of excess parts

No

Advantages

More material choices, simple device

Complex 3D food fabrication, varying textures

Complex 3D food fabrication, full colour potential, varying flavours and textures

More material choices, better printing quality, fast fabrication

Continued

3D Food Printing Technologies Chapter | 2

Factors affecting printing precision

Extrusion-Based Printing

21

Limitations

Extrusion-Based Printing

Selective Laser Sintering

Binder Jetting

Inkjet Printing

Incapable of fabricating of complex food designs, difficult to hold 3D structures in postprocessing

Limited materials, less nutritious products

Limited material, less nutritious products

Simple food design, only for surface filling or image decoration

Products

The products images were reproduced from the websites: (a) Natural Machines Co., available at https://www.naturalmachines.com/; (b) CandyFab Project, available at https:// candyfab.org/TNO; (c) 3D Systems Co., available at https://www.3dsystems.com/culinary/gallery; (d) FoodJet Printing Systems, available at http://www.foodjet.com/.

22 Fundamentals of 3D Food Printing and Applications

TABLE 2.1 Comparison of Different 3D Food Technologiesdcont’d

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2.2.1 Extrusion-Based Printing Extrusion-based printing, first known as fused deposition modelling, was first introduced to fabricate plastics products (Ahn et al., 2002). During the food printing process, the melted material or pastelike slurry is extruded out continuously from a moving nozzle and welds to the preceding layers on cooling. According to the temperature used in the deposition process, extrusion-based printing can be classified into melting extrusion-based printing and soft materials extrusion-based printing.

2.2.1.1 Melting Extrusion-Based Printing Melting extrusion-based printing has been widely applied to create customized 3D chocolate products (Hao et al., 2010; Mantihal et al., 2017). During the printing process, melted semisolid food polymer is extruded from a movable printhead and solidifies and welds to the previous layers almost immediately after extrusion. 2.2.1.1.1 Mechanism of Formation of Self-Supporting Layers In melting extrusion of chocolate, understanding the properties of the chocolate is critical to the quality of the printed objects due to the complex compositions and six different crystalline phases of cocoa butter (Marangoni and McGauley, 2003). The chocolate ink should be able to hold its structure during and after the layer-by-layer deposition process. This ‘self-supporting’ capacity relies on thermal properties like glass transition temperature (Tg) and melting point, which is critical in the postdeposition solidification process of the deposited layer (Mantihal et al., 2017). 2.2.1.1.2 Effect of Printing Parameters on Printing Behaviour The processing parameters, such as nozzle diameter, nozzle height, extrusion rate and nozzle moving speed, are also critical to the quality of the resulting printed constructs in melting printing process. Previous work (Hao et al., 2010) on the deposition of chocolate showed that the distance between the nozzle tip and build platform played an important role in the quality of built objects. This study showed that when a lower nozzle height than optimal height was applied, the volume of the extruded chocolate was too large for the space between the building platform and nozzle. Thus, the slurry was forced to spread in directions perpendicular to the deposited slurry line, and the resultant extruded objects displayed a squeezing effect and poor accuracy. Conversely, the application of a larger nozzle height, resulting in parts of the chocolate not reaching the marble build surface in time, led to massively inaccurate parts (Hao et al., 2010). The printing accuracy was also seriously affected by the extrusion rate and nozzle movement rate due to the bead diameter of chocolate track that decreased with the nozzle movement rate while increasing with the

24 Fundamentals of 3D Food Printing and Applications

extrusion rate (Hao et al., 2010). Temperature is also a critical factor to achieve successful hot melting extrusion printing, especially for chocolate printing (Mantihal et al., 2017). 2.2.1.1.3 Implications of Materials’ Thermal Properties on Melting Extrusion-Based Printing Temperature is a critical factor to a successful melting printing. Hao et al. (2010) investigated the material characterization on the quality of printed objects. During this process, a seed was added in the premelted chocolate to generate more V crystals which was desirable in the deposition of ‘good’ chocolate. Chocolate slurries with pseudoplastic properties at different temperatures were highly desirable in the deposition of 3D constructs (Hao et al., 2010). There are six major crystal polymorphs’ formation in cocoa butter. Form V, with melting temperature (Tm) ranging between 33.8 and 35
C, is the most important crystal and will give the final chocolate product more stable characteristics, a glossy finish and better texture. Thus, a proper and careful manipulation of the heat treatment is vital to gain Form V crystal (Mantihal et al., 2017). Mantihal et al. (2017) concluded that 32
C is the optimum temperature for chocolate printing with addition of magnesium stearate where most of the stable crystals are formed. 2.2.1.1.4 Application of Melting Extrusion-Based Printing in Food Creation The melting printing of chocolate was first conducted using a Fab@home system. Processing factors like temperature and extrusion rate affecting the printing accuracy during chocolate fabrication were investigated (Hao et al., 2010). The chocolate extrusion printing has been commercialized by Choc Edge’s Choc Creator, 3D System’s ChefJet, Hershey’s CocoJet and Chocabyte (Millen, 2012; Zhuo, 2015). A melting extrusion-based printer has been created by Natural Machines to be used for chocolate printing (Galdeano, 2015). Researchers from Massachusetts Institute of Technology used melting chocolate as a dispensing liquid and developed a printer named ‘Digital Chocolatier’ (Young, 2000; Zoran and Coelho, 2011). Mantihal et al. (2017) investigated the correlation of 3D chocolate printing behaviour with thermal properties and concluded that the application of 32
C showed the best performance.

2.2.1.2 Soft Materials Extrusion-Based Printing During the soft materials extrusion-based printing process, the pastelike food slurry is extruded out continuously from a moving nozzle and welds to the preceding layers on cooling, such as dough, mashed potatoes (MP), cheese and meat paste (Lipton et al., 2010; Yang et al., 2015). Three extrusion mechanisms have been applied in 3D food printing: screw-based extrusion, air

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pressure-based extrusion and syringe-based extrusion. In the screw-based extrusion process, food materials are put into the sample feeder and transported to the nozzle tip by a moving screw. During the extrusion process, food materials can be fed into the hopper continuously, thus realizing the continuous printing. However, the screw-based extrusion is not suitable for the food slurry with high viscosity and high mechanical strength; thus, the printed samples do not attain proper mechanical strength to support the following deposited layers and result in compressed deformation and poor resolution (Liu et al., 2018). The air pressure-based extrusion, during which food materials are pushed to the nozzle by air pressure, is suitable to print liquid or low-viscosity materials (Sun et al., 2018). The syringe-based extrusion unit is suitable to print food materials with high viscosity and high mechanical strength so that it probably can be used to fabricate complex 3D structures with high resolution. Some printed samples with a syringe-based printer are illustrated in Fig. 2.1 (Liu et al., 2018). However, it should be noted that the air pressure-based extrusion and syringe-based extrusion do not allow the continuous feeding of food materials during printing.

FIGURE 2.1 Printed objects using mashed potatoes with a syringe-based printer (Liu et al., 2018).

26 Fundamentals of 3D Food Printing and Applications

2.2.1.2.1 Mechanism of Formation of Self-Supporting Layers Though soft materials extrusion-based printing has been applied in the deposition of a wide variety of soft materials, the deposition of them into complex and delicate shapes is inherently limited, as they are fundamentally prone to distortion and warping. To fabricate delicate and complex shapes during the soft material extrusion process, it is necessary to print the additional structural objects to support the product geometry. The supporting constructs must be manually removed in the final stage. This is a time-consuming process and will slow printing speed and raise material costs (Von Hasseln, 2013; Von Hasseln et al., 2014; Von et al., 2015b). Therefore, it is necessary to fully understand the material properties and relevant technologies to be able to thus construct 3D structures. The highly desirable soft materials for extrusion 3D printing should not only possess suitable mechanical strength (yield stress and elastic modulus) to be capable of maintaining printed shapes, but also have shear-thinning behaviour to be easily extruded out from the nozzle tip in an extrusion-based type printer. A good balance must be made so that the mixture is as strong as possible to maintain the printed shape while it still could be printable and capable of adhering to previously deposited layers (Liu et al., 2018). 2.2.1.2.2 Effect of Printing Parameters on Printing Behaviour The effect of printing parameters on 3D printing behaviour has been investigated by many researchers (Wang et al., 2018; Yang et al., 2018). The application of a nozzle height lower than optimum height led to thicker extruded lines than intended, while a higher height led to parts of the extruded surimi lines not reaching the build surface before the nozzle turned a corner and thus resulted in massively inaccurate sections (Wang et al., 2018). The effect of various nozzle diameters on the built construct was simple to determine. A safe rule of thumb is to select the smallest nozzle tip that allows for easy material extrusion, as it is helpful to construct the object with the finest resolution and smooth surface during printing (Periard et al., 2007). Wang et al. (2018) concluded that the nozzle diameter affected the printing precision and surface smoothness considerably. The 3D printing of fish surimi displayed that the application of a small nozzle diameter (0.8, 1.5 mm) led to relatively poor models due to the inconsistent extruded surimi filament in its diameter along the length. Conversely, the use of a larger nozzle diameter could extrude consistent lines, but the resolution and accuracy of the objects were poor (Wang et al., 2018). Generally, a small nozzle diameter is beneficial to print objects with fine resolution, but it should be noted that the printing time required increased greatly when using a small nozzle size. A good balance must be made with the printing productivity and the printing precision. The extrusion rate and nozzle moving speed are also important in

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extrusion-based printing. It was suggested that the critical nozzle movement rate can be determined by Eq. 2.1 (Khalil and Sun, 2007): vN ¼

4Q pD2N

(2.1)

where vN is the optimal nozzle speed (mm/s), Q the material flow rate (cm3/s) and DN the nozzle diameter. It was shown that a nozzle velocity greater than vN would result in a smaller-diameter material bead than that of the nozzle, whereas a nozzle velocity less than vN would lead to a greater-diameter material bead than that of the nozzle. Neither of them were desired in printing (Khalil and Sun, 2007). Wang et al. (2018) suggested that the alteration of nozzle speed would affect the critical nozzle height when all other parameters were kept constant. Too-high speed (32 mm/s) resulted in the dragging effect, causing breaking of the extruded slurry filaments, while too-low moving speed (20 mm/s) resulted in the occurrence of flow instabilities of slurry and the formation of coils. They also suggested that there is a linear relationship between the extrusion rate and the diameter of surimi lines. Too-high extrusion rate (0.004 cm3/s) gave a larger extruded lines’ diameter than desired due to the extrusion of greater volume of material. Too-low extrusion rate (0.002 cm3/s) led to an inconsistent surimi slurry (Wang et al., 2018). In previous work (Zhuo, 2015) on the development of a 3D food printer, a positive linear relationship between nozzle moving speed and extrusion rate was studied (Zhuo, 2015). The printing temperature should also be fine-tuned, as the viscosity of the food material is directly correlated with the temperature. In the previous work of 3D printing Vegemite and Marmite (Hamilton et al., 2018), the viscosity decreased when the temperature increased. To extrude both materials at 25
C, 172 kPa of pressure was used, but it should be decreased to 103 kPa at 45
C. The application of a 172 kPa pressure to fabricate objects at 45
C led to too-large flow rate and the formation of a puddle of material. With a further increase of temperature to 65
C, too-quick extrusion of the material was formed even with the application of a very low pressure (4 Log CFU/g has been observed soon after printing. This research suggests that the sanitisation of each part in contact with food is greatly important to guarantee the microbial stability of 3D edible objects. Finally, an effective tool for extending the shelf-life of 3D vegetable smoothies could be the optimisation of the suitable stabilisation treatments (UV-C, microwave, etc.) and the storage conditions: packaging films, atmosphere (air or MAP) and temperatures.

TABLE 5.7 Changes in Antioxidant Activity, Total Phenolic Content, Mesophilic and Psychrophilic Bacteria in 3D Printed Smoothie Stored at 5
C in Air and Modified Atmosphere (MAP)

Time (days)

Antioxidant Activity (mg eq. trolox/100 g f.w.)

Total Phenolic Content (mg ac. gallic eq./100 g f.w.)

Air

MAP

Air

MAP

Air

MAP

Air

MAP

0

10.91 a

10.91 ab

18.8 a

18.8 a

5.02 a

5.02 a

4.27 a

4.27 a

3

10.84 a

11.66 a

13.0 a

14.6 a

4.65 a

4.93 a

4.10 a

5.02 a

6

10.29 a

10.85 ab

12.6 a

10.6 a

4.59 a

4.99 a

4.28 a

4.92 a

8

7.78 a

8.04 b

10.5 a

10.7 a

5.09 a

5.21 a

3.0 b

3.72 b

Mesophilic Bacteria (Log CFU/g)

Psychrophilic Bacteria (Log CFU/g)

Different letters indicate statistically significant differences during storage period (P < .05, Tukey’s test). From Severini et al. (2018).

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5.6 THE USE OF FRUIT AND VEGETABLE WASTE FOR 3D FOOD PRINTING AS FUTURE PERSPECTIVES The production of waste covers all of the food life cycle: from farm to fork. In developed countries, food waste is produced by households (42%), the food manufacturing industry (39%), food service sector (14%) and in retail and distribution (5%). Increasingly, industrial ecology concepts are considered leading principles for eco-innovation, aiming at ‘zero waste economy’, in which waste is used as a raw material for new products and applications. The great amount of waste from the food industry raises serious management problems, both from economic and environmental point of view (expenditure of energy and water) (Mirabella et al., 2014). The amount of residue from fruit and vegetables during preparation and industrial processing is estimated in one-third of the fresh products, equal to millions of tonnes per year, in many forms such as peels, pips, kernel and skins. In recent times, consumers and food industries have shown great interest in sustainability and environmental protection so that researchers are evaluating new solutions to recover food waste. A review of Kowalska et al. (2017) resumed the potentiality of fruit and vegetable by-products as animal feed, source of biomolecules, unconventional oil, antioxidants, antimicrobial compounds and flavouring, and also, they considered the use of by-products as a component of innovative food. Fruit and vegetable by-products have a high nutritional value, and they could be used as new food ingredients containing dietary fibre, polyphenols, vitamins and minerals, and also, depending on the nature of by-products, they could have functional abilities such as gelling, thickening, water-holding and binding capacities (Ayala-Zavala et al., 2011; Ayala-Zavala and Gonzalez-Aguilar, 2011; O’Shea et al., 2012). Among fruits, for instance, the apple is processed through a cold press to extract the juice; this results in much waste and generally refers to a mixture of peels, core and seeds. The apple residue contains bioactive compounds, such as polyphenols, vitamins and minerals (calcium, magnesium, zinc, iron and copper), simple sugars, water-soluble and insoluble carbohydrates, fibre and pectins. These last one present several characteristics such as gelling and thickening and can be used as a stabiliser of foods. It is possible to use the apple residues to prepare formulations, and, being a good source of fibre, they may be used to make low-calorie products for the good ability of all polysaccharides to bind water (Royer et al., 2006; Parra et al., 2015; Sharma et al., 2016). For instance, the tomato by-products that remain after industrial processes contain many nutrients and phytochemicals, among which are lycopene, a carotenoid, and fibre (50% on dry bases) (Del Valle et al., 2006). Several studies have evaluated the use of tomato waste as a novel

142 Fundamentals of 3D Food Printing and Applications

ingredient to improve the thickener and the red colour of tomato ketchup (Farahnaky et al., 2008) or to enhance the textural and sensorial properties of extruded snacks (Altan et al., 2008). Research was conducted to develop food products, biscuits and cereal bars, using the residues from the production of the drink, obtained with a mix of fruit and vegetables (orange, passion fruit, watermelon, lettuce, zucchini, carrot, spinach, mint, taro, cucumber and rocket). The plant residues were processed into flour which has a high capacity of water retention and high levels of carbohydrates (53%) and fibre (21.5%). The replacement of traditional flour by plant residue flour (20%e35%) was tested, and the results proved that the products obtained by using the by-product flour showed a high content of fibre, cellulose and minerals (Ferreira et al., 2015). However, pretreatments of fruit and vegetable by-products are a crucial step required in the initial stages of converting the fruit and vegetables ‘waste’ to a potential by-product ingredient that is microbiologically stable with minimum bioactive losses (polyphenols, carotenoids, etc.) and having a wide variety of health-enhancing benefits. In the development of by-product ingredients, many methods have been involved, such as wet milling fruits or vegetables to a certain particle size, washing to remove unwanted substances, drying (sun, oven drying and freeze-drying) and dry milling (to mill the dried fruit or vegetable to a defined particle size), which have been demonstrated and documented. Depending on the available nutrients and metabolites of the by-product, one or a combination of the above treatments can be used to produce a nutritious food ingredient (Larrauri, 1999). Here we want to point out that food by-products, in combination with 3D printing, could be a next promising application for a more sustainable food production system. We definitely believe that this could break the common approach of food production at different levels such as restaurant, gourmet shop restaurant and at home. According to this, the Wall Street Journal published an article entitled ‘What Are You Printing for Dinner?’ (9 June 2016) in which it was stated that the kitchens are ‘the most primitive thing in our house’ but soon ‘we’ll be able to download and print dinner’. As examples, the waste of fruit and vegetables obtained when preparing fruit juice by the most common, slow cold press juice extractor could be used as ingredient to print innovative 3D edible objects. Under this consideration, our research group printed a 10-faced pyramid using as edible-ink a blend of fruit and vegetables of residue after cold press extraction. This was a method to especially increase the viscosity of the blend by reducing its moisture content. For our experience, this step was essential to improve the printability of food paste without significant loss of nutrient and functional components. So, there is a new point of view that the use of food waste still containing nutrients and bioactive compounds could be used alone or in combination with other ingredients for a new generation of more sustainable printed foods.

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5.7 CONCLUSION Recently, more attention has been paid to the fundamental role of diet, rich in fruit and vegetables, in human health and well-being; also, personalised nutrition allows providing sufficient individual care, reducing the risks of disease and healthcare costs. In a modern market that pays more attention to the consumer needs, the application of 3D printing could be a useful technology to obtain functional and/or customised 3D edible objects by using fresh fruits and vegetables rich in antioxidant compounds, vitamins and minerals. To prepare a good blend of fruit and vegetables for the 3D printing process, the nutritional composition and the seasonality of each raw material are two important factors. In addition, to print a complex food formulation with a desired 3D structure is a hard work. Taking into account the low consistency of fruit and vegetable puree, the rheological, textural and mechanical properties of formulation are most important; therefore, the addition of thickeners is a useful tool to prepare a formulation with the suitable viscosity for the 3D printing process. Also, the correct setting of 3D printing variables is fundamental to define the conditions to get a 3D fruit and vegetable food, as much as possible, corresponding to the designed object. From all the studies conducted on the use of fruits and vegetables to prepare innovative foods, 3D printing has resulted as a useful tool, not only to preserve environmental sustainability, but also to obtain 3D edible objects enriched in bioactive compounds, fibre and minerals, with sensorial and textural properties. Also, 3D printing may be used to increase the appeal of fruit and vegetable products that usually are disliked by consumers. This is possible by printing blends of many ingredients adjusting taste, flavour or colour by using small amounts of more accepted ingredients. For instance, this is the case for broccoli or kiwi fruit that commonly are not appreciated from children but are very rich in antioxidants. Similarly, this technology is very effective in creating appreciated soft food to be served for people with dysphagia. In general, dysphagia is a physiological change occurring with ageing, and it affects the ability to swallow during eating and chewing foods. People who mainly consume liquid food might turn, during the long term of consumption, to a kind of dislike of food due to the lack of variety in meals. In this way, 3D printing may help to improve the variety of tastes, shapes, colours and flavours but keep the texture as a soft material. The use of 3D printing can be a very useful tool to obtain edible objects from fruits and vegetables for those people in categories that do not eat or have difficulty eating vegetables frequently, such as children and the elderly. Until now, it was thought that this type of application was not possible, but now some studies are already available.

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Cohen, D.L., Lipton, J.I., Cutler, M., Coulter, D., Vesco, A., Lipson, H., August 2009. Hydrocolloid printing: a novel platform for customized food production. In: Solid Freeform Fabrication Symposium, Austin, TX, pp. 807e818. Dai, Q., Borenstein, A.R., Wu, Y., Jackson, J.C., Larson, E.B., 2006. Fruit and vegetable juices and Alzheimer’s disease: the Kame project. The American Journal of Medicine 119 (9), 751e759. Danalache, F., Beira˜o-da-Costa, S., Mata, P., Alves, V.D., Moldao-Martins, M., 2015. Texture, microstructure and consumer preference of mango bars jellified with gellan gum. LWT - Food Science and Technology 62, 584e591. Dauchet, L., Amouyel, P., Dallongeville, J., 2005. Fruit and vegetable consumption and risk of stroke: a meta-analysis of cohort studies. Neurology 65 (8), 1193e1197. Dauchet, L., Amouyel, P., Hercberg, S., Dallongeville, J., 2006. Fruit and vegetable consumption and risk of coronary heart disease: a meta-analysis of cohort studies. Journal of Nutrition 136 (10), 2588e2593. Del Valle, M., Camara, M., Torija, M.E., 2006. Chemical characterization of tomato pomace. Journal of the Science Food and Agriculture 86 (8), 1232e1236. Derossi, A., Caporizzi, R., Azzollini, D., Severini, C., 2018. Application of 3D printing for customized food. A case on the development of a fruit based snack for children. Journal of Food Engineering 220, 65e75. Endrizzi, I., Framondino, V., Ciaghi, R., Gasperi, F., 2006. Towards a new fruit juice line with a high healthy power. Ingredienti Alimentari V, 1e7. Falguera, V., Aliguer, N., Falguera, M., 2012. An integrated approach to current trends in food consumption: moving toward functional and organic products? Food Control 26, 274e281. Farahnaky, A., Abbasi, A., Jamalian, J., Mesbahi, G., 2008. The use of tomato pulp powder as a thickening agent in the formulation of tomato ketchup. Journal of Texture Studies 39 (2), 169e182. Ferreira, M.S.L., Santos, M.C.P., Moro, T.M.A., Basto, G.J., Andrade, R.M.S., Goncalves, E., 2015. Formulation and characterization of functional foods based on fruit and vegetable residue flour. Journal of Food Science and Technology 52 (2), 822e830. Fu¨gel, R., Carle, R., Schieber, A., 2005. Quality and authenticity control of fruit pure´es, fruit preparations and jams e a review. Trends in Food Science and Technology 16 (10), 433e444. Garcia, E.L., Barrett, D.M., 2002. Preservative treatments for fresh-cut fruits and vegetables. In: Laminkra, O. (Ed.), Fresh-Cut Fruits and Vegetables. Science, Technology and Market. CRC Press, pp. 267e303 (Chapter 9). Gebbers, J.-O., 2007. Atherosclerosis, cholesterol, nutrition, and statins e a critical review. German Medical Science 5, 1e11. Godoi, F.C., Bhesh, S.P., Bhandari, R., 2016. Review. 3D printing technologies applied for food design: status and prospects. Journal of Food Engineering 179, 44e54. Hao, L., Mellor, S., Seaman, O., Henderson, J., Sewell, N., Sloan, M., 2010a. Material characterisation and process development for chocolate additive layer manufacturing. Virtual and Physical Prototyping 5 (2), 57e64. Hao, L., Seaman, O., Mellor, S., Henderson, J., Sewell, N., Sloan, M., 2010b. Extrusion behavior of chocolate for additive layer manufacturing, innovative developments. In: Design and Manufacturing - Advanced Research in Virtual and Rapid Prototyping, pp. 245e250. He, F.J., Nowson, C.A., Lucas, M., MacGregor, G.A., 2007. Increased consumption of fruit and vegetables is related to a reduced risk of coronary heart disease: meta-analysis of cohort studies. Journal of Human Hypertension 21 (9), 717e728. Imeson, A.P., 1992. Book: Thickening and Gelling Agents for Food. Springer ScienceþBusiness Media.

146 Fundamentals of 3D Food Printing and Applications Keenan, D.F., Tiwari, B.K., Patras, A., Gormley, R., Butler, F., Brunton, N.P., 2012. Effect of sonication on the bioactive, quality and rheological characteristics of fruit smoothies. International Journal of Food Science and Technology 47, 827e836. Kim, H.W., Bae, H., Park, H.J., 2018. Reprint: classification of the printability of selected food for 3D printing: development of an assessment method using hydrocolloids as reference material. Journal of Food Engineering 220, 28e37. Kowalska, H., Czajkowska, K., Cichowska, J., Lenart, A., 2017. Review. What’s new in biopotential of fruit and vegetable by-products applied in the food processing industry. Trends in Food Science and Technology 67, 150e159. Lanaro, M., Forrestal, D.P., Scheurer, S., Slinger, D.J., Liao, S., Powell, S.K., Woodruff, M.A., 2017. 3D printing complex chocolate objects: platform design, optimization and evaluation. Journal of Food Engineering 215, 13e22. Larrauri, J.A., 1999. New approaches in the preparation of high dietary fibre powders from fruit by-products. Trends in Food Science and Technology 10 (1), 3e8. Layman, D.K., 2014. Eating patterns, diet quality and energy balance: a perspective about applications and future directions for the food industry. Physiology and Behavior 134, 126e130. Le Tohic, C., O’Sullivan, J.J., Drapala, K.P., Chartin, V., Chan, T., Morrison, A.P., Kerry, J.P., Kelly, A.L., 2018. Effect of 3D printing on the structure and textural properties of processed cheese. Journal of Food Engineering 220, 56e64. Lille, M., Nurmela, A., Nordlund, E., Metsa¨-Kortelainen, S., Sozer, N., 2018. Applicability of protein and fiber-rich food materials in extrusion-based 3D printing. Journal of Food Engineering 220, 20e27. Lipton, J., Arnold, D., Nigl, F., Lopez, N., Cohen, D., Noren, N., Lipson, H., 2010. Mutlimaterial food printing with complex internal structure suitable for conventional post-processing. In: 21st Annual International Solid Freeform Fabrication Symposium - An Additive Manufacturing Conference. SFF, pp. 809e815. Lipton, J.I., Cutler, M., Nigl, F., Cohen, D., Lipson, H., 2015. Additive manufacturing for the food industry. Trends in Food Science and Technology 43 (1), 114e123. Liu, Z., Zhang, M., Bhandari, B., Yang, C., 2018. Impact of rheological properties of mashed potatoes on 3D printing. Journal of Food Engineering 220, 76e82. Malone, E., Lipson, H., 2007. Fab@Home: the personal desktop fabricator kit. Rapid Prototyping Journal 13 (4), 245e255. Mantihal, S., Prakash, S., Godoi, F.C., Bhandari, B., 2017. Optimization of chocolate 3D printing by correlating thermal and flow properties with 3D structure modelling. Innovative Food Science and Emerging Technologies 44, 21e29. Martin, C., 2013. The interface between plant metabolic engineering and human health. Current Opinion in Biotechnology 24 (2), 344e353. Max-Rubner-Institut, 2008. Bundesforschungsinstitut fu¨r Erna¨hrung und Lebensmittel. Nationale Verzehrsstudie (NVS), Teil 2, Haid-und-Neu-Str. 9, 76131 Karlsruhe, Germany. May, C.D., 1990. Industrial pectins: sources, production and applications. Carbohydrate Polymers 12 (1), 79e99. Medina, M.B., 2011. Determination of the total phenolics in juices and superfruits by a novel chemical method. Journal of Functional Foods 3, 79e87. Mirabella, N., Castellani, V., Sala, S., 2014. Current options for the valorization of food manufacturing waste: a review. Journal of Cleaner Production 65, 28e41.

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Morell, P., Fiszman, S., Varela, P., Hernando, I., 2014. Hydrocolloids for enhancing satiety: relating oral digestion to rheology, structure and sensory perception. Food Hydrocolloids 41, 343e353. Naska, A., Vasdekis, V.G., Trichopoulou, A., Friel, S., Leonha¨user, I.U., Moreiras, O., Nelson, M., Remaut, A.M., Schmitt, A., Sekula, W., Trygg, K.U., Zajka´s, G., 2000. Fruit and vegetable availability among ten European countries: how does it compare with the ‘five-a-day’ recommendation? In DAFNE I and II projects of the European Commission. British Journal of Nutrition 84, 549e556. Orsat, V., Changrue, V., Vijaya Raghavan, G.S., 2006. Microwave drying of fruits and vegetables. Stewart Post-Harvest Review 6, 4e9. O’Shea, N., Arendt, E.K., Gallagher, E., 2012. Dietary fibre and phytochemical characteristics of fruit and vegetable by-products and their recent applications as novel ingredients in food products. Innovative Food Science and Emerging Technologies 16, 1e10. Parra, A.F.R., Ribotta, P.D., Ferrero, C., 2015. Apple pomace in gluten-free formulations: effect on rheology and product quality. International Journal of Food Science and Technology 50 (3), 682e690. Periard, D., Schaal, N., Schaal, M., Malone, E., Lipson, H., 2007. Printing food. In: Proceedings of the 18th Solid Freeform Fabrication Symposium, Austin, pp. 564e574. Qian, N., 2006. Fruit and Vegetable Smoothies, and its Processing Method. Faming Zhuanli Shenqing Gongkai Shuomingshu CN 1817192. Rechkemmer, G., 2002. Fu¨nf am Tag e Obst und Gemu¨se. Die Gesundheitskampagne mit. Biss! Onkologe 8, 241e248. Roccaldo, R., D’addezio, L., Censi, L., Toti, E., Martone, D., D’addesa, D., Galfo, M., 2012. Indagine sulle preferenze di consumo di frutta e verdura nei bambini italiani. La Rivista Scientifica Dell’Alimentazione 41 (4), 7e19. Royer, G., Madieta, E., Symoneaux, R., Jourjon, F., 2006. Preliminary study of the production of apple pomace and quince jelly. LWT - Food Science and Technology 39 (9), 1022e1025. Saha, D., Bhattacharya, S., 2010. Characteristics of gellan gum based food gel. Journal of Texture Studies 41 (4), 459e471. Saleem, A., Husheem, M., Harkonen, P., Pihlaja, K., 2002. Inhibition of cancer cell growth by crude extract and the phenolics of Terminalia chebula retz. fruit. Journal of Ethnopharmacology 81 (3), 327e336. Salvini, S., Parpinel, M., Gnagnarella, P., Maisonneuve, P., Turrini, A., 1998. Banca dati di composizione degli alimenti per studi epidemiologici in Italia. Istituto Europeo di Oncologia, Milano. http://www.bda-ieo.it/wordpress/?page_id¼98. Schaal, N., 2007. “Printing Chocolate.” DuPont Manual High School. Severini, C., Derossi, A., Ricci, I., Caporizzi, R., Fiore, A., 2018. Printing a blend of fruit and vegetables. New advances on critical variables and shelf life of 3D edible objects. Journal of Food Engineering 220, 89e100. Severini, C., Derossi, A., 2016. Could the 3D printing technology be a useful strategy to obtain customized nutrition? Journal of Clinical Gastroenterology 175e178. Severini, C., Derossi, A., Azzolini, D., 2016. Variables affecting the printability of foods: preliminary tests on cereal-based products. Innovative Food Science and Emerging Technologies 38, 281e291. Sharma, P.C., Gupta, A., Issar, K., 2016. Effect of packaging and storage on dried apple pomace and fiber extracted from pomace. Journal of Food Processing and Preservation 41, e12913. https://doi.org/10.1111/jfpp.12913.

148 Fundamentals of 3D Food Printing and Applications SINU (Societa` Italiana di Nutrizione Umana), 2014. Livelli di Assunzione di Riferimento di Nutrienti ed energia per la popolazione italiana IV revision. SICS, Italy. Siriamornpun, S., Kaisoon, O., Meeso, N., 2012. Changes in colour, antioxidant activities and carotenoids (lycopene, beta-carotene, lutein) of marigold flower (Tagetes erecta L.) resulting from different drying processes. Journal of Functional Foods 4 (4), 757e766. Sun, J., Zhou, W., Huang, D., Fuh, J.Y., Hong, G.S., 2015. An overview of 3D printing technologies for food fabrication. Food and Bioprocess Technology 8 (8), 1605e1615. Takagishi, K., Suzuki, Y., Umezu, S., 2018. The high precision drawing method of chocolate utilizing electroctatic ink-jet printer. Journal of Food Engeneering 217, 138e143. Teichmann, A., Dutta, P.C., Staffas, A., Jagerstad, M., 2007. Sterol and vitamin D2 concentrations in cultivated and wild grown mushrooms: effect of UV irradiation. LWT - Food Science and Technology 40, 815e822. Van der Linden, D., 2015. 3D Food Printing Creating Shapes and Textures. Vancauwenberghe, V., Katalagarianakis, L., Wang, Z., Meerts, M., Hertog, M., Verboven, P., Moldenaers, P., Hendrickx, M.E., Lammertyn, J., Nicolai, B., 2017a. Pectin based food-ink formulations for 3-D printing of customizable porous food simulants. Innovative Food Science and Emerging Technologies 42, 138e150. Vancauwenberghe, V., Mbong, V.B.M., Vanstreels, E., Verboven, P., Lammertyn, J., Nicolai, B., 2017b. 3D printing of plant tissue for innovative food manufacturing: encapsulation of alive plant cells into pectin based bio-ink. Journal of Food Engineering. https://doi.org/10.1016/ j.jfoodeng.2017.12.003. Vancauwenberghe, V., Mbong-Mfortaw, V.B., Kokalj, T., Wang, Z., Verboven, P., Lammertyn, J., Nicolai, B., 2015. Pectin based bio-ink formulations for 3-D printing of porous foods. In: Proceedings of 29th EFFoST Conference, 10-12 November, Athens, Greece, pp. 409e414. Wang, L., Zhang, M., Bhandari, B., Yang, C., 2018. Investigation on fish surimi gel as promising food material for 3D printing. Journal of Food Engineering 220, 101e108. Watzl, B., 2008. Smoothies e wellness aus der Flasche? Erna¨hrungsumschau 6, 352e353. Woodside, J.V., Young, I.S., McKinley, M.C., 2013. Fruits and vegetables: measuring intake and encouraging increased consumption. Proceedings of the Nutrition Society 72, 236e245. World Health Organization, 2008. WHO European Action Plan for Food and Nutrition 2007/2012. http://www.euro.who.int/__data/assets/pdf_file/0017/74402/E91153.pdf. Yang, F., Zhang, M., Bhandari, B., Liu, Y., 2018. Investigation on lemon juice gel as food material for 3D printing and optimization of printing parameters. LWT - Food Science and Technology 87, 67e76. Zhang, Y., Vareed, S.K., Nair, M.G., 2005. Human tumor cell growth inhibition by nontoxic anthocyanidins, the pigments in fruits and vegetables. Life Sciences 76, 1465e1472.

FURTHER READING Keenan, D.F., Brunton, N.P., Gormley, T.R., Butler, F., Tiwari, B.K., Patras, A., 2010. Effect of thermal and high hydrostatic pressure processing on antioxidant activity and colour of fruit smoothies. Innovative Food Science and Emerging Technologies 11, 551e556. Kouzani, A.Z., Adams, S., Whyte, D.J., Oliver, R., Hemsley, B., Palmer, S., Balandin, S., 2017. 3D printing of food for people with swallowing difficulties. In: The International Conference on Design and Technology. KEG, pp. 23e29. https://doi.org/10.18502/keg.v2i2.591. Ozmianski, J., Lee, C.Y., 1990. Inhibition of polyphenol oxidase activity and antibrowning by honey. Journal of Agricultural and Food Chemistry 38 (10), 1892e1895.

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Pallottino, F., Hakola, L., Costa, C., Antonucci, F., Figorilli, S., Seisto, A., Menesatti, P., 2016. Printing on food or food printing: a review. Food and Bioprocess Technology 9 (5), 725e733. Schutyser, M.A.I., Houlder, S., de Wit, M., Buijsse, C.A.P., Alting, A.C., 2018. Fused deposition modelling of sodium caseinate dispersions. Journal of Food Engineering 220, 49e55. Zhang, B., Zhang, Y., Yang, L., Chen, J., 2001. Study on the crystalline structure and property of corn, cassava and potato starch granules. Food Science 22 (2), 11e13.

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Chapter 6

3D Printing Chocolate: Properties of Formulations for Extrusion, Sintering, Binding and Ink Jetting Matthew Lanaro, Mathilde R. Desselle, Maria A. Woodruff Queensland University of Technology (QUT), Science and Engineering Faculty, Brisbane, QLD, Australia

Chapter Outline

6.1 Introduction 6.2 Properties of Chocolate 6.2.1 Chocolate Structure 6.2.2 Chocolate Rheology 6.3 Chocolate Formulations 6.3.1 Common Chocolate Products 6.3.1.1 Moulding 6.3.1.2 Enrobing 6.3.1.3 Panning 6.3.1.4 One Shot 6.3.2 Specialty Chocolate Products

151 152 155 157 158 158 158 159 159 160

6.3.2.1 Ice Cream Chocolate 6.3.2.2 Heat Resistance 6.4 3D Printing Platform 6.5 3D Printing Chocolate: Extrusion 6.5.1 Process Optimisation 6.6 3D Printing Chocolate: Sintering and Binding 6.7 3D Printing Chocolate: Inkjet 6.8 Future Trends References

160 160 161 163 166 168 169 171 171

160

6.1 INTRODUCTION In a consumer-driven market where chocolate is estimated to account for 55% of global confectionary sales (Marketsandmarkets.com, 2011), the confectionary industry is embracing 3D printing to create new product categories in personalised cake decorations, promotional products and cocktail garnishes. Advanced manufacturing giant 3D Systems has been active in this space with their 3D printing culinary innovation centre opened to allow food industry, chefs and mixologists to discover the ChefJet Pro professional food printer. Fundamentals of 3D Food Printing and Applications. https://doi.org/10.1016/B978-0-12-814564-7.00006-7 Copyright © 2019 Elsevier Inc. All rights reserved.

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Furthermore, a collaboration with Hershey saw a prototype of a chocolate 3D printer CocoaJet arrive on the scene in 2015. In Australia, the Retail Food Group is trialling in-store chocolate 3D printing for personalised cake messages in its Michel’s Patisserie franchise with the intention to roll it out to the national market in 2018. Belgian chocolate shop Miam Factory, a spin-off from the University of Liege’s Smart Gastronomy Lab in 2017, produced a 3D printer that can create chocolate logos and uniquely shaped products not obtainable using classic chocolate moulding techniques. The company modified a commercial printer and successfully obtained a ‘food grade’ by the Federal Agency for the Safety of the Food Chain. One university group in particular has made a large impact on open-access 3D food printing, the Fab@Home (Malone and Lipson, 2007) desktop fabrication kit, which provided the framework for an open-access extrusion-based printer. At its time, this significantly reduced the cost of entry to the market and allowed a large number of systems to be constructed and foods to be tested. The maker movement has also supported consumer platforms such the DISCOV3RY COMPLETETM by Structur3D Printing which works from an open-access printer with an attachable food extruder. Open-access and commercial printers can be upgraded with custom-made extruders, allowing many new chocolate printers to flood online open innovation and crowdfunding platforms. While large-scale production machines have not yet made their way into to the industrial kitchens of the confectionery industry, a number of platforms and services are becoming increasingly available for restaurants and bakeries. Three-dimensional printing of chocolate requires specialist skills to design and operate the printers, influencing the cost/risk/benefit ratio. Printing chocolate is a complex and difficult process where each step of the process, from the processing of cocoa beans to the manufacturing of the chocolate formulation and setting of all the individual printing parameters, greatly influences the final product. The objective of this chapter is to review and compare the structural and rheological properties of chocolate formulations for use in traditionally manufactured chocolate products and 3D printed chocolate products produced by extrusion, sintering, binding and ink jetting techniques.

6.2 PROPERTIES OF CHOCOLATE The process of making chocolate has a significant impact on the flavour, structure and rheology of the final product (Fig. 6.1). This long process begins on the cocoa farm, where harvesting, fermenting and drying of the cocoa beans all take place. Drying renders the beans inert, which is an important factor for both large and small landholders, as the beans can be stored and transported. After the dried beans arrive at the factory, they will be roasted, milled and conched. After conching, chocolate is ready to be formed into the final product.

3D Printing Chocolate: Properties of Formulations Chapter | 6

(A)

(B)

(C)

(D)

(E)

(F)

153

FIGURE 6.1 The process of making chocolate involves harvesting, fermentation, drying, roasting, milling and conching. Cocoa beans shown on the tree (A) are gathered together and fermented (B). It is then necessary to dry the beans (C) to render the crop inert for long term storage or shipping. Next, the beans are roasted (D) and then the cocoa nibs are milled (E). Conching (F) occurs when the milk solids, sugar, emulsifiers and/or other ingredients are added. All photographs licensed from Bigstock, (A) Bestforbest. Cocao Tree (Theobroma cacao). Organic cocoa fruit pods in nature. Bigstock. 4 January 2018. (B) kaiskynet. Fermented and fresh cocoabeans lying in the wooden box. Bigstock. 3 January 2018. (C) alejomiranda. View of cocoa beans on rustic wooden table drying inside a greenhouse. Bigstock. 4 January 2018. (D) ArtifyAnalog. Roasted cocoa beans for making chocolate from scratch bean to bar. Bigstock. 3 January 2018 (E). akvals. Ingredients for making chocolate e raw cocoa butter, beans, powder, sugar and chocolates on a white plate. Bigstock. 3 January 2018. (F) Deyan Georgiev. Machine for mixing chocolate. Close up. Sweet desserts. Bigstock. 3 January 2018.

We will discuss the specific manufacturing process that occurs after conching to create the final product in Section 6.3, ‘Chocolate Formulations’. Cocoa beans (nibs) are the seeds contained within the fruit (pod) of the cocoa or cacao tree (Theobroma cacao L.). The cocoa tree is relatively small and occupies the understory area of its natural rainforest habitat in South and Central America (Mossu and Technical Centre for Agricultural and Rural

154 Fundamentals of 3D Food Printing and Applications

Co-operation, 1992). Due to its natural climate, the cocoa tree requires a stable high temperature and humidity which can be found within 20 degrees of the equator. The three main growing regions within this area include West Africa, Southeast Asia and South America. The main exporting variety of cocoa is forastero, which represents around 80% of the world’s cocoa plantations (CBI Trade Statistics: Cocoa in Europe, 2016) and starts producing pods containing about 30 beans each after 2e3 years, with a full yield at 6e7 years. Other cocoa beans can be used to provide a finer-grade chocolate such as Criollo and Trinitario which are commonly described with fuller, mild and nutty flavours (Cook and Meursing, 1982). Fermentation occurs immediately after and usually at the site of harvest. Fermentation times vary between regions, and varieties, however, usually last 5 days. Beans can be left in boxes, under banana leaves or stacked in breathable bags. Natural yeasts and bacteria multiply and break down the sugars in the bean, generating the chocolate flavour precursors and preventing the germination of the bean (Ziegler, 2009). When fermentation is complete, beans are dried to be rendered into a nonperishable commodity crop. The most traditional method to dry the beans is to lay them on the ground and rely on the sun to dry them out. This is only possible if weather permits and considerable effort is made to protect the beans from the rain. These can include using mats that can be rolled up, trays that can be moved, moveable tent shelters or transparent plastic covers. If the weather does not permit, artificial methods can be employed, such as wood fires or forced air dryers. Wood fires are risky, as the gases produced can spoil the chocolate flavour. Once moisture has been reduced from approximately 60% to between 6% and 8% (Dina et al., 2015), the cocoa is ready for longterm storage and transport. Roasting of the cocoa beans is a vital step that involves separating the nibs from the husk, developing the flavour and destroying any microbiological undesirables. Historically, roasting involved heating the entire bean (nib and husk) and then winnowing (removal of the husk). There are several disadvantages to this method, as energy is wasted on heating the husks and some cocoa butter leaks from the nib into the husk, which is then thrown away. Due to these disadvantages, modern manufacturing techniques involve winnowing the bean before roasting. After winnowing, the nib can then either be roasted and then ground up, or ground up to form a liquid and then roasted (Kamphuis, 2009). Roasting is an important step in developing the flavour precursors into a more recognisable ‘chocolate’ flavour (Milliard reaction) while at the same time removing many of the volatiles such as ethanoic acid. Destroying any microbiological contaminants such as Salmonella and other vegetative bacteria is a vital part of roasting, which is sometimes conducted at a different factory to reduce the risk of contamination (Burndred, 2009). It is necessary to mill solid particles of cocoa and sugar so that they can be later mixed to make chocolate. At the microscale particle size, the cocoa cells

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will break apart, releasing cocoa butter (fat). Once released, the fat coats the cocoa cell surfaces, resulting in a reduced viscosity. After a certain amount of milling, however, all fat is released and surface cells are further broken apart which creates a higher surface area; with no extra fat, the viscosity increases (Ziegler and Hogg, 2009). Depending on the chocolate recipe, sugar and milk solids can be added during or after milling. Conching is a process unique to chocolate production involving the slow mixing of ingredients which significantly impact the flavour and viscosity (Beckett, 2009b). The dry ingredients, if not combined during milling, are now added together. During this phase, the conche will slowly stir the crumbly mass of ingredients, allowing some of the moisture to evaporate and giving the cocoa butter a chance to coat the other ingredients. As these dry particles are coated with cocoa butter, the mass of ingredients turns more pasty and thick, which requires a higher work input by the stirring mechanism. In its final phase, the mass of ingredients now resembles liquid chocolate, and viscosity can be adjusted by adding more fat (cocoa butter) or emulsifiers. The improvements in flavour noticed after conching are attributed to flavour particles transferring onto the other ingredients and some of the undesirable acidic flavours being removed.

6.2.1 Chocolate Structure The fat within chocolate (cocoa butter) is highly polymorphic and can assume a number of different forms. Typically, fats are usually designated a, b0 and b; however, the fat within chocolate can exist in many additional forms. Two researchers published results in 1966 that showed there were six forms of fat within chocolate, denoted with Latin and Roman nomenclature g, a, b02 , b01 , b2, b1 (Larsson, 1966) and I, II, III, IV, V, VI (Wille and Lutton, 1966), respectively. Roman nomenclature has been adopted as the standard nomenclature used in industry. More recent work has only found evidence of five forms of chocolate, where form III and IV actually represented a range of forms that should be labelled under one heading (Table 6.1) (Van Malssen et al., 1999). The many forms of fat crystallisation in chocolate give rise to a number of different properties. In general, lower forms are less stable and tend to transform into more stable higher forms with a higher melting point. During this transition, the fat can change volume or migrate, which can have negative impacts on the chocolate due to increasing surface roughness or fat bloom (visible recrystallization). Form I has a melting point of between 5 and 5 C, this is the most unstable form which will rapidly transform to form II/a. Chocolate will then transform more slowly into forms III/b0 and IV/b0 . Form IV/b0 is relatively stable but is soft and will not have any snap when broken. Form V/bV will occur over a period of days and is the first triple-chain packing form, very stable with great properties for industrial applications. Form VI/bVI

156 Fundamentals of 3D Food Printing and Applications

TABLE 6.1 Chocolate Forms and Melting Points Original Convention (1966) Wille and Lutton (1966)

Updated Convention (1999) Van Malssen et al. (1999)

Form

Melting Point

Form

Melting Point

I

17.3

y (sub - a)

(5 to 5)

II

23.3

a

5 to 22

III

25.5

bʹ

15e27

IV

27.5

bʹ

15e27

V

33.8

bV

22e27

VI

36.3

bVI

22e27

is also a triple-chain packed, a very stable formation that is usually only formed by solid-to-solid transformation after months or years, accompanied by a fat bloom. Form V is most desirable to industry due to gloss, snap, no fat bloom and is reliably achieved with tempering. Tempering is the specific process needed to produce highly stable form V chocolate that has good glass, snap and viscosity. The first step is to heat the chocolate to 50 C (values vary depending on recipe) which has the effect of melting out all the fat crystals, erasing thermal memory. Next, the chocolate is cooled down to 27 C, where both unstable form IV and stable form V crystals will form. If chocolate was left at this point, the product would over time transform to form V but would introduce a fat bloom. By tempering, the temperature is raised again to 30e32 C, which will melt out the unstable form IV crystals. This process requires large amounts of energy; therefore, another method of tempering has been developed, known as tempering by seeding. The time- and energy-consuming process of tempering chocolate by switching between the different temperature steps can be circumvented by another technique called ‘seeding’, a process based on secondary nucleation (Hachiya et al., 1989). Solid polymorph crystals of form V serve as ‘seeds’ and are brought into contact with still-melted triglycerides so that these liquid crystals assume the same polymorph crystal state as the seeds. In a first step, the chocolate is heated up and melted before being cooled down again to 32 C. In a second step, the seed crystals are added to the mixture under mixing. The bulk mixture of chocolate needs to be at a temperature where thermodynamically less stable forms are in a liquid state, whereas more stable form V and VI crystals in the added seeds are already in a solid crystal state. Best crystallization results are achieved using high concentrations of seed crystals of high thermal stability of forms V or even VI in form of powders of just circa 150 mm size, as well as

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applying shear forces through mixing (Hachiya et al., 1989). Tempering by seeding is therefore easier to conduct, allows for a direct control of the type and amount of seed crystals in the cocoa butter mixture as well as prevents undesirable side effects like an increase in viscosity due to the crystallisation of trisaturated triglycerides.

6.2.2 Chocolate Rheology Rheology (the study of the flow of liquid) plays a vital role in the manufacturing process of chocolate products. The complex arrangement of fats and interactions within the microstructure give rise to complex rheological properties. When a shear rate is applied to chocolate, it will initially appear to be very viscous. It will, however, appear to be less viscous when higher shear rates are applied to the chocolate. This behaviour can be described as nonNewtonian and shear thinning. Both the International Office of Cocoa, Chocolate and Sugar Confectionery and the International Chocolate Awards publish standards on the rheological testing of chocolate. The most important data from these tests are the yield and plastic viscosities, which represent viscosity at rest and viscosity in movement. It is the goal during chocolate manufacture to achieve an appropriate viscosity profile based on the product to be made; see Section 6.3, ‘Chocolate Formulations’. In this section, we will describe the factors that influence the chocolate rheology, including particle size, fat content, emulsifiers and moisture. Particle size plays an important role in the viscosity of chocolate due to the semisolid nature of chocolate and the interactions between the free liquid fat, solid particles and packing density. It is necessary to reduce the particle size during milling to less than 30 mm, as any particle larger will taste ‘gritty’ to the consumer. During conching, the entire surface area will need to be coated by liquid fat to allow particles to flow past one another. As a general rule, the smaller the particles and higher the surface area, the more force it will take for the chocolate particles to shear and flow past one another. Plastic viscosity is therefore largely affected by the size of particles within chocolate (Beckett, 2008). The role of cocoa butter or fat content in chocolate is to occupy the space between and coat all the solid particles, sugar and cocoa so that they can move past one another. Cocoa butter (fat) also impacts the crystallinity and melting point of the chocolate. This causes the chocolate to flow more easily, which can be measured by an increase in the plastic viscosity. Clearly, the viscosity of the chocolate can be altered by increasing or decreasing levels of cocoa butter. However, cocoa butter is very expensive, and it is perhaps desirable to use surface-active ingredients or emulsifiers to achieve the same effect (Afoakwa, 2010). Emulsifiers, or surface-active agents, have a similar role to the cocoa butter (fat) in binding to solid particles and decreasing the plastic viscosity. Lectin is

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the most common emulsifier used in chocolate, which binds to solid particles much more effectively than cocoa butter, and therefore, a much smaller amount can be used. Another emulsifier that is used is polyglycerol polyricinoleate, which has the effect of reducing the yield point and in effect renders chocolate into a Newtonian fluid (Beckett, 2008; Afoakwa et al., 2007). It is imperative to remove as much moisture as possible from chocolate, as it significantly increases the viscosity. Moisture is kept away from the ingredients as much as possible during processing, and the first stage of conching will remove more; however, approximately 1% is bound within the lactose and cocoa cells. It is thought that water makes the sugar particles agglomerate together. As little as 0.3% moisture requires 1% cocoa butter to restore viscosity; it is therefore efficient to remove as much moisture as possible (Beckett, 2009a).

6.3 CHOCOLATE FORMULATIONS Chocolate is a successful product that is sold in many forms to the general public and specialist markets. From chocolate bars, confectionary items, biscuits and ice cream, chocolate is a popular flavour that is enjoyed by many consumers. All these products use various chocolate formulations that require different recipes and structural or viscosity requirements. For some products, the shape of the product will require specific viscosity requirements, such as chocolate bars or enrobing operations. Alternatively, specialty products like ice cream toppers and heat-resistant products require a significant change to the structure and recipe.

6.3.1 Common Chocolate Products Some of the most common chocolate products come in the form of a bar or as a coating on centre made from other confectionary items (Fig. 6.2). All these processes require that the chocolate is tempered (form V) prior to further handling.

6.3.1.1 Moulding Chocolate moulding (or casting) involves the deposition of well-tempered chocolate, with the manual or mechanical pouring of chocolate, into a mould to create a basic chocolate bar, or more complex shell-forming operations with various fillings. It is critical that the mould temperature is within one Celsius degree plus or minus of the chocolate temperature to ensure that the chocolate maintains its temper, as distempering can lead to softer chocolate sticking to the mould, fat bloom and loss of gloss (Gray, 2009). Maintaining a consistent temperature can help with demoulding as well as ensuring the relative humidity is extremely low and chocolate is cooled to between 10 and 15 C (Keijbets et al., 2010).

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FIGURE 6.2 Some of the most common chocolate products use moulding (A), enrobing (B), oneshot (C), or panning (D) operations. All photographs licensed from Bigstock, (A) Wavebreak Media Ltd. Close-upofmouldfilledwithmeltedchocolateinfactory.Bigstock.3January 2018.(B) vladm.Production of chocolate factory conveyor, conveyor belt. Bigstock. 4 January 2018. (C) belka35. White chocolate candy isolated over the white background. Bigstock. 4 January 2018. (D) ksena32. Peanuts in chocolate on a white background. Bigstock. 4 January 2018.

6.3.1.2 Enrobing Enrobing is used to coat another confectionary item in chocolate; usually the cores are made from biscuit, nougat, wafer or caramel. The confectionary items are placed onto a wire belt, which moves under a chocolate curtain (waterfall) to coat with chocolate. A series of operations including licking, blowing, vibration and decoration are then used to remove excess chocolate and bubbles and decorate the chocolate (Tscheuschner and Markov, 1986). Enrobing allows complex shapes to be covered in chocolate. Some cases use multiple double- or triple-stage coaters. In the first stage, a low-yield chocolate is used to ensure complete coverage; the next stages can use a higher-yield chocolate to give finial texture and allow for surface blowing and decorating (Beckett, 2008). A slight undertemper gives a more fluid chocolate, which can result in a more uniform coating. Double enrobing can also provide a better moisture or fat barrier to prevent blooming. 6.3.1.3 Panning Panning involves the application of chocolate layers to a kernel (centre). This is similar to enrobing; however, the method of applying a chocolate coating is different and involves three stages: pretreatment, panning and finishing. Precoating is not a necessary step; however, it allows chocolate to stick to the

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centre more easily and acts as a barrier so no fats or moisture can cause a chocolate fat bloom, increasing product shelf-life (Geschwindner and Drouven, 2009). Delicate centres also benefit from a pretreatment to lend more rigidity for panning. During the panning process, the kernels are placed in a machine that resembles a concrete mixer. As the chocolate is added, it should coat each surface uniformly, and cold air is used to harden each layer. Further layers are added until finial weight/size is obtained. The plastic viscosity of the chocolate is of lesser importance than the yield value during panning. This is because the coated kernels need to be able to move around in the mixer to evenly coat each surface. High shear stresses can cause damage to the centre or separate the coating from the kernel. Therefore, low yield values are better suited for light and low-density centres to prevent clumping of the product. Higher yield values may be used on heavier or denser centres, as these can move past each other more easily. Higher-yield coatings can build up unevenly on kernels that cannot freely move around, while less viscous chocolate can result in insufficient adhesion and bare patches (Aebi, 2009).

6.3.1.4 One Shot One shot is an extrusion-based method where chocolate is deposited via a needle and where a second needle located inside the first deposits a second, third or fourth chocolate or confectionary product. This method offers a way to significantly reduce the length of the production line, saving energy and setup costs. The rheological properties of the materials must be very similar for the process to work; otherwise, the shell will melt and fall away from centre. The temperature of materials must also be similar so as to not detemper the chocolate. Moisture and fat migration challenges remain, as with other methods (Meyer, 2009).

6.3.2 Specialty Chocolate Products 6.3.2.1 Ice Cream Chocolate Chocolate that is formulated to be kept at low temperatures such as a coating on ice cream has significantly different properties than other chocolate products. For example, tempered chocolate has a much higher melting temperature than freezer-held products and would therefore require significant energy to melt. This results in a hard chocolate which does not have desirable eating properties. To ensure a better consumer experience, form I or II is preferred due its softer nature and lower melting point. This will result in the chocolate melting far sooner in the mouth. To further soften the chocolate, a high fat and vegetable oil content is also used (Beckett, 2008; Wohlmuth, 2009). 6.3.2.2 Heat Resistance In hot climates, heat can cause the chocolate to melt, which can lead to a number of negative consequences such as fat bloom, loss of form and sticking

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to wrapper and hands. There are three methods to formulate a chocolate product to make it more suited to hot climates: modifying the fat phase, using transparent coatings or adding moisture (Wohlmuth, 2009). Modifying the fat phase can involve using other sources of cocoa butter with a higher melting point or vegetable fats. Transparent coatings have a shiny appearance that can be obtained by spraying or effectively in the panning process. Lastly, water has a significant effect on the viscosity of chocolate; therefore, a high moisture content will help retain shape. This can be achieved with a moist core which can migrate water to the chocolate.

6.4 3D PRINTING PLATFORM Three-dimensional printing or additive manufacturing involves the layerby-layer construction of an object with the use of controllable X-Y-Z Cartesian gantry system. This high degree of control over the finial object allows the manufacture of complex and intricate shapes not possible by any other method. There is, however, an associated disadvantage in the time it takes to manufacture an object, as the amount of printing parameters such as number of layers and speed of extrusion or the X-Y-Z gantry can all increase the production time. The additive manufacturing method is fundamentally different from traditional manufacturing methods such as moulding or one-shot deposition where the entire chocolate mass is deposited at once. Due to the time limitations compared to currents methods, 3D printing will not replace traditional methods for manufacturing, but will find new markets and niches that take advantage of the ability to create complex objects with little or no retooling costs. A 3D printed object begins life as a file in a computer-aided design (CAD) software environment. Every aspect of the object is defined, altered, refined and optimized within the 3D design software. When ready, the object is saved as an .stl file (standard triangle/tessellation language) and transferred to a 3D printing software interface. There are many 3D printing programs that are open source and free to use. The 3D printing software will ‘slice’ the object into layers, and individual commands will be actioned by the 3D printer itself. A number of parameters can be set via the same 3D printing software, such as layer height, speed, temperature, infill and shell thickness. The resulting design and parameters are exported in a G-code format that will be uploaded on the 3D printer. In Figs. 6.3A and B, Windows Ultimaker Cura free 3D printing software is shown with a simple cube ready to print. A 3D printer actions a sequential list of commands, known as G-codes. Each G-code tells the printer where to move and how much polymer to extrude. Therefore, the instructions to 3D print a cube are contained within a list of singular commands called G-codes. A single G-code line is shown in Eq. 6.1. G01 X10 Y5 Z0 E0:08 F650

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FIGURE 6.3 (A) Software model of a simple cube to 3D print in Microsoft Ultimaker Cura. (B) Slicing of model outputs code made up of commands for each layer: yellow (white in print version) is infill; red (grey in print version) is outline. (C) X-Y-Z gantry system of common commercial fused deposition modelling (FDM) printer (Tas 5, lulzbot). (D) Close-up of print.

where G01 signals to the program that the following command is a linear movement from the current position to the newly defined position at X, Y and Z, point{10, 5, 0} (in mm). E defines the amount to extrude (0.08 mm), while F is the speed at which the tool head should move (650 mm/min). A fused deposition modelling (FDM) or free-form fabrication (FFF) printer is very similar to a printer used for chocolate printing; the difference lies in how the chocolate is built up into a 3D printed object. Depending on whether the method is extrusion, sintering or binding will depend on the tooling head and bed setup. In Section 6.5, ‘3D Printing Chocolate: Extrusion’, we will discuss the most common form of food printing and how printing parameters are optimised. In Section 6.6, ‘3D Printing Chocolate: Sintering and Binding’, we will discuss another method to create complex objects created based on powder beds. Lastly, in Section 6.7, ‘3D Printing Chocolate: Inkjet’, we will look at the less widely utilised technique for 3D printing, ink jetting.

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6.5 3D PRINTING CHOCOLATE: EXTRUSION Extrusion is a method to 3D print complex food objects that share many similarities with the popular commercial FDM 3D printing. The FDM or FFF method is based on a filament that is drawn by gear teeth into a heater and extruded onto the collection plate. The difference with a food extrusion technique is that the printing material is stored in the printing head, and a plunger is driven into a syringe instead of pulled with gear teeth. If the material to be printed requires heat, it is necessary to heat the entire food mass. By using a syringe, a food-grade easy-to-exchange storage mechanism is easily adopted. This allows for a wide variety of foods to be processed in this fashion, the limiting factor being the capacity of the food to be pushed through a needle at reasonable pressure possible on the small 3D printing system. The behaviour of chocolate during extrusion is the subject of much research. The complex structure of chocolate gives rise to a unique behaviour when chocolate is extruded at or below room temperature. Termed ‘cold extrusion’, chocolate has unique shape-retaining properties, which are possible due to the semisolid nature of chocolate (Chen and Mackley, 2006; Ovaici et al., 1998). Manufacturers have used this technique to create uniquely shaped chocolate products of rope or netting (Beckett, 2009c). Further testing has shown that the chocolate after cold extrusion is softened due to work-induced phase changes, where the fat triglyceride molecules melt and then recrystallise after a certain amount of time (Engmann and Mackley, 2006). During this time, the characteristic shape-retaining properties of chocolate are evident. Other research shows that the high shear rates within the needle of an extrusion system have the ability to breakdown agglomerates and collapse bubbles within chocolate, which can be measured with the use of a pressure sensor (Russell et al., 2006). On a 3D food printer, the possible extrusion pressures are lower than in an industrial extruder, and chocolate is usually extruded as a heated liquid. The form of cocoa butter fat within chocolate can usually be controlled using the heating system, so tempered chocolate is possible. In Section 6.2.2, ‘Chocolate Rheology’, a number of factors that affect the viscosity were mentioned, but usually the chocolate is shear thinning, and the yield viscosity is significantly higher than the plastic viscosity. For a large number of current chocolate 3D printers, a basic syringe is used to house the chocolate which is extruded by an electric motor applying linear displacement to the plunger. Fig. 6.4 shows an example of a melt extrusion head to be used on a 3D printing platform. As the gantry system moves the extrusion head, the chocolate is extruded a set amount onto the bed. This is built up layer by layer until the object is completed (Fig. 6.5). The use of a motor-driven plunger can be modelled with a small amount of elasticity in the plunger mechanism. When combined with a high-yield viscosity, backpressure can build up in the extrusion head, and issues arise when starting and ending chocolate flow. For example, if in a linear move, there is to

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FIGURE 6.4 (A) Printing head, highlighted slot where thermocouple is placed. (B) Exploded view of chocolate extruder mechanism showing syringe, housing for stainless steel heating jacket, bearings, traveling nut, coupling, motor and screw-thread plunger depressor. (C) Air cooler design consisting of a Peltier module situated between two heat sinks. Air is pushed over the heatsinks, which is then directed to the chocolate extruder through an insulated duct. The hot side of the Peltier module is cooled with a heat sink and fan, with the exhaust air vented to atmosphere. (D) Cut view of printing head; insulated duct connects to housing where a channel directs air down onto printing filament. Also seen is location of heating cartridges (Lanaro et al., 2017). Reproduced with permission from (2017) Elsevier.

be no extrusion, then the back pressure will, in effect, keep extruding chocolate for a period. When the next command arrives to continue extrusion, the chocolate may be in the yield viscosity region again, and chocolate may not extrude due to the elastic storage of force for another period. The simple way

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FIGURE 6.5 Melt extrusion chocolate objects. (A) No air cooling used; simple 2D structures were made (height is 9 mm). (B) More complex structures were attempted, such as a chocolate bunny without cooling (height is 30 and 42 mm). (C) Using cooling, a complex 3D bunny was made (height is 94 mm). (D, E) complex 2D patterns can be easily fabricated using melt extrusion (Lanaro et al., 2017). (AeC) Reproduced with permission from (2017) Elsevier. Images (D and E) were reproduced from data available at https://3dprintingindustry.com/news/choc-edge-christmas37258/.

to deal with this may be the addition of emulsifiers to alter the shear thinning behaviour of chocolate for 3D printing; however, in practice, printing can be limited to objects which require little or no printing moves with no extrusion. In Fig. 6.5, a number of chocolate 3D printed objects are shown, none requiring much stopping of chocolate flow and moving to another position. The basics of a 3D printing system were discussed in Section 6.4, ‘3D Printing Platform’; however, there are a number of parameters that are specific to melt extrusion 3D printing, such as extrusion, tip-to-collector distance and movement speed. Extrusion is measured by the amount of linear displacement the plunger moves during a linear movement of the extrusion head. Extrusion is typically configured to extrude a bead of material that is equal in diameter to the needle; however, the volume of extrusion to give a flattened circle of

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defined height and width can also be used. The needle diameter is therefore vital and influences the time it takes to print and should set the shear rate to within motor specifications. The movement speed further complicates the amount to extrude; too high and the chocolate will extrude in a thinner diameter than the needle, and surface tension will eventually cause the strand to clump. If the movement speed is too low, then the amount of extruded material will be significantly more than calculated, resulting in a less aesthetically pleasing end product. The resulting chocolate 3D printed objects have identifiable lamination lines between each layer (Fig. 6.5). These can be reduced with a smaller layer height or possibly removed with a postprocessing heating operation.

6.5.1 Process Optimisation Three-dimensional printing is a complex process that not only requires an understanding of material properties, but how printing parameters will affect the deposition of material to create an accurate representation of the 3D object. Furthermore, the deposited chocolate strands have to fulfil a number of requirements such as aesthetic appeal, shape retention and the ability to support their own weight. This can be achieved with the optimisation of a number of parameters such as layer height, extrusion, movement speed, temperature of chocolate, temperature of bed, nozzle size and active cooling. The difficulty in defining what a good print is and the large number of variables to achieve this has led researchers to approach this problem in a number of different ways. Initially, researchers would attempt to optimise each printing parameter in turn (Hao et al., 2010). The distance between the plate and the nozzle was found by varying the height until the strand began to flatten out, which indicated the chocolate was then being squeezed between the plate and nozzle. The speed could be optimised by comparing the diameter of the nozzle and chocolate strand, which should be equal. Lastly, square tests, where chocolate was extruded into a 3D square shape, could allow the testing of optimisation of different layer heights (Hao et al., 2010). More recently, modern software developed for open-source and commercial 3D printers automatically assigns a number of these variable values. The correct nozzle-to-plate distance must be established in the same manner; however, the printer will extrude the correct amount to create a chocolate strand of equal diameter as the nozzle. Bridging is a common term in FDM 3D printing, which means the distance that a filament can span unsupported between two supports. This allows the testing of the ‘self supporting’ capacity of the filament. Researchers tested bridging against movement speed, extrusion multiplier and active cooling (Lanaro et al., 2017) (Fig. 6.6). They found that the movement speed (controlling for an equal cylindrical strand) did not affect the distance of a chocolate strand bridging and that a leaner extrusion multiplier of 0.8 (scaling value) allows chocolate to bridge further. They also

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FIGURE 6.6 (A) A simulation of a simple bridging experiment where maximum bridging distance is 8 mm. (B) This test was scaled up using a custom 3D printed testing rig. (C) The effect of varying extrusion multiplier from 0.6 to 1.4. (D) The effect of movement speed was varied over 300e700 mm/min. (EeG) The effect of increasing the air flow from 20% to 100% using both room temperature at 23.7 C and chilled air at 19.9 C. Note that all tests were conducted for chocolate at temperatures of 31e32 C, 33e34 C and 35e36 C (Lanaro et al., 2017). Reproduced with permission from (2017) Elsevier.

found that actively cooling and directing air onto the chocolate significantly increased the distance a chocolate strand could bridge (Lanaro et al., 2017). An alternative method to optimise the 3D printing can be done by using smoothed-particle hydrodynamic modelling. Here, researchers have shown that high viscosity and slow injection (extrusion) speed are favourable to produce objects which retain their shape (Makino and Fukuzawa, 2017; Makino et al., 2017). A high yield value will help the chocolate to resist deformation and more accurately resemble the geometric software model. However, in practice, this can be difficult to achieve since lower viscosities allow foods to flow more easily.

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6.6 3D PRINTING CHOCOLATE: SINTERING AND BINDING Both sintering and binding techniques can be used with a 3D printing system to create complex chocolate objects. For sintering, hot air (Fig. 6.7) or a laser can be used to sinter powder together to form a conglomerate. When binding, a liquid is used to bind the powder together. Both methods are only effective a certain distance down into the powder; therefore, another layer of powder is deposited on top in an additive manufacturing, layer-by-layer approach. Parts made using a sintering or binding method are naturally supported in a bed of powder. This allows more complex objects to be fabricated; however, an additional powder removal postprocessing stage is required. The agglomeration of food powders can be achieved with a number of mechanisms such as pressure, extrusion, rewetting, spray-bed drying, steam jet, heat/sintering and binders. Agglomeration describes the sticking of particulate solids, which is caused by short-range physical or chemical forces as a result of physical or chemical modification of the surface of the solid (Dhanalakshmi et al., 2011). Sintering occurs below the material melting temperature, where the reduction of total free surface energy causes powder to agglomerate together in a porous fashion. Binding can occur through a number of mechanisms; however, during wet granulation, the powders enlarge in size to form a conglomerate. One of the first 3D food printing systems to use sintering was designed to be accessible to the general population, so it was made from low-cost and easily accessible parts (Oskay and Edman, 2009). The system sintered sugar together with hot air to create a wide variety of sugar objects (Fig. 6.8).

FIGURE 6.7 Hot air sintering 3D printer is shown with a bed of sugar. The lines indicate where the sugar has been sintered together. Image was reproduced from data available at https:// 3dprintingindustry.com/news/choc-edge-christmas-37258/.

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FIGURE 6.8 Sugar has been selectively sintered together in (A and D) using hot air, whereas in (B and E), Nesquik has been selective laser sintered. Objects (C and F) are made from ChefJet (3D Systems) using liquid binding. Images (A and D) were reproduced from data available at https:// candyfab.org/. (C) was reproduced from data available at http://3dinsider.com/3d-printing-chocolate/. (B and E) were reproduced from data available at https://ec.europa.eu/jrc/sites/jrcsh/files/ 20150225-presentation-jan-sol.pdf. (F) was reproduced from data available at https://makezine. com/2014/01/07/3d-systems-breaks-the-mold-sugar-chocolate-ceramic-and-full-color-powder-3dprinting-on-your-desktop/.

Researchers found that a more accurate head that could supply hot air in precise amounts was key to improving the accuracy of the platform. Later, they showed that other materials, such as high-density polyethylene, could also be sintered on the same printer. Nesquik has been used in a selective laser sintering printer to create simple objects (Fig. 6.8) (Sol etal.,2015),while 3DSystemshas developeda liquidbinding printer, ChefJet, to print objects of high fidelity (Fig 6.8) (3D Systems, n.d.). For powdered bed 3D printing technologies to work, the food material used must follow a specific recipe to allow agglomeration. While 100% sugar was used for the candy lab (Oskay and Edman, 2009), the Netherlands Organisation for Applied Scientific Research (Sol et al., 2015) used Nesquik, which, according to Food Standards Australia and New Zealand labelling information, states Nesquik is 39.3% sugar. The same amount of sugar is within the range used in white, milk or dark recipes (Wohlmuth, 2009). The fat in Nesquik, however, is significantly less, sitting at 1.7% compared to 26% to 40% for typical white, milk and dark chocolate recipes (Wohlmuth, 2009). This indicates that the taste of sintered 3D printed chocolate objects will be significantly dissimilar to traditional chocolate products.

6.7 3D PRINTING CHOCOLATE: INKJET Inkjet or ink jetting describes a range of techniques where material is deposited as a droplet onto a product or collection plate. The most widely

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known application of this technology is found in the home and office as the humble printer. The amount of material to be deposited is very small, in the micro or nano range, and can be deposited continuously or on demand (Hudd, 2009). The continuous inkjet technique describes the constant dripping of material which can be used for product markings or coatings. Continuous ink jetting operations can achieve high speed, which have applications in industrial product marking. Drop-on-demand occurs when a single drop can be programmed to fall at a particular time and/or a particular location with the use of a gantry system. There are three methods to initiate the drop: thermal, piezo or electrostatic. Thermal techniques are based on vaporising some of the material to form a bubble, which collapses, and the resulting pressure wave deposits a drop. Piezo techniques are the most common method, based on the change of shape of a material from an electrical current. Electrostatic forces can also be used to deposited material but are rarely used. Due to the large number of ink jetting mechanisms, it is possible that a wide range of chocolate formulations can be used in this technique. It seems unlikely that a chocolate printer could utilise either continuous ink jetting or a mechanism based off thermal principles since that requires the vaporisation of chocolate. One group of researchers were able to show ink jetting of chocolate with an electrostatic system using Hershey’s shell topping (Fig. 6.9) (Takagishi et al., 2018). Another company, FoodJet, seems to be able to use chocolate as a topping for a number of food products. Unlike powder bed techniques, it is possible that the chocolate used in an inkjet printer could resemble chocolate flavours present in traditional products.

FIGURE 6.9 Schematic of the ink jetting experimental setup (1: nozzle; 2: x-y linear stage; 3: metal plate; 4: z mechanical stage; 5: printing material; 6: high-voltage device; 7: Peltier device; 8: pressure device; 9: microscope) (Takagishi et al., 2018). Reproduced with permission from (2017) Elsevier.

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In Section 6.6, ‘3D Printing Chocolate: Sintering and Binding’, it was shown that an inkjet head could be used in combination with a powdered bed to create complex 3D models. To the authors’ knowledge, there has not been any truly 3D chocolate object printed using inkjet techniques alone. Twodimensional objects are commonly made using ink jetting such as edible ink cartridges for a Canon PGI 670/CLI 671 printer (EIS, n.d.) or a patent for a ‘method of photocopying an image onto an edible web for decorating iced and baked goods’ (Stewart, 1998). Whether or not ink jetting should be considered a full 3D printing technique is the subject of discussion (Pallottino et al., 2016). On the one hand, ink jetting techniques use the same workflow of other 3D printing techniques such as the use of CAD and a gantry system (Takagishi et al., 2018). However, ink jetting is almost only ever used to create edible 2D objects, as decorations or to recreate digital images (Pallottino et al., 2016).

6.8 FUTURE TRENDS The structure and rheological properties of chocolate can be formulated and optimised to each manufacturing process. Three-dimensional printing is a platform that can make use of a number of different techniques to manufacture complex 3D chocolate objects. With extrusion, a traditional chocolate formulation can be used where the structure can be tempered and viscosity finely tuned. The powdered bed techniques of sintering and binding both use a rapidly different chocolate formulation that must exist in powdered form with high amounts of sugar and low amounts of fat. Ink jet techniques to create chocolate objects are mainly limited to 2D; however, it may be possible in the future to manufacture complex chocolate objects with inkjet printing. In summary, 3D printing is an exciting platform technology which has provided positive improvements in the chocolate industry to enable rapid, complex 3D structures to be created.

REFERENCES 3D Systems, n.d. Culinary 3D Printing. https://au.3dsystems.com/culinary. Aebi, M., 2009. Chocolate panning. In: Beckett, S.T. (Ed.), Industrial Chocolate Manufacture and Use: Fourth Edition, pp. 367e384. Afoakwa, E.O., 2010. Chocolate Science and Technology, second ed. Wiley. Afoakwa, E.O., Paterson, A., Fowler, M., 2007. Factors influencing rheological and textural qualities in chocolate - a review. Trends in Food Science and Technology 18 (6), 290e298. https://doi.org/10.1016/j.tifs.2007.02.002. Beckett, S., 2008. The Science of Chocolate. “The Science of Chocolate”, second ed. Royal Society of Chemistry https://doi.org/10.1089/jam.2007.0571. Beckett, S.T., 2009a. Chocolate flow properties. In: Beckett, S.T. (Ed.), Industrial Chocolate Manufacture and Use: Fourth Edition, pp. 224e245.

172 Fundamentals of 3D Food Printing and Applications Beckett, S.T., 2009b. Conching. In: Beckett, S.T. (Ed.), Industrial Chocolate Manufacture and Use: Fourth Edition, pp. 192e222. Beckett, S.T., 2009c. Non-conventional machines and processes. In: Beckett, S.T. (Ed.), Industrial Chocolate Manufacture and Use: Fourth Edition, pp. 385e407. CBI Trade Statistics: Cocoa in Europe, 2016. https://www.cbi.eu/sites/default/files/market_ information/researches/trade-statistics-europe-cocoa-2016.pdf. Chen, Y.W., Mackley, M.R., 2006. Flexible chocolate. Soft Matter 2, 304e309. https://doi.org/10. 1039/b518021j. Cook, L.R., Meursing, E.H., 1982. Chocolate Production and Use. Harcourt Brace Jovanovich. https://books.google.com.au/books/about/Chocolate_Production_and_Use.html? id¼Nt68PQAACAAJ&redir_esc¼y. Dhanalakshmi, K., Ghosal, S., Bhattacharya, S., April 14, 2011. Agglomeration of food powder and applications. In: Critical Reviews in Food Science and Nutrition. Taylor & Francis Group. https://doi.org/10.1080/10408391003646270. Dina, S.F., Ambarita, H., Napitupulu, F.H., Kawai, H., 2015. Study on effectiveness of continuous solar dryer integrated with desiccant thermal storage for drying cocoa beans. Case Studies in Thermal Engineering 5, 32e40. https://doi.org/10.1016/J.CSITE.2014.11.003. EIS, n.d. EIS Edible Ink Cartridge Set for Canon PGI 670/CLI 671 Printer Type. https://www. edibleimagesupplies.com.au/edible-ink-cartridges?product_id¼98. Engmann, J., Mackley, M.R.M.R., 2006. Semi-solid processing of chocolate and cocoa butter: modelling rheology and microstructure changes during extrusion. Food and Bioproducts Processing 84 (2), 102e108. https://doi.org/10.1205/fbp.05103. Burndred, F., 2009. Food safety in chocolate manufacture and processing. In: Beckett, S.T. (Ed.), Industrial Chocolate Manufacture and Use: Fourth Edition, pp. 530e549. Geschwindner, G., Drouven, H., 2009. Manufacturing processes: chocolate panning and inclusions. In: Talbot, G. (Ed.), Technology of Coated and Filled Chocolate, Confectionery and Bakery Products, pp. 397e412. Gray, M.P., 2009. Moulding, enrobing and cooling chocolate products. In: Beckett, S.T. (Ed.), Industrial Chocolate Manufacture and Use: Fourth Edition, pp. 320e357. Hachiya, I., Koyano, T., Sato, K., 1989. Seeding effects on solidification behavior of cocoa butter and dark chocolate. II. Physical properties of dark chocolate. Journal of the American Oil Chemists’ Society 66 (12), 1763e1770. https://doi.org/10.1007/BF02660744. Hao, L., Mellor, S., Seaman, O., Henderson, J., Sewell, N., Sloan, M., 2010. Material characterisation and process development for chocolate additive layer manufacturing. Virtual and Physical Prototyping 5 (2), 57e64. https://doi.org/10.1080/17452751003753212. Hudd, A., 2009. Inkjet printing technologies. In: Shlomo, M. (Ed.), The Chemistry of Inkjet Inks, pp. 3e18. https://books.google.com.au/books?hl¼en&lr¼&id¼awnGCgAAQBAJ&oi¼fnd& pg¼PA3&dq¼inkjetþfood&ots¼KOH3zuOD-7&sig¼AZMjkI5pxc-P9YpI2GZtEkhVxo#v¼onepage&q&f¼false. Kamphuis, H.J., 2009. Production and quality standards of cocoa mass, cocoa butter and cocoa powder. In: Beckett, S.T. (Ed.), Industrial Chocolate Manufacture and Use: Fourth Edition, pp. 121e140. Keijbets, E.L., Chen, J., Vieira, J., 2010. Chocolate demoulding and effects of processing conditions. Journal of Food Engineering 98 (1), 133e140. https://doi.org/10.1016/j.jfoodeng.2009. 12.019. Lanaro, M., Forrestal, D.P., Scheurer, S., Slinger, D.J., Liao, S., Powell, S.K., Woodruff, M.A., 2017. 3D printing complex chocolate objects: platform design, optimization and evaluation. Journal of Food Engineering 215, 13e22. https://doi.org/10.1016/j.jfoodeng.2017.06.029.

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Larsson, K., 1966. Classification of glyceride crystal forms. ACTA Chemica Scandinavica 20 (8), 225e2260. https://doi.org/10.3891/acta.chem.scand.20-2255. Makino, M., Fukuzawa, D., 2017. Simulation of 3D food printing extrusion and deposition. SPIE Smart. http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid¼2621694. Makino, M., Fukuzawa, D., Murashima, T., Kawakami, M., Furukawa, H., 2017. Analysis of deposition modeling by particle method simulation. Microsystem Technologies 23 (5), 1177e1181. https://doi.org/10.1007/s00542-016-3047-4. Malone, E., Lipson, H., 2007. Fab@Home: the personal desktop fabricator kit. Rapid Prototyping Journal 13 (4), 245e255. https://doi.org/10.1108/13552540710776197. Marketsandmarkets.com, 2011. Global Chocolate, Cocoa Beans, Lecithin, Sugar and Vanilla Market by Market Share, Trade, Prices, Geography Trend and Forecast (2011-2016). Meyer, J., 2009. Manufacturing processes: deposition of fillings. In: Talbot, G. (Ed.), Technology of Coated and Filled Chocolate, Confectionery and Bakery Products, pp. 427e441. Mossu, G., Technical Centre for Agricultural and Rural Co-operation, 1992. Cocoa. Macmillan published in co-operation with the Technical Centre for Agricultural and Rural Co-operation. https://books.google.com.au/books/about/Cocoa.html?id¼Kh9IAAAAYAAJ&redir_esc¼y. Oskay, W., Edman, L., 2009. The CandyFab Project. Ovaici, H., Mackley, M.R., McKinley, G.H., Crook, S.J., 1998. The experimental observation and modeling of an “Ovaici” necklace and stick-spurt instability arising during the cold extrusion of chocolate. Journal of Rheology 42 (1), 125e157. https://doi.org/10.1122/1.550885. Pallottino, F., Hakola, L., Costa, C., Antonucci, F., Figorilli, S., Seisto, A., Menesatti, P., 2016. Printing on food or food printing: a review. Food and Bioprocess Technology 9 (5), 725e733. Springer US. https://doi.org/10.1007/s11947-016-1692-3. Russell, B.D., Ovaici, H., Lasenby, J., Beckett, S.T., Wilson, D.I., 2006. Real-time monitoring of chocolate extrusion by signal processing of pressure transducer data. Food Control 17 (11), 862e867. https://doi.org/10.1016/j.foodcont.2005.06.003. Sol, I.E.-J., Linden, D.V.D., Bommel, K.V., 2015. 3D Food Printing: The Barilla Collaboration. Stewart, D.R., 1998. Method of Photocopying an Image onto an Edible Web for Decorating Iced Baked Goods. https://www.google.com/patents/US6319530. Takagishi, K., Suzuki, Y., Umezu, S., 2018. The high precision drawing method of chocolate utilizing electrostatic ink-jet printer. Journal of Food Engineering 216, 138e143. https://doi. org/10.1016/j.jfoodeng.2017.08.017. Tscheuschner, H.-D., Markov, E., 1986. Instrumental texture studies on chocolate iii. Processing conditioned factors influencing the texture. Journal of Texture Studies 17 (4), 377e399. https://doi.org/10.1111/j.1745-4603.1986.tb00560.x. Van Malssen, K., Van Langevelde, A., Peschar, R., Schenk, H., 1999. Phase behavior and extended phase scheme of static cocoa butter investigated with real-time X-ray powder diffraction. JAOCS. Journal of the American Oil Chemists’ Society 76 (6), 669e676. https://doi.org/10. 1007/s11746-999-0158-4. Wille, R.L., Lutton, E.S., 1966. Polymorphism of cocoa butter. Journal of the American Oil Chemists Society 43 (8), 491e496. https://doi.org/10.1007/BF02641273. Wohlmuth, E.G., 2009. Recipes. In: Beckett, S.T. (Ed.), Industrial Chocolate Manufacture and Use: Fourth Edition, pp. 434e450. Ziegler, G., 2009. Flavour development in cocoa and chocolate. In: Beckett, S.T. (Ed.), Industrial Chocolate Manufacture and Use: Fourth Edition, pp. 169e188. Ziegler, G.R., Hogg, R., 2009. Particle size reduction. In: Beckett, S.T. (Ed.), Industrial Chocolate Manufacture and Use: Fourth Edition, pp. 142e166.

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Chapter 7

Potential Applications of Dairy Products, Ingredients and Formulations in 3D Printing Megan M. Ross, Alan L. Kelly, Shane V. Crowley School of Food and Nutritional Sciences, University College Cork, Cork, Ireland

Chapter Outline

7.1 Introduction 7.2 Overview of Relevant 3D Printing Technologies 7.3 Structure-Forming Mechanisms Involving Milk Components 7.3.1 Milk Proteins 7.3.2 Milk Fat 7.3.3 Lactose 7.4 Studies of Printable Dairy Structures 7.5 Analytical Tools for 3D-Printed Dairy Applications

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7.6 Case Study: 3D Printing of Processed Cheese 7.7 Research Needs, Challenges and Opportunities 7.7.1 Safety and Acceptance 7.7.2 Research Challenges 7.7.3 Industrial Advantages and Disadvantages References Further Reading

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7.1 INTRODUCTION 3D printing is being investigated for a broad range of applications, including printing of replacement parts for automobiles (Schniederjans, 2017), printing of tissues and organs in regenerative medicine (Murphy and Atala, 2014) and, quite recently, the printing of food as solid structures with unique visual and textural attributes (Sol et al., 2015; Sun et al., 2018). As a novel technology, 3D printing has gathered some momentum in recent years, but has yet to penetrate most home kitchens and food businesses. 3D printing of certain foods, such as chocolate and other confections, has been the subject of both academic research (e.g., Mantihal et al., 2017) and commercial applications (Choc Edge, 2017). In comparison, few scientific studies have focused on the Fundamentals of 3D Food Printing and Applications. https://doi.org/10.1016/B978-0-12-814564-7.00007-9 Copyright © 2019 Elsevier Inc. All rights reserved.

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printing of dairy-based foods, little is known about optimising the printing of dairy formulations, and no current-generation 3D printer is specifically engineered to print these materials. The dairy category spans a broad range of products and ingredients with diverse compositions, functionalities and structures, making dairy a promising source of raw materials for the 3D printing of food. The printability of dairy products (e.g., cheese, yoghurt, butter) and ingredients (e.g., protein isolates, edible lactose, milk minerals) is not well characterised despite the considerable opportunities they present for the preparation of foods that are both nutritious and flavoursome. There is significant scope to exploit the strong structure-forming properties of dairy systems during 3D printing through, for example, manipulation of gelling mechanisms, melting behaviour and ingredient interactions. To realise the potential of dairy in 3D printing, different model formulations will need to be tested and optimised for printability, with successfully printed objects subjected to multiscale characterisation to determine their post-printing integrity and functionality. The evolution of 3D dairy will be interwoven with the broader narrative of food printing. Lupton (2017) studied online news outlets for their coverage of developments in 3D printing of food between 2013 and 2016 and organised results into the five major promissory themes of Futuristic (e.g., ‘Kitchen of the future’), Creative (e.g., ‘Customised foods’), Healthy (e.g., ‘Foods for people with dysphagia and the elderly’), Efficient (e.g., ‘Food for plane travellers’) and Sustainable (e.g., ‘Use of alternative edible substances in food products’). Indeed, the opportunities afforded by 3D printing of dairy can be said to fit within these thematic areas. The inherent ‘promise’ of 3D food printing should be tempered by the many practical challenges the technology presents to food researchers, which are not limited to issues of retail price and user friendliness. In terms of personalised nutrition, many formulated products used currently in ‘healthy’ nutrition (e.g., elderly, dysphagia) applications, for example, contain milk protein ingredients as their primary protein source, yet little is known about their printability. As well as the processing-related challenges related to the effective and safe printing of such foods, there are questions associated with appropriate methodologies for analysing printed artefacts, which may have levels of geometrical complexity that are unprecedented for food. More broadly, much of the health-orientated imaginings of food printing are characteristic of a pervading discourse in food and nutritional science that has been strongly criticised as ‘nutritionism’ (Scrinis, 2008); for example, some imagine a dietary approach that merges the ‘quantified self’ movement with 3D food printing, in which self-tracking of biomarkers dictates the nutritional profile of the printed meal (Khot et al., 2017). Furthermore, 3D printing as ‘additive manufacture’ is frequently referred to as being ‘waste free’ and therefore sustainable, but this characterisation is not so straightforward. If dairy-derived ingredients are to be used in printing applications, then their entire life cycles,

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encompassing associated by-products, emissions and consumer food waste behaviour, will dictate to what degree the printed object is indeed environmentally friendly. These and other issues need to be considered in parallel with technological developments in food printing. Nonetheless, efforts to realise the potential of 3D printing in the food industry continue apace. Many individuals are more concerned with diet, desiring greater control over what they eat without sacrificing modern conveniences (Petty, 2017). Three-dimensionalprinted snack vending machines are being developed at present, with the object of delivering healthy printable snacks on the go (Gao et al., 2015). In this way, 3D printing is envisaged as facilitating the accurate ‘metering’ of ingredients/nutrients in printed meals. In this chapter, an overview of printing technologies of potential relevance for dairy printing will be provided. The structural transformations that occur in dairy systems will then be discussed, with the aim of gaining insights into future possibilities in printable dairy. The relatively sparse literature on the topic of 3D printing of dairy systems will then be reviewed. Some analytical tools to analyse dairy systems before, during and after 3D printing will then be proposed. Finally, a case study on the 3D printing of processed cheese that integrates the preceding topics will be presented.

7.2 OVERVIEW OF RELEVANT 3D PRINTING TECHNOLOGIES Over the past decade, the range of 3D printing technologies has expanded rapidly, particularly for the printing of nonedible materials, such as plastics and metal powders; however, food printing technologies are also being developed and are beginning to emerge in the consumer world. The equipment and materials available today are far more sophisticated than when 3D printing technology was first developed (Hull, 1986), when the first patent was issued for a stereolithography apparatus that could print plastics. A decade ago, 3D printers were an expensive hobby costing about the same price as a family car; in more recent times, a basic printer incurs roughly the same cost as a low-end laptop (Miller, 2016). This section will contain a brief overview of how a 3D-printed product is created from computer code and the printing technologies of potential relevance to dairy applications, as well as the advantages and disadvantages of these technologies. The majority of printing techniques require modelling software such as computer-aided design (CAD) or 3D scanning equipment to create a digital file of the 3D design (3D Systems, 2017). This file will contain information pertaining to the dimensions of the object to be printed. As seen in Fig. 7.1, the most common file format for the 3D model is Standard Tessellation Language (STL), which can be transformed into ‘G-code’ using a slicing programme such as Slic3r or CuraEngine, both of which are commonly used open-source software applications in 3D printing. This slicing software works by taking the

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FIGURE 7.1 Example of slicing software used by Choc Creator. Displays step-by-step guide from basic sketch of an idea to final 3D printed product (Choc Edge, 2017).

object in the STL file and ‘slicing’ it into individual layers, which then act as printing instructions in the form of G-code, guiding where the printer must print the material in order to form the shape (Hamilton et al., 2018). A common technology that has been used when printing desserts and confectionary is fused deposition modelling (FDM) (Fig. 7.2). This type of technology operates by extruding heated food material from a nozzle or syringe that is guided within the Cartesian coordinate space (X-, Y-, and Z-axis) during printing, with the rate of deposition being controlled by computer-regulated motors. This allows defined layer-by-layer geometries to be constructed using the most efficient pathway possible, with minimal excess material being deposited in the process. As each layer is extruded, the food material cools and hardens, providing a physical support for the subsequent layers (Additively Ltd., 2017).

FIGURE 7.2 Fused deposition modelling (FDM). Food material in liquid/semiliquid state is extruded through a narrow orifice and deposited onto a preprogrammed design, layer by layer.

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This form of printing often produces a visible layer-by-layer definition that may not be suitable for applications that, for example, require a smooth finish, such as detailed chocolate-based designs. Printing using FDM technology also has the advantage of being able to directly dose structure-building agents (e.g., hydrocolloids, transglutaminase) during printing by incorporating a side inlet embedded in the nozzle (Schutyser et al., 2018). Examples of FDM applications that are available on the market (at the time of writing) include Choc Creator and Foodini (Sun et al., 2018); these machines are claimed to be able to print confectionary-/chocolate-based structures and fruit-/vegetable-/ cereal-based structures, respectively. Another form of FDM printing technology is coextrusion printing. This technology was patented by Guillemette and Peters (2015), which mentions the potential for using coextrusion printing in food applications. In the food industry, extrusion technologies are commonly used to make pasta, dried snack foods, breakfast cereals and confectionary (Ding et al., 2006); however, extrusion technology can be combined with 3D printing to provide customisable layering, enrobing or filling capabilities in various food stuffs. The technology enables users to combine materials in different ways through different nozzle configurations. For example, a food material, such as semimolten chocolate, could be extruded through a nozzle, while a different food material, such as strawberry jam filling, flows through a narrower nozzle embedded within the main nozzle. In another configuration, different ingredients or formulations could be extruded from adjacent nozzles, creating side-by-side layers in a visibly stratified product. Guillemette and Peters (2015) have claimed that their coextrusion technology has the potential to incorporate localised preservatives, alternating flavours or colours in layered food products as a useful method to build functional, sensorial and visual complexity. This type of technology might also be useful in the pharmaceutical industry, where purified lactose, a dairy-based ingredient, is used as a bulking agent in pills and tablets. Three-dimensional printing pharmaceutical-grade lactose and medical drugs into tablets is a cost-effective production method for on-demand manufacturing, as well as individualised dosage (Sadia et al., 2016). Bilayer tablets are used as a controlled-release formulation to provide a way of successful drug delivery system into the body (Divya et al., 2011). Khaled et al. (2014) demonstrated the manufacture of relatively complex pharmaceutical formulations printed into bilayer tablets using an inexpensive desktop 3D printer. It was found that the 3D-printed formulation could match the controlled-release performance of a commercial manufactured bilayer tablet using conventional tablet compression methods. The authors proposed that there was clear potential for 3D printing to allow entirely new formulation types, for instance, new geometries and complex multilayer or multireservoir tablets and others.

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Calcium phosphate is a mineral naturally present in milk and also in human bone. Xilloc (2017), a Dutch medical engineering company, developed a bone implant consisting of pure pharmaceutical-grade calcium phosphate that can be used in non-load bearing areas such as the skull. Calcium phosphate was found to be printable using bioceramic printing technology, a type of FDM where calcium phosphate is made into a wetted mixture which can then be 3D-printed. Calcium phosphate forms durable but porous structures when printed. This may be an interesting area to explore for food researchers, where edible-grade milk minerals (i.e., calcium phosphate, zine, magnesium, iron, etc.) may form hard, rigid structures using 3D printing technology. When printing with dry, unwetted powders, however, a different form of technology called powder bed printing (PBP) is used to fuse or melt the particles together to create a solid structure. Selective hot air sintering and melting technology is a type of PBP and operates using hot air, which in turn fuses powdered food substances into a layered structure (The-CandyFab-Project, 2008). Initially, the powdered food material is spread out evenly and thinly using a levelling roller and subsequently undergoes melting when exposed to hot air. The roller then proceeds to level freshly introduced powder over the melted surface, fusing the layers together. This process is repeated to build the desired structure layer by layer in this fashion (Holland et al., 2018). This method can also use lasers in lieu of hot air to melt and fuse particles together (Fig. 7.3). This technology is called selective laser melting, also known as selective laser sintering (SLS). Diaz et al. (2014) patented this technology as a method of producing edible objects. The authors claim that in conjunction with a nonmelting powder component, a ‘binder’ can be used to

FIGURE 7.3 Principle of a laser sintering: a laser melts the fine layer of powdered material to cause it to fuse together into a solid structure. The levelling roller scrapes each layer to provide an even surface for the subsequent lasering.

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provide structural support. The binder component will melt at the temperature of the laser (140e180
C) and connect the nonmelting component particles. Sources of binders that may be used in the SLS process include polysaccharides, fats and waxes, and also proteins like those found in milk (i.e., casein). Liquid binding (LB) is another variation of PBP technology, which was originally patented by Bredt and Anderson (1999) as 3D printing. This 3D printing method, when applied to food, involves edible objects being produced by jetting a liquid food or ‘binder’ onto a print bed layered with edible powder. This powder can be composed of a water-soluble protein and/or a hydrocolloid to fabricate solid structures, as described by Godoi et al. (2016). The binder joins adjacent powder particles together due to dissolutionefusion or crosslinking of surface particles, thereby creating a 3D matrix. The technology can also be adapted to print flavoured edible binders which will allow the creation of interesting flavoured powdered structures, which can be rehydrated with a liquid if desired (Wegrzyn et al., 2012). There is limited evidence of this technology being applied in dairy formulations.

7.3 STRUCTURE-FORMING MECHANISMS INVOLVING MILK COMPONENTS Milk is a complex biological fluid consisting of multiple macronutrients potentially suited to 3D printing due to their structure-forming capabilities. The solids in bovine milk are comprised of lactose, fat and protein, in order of decreasing abundance, in addition to minerals, vitamins and other minor compounds (Fox, 2008). The physicochemistry of major milk components will be described in this section to establish the principle mechanisms that could be exploited in the printing of solid dairy structures.

7.3.1 Milk Proteins Two protein families are contained within the milk system, namely casein and whey protein. These proteins are present in bovine milk at a ratio of 80:20 casein:whey protein. Casein and whey protein have different structures and functionalities, with each family further subdividing into different proteins with unique properties (O’Mahony and Fox, 2013). Whey products are widely used as ingredients in food formulations due to their excellent functional and nutritional properties. Native whey proteins are globular in structure and, following heating (>70
C), will denature and aggregate. In order to gel, whey proteins must be present at sufficient levels of protein (6%) and will gel on heating or cooling. However, many factors affect the gelation of whey proteins, such as pH, heating rate, temperature,

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time and solutes (Lucey, 2008). It is generally agreed that whey protein gels can be classified as being either fine-stranded or particulate, or a mixture of both (Foegeding et al., 1998). These types of gel differ in functional properties. Fine-stranded gels are translucent and retain large quantities of water, while particulate gels are opaque and readily expel water. This influences mouthfeel in vivo where, for example, fine-stranded whey protein emulsion gels have smooth surfaces, express minimal fluid during chewing, with a low degree of cohesiveness and adhesiveness. In comparison, particulate gels have rougher surfaces, release higher levels of moisture during chewing and have a high degree of cohesiveness and adhesiveness (Gwartney et al., 2004). The type of gel formed can be controlled through certain factors and therefore manipulated to create a gel that will be ‘printable’, without being too thick or too liquid, in order to form a structure. For example, filament gels will form equally well at pH 2.0 and 7.0 in conditions of low ionic strength, whereas particulate gels will form at a higher ionic strength at or close to pH 7.0 (Foegeding, 2006). Changing the pH or salt concentration of the dairy formulation could thus enable the user to control the texture of the desired printed food. Fig. 7.4 shows these physiochemical differences between fine-stranded and filament gels in more detail. Whey proteins, unlike caseins, are considered more ordered in their structure. Whey proteins form gels due to a combination of noncovalent (e.g., hydrophobic) and covalent (e.g., disulphide linkages) bonds between denatured proteins (Anema and Li, 2003). In yoghurt, for example, whey protein gelation is important, as milk must be heated to allow for denaturation of the protein, which, in turn facilitates interaction with casein and therefore incorporation of whey proteins into the casein-based gel matrix (Anema, 2008). Whey proteins can undergo extensive aggregation during heating and form strong gels on cooling (Damodaran and Parkin, 2017). This cold-set gelling mechanism is amenable to FDM, as the solution could be heated prior to

FIGURE 7.4 Table with physiochemical property differences between fine-stranded and filament whey proteins.

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printing to maintain a flowable consistency and promote denaturation and subsequently undergo cooling on the printer bed to initiate gelation. However, at temperatures of 70
C and above, an increased viscosity could lead to fouling issues on extruding through a narrow orifice, where the coagulated particles clog the printing nozzle (Chandan, 1997). Caseins are large, self-associated assemblies of individual caseins linked together with calcium phosphate, forming casein micelles, which are porous and roughly spherical colloidal particles (Chandan, 1997). The casein micelle has a dynamic structure and is continuously exchanging components (i.e., ions) with the aqueous phase in which it is suspended to maintain chemical equilibria. Micelles also respond to changes in the surrounding environment, such as temperature, pH and pressure, accordingly. There are four subtypes of casein proteins, called aS1-casein, aS2-casein, b-casein and k-casein. The k-casein is located at the surface of the casein micelle and stabilises the structure sterically and electrostatically. This particular protein is easily accessed by chymosin, or other proteinases with comparable specificity, which cleaves a bond (Phe105eMet106) specific to k-casein. This, in turn, initiates the gelation of milk by allowing coagulation of the caseins in the presence of calcium, which is the basis of cheesemaking (Huppertz, 2013). Acid-induced gelation is also a method of coagulating casein and is commonly used in the manufacture of soft cheeses and yoghurt. Unlike rennetinduced gelation, bacterial cultures are added to liquid milk which ferment lactose into lactic acid, thereby lowering the natural pH of milk from pH 6.7 to pH 4.6, the isoelectric point of casein, where electrostatic repulsion is minimised (Lucey and Singh, 2003). Acidification may also be achieved through the addition of mineral acids (e.g., hydrochloric acid) in combination with warming, which is used to produce the ingredient acid casein. Caseins are relatively heat stable as a consequence of their open structure and do not denature or unfold on heating (Holt et al., 2013). When combined with hydrocolloids (thickening and gelling agents derived from carbohydrates, animals and seaweeds) such as carrageenan, caseins can generate network structures which stabilise multiphase dispersions (Puvanenthiran et al., 2003). Verbeken et al. (2006) combined k-carrageenan, milk proteins and modified starch to form gelled, sterilised dairy desserts. The study found that modified starch imparts a large influence on the complex modulus of the gel due to the exclusion effect of the swollen starch granules, which act as noninteracting fillers, which in turn concentrates the carrageenanemilk protein solution in the continuous aqueous phase, allowing a strong gel to form. Such approaches could potentially be applied to printed dairy products, depending on their desired attributes and functionality. Oleogels are an interesting development in emulsion science, which have been proposed as an alternative replacement to trans and saturated fats (Dassanayake et al., 2011), and often rely on the structuring function of dairy proteins. Oleogels can be defined as an organic liquid (i.e., liquid fat)

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entrapped within a thermoreversible 3D protein gel network (Stortz et al., 2012). According to Marangoni and Garti (2011), the major approach in producing oleogels is to incorporate specific molecules (i.e., polymers such as proteins) into the oil components to alter the physical properties of the oil. This leads to a decrease in fluidity, giving rheological properties that are similar to those of fats. Oleogels have been effectively used by Stortz et al. (2012) to replace hardstock fats (i.e., solid phase in margarine) in creams and cookies, and potentially other dairy-based foodstuffs such as cheese and ice cream. Oleogels could be a potentially printable substance to enhance nutritional profiles of food through encapsulation through the addition of plant sterols, lycopene or coenzyme Q10 to the proteineoil matrix (Zetzl and Marangoni, 2012; Zhang et al., 2015). This could be achieved using 3D printing technology where the nutrient can be added at the last step as the material leaves the nozzle and cools on the print bed.

7.3.2 Milk Fat Raw milk is an oil-in-water emulsion, consisting of fat globules protected by a thin layer called the milk fat globule membrane (MFGM) suspended in the aqueous phase, which stabilises the emulsion through lowering of the interfacial tension surrounding the fat globule. In the manufacture of butter, the fat fraction of milk (i.e., cream: 40% milk fat) is separated from skim milk and pasteurised. The cream is then churned at cold temperatures (approximately 14
C) using an augur or similar disruptive force to disrupt the MFGM, leading to an inversion to a water-in-oil emulsion. Buttermilk is then separated from the butter grains, and the butter is subjected to a second churning stage in order to further remove excess buttermilk. At this stage, moisture levels can be adjusted and salt or cultures added if desired. Ghee is clear butter fat which originated from India, and is typically made by heating butter and evaporating the remaining moisture, resulting in a buttery-flavoured product with an extended shelf-life (Kratochvil and Vedlich, 1974). Triglycerides (TG) are the primary fat component present in liquid milk, along with carotenoids and vitamins. TG content can be controlled though the diet of the animal, by feeding sources of unsaturated or saturated fatty acids. Milk fat has an extremely diverse fatty acid profile and therefore a varied TG composition, which contributes to a wide range of melting temperatures, spanning from 40
C to 40
C (Rønholt et al., 2014). Butter has been used as decoration and ornamentation on hotel and restaurant tables for decades, as the unique texture of butter allows it to be easily moulded, shaped and sculpted. Schnell (2013) discussed the work of Pamela Simpson and Caroline Brooks, who were renowned for their famous butter sculptures, including a life-size bust of Teddy Roosevelt, the 26th US president.

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There are many factors that can affect the structure of fat that may be relevant during printing of dairy products. This includes whether the butter has been subjected to thermal treatment, which can influence crystal polymorphism (change of crystal fat structure). In addition to this, the number and sizes of fat crystals created, as well as crystalecrystal interactions within the product, are critical determinants of texture (Rønholt et al., 2013). The process of fat crystal formation and growth are vital elements in developing the fat crystal network within a dairy fat product such as butter. Consequently, properties such as spreadability, mouthfeel, appearance and product functionality are affected by the fat crystal network. It is generally accepted that the presence of fat globules produces a softer product in comparison with milk fat-based products without any fat globules present (Mulder and Walstra, 1974). During printing, the food extruded is subjected to a certain stress when pushed through a narrow orifice or nozzle. Paragraph break Three-dimensional butter printing has never been studied to the authors’ knowledge; however, the rheology of butter has been well characterised and may give some indication of how the butter will print. When a small stress is applied to butter, the crystal network may distort, resulting in reversible breakage of some crystal bonds. In contrast, when a large stress is applied, this will rearrange the network or cause fracturing, resulting in irreversible breaking of the bonds (Rønholt et al., 2014). Although studies have yet to be performed on the printability of butter and other dairy fat-based products, butter is known to be easily sculpted, holds its shape well at refrigeration and ambient temperatures, and has been well studied for its meltingesolidification behaviour.

7.3.3 Lactose Lactose, the sugar in milk, is a disaccharide of glucose and galactose joined by a glycosidic linkage. Lactose is present in whey and can be recovered in purified form through a crystallisation process for food or pharmaceutical use (Paterson, 2017). Lactose is used in a variety of different food applications, such as ice cream, to increase viscosity or improve texture without imparting an excess level of sweetness. Lactose has flavour-, aroma- and colourabsorbing properties, which can be beneficial in a product that requires the release of fragrant aromas or intense flavours over time (e.g., confectionary). In the baking industry, the role of lactose in the Maillard reaction or browning process is taken advantage of in creating a caramelised flavour and improved appearance of baked products. Lactose is primarily used in the production of humanised infant formula where its main role is to correct the balance between carbohydrate and protein of cow’s milk to make it more comparable to human breastmilk. Lactose is relatively slow to digest and has bifogenic activity, meaning the infant has prolonged energy and maintains a healthy intestinal flora in the gut. Lactose can also be added to other powders in order to increase the free-flowing properties of powdered foods (Holsinger, 1997).

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During an SLS process, powders must be free-flowing in order to create an even surface for the laser to penetrate a thinly layered powder. In this type of 3D printing, the powder bed process, sugars such as lactose provide the scaffolding or framework of the printed structure. Factors affecting the flowability include the compressibility and density of the powders themselves (Berretta et al., 2014; Godoi et al., 2016). In comparison with other sugars, lactose has a relatively low level of solubility (Holsinger, 1997). This becomes important when lactose is added to a formulation and printed using FDM technology, as the solution must remain homogenous and flow readily without clogging the nozzle. However, solubility of lactose when dissolved can be controlled through mutorotation or interconversion between the two forms of lactose, a and b, each form having distinctly different solubilities. Of the two, a-lactose has a lower solubility in water at temperatures 7.0 result in very rapid mutorotation. Temperatures above 70
C also allow mutorotation to occur in minutes rather than hours at room temperature (Huppertz and Gazi, 2016). Lille et al. (2018) studied the 3D printing properties of skimmed milk powder (SMP) which contains 53% lactose, and semiskimmed milk powder (SSMP), which was hydrolysed to create a lactosefree powder. Comparing the printing quality between these two food materials may be useful in determining how lactose may contribute to structure. Using 60% SSMP paste solution, the authors were able to print a square grid (25 mm  25 mm) with excellent printing precision and shape retention (i.e., no warping or spreading of the layers). In contrast, 50% and 60% SMP prints sticky and dry, crumbly prints, respectively. However, it is not understood completely whether lactose is the contributing factor to a lower-quality print, and further research must be considered in this area.

7.4 STUDIES OF PRINTABLE DAIRY STRUCTURES Despite recent progress with 3D food printing technology, only a small group of food products have been successfully printed. Dairy materials that may be applicable in 3D printing will be discussed in this section, including SSMP, SMP, sodium caseinate (NaCas), micellar casein concentrate (MCC) and processed cheese. Processed cheese will be the subject of a detailed case study later in this chapter. SSMP is a dairy ingredient in which the fat/cream in whole milk (3.5% fat) is removed by centrifugation and then reincorporated at approximately half the level of the original milk; the reduced-fat milk is then evaporated and

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spray-dried to generate a powder. SMP is a similar product except that the fat is not reincorporated after it has been removed (Lewis and Deeth, 2009). SSMP has been demonstrated to be compatible with 3D printing after reconstitution to a high solids content (60% w/v). Lille et al. (2018) conducted 3D printing experiments with protein- and fibre-rich foods. Print quality (e.g., precision, shape) was assessed visually from photographs using a scale, ranging from 1 ¼ poor quality to 5 ¼ good quality. The authors used lactosefree SSMP, in which the lactose, a disaccharide, was enzymatically hydrolysed into its component monosaccharides, glucose and galactose. SSMP at 60% solids scored 5 in print quality, SMP (60%) scored 1 and starch (15%) scored 3. The superior printability of SSMP was suggested to be due to its higher fat and lower carbohydrate content, allowing a more free-flowing print. Although SMP or starch were unsuitable for printing when either were used alone, Lille et al. (2018) observed that a mixture of starch (10%) and SMP (15%) was more printable (print quality value ¼ 4). Derossi et al. (2018) used SMP as an ingredient during a study on the 3D printing of fruit-based snacks for children. Fresh bananas, dried mushrooms, canned white beans, lemon juice, pectin and ascorbic acid were used in combination with the SMP to create a cube-shaped snack containing 5%e10% of the total daily energy requirement for a child. X-ray microtomography analysis of the snacks showed that the most structurally uniform sample was printed at a flow level of 130%, which indicates the amount of material extruded during printing, and a printing speeds of 70 mm/s compared to those at a lower flow rate (100% and 70%) and print speed (50 and 30 mm/s). A flow of 130% means a 30% increase in speed of the mechanism extruding the paste (e.g., motor driving extrusion pump) and therefore a 30% increase in millimetres of paste extruded from the nozzle. Printing speed refers to the rate at which the physical nozzle of the printer moves at. At a lower flow rate (i.e., 70% and 100%), the cube-shaped snack appeared irregular, depositing broken material line pathways and large undesirable cavities. Many milk protein ingredients exhibit thermoreversible solegel transitions and could be used at lower concentrations than the previous SMP/SSMP examples by exploiting phase transitions induced by temperature changes. NaCas suspensions at high concentrations display such thermoreversible properties and have been studied in 3D printing applications (Schutyser et al., 2018). NaCas is manufactured by adding sodium hydroxide to acid casein (e.g., casein prepared from milk by acid precipitation) curds or powder to create a solution of pH w6.6, under which conditions the caseins become more soluble and functional. NaCas displays a thermoreversible transition from a solution to a gel at or above a critical concentration (140 g/L) with added salt (1.53 M NaCl), existing as a liquid at >50
C and a solid gel at 5
C (Carr and Munro, 2004). Schutyser et al. (2018) 3D-printed hot NaCas-based emulsion systems that solidified on a cold printing stage. The authors used a nozzle with a side inlet to incorporate coloured vegetable oil droplets into the

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protein matrix during printing. Using the dispenser with a side inlet created a unique structural design with a controlled spatial distribution of oil droplets. According to the authors, this technique may afford more freedom and creativity in the customisation of healthy foods, where vitamins and minerals can be encapsulated and incorporated into a protein matrix. MCC is similar to NaCas in that it forms cold-set thermoreversible gels. MCC is manufactured using microfiltration of milk in order to concentrate the casein protein (without precipitation) and remove whey protein, lactose and soluble minerals (Schuck et al., 1994). Nutritionally, MCC is much higher in minerals (especially calcium and phosphorous) than NaCas, and, functionally, it generates more opaque gels. MCC will form a thermoreversible gel at low temperatures, and on subsequent ‘melting’, should not display any alteration in functionality compared to the initial liquid (U.S. Dairy Export Council, 2015). Amelia and Barbano (2003) confirmed the thermoreversible behaviour of MCC by using 18% MCC held in a suspension. A gel is formed when the solution is cooled to 4
C, but reverts back to a liquid when heated above from 4 to >22
C. Lu et al. (2015) also studied the thermoreversible properties of MCC, where MCC formed a cold-set gel at 38
C at 23% protein concentration. Cheese has also been reported to be suited to 3D printing applications, with mozzarella or burrata cheese being printed on pizzas (BeeHex, 2017), for example, and processed cheese or mascarpone being printed into various shapes (Le Tohic et al., 2018). Certain cheeses may be more appropriate for 3D printing than others, which may depend on factors such as their composition (e.g., fat, protein, lactose) and functional properties (e.g., meltability, flowability). However, at the time of writing, published research on the 3D printing of different varieties of cheeses is solely limited to processed cheese (Le Tohic et al., 2018; Lipton et al., 2010).

7.5 ANALYTICAL TOOLS FOR 3D-PRINTED DAIRY APPLICATIONS To print effectively, an understanding of the impact of heating/cooling and shearing forces on the macro- and microstructure within a food product is vital. Food formulations can be constructed using this information to add and subtract or manipulate the ingredients to suit the application. Using analytical techniques to examine the foodstuff is essential to gathering this information such as gel strength, textural properties (e.g., hardness, stickiness), colour, porosity, melting characteristics and viscosity. Analysis of 3D-printed food material may be divided into preprinting (e.g., melting, gelation and powder properties) and postprinting (e.g., texture profile analysis [TPA], colour, microscopy, X-rays) testing. Some tools used to measure these parameters, as well many other quantifiable measures, will be discussed in this section, beginning with rheology.

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Understanding the rheological and mechanical properties of various dairy products is important in the design of flow processes in 3D printing (Foegeding et al., 2011). Rheometers are used to characterize the flow and deformation behaviour of a food material. They can apply oscillatory as well as rotational motion to the spindles, which can quantitatively measure parameters such as shear rate, percent deformation and shear stress. The gelation point of a dairy ingredient-based gel can be measured using small-amplitude oscillatory rheometry, for example. The solution is subjected to sinusoidal deformation or waves using a specific head geometry (e.g., cone and plate, parallel plate) to suit the viscosity of the solution. The gel point is defined as the point at which the storage modulus (G0 ) becomes larger than the loss modulus (G00 ), indicating that the fluid has transitioned from fluid-like flow behaviour to solid elastic behaviour (Phillips et al., 1994). Rheometers can also apply large step changes in stress and strain to determine viscoelastic properties as well as flow properties (Metzger, 2006). This can become useful in comparing flow properties of various dairy-based food ingredients and therefore determine optimum flow conditions suitable for printing that food type. Rheometers also tend to offer a wide range of sampling accessories, such as temperature control units to study materials under a wide range of conditions, which can simulate thermal processing or printing conditions over time (ATA Scientific Instruments, 2010). This may be applicable to printing in examining how food will flow through a nozzle, whether it will increase in viscosity over time with constant temperature and shear rate or whether the structure will be disrupted and become more liquid as more shear is applied. In contrast, a rotational viscometer has a far more limited range of applications, where the equipment only measures viscosity (h) of various liquid/ semisolid foods by rotating the spindle in one direction. The rotational or shear rate can be increased or decreased depending on the initial viscosity of the food. For example, in a chocolate printer used in a study by Mantihal et al. (2017), the chocolate was melted in a syringe whilst being mixed using a rotating auger within the reservoir. The temperature of the food can be altered or maintained through the use of a heating and cooling jacket surrounding the sample container. This allows the sample to be subject to temperature sweeps, mimicking the printing process, where the food may be heated in the syringe or reservoir, and cooled on a prechilled printer stage (ATA Scientific Instruments, 2010). Melting properties are important attributes to measure, especially in the context of dairy-based foods, such as cheese. For example, a Discovery Hybrid Rheometer (TA Instruments, United States) was used in a processed cheese 3D printing study by Le Tohic et al. (2018) in order to assess the flow behaviour and melting properties of cheese samples in the linear viscoelastic region (LVR). Using a dynamic temperature sweep test and a stainless steel parallel plate attachment, the LVR was determined using a dynamic sweep test using

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the method described by Prow and Metzger, (2005). It was found that the ratio of G0 to G00 , called the loss tangent, tan (d) represents the temperature at which the food material yields to a solid-to-liquid transition (Foegeding et al., 2011). This is useful information in terms of printing to determine the most suitable viscosity for a dairy product, both for extrusion without any issues of clogging, but also for determining the point where the product gets too fluid-like or ‘runny’ and is uncontrollable during the printing process (Lanaro et al., 2017). In PBP applications, powder properties such as particle size, flowability and wettability are important to consider. Holland et al. (2018) suggests that a mixture of small and larger particles is the most suitable for use in 3D printing. Smaller particles will fill the gaps created between larger particles, therefore reducing unwanted porosity in the finished product. Particle size can be measured using a laser diffraction particle size analyser, which measures the angular variation of light intensity of a laser beam as it passes through a dispersed particulate sample. The sizes of the particles are inversely related to the measurement of the angles of light scattered (Levoguer, 2013). Flowability also plays an important role in PBP, especially when the powder must be spread evenly, allowing the buildup of thin layers. Low flowability (i.e., restricted movement of the powder) will lead to insufficient recoating of the previous layer, therefore creating weak and porous structures (Berretta et al., 2014). Yang and Evans (2007) showed that high particle sphericity improves powder flowability. The authors also concluded that coarse powders flow easier than fine powders, and factors such as high temperature and humidity affected the flow negatively. Flowability of powders can be analysed using shear cell testers such as the Brookfield Powder Flow Tester, where a sample is sheared and compressed simultaneously using whilst measuring the torque resistance of the powder (Salehi et al., 2017). Wettability of particles is also an important physicochemical property, especially in LB printing technology. The volume of binder dispensed onto the powder bed and the amount of binder absorbed by the particles dictates the quality of resolution and structural properties of the print. Low wettability of fine particles results in powder bed instability, and high wettability combined with low flowability may cause the particles to clump together, negatively affecting the quality of the print (Shirazi et al., 2015). The Washburn method is an analytical technique that can be used to determine wettability of a powder, where a column with powder lowered into contact with a liquid and the uptake of liquid are monitored as a function of time. Displacement or mass uptake is plotted against time to obtain the wettability (Thakker et al., 2013). Accuracy and consistency of the print are important selling points of 3D printing. It is essential to be able to evaluate the performance and precision of the print in order to avoid any errors or discrepancies between samples. Lanaro et al. (2017) described a line test in which the calculated amount of extruded chocolate could be compared to the actual amount of extruded chocolate. Using a calculated flow equation integrating syringe plunger displacement,

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nozzle diameter and syringe internal diameter values, the amount of extrudate was made to equal the inner diameter of the needle. To conduct the line test, the printer was programmed to extrude chocolate in a back-and-forth motion, where the diameter of the line could be measured. To do this, image analysis software was used, and as the food was extruded, the predicted could be compared to the actual diameter of chocolate extruded, which is a useful calibration and optimisation technique in 3D printing. Texture analysis is the collective term for the destructive compression tests: TPA and uniaxial compression testing. TPA is an instrumental method of measuring critical sensory attributes (Steffe, 1996). TPA uses two uniaxial compressions and results in a plot from which parameters such as degree of firmness, cohesiveness, resilience, springiness and adhesiveness can be calculated (Chen and Opara, 2013). Uniaxial compression, however, works by only compressing the food sample once in one single direction. This method yields values for Young’s modulus, fracture stress/strain, work of fracture and hardness (Hamann et al., 2006). Uniaxial compression can also be used to test structural stability and softness of a food substance postprinting, where a flatheaded probe attachment is used to compress the food to a certain point and then released. The force needed to compress the sample to a certain height is measured, where a larger force equals a harder, more solid food, and a lesser force equals softer, more elastic food. For example, Le Tohic et al. (2018) used this method to compare hardness between printed substances versus nonprinted processed cheese cylinders. It was found that the printed processed cheese required less force than nonprinted cheese, leading to the conclusion that printed cheese was softer than the control (see Section 7.6 for more detail). This technology can also be used to determine optimal geometries to achieve certain sensory characteristics in printed chocolate (Mantihal et al., 2017). Snap quality is an important parameter in chocolate manufacture, with a stronger snap often being more desired, as it can suggest a higher-quality chocolate. In the above study, three different structural supports were tested for a printed hexagonal prism-shaped chocolate: a crossed biaxial support, a parallel support and no support present, as seen below in Fig 7.5. It was found that the chocolate design with cross-support required a higher force to break the chocolate structure, indicating a better snap quality than the other designs. Another important group of methods that can be helpful in analysing 3Dprinted products is microscopy. Microscopy allows the observation of the types of aggregates, location of nongelling components such as fat, structure porosity and homogeneity of the gel. Confocal scanning laser microscopy (CSLM) is a more recent development in microscopy technology, which is relatively noninvasive to the sample. The sample, in liquid, solid or powder format, is optically sectioned into X, Y and Z axes, which allows the viewer to observe each layer individually (Sozer, 2016). Foegeding (2007) used CSLM to view the effect varying the protein content of gels would have on the

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FIGURE 7.5 Three different structural designs of printed chocolates analysed for snap quality using uniaxial compression (Adapted from Mantihal et al., 2017).

fracture strength. The authors found that gels containing 6% protein had a lower fracture stress, higher fracture strain and a porous structure, and protein clusters rotate during deformation. In comparison, gels containing 12% protein had higher fracture stress and lower fracture strain, and their microstructure showed considerably less change in deformation. Le Tohic et al. (2018) also used CSLM, in combination with staining to observe microstructural changes between printed processed cheese and untreated processed cheese. CSLM enables the users to stain particular items of interest (i.e., proteins, phospholipids, fat globules) to differentiate between different components within the structure (Keogh and Auty, 1998). Porosity can influence flavour release, texture and degree of syneresis. This value can be measured using X-ray microtomography. X-ray microtomography is a powerful nondestructive technique which provides direct images of internal structures and is typically used to assess microstructural details (Babin et al., 2007). X-ray microtomography can be used to determine the air bubble/ pocket size, distribution, orientation and their position within the food matrix. Defects such as altered support structures and abnormal porosities can be quantified through the use of this technology (Guillermic et al., 2018). Such defects can be caused by undesirable air pockets created within the food matrix which can cause gaps during printing travel across the print bed. Applying a vacuum to minimise air inclusion can remedy this issue (Liu et al., 2018). Kuo and Lee (2014) suggested that a more porous structure enabled a maximum rate of sodium release during initial gel compression, and flavour released at a faster rate. However, porous gels can also lead to greater degrees of syneresis which is typically undesirable in certain products such as yoghurt, but desirable in cheese (Harwalkar and Kalab, 1986). X-ray microtomography has also been used in non-3D-printed food applications by Laverse et al. (2011a,b) in both cream cheese and yoghurt, respectively. In these cases, this technology was used to determine an accurate percentage of the volume of the fat present and also the spatial distribution of those fat globules. Similar to the processed cheese study by Le Tohic et al. (2018), this

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technology is useful in understanding how 3D printing might structurally alter morphology and distribution of fat globules and what implications this might have on texture. Shape stability during postprinting processes are also important parameters to consider. The vast majority of 3D food printers are limited to single-step processes, and any cooking/baking steps require an additional separate step. Lipton et al. (2015) considers the possible implications of combining the printing and cooking process a single step on the food structure. In order to compare deformation and shape consistency, the authors measured the height, length and width of the 3D-printed cube-shaped dessert directly after printing and again after baking. It was found that an increase in butter quantity in the formulation led to a decrease in shape stability. The mixture became easily extrudable when butter quantities were increased by 150%; however, it was unable to retain its shape at room temperature. Determining the colour change of dairy-based foods before and after printing can be meaningful. At times, this can be desirable if Maillard browning is required to achieve a caramel-like flavour; however, in many other applications, a change in colour may not be desirable. Colour measurements of food samples can be assessed using a Chroma Meter CR-300 (Minolta Camera Co., Osaka, Japan) or similar colorimeter. The equipment must be calibrated using a referenced plate, and then Hunter L, a and b values can be recorded in triplicate at the surface of the food samples. L describes lightness and varies from 0 (black) to 100 (white). The magnitude of a and b both vary between 300 and 299, which describe green to magenta and blue to yellow, respectively. Relative differences for L (DL), a (Da), and b (Db) enable the user to determine overall colour difference, DE, using an non-3D-printed sample as a reference (Le Tohic et al., 2018).

7.6 CASE STUDY: 3D PRINTING OF PROCESSED CHEESE In this section, a brief overview of the recently published findings of the paper, ‘Effect of 3D printing on the structure and textural properties of processed cheese’, will be presented and also the mixed media interest that accompanied this recent report. Researchers at University College Cork, Ireland, first identified 3D printing potential in processed cheese in 2015 when trialling a variety of cheeses that may be suitable for the printing process. Processed cheese is manufactured using methods that in some way mimic the 3D printing technique, where ingredients are mixed at a high temperature under vacuum and then moulded into a cylindrical shape. The sample delivery system was modified from a traditional 3D printer designed to print plastic such as polylactic acid. Several design options were created, with the final construction being a 20-mL syringe where a rotating metal threaded rod pushed the syringe plunger downward and extruded the cheese sample from the nozzle at a constant flow rate.

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Processed cheese was shown in preliminary tests to be suitably flowable to be distributed via a narrow nozzle, but also sufficiently viscous to set into a buildable structure during printing. The effect of speed of printing on the structure and textural properties of the cheese was studied, whereby samples were printed at flow rates of 4 or 12 mL/min, respectively. These were compared against an untreated processed cheese and melted (but not extruded) cheese sample to differentiate between the changes in properties. The melted cheese was heated at 75
C for 15 min and then cooled at room temperature for 30 min, followed by storage in refrigeration conditions. The samples for printing were treated in a similar fashion; however, they were heated for 12 min to achieve comparable melting characteristics as the melted cheese sample, as these samples would be subjected to further disruption when sheared by way of extrusion through the printer nozzle. After printing, analysis was carried out on the cylindrical cheese samples to determine how the texture and structure was altered during printing. The cheese was allowed rest for 30 min postprinting and then refrigerated for 24 h before analytical evaluation. The textural analysis consisted of two compressionedecompression cycles, separated by a time interval of 5 s at a rate of 1 mm/s, using a cylindrical aluminium head with a diameter of 35 mm. The probe compressed the sample to 25% (5 mm) of its initial height (20 mm) before decompression. The figures below indicate that the printed cheeses (C) and (D), required less force to compress the sample, meaning the cheese is softer. The untreated cheese (A) required almost twice as much force, implying that the sample was harder than printed cheese (Fig. 7.6).

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FIGURE 7.6 Texture profile analysis (TPA) profiles of (A) untreated cheese (UC), (B) melted cheese (MC), (C) low-speed printed cheese (LSPC), and (D) high-speed printed cheese (HSPC): two compression tests with 5-s intervals (Le Tohic et al., 2018).

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FIGURE 7.7 Confocal laser scanning micrographs of cheese samples. (A) Untreated cheese (UC), (B) melted cheese (MC), (C) low-speed printed cheese (LSPC), and (D) high-speed printed cheese (HSPC) (Le Tohic et al., 2018).

There was not a comparable difference between the two extruded cheeses in texture and softness; however, there was a more significant difference when the structures of the cheese samples were observed under a confocal laser scanning microscope. Here, a red stain shows fat structure, and a green stain illustrates the protein network within the cheese sample’s structure. In Fig. 7.7, it is possible to make out the fat globules as the lighter white/grey areas and the darker, deeper grey/black areas as the protein network. It can be seen that the untreated cheese (A) shows a well-characterised and uniform distribution of round fat droplets within the continuous protein phase. The melted cheese displays similar structural elements; however, the fat droplets are visibly larger than those of the untreated cheese, presumably due to the fat coalescing on melting. In contrast, the more slowly printed cheese (C) presents a discontinuous protein phase and random fat regions varying in

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size and shape. The micrograph image of the faster printed cheese (D) suggests similar sized fat globules than those of the slower printed cheese, yet the lipid droplets appeared to be smaller and slightly more uniform (C). The higher shear rate being utilised during faster printing should contribute to greater fat globule disruption, resulting in this particular network formation. Consequently, the disruption of fat globules confirms the rheological and textural data shown in Fig. 7.7, where the interruption of the protein and fat phase produced a softer, more easily meltable cheese. Another comparable difference found was that the printed cheese was notably darker in colour with a lightness value, L, of 80.8 for high-speed printed cheese than the untreated cheese sample with an L value of 83.3. This is also due to the modification to the fat globule size and morphology and nonuniform protein network formation, where the higher-speed printed cheese was slightly darker as a consequence of the presence of larger fat globules than the slower printed cheese (Le Tohic et al., 2018). The media coverage on this topic began in early March 2017, when articles began to be published online on websites such as Dairy Reporter, 3D print.com, Live Science and IFL Science, with headlines ‘Study on 3D Cheese Printing Offers Possibilities’ (Cornall, 2017) and ‘Let’s Cut to the Cheese: Researchers Publish Study on How 3D Printing Affects the Structure and Texture of Processed Cheese’ (Saunders, 2017), to name a few. Within 10 days, there were over a dozen articles written, and video footage of the 3D-printed cheese went viral on social media platforms such as Facebook and Twitter. The video itself has been viewed 4800 times (at the time of writing in October 2017) on the CNN Facebook page alone, as well as many multiple thousands of views on other scientific- and technology-related pages. There were positive reactions from the online community to the concept in addition to sceptical comments relating to feasibility in everyday use, relevance of the technology to current global challenges and disappointment that processed cheese was the source material rather than cheese itself. Few commentators reflected on the possibilities for the technology to be adapted to other food systems beyond processed cheese. The mixed commentary echoed the report by Lupton and Turner (2016) in their survey of responses to the concept of 3D food printing by an online discussion group (titled ‘Both Fascinating and Disturbing’). In general, most articles embraced the concept and its novelty while indicating that research for 3D-printed edible food is at an early stage of development. Since the publication of the research paper and attention from the media, Professor Alan Kelly, as lead author of the research paper, has been invited to speak at multiple 3D printing-related events and conferences in 2017. It is now understood that more research will continue into how other dairy structures can be used for dairy printing applications and perhaps produce snack and meal concepts with a range of compositions and applications.

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7.7 RESEARCH NEEDS, CHALLENGES AND OPPORTUNITIES In spite of the most recent developments, the majority of technologies for 3D food printing are still undergoing research and in the growth phase. This is due to the challenges that researchers face in terms of creating a technology that will incorporate traditional methods of cooking and baking whilst modifying these foods to suit the 3D printing process and still remain appetising. Consumer acceptance of new technologies is another factor that creates obstacles for the emergence of 3D printing. Other considerations in terms of research needs, challenges and opportunities include how 3D printing will affect food supply chains, whether the food is considered safe and whether 3D printing will help or hinder our current relationship with food.

7.7.1 Safety and Acceptance Food safety is one of the most important aspects of food manufacture. Due to 3D printing being a novel food technology, it will undoubtedly be met with a reasonable amount of scepticism by the general public. The name ‘3D printing’ is another aspect that generates confusion amongst the general public. People may associate printing with ink and high level of processing if care is not taken to introduce the technology with due transparency and clarity regarding its operating principle (Brunner et al., 2018). Consumers may view novel food technologies with suspicion (Popa and Popa, 2012); however, not all new food technologies and food trigger the same ‘neophobia’. Both the technology itself and the individual’s own experience and knowledge background play a determining role in the evaluation process. Repeated exposure to different types of novel food and visual representations of them can also contribute to making new processing techniques and new food more familiar to consumers, which may positively affect consumer attitudes (Brunner et al., 2018). The importance of ‘naturalness’ is also a key implication of how 3D printers will be accepted by consumers. Consumers may have conflicting interests in that they may view the potential convenience and creativity associated with 3D printing positively, but may also link the technology with undesirable, overly processed and unhealthy foods (Roma´n et al., 2017). Nutrition-focused 3D food printers are being developed (Natural Machines, 2016), although much coverage has been given to food printers focused on convenience food products (BeeHex, 2017) and luxury food items (Choc Edge, 2017).

7.7.2 Research Challenges In order for 3D printing technology to be feasible in industry and for everyday use, the individual food formulations must have suitable rheological characteristics for printing, such as a flowable consistency that will maintain a

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constant viscosity during printing. At the time of writing, there has been very little research carried out on the fundamental principles of how the printing process affects dairy food microstructures. Food matrix interactions at a microscopic level are potentially important in order to understand physical and rheological behaviour and textural and sensorial traits of foods (Aguilera, 2005). Further research into the effects of 3D printing on both properties and texture is needed to allow greater diversification in more application areas. The lack of understanding of how structural change occurs during printing, which can influence printing accuracy and shape stability, is one of the biggest challenges in 3D food printing to date. For example, a study by Lipton et al. (2010) showed that when a dessert product with reduced fat was baked after printing, this led to increased shape stability after baking, whereas an increase in egg yolk concentration improved width/length stability but lowered height stability following baking. It was also reported by Lille et al. (2018) that a high yield stress was necessary to achieve acceptable shape stability postprinting, whilst a high solids content (samples with 60% SSMP) was shown to be most effective in retaining shape and structure in postprocessing by oven drying. This also shows the added challenge of compatibility of 3D printing technology with traditional food processing methods such as baking (Lille et al., 2018). The ideal situation is to incorporate cooking (e.g., baking, steaming) while the product is being printed to eliminate two-step print-then-cook processes. To the authors’ knowledge, there are no such printers available on the market at present. Furthermore, there are additional technological challenges to tackle, as illustrated by the printing of batters, where the food material is strongly dependent on oscillations during its pumping process to maintain viscosity, which will consequently have an impact on the final quality of the printing (Millen, 2012). Three-dimensional printing dairy-based products could benefit from the addition of novel additives, such as bacterial nanocellulose (BNC), a product of fermented waste coconut water, to improve shape stability and structural integrity of the food matrix. BNC could potentially be suited to 3D printing due to its own natural 3D nanofibrillar arrangement of pure cellulosic fibres, which will enable a stronger and more supported printed food structure (Gama et al., 2016). Other ingredient combinations have been used to create a multitude of texture varieties in order to recreate the texture that can be lost through the printing process. Cohen et al. (2009) printed various combinations of hydrocolloids to develop a certain ‘mouth-feel matrix’, measuring the strength and texture spectrum of a food material. This study showed that pure xanthan gum and gelatin added separately were more affected by the scale of strength of gel, rather than smoothness, with 0.5% gelatin resulting in a milklike texture and 4% gelatin producing a mushroom-like texture. When two hydrocolloids were combined, the degree of textural smoothness was affected, whereby 1% gelatin and 4% xanthan gum brought about a risotto-like texture, and 1% gelatin and 8% xanthan gum created a tomato-like texture.

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7.7.3 Industrial Advantages and Disadvantages Other benefits predicted for 3D printing of food materials include flexibility, configurability and high-material-use efficiency (Hopkinson et al., 2006). The flexibility of 3D printing technology will enable the use of alternative dairy-based food ingredients in creating improved products with respect to nutritional content and health benefits. Broadly speaking, enterprises have been interested in the environmental benefits of 3D printing (SPI Laser LTD, 2017). This might apply more notably to the dairy industry, as it falls under increasing scrutiny and increased concern regarding its sustainability (Von Keyserlingk et al., 2013). Three-dimensional printing would potentially allow goods to be printed and sold close to their point of consumption. The novel technology presents an opportunity to ‘reshape’ the manufacturing supply chain to produce cheaper products through a reduction in the number of stages in the traditional supply chain (Berman, 2012). Additive manufacturing technology offers the opportunity to redesign products and with fewer components. The combined effect is the reduction in the need for storage, transportation and packaging (Gebler et al., 2014). Several researchers have investigated the use of 3D printing in the spare parts supply chain, where printers would have the ability to print their own replacement parts and therefore reduce manufacturing downtime. According to Siddiqui et al. (2016), 3D printing is a viable option in printing parts for food processing operations, for example, feed spacers for membrane filtration technology, which is commonly used in to separate specific particles (e.g., fat, lactose, proteins, bacteria, salts) from milk depending on the pore sized used (Mercier-Bouchard et al., 2017). Feed channel spacers are placed on top of the filter membrane to facilitate feed flow and retentate recovery while promoting turbulence. Three-dimensional printing technology is considered a suitable tool in rapid, low-cost production of spacers with a thin and complex geometry design that may improve cleanability (Siddiqui et al., 2016). However, 3D food printing also has practical limitations. In the case of FDM printing, food materials must be converted to a paste, of which not all foods are suitable candidates. This can be due to potentially undesirable changes in texture or taste or negative interactions with other food contained within the paste (e.g., syneresis, browning, off flavours). Pastes might also be limited by their shelflives due to their high moisture content leading to a possible microbial risk. According to Lipton et al. (2015), regulatory agencies, mechanical engineers, chemists and other experts will have to collaborate to ensure that the right materials, processes and standards are in place. Speed of printing is a common concern amongst industrial companies considering implementing the technology in their manufacturing lines. Printing speed has improved in recent years but has yet to reach speeds capable of efficient production standards. To put this into context, the Choc Creator chocolate 3D printer is capable of printing speeds of 20 mm/s (Choc Edge, 2017).

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Choc Edge (2017) states that to create a design which is up to 3.75 cm in height and 4 cm in width/length will take between 20 and 45 min, depending on intricacy of the print. One other final concept that is moving 3D printing a step further in terms of creativity and innovation is the term ‘4D printing’. This term is relatively new and much less developed than 3D printing. Wang et al. (2017) have introduced this concept through their experiments with pasta, where the initially flatshaped pasta will twist and curl up in a unique pattern when hydrated and/ or heated. The authors took 3D-printed edible films made of common food materials such as protein, cellulose or starch in order to achieve this ‘4D’ effect. How such an effect could be achieved using dairy-based 3D printing is an interesting question. Overall, 3D printing is an exciting technology at present, presenting researchers with many opportunities and challenges. Three-dimensional printing has captured the imaginations and attention of researchers, businesses and citizens. Successful exploitation of the diverse functional and nutritional properties of dairy ingredients could be an important contributor to progress in the field of 3D food printing.

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206 Fundamentals of 3D Food Printing and Applications Yang, S., Evans, J.R.G., 2007. Metering and dispensing of powder; the quest for new solid freeforming techniques. Powder Technology 178, 56e72. Zetzl, A.K., Marangoni, A.G., 2012. Structured Oils and Fats (Organogels) as Food Ingredient and Nutraceutical Delivery Systems, Encapsulation Technologies and Delivery. Elsevier, pp. 392e411. Zhang, Z., Zhang, R., Tong, Q., Decker, E., McClements, D., 2015. Food-grade filled hydrogels for oral delivery of lipophilic active ingredients: temperature-triggered release microgels. Food Research International 69, 274e280.

FURTHER READING Huang, S.H., Liu, P., Mokasdar, A., Hou, L., 2012. Additive manufacturing and its societal impact: a literature review. International Journal of Advanced Manufactured Technology 67, 1191e1203.

Chapter 8

Material, Process and Business Development for 3D Chocolate Printing Liang Hao, Yan Li, Ping Gong, Weil Xiong Advanced Manufacturing Research Centre for Jewellery, Gemmological Institute, China University of Geosciences, Wuhan, China

Chapter Outline

8.1 Introduction 8.2 Commercial Feasibility Study 8.2.1 Chocolate Background 8.2.2 Chocolate Status Quo 8.2.3 Research on the 3D Chocolate Printing Business Model 8.2.3.1 Food Supply Chain Business Model 8.2.3.2 Traditional Chocolate Production and Management Model 8.2.3.3 Manufacturer-Led and Retailer-Led Chocolate Production Model 8.2.3.4 Conclusion on Computational Simulation of Business Model 8.3 Development of Chocolate 3D Printing Technology 8.3.1 Chocolate Features 8.3.1.1 The State and Texture of Chocolate

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8.3.1.2 Chocolate Viscosity and Flow Properties 8.3.1.3 Chocolate Crystallisation and Tempering Chocolate Additive Layer Manufacturing Experimental Results and Discussion 8.3.4.1 Rheological Behaviour of Chocolate 8.3.4.2 Optimisation of Nozzle Height 8.3.4.3 Optimisation of Nozzle Aperture Size 8.3.4.4 Optimisation of the Extrusion Rate and Nozzle Moving Speed 8.3.4.5 Extrusion Optimisation for Multilayer Components Conclusions

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208 Fundamentals of 3D Food Printing and Applications 8.4 Optimisation of Chocolate 3D Printing Technology 8.4.1 Adaptive Extrusion Layer Thickness Optimisation Based on Area Change Rate 8.4.1.1 Extruded Layer Thickness Optimisation Calculation 8.4.1.2 Extruded Layer Thickness Optimisation Experiment 8.4.1.3 Compression Layer Thickness Optimisation Data Comparison 8.4.2 Layer Scanning Speed Optimisation Based on Perimeter Change Rate 8.4.2.1 Speed Optimisation Calculation 8.4.2.2 Speed Optimisation Experiment 8.4.2.3 Scan Speed Optimisation Data Comparison 8.4.3 Conclusions

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8.5 Extension of Chocolate 3D Printing Application Technology 8.5.1 Healthcare Products and Chocolate 3D Printing 8.5.1.1 Healthcare Products and Chocolate Medical Value 8.5.1.2 The Combination of Chocolate and Health Products 8.5.2 Feasibility Experiment of Adding Healthcare Products 8.5.2.1 The Addition of Vitamin C 8.5.2.2 Lutein Addition 8.5.2.3 The Addition of Cranberry Extract 8.5.2.4 Verification of Collapse 8.5.2.5 The Addition of Methyl Cellulose 8.6 Summary and Outlook References Further Reading

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8.1 INTRODUCTION Among all the three-dimensional (3D) printing applications, food 3D printing (3DP) is most noticeable as the closest lifestyle item, and the sweetest and most tempting choice of 3DP material is chocolate. Initially, many people asked me, ‘How do you think of studying on chocolate 3D printer?’ Actually, the earliest contact with 3DP was when I attended an international industrial conference in Portugal in 2004. The strongest feeling to me at the conference was that 3DP was probably to become a mainstream application in the next decade. A lot of the feasibility of 3DP can be seen in the future. At the very beginning, I had done quite a lot of literature research on 3DP in the field of aviation and medicine, and it took me quite a long time to get familiar with this field, including the business scale as well as 3DP limitations. Until 2007, a French friend jokingly asked me if I could print a piece of chocolate for himself, As a result, 3DP was inspired by the commercial market, and at the same time, I started my journey into the chocolate industry with the hope of using 3DP in a variety of ways in different places.

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After working in this field, I discovered that chocolate has a very strong cultural and creative background. During the very early ages, it was a very luxurious drink that flourished in the aristocracy, especially the cocoa flavanol in chocolate, which was considered to have great benefits to people’s health. Meanwhile, it had also been used as a currency due to the high additional value product of chocolate bean itself. Also, 3D printing also gives us a lot of free space to work wonders and make creations because of the freedom of the production method. One can see a high additional value depending on individual creation and design. In April 2011, I was invited by a Belgian company to attend their annual conference, which was a fashion show. I was so surprised that there were many 3D printers involved in the oral presentations, confirming 3DP as a stylish product. Threedimensional printing could have a very high value of art and appreciation, providing creative ideas for 3DP workers. As for myself, I will focus on 3DP more in the field of cultural creativity. One of the most crucial aspects of cultural creativity is to realise industrialisation. There are many kinds of modes for industrialisation. One mode is for everybody; you can create ideas and then submit your own products. The other mode is a Belgian company’s high-end works of art, the limited-edition products created by the artists; the third mode is the children’s toy made by British company, which not only can be designed as some 3DP models, but also can be designed with some decorations. Definitely, it focuses not only on a creation, but also a game with lots of interesting factors. Therefore, Choc Edge Ltd. came into being with aims to combine science and technology with art after 5 years of continuous exploration. There may be all sorts of elements such as materials, equipment and software. The most critical factor, I think, is still its creativity. Fig. 8.1 is a sample of our earlier printing works, which I think is a very simple product for 3DP experts; however, it took quite a long time for the 3DP chocolate industry due to the great complexity. In addition, from the 3DP point of view, this processing time was very quick. As for me, chocolate 3DP belongs to a kind of cultural

FIGURE 8.1 The earlier 3D printing chocolate work.

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creativity, a kind of originality of content and digitisation. It’s like music, but more art. I wish our group can make it a direct download, then individual design and finally commercialise in the future.

8.2 COMMERCIAL FEASIBILITY STUDY 8.2.1 Chocolate Background A US food magazine conducted a survey on a simple question ‘what is your favourite food?’ Among the 40,000 answers received from questionnaire, more than half of the readers chose chocolate among 50 different kind of foods. It showed that among all the food in the world, chocolate was the one that people would spend on the most. There have also been statistics that American people would spend 14 billion US dollars on chocolate per year on average. Almost no one can resist the temptation of chocolate since the advent of chocolate. Its growing charm attracts different cultures, countries, ages and genders. Cocoa beans, the main source of chocolate, were first discovered by the Maya. Later, Aztecs crushed the cocoa beans into paste-like form, along with some seasonings, to create it as a delicious, multinutrient beverage. By the 16th century, European explorers found this drink with a sweetening additive that basically tasted the same as our current chocolate drinks. But in the 16th century, it was an aristocratic drink, known as an expensive luxury. By the 19th century, with the invention of mould-casting technology, the solid state of the chocolate became popular. The cocoa beans were mechanically pressed into fine powders. The powders were poured into a mould through heating. After cooling, it can be made into all kinds of solid chocolate, which was also the prototype of today’s chocolate.

8.2.2 Chocolate Status Quo Nowadays, chocolate has permeated all aspects of people’s lives and has been widely used in all kinds of commercialisation. Previously, the businesspeople used the story of Tyson bit Holyfield’s ear during the Boxing World Cup competition, making a ‘chocolate ear’ to attract the customers to buy. There are also businesses using chocolate to make Beckham-like celebrities in window displays to attract customers’ attention. All of the above confirms that a single shape of chocolate product has been unable to meet various consumer demands. After the investigation of the market, we also found that today’s traditional chocolate makers such as Dove, Cadbury, Hershey and Ferrero sell the chocolates mainly in the form of standard shapes or bars, accounting for most of the confectionery market share. Of course, there are also some small- and medium-sized chocolate manufacturers, such as bouquets manufacturers, who sell handmade chocolates primarily through e-commerce platforms such as

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eBay or Amazon. In addition, there are also top-grade chocolate makers like Teuscher, who have been able to mix and combine chocolate with more than 27 billion possibilities through the addition of fruit, fragrance, candies, white milk and black cocoa. Although it indicates that the customised chocolate products meet the growing customer demand for the personalised market, it faces two major problems. First of all, personalisation takes a long time, and secondly, the personalisation requires the development of the corresponding mould. Therefore, the cost would be two to three times higher than that of the traditional-style chocolate. As the market demand for custom chocolate continuously grows, how to meet the customisation of chocolate at the low cost still faces great challenges. Hence, chocolate 3DP technology will be a kind of application innovation, not only shortening the custom cycles but also saving a lot of the production costs.

8.2.3 Research on the 3D Chocolate Printing Business Model The 3D-printed chocolate can be referred as a type of smart food, which is made through improved technologies or innovative technologies such as artificial ingredients or human intervention. Nowadays, smart foods attract a great deal of attention because they save more nutrients than the conventional foods, and thus, they have more functions to meet the needs of different people. In order to develop our smart food, we chose 3DP technology because it can create almost any shape to meet the individual needs of customers. Obviously, this new technology represents great potential to reconstruct food innovation, production and supply chains in the future, especially the lowcarbon food value chain. A strong and viable business model is necessary to ensure the economic sustainability of 3D chocolate printing. It should take into account the profitability of supply chain components, the manufacturers, the retailers and the utility of the final users (for example, allowing the shape and mixed customisation of chocolate products). As a result, while developing the 3D chocolate printing technology, the Exeter University team, the initial developer of prototype 3D chocolate printing technology, also engaged in a feasibility study of the business models with 3D chocolate printing as a supply chain using the computational simulation models to predict and analyse the outcome of different business models for 3D chocolate printing. The computational model will consider supply chain components and simulate the profitability of the 3D chocolate printing under manufacturer-led as well as retailer-led business operations. It will be further discussed in the following section.

8.2.3.1 Food Supply Chain Business Model Food supply chain (FSC) consists of several interdependent steps and operations, for example, farming, food processing, distribution, retailing and

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consumer handling (Vorst, 2000). Between these operations, storage, packaging and transport need special considerations due to food safety issues (Jennings, 2005). As a result of the long-term process and food storage, the logistics cost is high. With regard to FSC for chocolates, the chocolate production process has strict requirements for temperature control, which makes the cost more expensive (Aasted, 1998). The main challenges of the traditional FSC are how to shorten the food processing, reduce the cost of logistics and warehousing and to enhance the consumption value of products (Christopher, 2011). Nowadays, supply chain and logistics managers face another challenge of reevaluating their strategies and tactics to make the FSC more sustainable (Flint et al., 2008). The traditional FSC and production lines are more appropriate for mass manufacturing of standard products or limited personalisation products; on the other hand, personalised products require the expertise of hand decoration, often associated with high labour costs (Berkes et al., 1984). Personalisation involves treating each customer as a potential market segment, designing and producing an individualised product and quickly delivering it to each customer (Fitzgerald, 1995). Boland (2008) illustrated that there is an increasing number of consumers who require personalised nutrition and are willing to pay a premium price to buy innovative food (Cohen et al., 2009; Hendry, 2010). Personalised nutrition becomes mainstream in affluent societies (Boland, 2008) with the goal of a healthy lifestyle (Boland, 2008; Martı´nez, 2008). Meanwhile, customers want to receive a personalised product and service (Gilmore and Pine, 1997; Franke et al., 2009). The relationship between manufacturers and customers has been enhanced as manufacturers decide to configure their products to match the individual preferences of each customer (Wong and Eyers, 2011; Simonson, 2005). However, the manufacturer’s total cost (e.g., production and logistics) would increase linearly with the number of products available in the market (Banerjee and Golhar, 2013). Furthermore, manufacture companies are struggling to simply expand product offerings in the face of fierce market competition and diversified product offerings in the market, with insufficient flexibility to respond to this drastic change in customer demands (Wang, 2011), such as product designs, colour, sizes and packaging (Childerhouse et al., 2002; Wang, 2011). Therefore, it is a common trend to continuously improve the market personalisation of FSC-produced standard products (Lyons et al., 2013).

8.2.3.2 Traditional Chocolate Production and Management Model Traditional chocolate making is a highly sophisticated process using specialised machinery. The production methods may involve moulding (e.g., casting moulding), dipping and roll forming, etc. (Aasted, 1998; Beckett, 2008).

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In addition, different mouldings require different chocolate production machines and lines (Jeffery et al., 1977). The traditional methods of chocolate production focus primarily on standard products and large-scale production (Akutagawa, 1983; Hunter, 1927), accounting for the majority of the market share. However, they cannot match customer demands for personalised chocolates (Beckett, 2008). Although traditional methods can manufacture such products, they are expensive and time-consuming, as they frequently necessitate the manufacture of personalised moulds (Aasted, 1998).

8.2.3.3 Manufacturer-Led and Retailer-Led Chocolate Production Model The manufacturer-led production model (Fig. 8.2) is the business model that the manufacturers use as 3DP technology at the factory. The manufacturers then sell products through retailers and e-commerce platforms. The retailerled production model is the business model that the retailers use the technology. Final 3DP production takes place at retail stores which sell 3D printed products through their stores and online platforms. Fig. 8.2 shows the customer demand for finished products (i.e., standard chocolates); Df is the demand for customised chocolates that are ordered and delivered through the retailer channel Dc and those ordered online and transported directly from the manufacturer D’c ; the corresponding prices are Pf, Pc and P’c , respectively. Finally, the variables Wf and Wc refer to the price the retailer has to pay the manufacturer for the standard and customised chocolates.

FIGURE 8.2 Manufacturer-dominant business model.

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The manufacturer’s inventory cost takes into account the following: (1) the cost of finished product divided into two components; the first pertains to the m ), and the second is related raw material cost for the semifinished product (Csu m to the semifinished product inventory cost (Csh ). The subscripts denote the parameters associated with semifinished products; (2) the cost of customised product also consists of two parts. The first part is for costs pertaining to m ); customised chocolates are manufactured individually, customisation (Ccp thereby increasing the labour, equipment and operating costs, so the cost of customised product cost is higher than finished products; (3) subsequent to the introduction of the customised product, the setup cost of the finished product m ) is decreased; (4) customised chocolates are distributed by the third-party (Cfp logistics; Cn is the operation cost of the online channel; and (5) since customised products are directly distributed subsequent to production, the inventory cost is not considered; the shortage cost related to the customised m ) is added to the cost for the manufacture. Manufacturer’s products (Css profit (MP) is the manufacturer’s wholesale income minus raw material cost of finished products, produce cost and inventory holding cost. After the introduction of customised production, the profit of double-channel supply chain under manufacturer-dominant model is Xk   m   m m MP ¼  C þ W  C W Q Dc þ f c fu s su 1  ’  m m m m m m  Css  Csp  Ccp  Cfp  Cfh  Cfsm Pc  Cn Dc  Csh (8.1) T where T is the operation cycle of simulation, k is the order times contained in a simulation cycle and n is the produce times contained in a simulation cycle. The computer simulates the use 3DP technology by manufacturers and retailers and the traditional chocolate business model, respectively, to calculate the maximum profit of different supply chain models through variables such as chocolate price, inventory cost and consumer demand. Computational results (see details) show that the retailer-dominant model (Fig. 8.3) via the use of 3DP technology, representing a substantial increase in the profits of retailers. The profit of the manufacturer is between that of the traditional and manufacturer-dominant models. The retailer places more orders on the manufacturer for semifinished products for its own personalised product (retailers or manufacturers) using 3DP technology, which, compared with the traditional model, increased by about 20%. The variables shown in Fig. 8.3 are similar to those in Fig. 8.2, since in both scenarios, customer demand exists for standard chocolate. However, unlike the previous scenario wherein the manufacturer fulfilled the order, in the retailer-dominant model, the customer receives the chocolate from the retailer. The price for Df, Dc and D’c are Pf, Pc and P’c , respectively. Similarly, the variables Wf and Wc refer to the price the retailer has to pay the manufacturer for standard and semifinished chocolates.

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Under the retailer-dominant supply chain, the customised product is manufactured by the retail (Fig. 8.3). In the model, the retailer’s inventory pattern for standard product remains the same. For enabling the on-demand manufacture of customised chocolates using 3DP, the retailer has to set up a semifinished product inventory. As a result of the introduction of semifinished products’ inventory, retailers’ total inventory cost will be higher compared to manufacturer’s model since it would include the semifinished r ), shortage cost for semifinished prodproducts’ inventory holding cost (Csh r r ). At the same time, ucts (Css ) and ordering cost for semifinished products (Cso r this will create a shaping process cost (Ccp ), but retailer’s inventory of customised products can also be treated as a virtual inventory. The semifinished product cost of each product will be Ws. Retailers’ profit is the sum of profits from the sale of both standard products and customised products. The profit function is   RP ¼ ðPf  Wf ÞDf þ ðPc  Ws Þ Dc þ D’c  r r r r r r Cfh  Cfsr  Cfo  Ccp  Cso  Css  Csh (8.2) T

8.2.3.4 Conclusion on Computational Simulation of Business Model In this chapter, the computational model was used to simulate the supply chain constituents and their profitability functions and to evaluate the economic viability of the new 3D food printing-enabled business models in the food processing industry. Two typical models of 3D-enabled chocolate printing supply chains led by chocolate manufacturers and retailers were conducted, respectively. It has shown that these two models are feasible solutions for manufacturers and retailers to adopt 3D chocolate printing and compare the profit under each scenario/model. The simulation results show that (1) among

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chocolate retailers and manufacturers, whoever adopts the 3D chocolate printing technology first would gain higher profits; (2) if retailers adopt this technology, when q > 0.24 (the ratio of personalised and standard products) for the retailers, successful commercialisation with dominance in the market, the chocolate manufacturers would risk being eliminated from the market.

8.3 DEVELOPMENT OF CHOCOLATE 3D PRINTING TECHNOLOGY In this chapter, the development and deposition of a chocolate additive layer manufacturing technology will be introduced in combination with the materials and properties of chocolate to verify the effect of deposition parameters on the geometric accuracy and size of the deposited chocolate. It also presents the optimisation of process parameters in order to print high-quality chocolates to meet the market demand for personalised chocolate.

8.3.1 Chocolate Features Chocolate is a science-based processing of cocoa products (cocoa liquor, cocoa powder, cocoa butter), sugar, dairy products, spices and surfactants as the basic raw materials after mixing, grinding, refining, tempering, pouring, moulding and other scientific processing. It can form a unique colour, aroma, taste and fine texture of sweet solid food. The unique hard, brittle, nongreasy texture of chocolate, as well as its melting properties that melt only in the mouth, give it a good mouthfeel and flavour and are loved by the public. The chocolate production technology, undergoing long development and evolution, has become a unique category in the modern food industry. Chocolate production technology, from the beginning of a small handicraft workshop, gradually developed into large-scale mechanised continuous production, and some have adopted more advanced electronic computer to control the production mode.

8.3.1.1 The State and Texture of Chocolate From the colloidal chemistry point of view, the physical state of chocolate belongs to a coarse-grained dispersion system in which fat is the dispersion medium and the sugar, cocoa and milk solids act as the disperse phase distributed in the cocoa butter phase. Most of the dispersed phase has the diameter of 20e30 mm, a small portion of the 40e60 mm diameters, a very small portion of the 15 mm below. Meanwhile, a small amount of moisture and air are also dispersed in this system, so the chocolate is a very complex heterogeneous dispersion system. When the chocolate is melted, the fine solid particles are dispersed in the liquid fat as a suspension. When the chocolate is solidified, the fat recrystallises to form a regular lattice, and the various plasmids are immobilised between the lattices. Therefore, refined chocolate,

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above 40 C, can be seen as a liquid mixture; it is a solid mixture at room temperature (RT). All solid phases of this solid-state mixture have been dispersed into very fine and smooth plasmids and form a highly dispersed emulsion with fat, successfully exceeding the identifiable limits of the tongue sensation. The main source of the raw materials for chocolate products is the cocoa beans. The cocoa butter derived from cocoa beans is the most critical component. The cocoa butter is a type of plant stearin from the processed cocoa beans with unique cocoa scent and short plastic range. Below 27 C, the chocolate product is almost solid and starts to melt at 27.7 C. As temperature increases, it is melted rapidly and becomes completely melted when temperature reaches 35 C. Therefore, it is a blended grease of multiply triglycerides with hardness and is quickly dissolving. Therefore, chocolate is a heat-sensitive food. And the heat sensitivity depends mainly on the type and nature of fat. Due to the limitations of the cocoa bean production, environment and conditions, cocoa butter appears to be sparse and expensive. Hence, many alternatives to cocoa butter are used in the market. Basically, the raw materials and properties can be divided into three categories: cocoa butter equivalent, nonlauric acid-type cocoa butter replacer and lauric acid-type cocoa butter substitute. Among them, cocoa butter equivalent is a kind of artificial cocoa butter, which is mainly made from natural vegetable fat. The triglyceride fat has three components very close to the natural cocoa butter, so its performance is very similar. The performance of mutual solubility is very good. Cocoa butter is a type of rapidly meltable artificial stearin. The triglycerides composition is quite different from that of natural cocoa butter, but physically close to that of natural cocoa butter. Also, the melting curve is similar. Lauric acid-type cocoa butter with lauric acid as the main fatty acid has good hardness, brittleness and shrinkage. The process of its crystallisation is fast, but the lipolytic enzyme could easily lead to lipolysis, resulting in soap-like flavour. Nonlauric-type cocoa butter has the advantages of good heat resistance and soap-free taste, but its taste is poor with a waxy-like feeling. The following experiments will take the Cadbury Ltd. market milk chocolate as a representative example; similar to many commercial chocolates, it contains cocoa butter, during the control and adjustment of temperature, in which triglycerides can form crystallised cocoa butter.

8.3.1.2 Chocolate Viscosity and Flow Properties The viscosity and fluidity of chocolate is a very important physical index in the process of chocolate production and processing. The chocolate in the molten state should have good fluidity to ensure the smooth and continuous material deposition based on 3DP. At different temperatures, chocolate has different viscosities. Increasing the temperature can effectively reduce the viscosity of the melted chocolate. At the same time, the increase of cocoa butter lipids can

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reduce the viscosity of the chocolate, however, the cocoa butter lipids are expensive, most of the chocolate in the market will be added phospholipids to reduce the viscosity of the materials, also known as the diluting agent in chocolate production.

8.3.1.3 Chocolate Crystallisation and Tempering In the chocolate composition, the content of fat normally accounts for more than 30%. Cocoa butter acts as a uniform continuous phase; when the outside temperature exceeds the average melting point of cocoa butter, the cocoa butter will be melted, and the chocolate will become liquid. If the outside temperature is below the melting point, the cocoa butter will solidify, and the chocolate will be solid. With the change of temperature, the transition of cocoa butter from liquid to solid state occurs in the form of the crystallisation which appears as a continuous and changing process. The modern X-ray diffraction analysis of cocoa butter crystallisation state showed that the cocoa butter crystal can be divided into five forms: the initial appearance of the r crystal, which has poor stability and the melting point in the range of 16e18 C; the cycle is very short, followed by a crystalline form with a melting point in the range of 21e24 C, it is an unstable form; continuing to maintain at 20 C, the crystalline form of a will gradually become b00 crystalline form with a melting point in the range of 27e29 C, which belongs to a relatively stable crystal form; under certain conditions, b00 will be changed into b’ crystal form and eventually become b crystal form, with a melting point in the range of 34e35 C. b crystal is the most stable cocoa butter crystal. The traditional chocolate manufacturing methods must well control the temperature, generally, in the first phase, the material from a higher temperature entering into a lower temperature state could produce and form more stable crystalline, the chocolate material at 45 C through the cooling medium for rapid heat exchange, the temperature dropped to about 29 C, at this time, the material began to produce large amounts of fat within the tiny crystal nucleus and unstable crystalline form began to change into more stable crystals. In the second stage of temperature control, the material continues to cool down to about 27 C; then the fat crystals change from a relatively stable crystalline form to a stable crystalline form. As the temperature decreases, a large amount of fat crystals will form, and the viscosity of the material increases and becomes thicker. In the third stage, the temperature of the material is restored from 27 C to 29e30 C. The rising temperature of the material will reduce the polycrystalline that appears in the material. The unstable crystal melting below 29 C will melt and disappear. The melting point of b0 and b crystal is higher than 29 C, and they will remain in the chocolate material and make the quality of the cured chocolate stable. Therefore, the good chocolate needs the formation of many stable b crystals. In this experiment, in order to achieve this, the temperature was carefully

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FIGURE 8.4 The differential scanning calorimetry (DSC) analysis of as-received and tempered CMC chocolate.

manipulated during crystallisation of the chocolate during cooling. To accomplish the adjustment of temperature, the chocolate is heated up to a predetermined 40e45 C and added new chocolate seeds so that seeds rich in triglyceride-rich and stable polymorphic (tempered chocolate) are added to the chocolate, which has many advantages (Beckett, 2008): (1) the correct amount of correct seeds in chocolate can be ensured; (2) the viscosity increase associated with the crystallisation of trisaturated triglycerides can be prevented; and (3) the equipment required is simple (simple mixing pump and heat exchanger). Differential scanning calorimetry (DSC) analysis was used to identify the form V crystals in the seed chocolate compared with the commercially tempered chocolate as received Cadbury Ltd milk chocolate (CMC). DSC thermogram (Fig. 8.4) of the CMC chocolate showed that the melting peaks occur within the same temperature range and form the same crystalline phase. Therefore, the seeded tempering method provides appropriate palatability. Rheological data using the parallel plate configuration was generated over the temperature range with 2 C intervals at which the chocolate samples were affected during deposition.

8.3.2 Chocolate Additive Layer Manufacturing Additive layer manufacturing (ALM), also known as solid freeform fabrication, rapid prototyping or rapid manufacturing, is a process that works on an ‘additive’ principle by laying down material in layers. This type of manufacture is unconstrained by many of the limitations of conventional

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(abatement or formation) processes. ALM allows the production of complex, high-quality parts without the need for expensive and time-consuming retooling or labour-intensive machining; it also enables the economically viable production of customised products. The term ALM relates to a rapidly growing number of machines and processes, including stereolithographic, selective laser sintering, laminated object manufacturing, 3DP and fused deposition modelling. The deposition-based ALM process usually involves extruding plastic filament or metal wire through a nozzle that transverses in the x- and y-directions to create each two-dimensional (2D) layer. The nozzle is heated to melt the material, and its movement is controlled by a numerically controlled mechanism and directly controlled by a computer-aided manufacturing software package. The material will be cooled down or cured after extrusion from the nozzle and is built when each new 2D layer is laid onto the previously layer. The material used is preferably one which melts at a preselected temperature and rapidly cures upon adhering to the previous layer (Sood et al., 2010). Separate nozzles are used to deposit support structures which allow the creation of complex parts with protrusions. The resolution and accuracy of model is limited by the diameter of the nozzles, and the established speed as the nozzle needs to physically transverse the build area (Hopkinson et al., 2006). The literature suggests the full-scale application of ALM has not gained much attention due to the compatibility of currently available materials with ALM technology. In deposition-based ALM processes, inferior mechanical properties and surface finish of final products (in comparison to conventionally fabricated parts) lead to its limited application. Some researches (Anitha et al., 2001; Bellehumeur et al., 2004; Thrimurthulu et al., 2004; Wang and Shaw, 2005; Galantucci et al., 2009; Sood et al., 2010) have been focused on the effects of process parameters on these properties; however, they are confined to a limited range of materials. This article extends the research to the study of commercial chocolate. Chocolate is manufactured through pouring tempered liquid chocolate into moulds or in sweet centres at temperatures of around 308 C, where the chocolate acts as a viscous fluid. The cooling process is followed to allow the solidification of the chocolate’s lipid components (i.e., cocoa butter, possibly cream fat) and facilitate moulding release and packaging (Beckett and Royal Society of Chemistry [Great Britain] 2008, Beckett, 2008). Whilst most of the chocolate products are still produced by these conventional methods, researches (Chen and Mackley, 2006; Engmann and Mackley, 2006a,b) have shown that it is possible to process chocolate through cold extrusion. This research shows that extrudates possess interesting temporary flexibility and shape retention ability which may provide opportunities to form shapes that cannot be manufactured by traditional chocolate production methods. As the extrudate behaves as a semisolid and it does not bond with adjacent lines or layers to form complex shapes, there are limitations to the final product design. Attempts have been made to deposit the chocolate

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directly into a 3D object using the Fab@home ALM system (Schaal, 2010); however, neither material characteristics nor geometrical accuracy of the extrudate have been recorded. The ALM of premium chocolate product is a difficult task because chocolate is a very complex soft material consisting of various ingredients. The material presents many challenges when used in this application; for example, if the final product needs to have all the desired properties with respect to taste and appearance, the chocolate crystalline phase (of which it has six different phases) must be controlled throughout the deposition. Chocolate is also a non-Newtonian fluid, and there are problems with understanding the flow properties of the material (the relationship between the shear stress and the strain rate is nonlinear). In this study, the material properties of chocolate were characterised, and the relationship between process parameters and resulting chocolate properties were investigated to establish a chocolate additive layer manufacture (ChocALM) process as a production approach.

8.3.3 Experimental The CMC was extruded using the ChocALM system and developed through an interdisciplinary group student project at the University of Exeter. Since the proof of concept, the project team has been working on developing a robust system to manufacture accurate, delicious, 3D chocolate products from computer-aided design models. The system consists of four subsystems (Fig. 8.5): (1) the tempering chamber for the pretempering of the chocolate, (2) a delivery

FIGURE 8.5 Schematic of chocolate additive layer manufacturing (ChocALM) system.

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system for transportation of the material to the deposition head, (3) a deposition head for the extrusion of the chocolate, and (4) an XeYeZ positioning system. The pressure exerted on the chocolate within the deposition head was applied via an Archimedes screw. The chocolate samples were extruded onto a polished marble plate with circular nozzles with diameters of 1, 1.25 and 1.5 mm. The motion and positioning control was provided by a computer with specifically designed Java programs and a microcontroller. In order to determine the effects of process parameters on the extrudates geometry, a variety of tests were used. A simple square, with a side length 15 mm and a vertical height of 15 layers in the z direction, was used to evaluate the adhesion between layers as well as the consistency of the input dimensions and the shape of the final product. Previous work (Wang and Shaw, 2005) on the deposition of dental porcelain slurries showed that the distance between the nozzle and build plate was highly critical to the quality of the resulting built components. It suggests that the critical nozzle height can be found using the following equation: vd hc ¼ (8.3) v n dn where Vd is the volume of the material extruded per unit time (cm3/s), Vn is the nozzle moving speed (mm/s) and Dn is the nozzle diameter (mm). It was noted that when the nozzle height was less than hc, there was a ‘squeezing’ effect, resulting in geometrically inaccurate parts (Wang and Shaw, 2005). This theory was tested through increasing the build height using the ChocALM software. To assess the effect of the x- and y-axis velocity on the extrudate geometry, simple lines were extruded in one axis direction. Once the chocolate had solidified, the diameter of the chocolate bead was measured. Previous work has determined that a critical nozzle movement rate would result in a bead of extruded material with a diameter equal to that of the nozzle (Khalil and Sun, 2007); this critical nozzle movement rate could be found from the following equation: vn ¼

4Q pD2N

(8.4)

where Q is the volumetric material flow rate, and DN is the diameter of the nozzle. It has been suggested (Khalil and Sun, 2007) that a nozzle velocity greater than the critical value would result in a material bead with a diameter less than that of the nozzle, whereas a nozzle velocity below the threshold would result in a material bead with a diameter greater than that of the nozzle. An extrusion rate test was conducted to determine the volumetric flow rate of chocolate for varying extrusion rate settings in the ChocALM software. These involved extruding molten chocolate into sample dishes, at varying extrusion rates, for a known time period. These were then weighed, and by using the

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density of the chocolate (1277 kg/m3), the extruded volume could be calculated. This would be required for assessing whether the nozzle velocity and volumetric flow rate equation mentioned above was suitable for the ChocALM case. In order to assess the interlayer bonding of the multilayer components, optical microscopy was used to observe their cross-section. The microscope used was a Zeiss 47 50 52 fitted with a Kodak Digital Science DC120 Zoom Digital Camera for image capture. It is believed that cutting a sample can result in blurring of the individual layers; therefore, snapping the sample may give the best possible observation. However, it was found that due to the shallow depth of focus inherent with optical microscopes, cutting the sample with a scalpel provided better results. Using a scalpel ensured the face was detached as close as possible to a straight line; hence, the entire face was in focus.

8.3.4 Results and Discussion 8.3.4.1 Rheological Behaviour of Chocolate Rheological data using the parallel plate configuration was generated at 28 intervals throughout the temperature range, which the chocolate samples were subjected to whilst within the ChocALM machine. Fig. 8.6 showed the compiled rheological data for CMC from 30 to 40 C. Between 40 and 32 C, the viscosity was between 3.5 and 7 Pa s and remained relatively constant, with a deviation of 90.5 from a strain rate of 0.4 and above.

FIGURE 8.6 Viscosity data for CMC at various operating temperatures.

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8.3.4.2 Optimisation of Nozzle Height It was found that extruded lines below the optimal build height resulted in greater thickness than expected and that above the optimal build height resulted in a portion of the chocolate not reaching the marble build surface before the build turning a corner, leading to massively inaccurate component. This was consistent with previous similar work (Wang and Shaw, 2005). The optimal build height was determined to be 2.9 mm, which did not concur with the theoretically derived formula mentioned (Wang and Shaw, 2005). According to Eq. 8.3, the critical nozzle height would be: hc ¼

vd 2:42052  103 ¼ 0:102 mm ¼ vn dn 19  1:25

From this result, it was clear that the critical nozzle height formula (Wang and Shaw, 2005) cannot be applied to the case of ChocALM. This was potentially due to the different material used; the formulas suggested by Wang and Shaw (2005) were designed for porcelain dental slurries, rather than chocolate. The difference in materials was likely to determine a significant difference in extrusion height.

8.3.4.3 Optimisation of Nozzle Aperture Size The effect of varying the nozzle aperture diameter on the built block was relatively simple to optimise. It soon became apparent that the optimal nozzle diameter was determined to be 1.25 mm (Fig. 8.7). The use of a nozzle with a diameter of 1.00 mm resulted in relatively poor models, as the extruded chocolate bead has inconsistent diameter along its length. A 1.50 mm diameter nozzle extruded a consistent chocolate bead, but apparently as shown in Fig. 8.8, the resolution of the built parts was poor.

FIGURE 8.7 The chocolate square with good layer-by-layer bonds and geometry accuracy.

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FIGURE 8.8 The chocolate square with poor geometrical accuracy.

8.3.4.4 Optimisation of the Extrusion Rate and Nozzle Moving Speed To evaluate the effects of the extrusion rate and nozzle speed on the extrudates’ geometry, line tests were used. The previously established optimal settings for build height and nozzle were applied. The lines of chocolate were extruded at varying extrusion rates for different y-axes of movement rates; these diameters were then measured (Fig. 8.9). In order to confirm that uniform chocolate beads were extruded, the line test results were then cut to a known length and weighed. To calculate the volume extrusion rate, the velocity of the nozzle was measured at varying x- and y-axis movement rates.

FIGURE 8.9 Line testing and measurement.

226 Fundamentals of 3D Food Printing and Applications Plot showing the necessary extrusion speed to obtain a bead width of 1.25mm, for various axis movement speeds (using experimental and predicted data) 4.5

y = 0.064x – 12 R2 = 1

Bead width (diameter) (mm)

4 3.5

y = 0.048x – 9 R2 = 1

3

y = 0.0315x – 5.9834 R2 = 0.9345

2.5 2

255 254 253 252

1.5 1 0.5 200

y = 0.0167x – 3.0945 2 R = 0.7738 210

220 230 240 Software extrusion speed

250

260

FIGURE 8.10 Relationship between software extrusion rate and resulting bead diameter.

As shown in Fig. 8.10, when the y-axis movement rate is fixed at 255 and 254, there is a linear relationship between the extrusion rate value used in the ChocALM software and the bead diameters collected from the experimental result. As expected, the prediction of the movement rate at 253 and 252 showed similar results. This was because the higher the extrusion rate, the greater volume or the mass of chocolate, resulting a larger bead diameter. Fig. 8.11 showed the relationship between the extrusion rate and the mass (and therefore the volume) of chocolate extruded. The average value of the mass/volume of the chocolate extruded increased with the extrusion rate. At a constant extrusion rate, there was a variation in the mass of chocolate extruded between varied tests. The range of the variation was decreased with

500

Plot showing relationship between extrusion rate setting and mass of chocolate extruded in 10s

450 400 Mass (mg)

350

11351

y = 2E–25x R2 = 0.982

300

Average

250

Test 1

200

Test 2

150

Test 3

100 50 0 235

240

245 250 Extrusion rate setting

255

260

FIGURE 8.11 Relationship between extrusion rate software setting and mass of chocolate extruded over a period of 10 s.

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the increasing extrusion rate. This indicated that the extrusion was more constant at the relatively high extrusion rate than at the relatively low extrusion rate. Fig. 8.9 also showed that with the same extrusion speed, the bead width decreased as the y-axis velocity increased from 252 to 255. The increased y-axis velocity showed that the same amount mass/volume of the chocolate covered larger surface area and therefore elongated the extruded chocolate filament and reduced the width of the bead. The experimental results of the nozzle velocity were 255 and 254, compared to predicted results of 253 and 252. The volumetric material flow rate of chocolate directly depends on the extrusion rate. Meantime, the critical nozzle velocity determines the length of the deposited chocolate orbit and the width of the weld. Based on this relationship, the extrusion rate and axis movement rate can be determined in order to give a bead diameter of 1.25 mm, as shown in Fig. 8.12. According to this data, any combination of extrusion and x- and y-axis velocities along this linear relationship line of best fit will result in a chocolate bead of 1.25 mm diameter. As the velocity in the software can only be input as integer values, the fastest extrusion rate and axis movement rate were 253 and 253, respectively, for the deposition of 1.25 mm diameter chocolate track. From the view of the manufacturing efficiency, these settings provided the fastest rate for part building with appropriate geometry accuracy. However, these data slightly disagree with the data presented in Fig. 8.10, indicating either an axis movement rate of 254 with an extrusion rate of approximately 228, or an axis movement rate of 253 with an extrusion rate of about 215, which provides the optimum results. Although both of these methods involved data extrapolation and manipulation, it is likely that

FIGURE 8.12 The extrusion and y-axis movement rate required for the deposition of 1.25 mm bead diameter.

228 Fundamentals of 3D Food Printing and Applications

Fig. 8.11 will provide more valid results; this has proven to predict the optimum nozzle velocity (2) and is applicable to the ChocALM case. This was proven by ‘reversing the work’ of the formula and comparing actual velocity measurements with the predicted value of formula. In the key operating range (approximately 250e255), where there is the most dramatic change in velocity, the formula predictions are very close to the experimental data. Fig. 8.10 may not be as accurate as the prediction results obtained by observing trends in the experiment data and applying them to other axis movement rates. Due to some variation in the data collected through experiments, the chocolate deposition may not be very constant. Further improvement has to be done in order to have a precise control of the chocolate deposition.

8.3.4.5 Extrusion Optimisation for Multilayer Components The previously optimised process parameters were used in the aforementioned ‘square test’ to assess the results of process optimisation for multilayer components. Images were taken to evaluate the variation in wall thickness and move vertically through the sample. From these images, it is clear that there is a difference in wall thickness between the base and top of the part (Fig. 8.13). Pleasantly, however, this difference is not too great; the minimum wall thickness at the bottom of the part is approximately 85% of the maximum wall thickness, and the minimum at the top of the part is approximately 70% of the maximum wall thickness.

FIGURE 8.13 Cross-sectional images of the wall thickness at the (A) bottom and (B) top of the sample.

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8.3.5 Conclusions This paper has presented a study on the extrusion behaviour of chocolate for the newly developed ChocALM. The viscosity of the chocolate was found to be relatively constant at the temperature range of 32e40 C and in the range of 3.5e7 Pa s. Through the theoretical analysis and experimental study, it was confirmed that the nozzle aperture diameter, the optimum nozzle height, the extrusion and the axis movement speed were critical parameters to control the geometrical accuracy of the chocolate deposition for layer-by-layer building. The ‘square test’ revealed that the 1.25-mm nozzle aperture size and 2.9-mm nozzle height were the optimal parameters to provide good bonding between layers to maintain the proper geometry. The ‘line test’ showed that the bead diameter of the chocolate track increased in parallel with extrusion rate and decreased with an increasing axial linear rate. The combination of the experimental study and analytical work demonstrated there was a series of parameter combinations to deposit a chocolate track with the bead diameter of 1.25 mm with the same nozzle aperture diameter. The setting of extrusion rate of 253 and the axis movement rate of 253 in the ChocALM software gave the fastest building rate to deposit 1.25 mm diameter track for the fabrication of 3D chocolate with quality geometric accuracy. At the same extrusion rate, the variation existed in the mass/volume flow rate of the chocolate, especially when the extrusion rate was relatively low. Further work will be needed to improve the precise control of the chocolate deposition and to understand the filling strategy of dense parts and the overhang cantilever construction of complex parts. Fig. 8.14 shows some of the parts produced by the ChocALM system.

FIGURE 8.14 Images of CMC parts printed by ChocALM system on white chocolate bases: (A) a 3D heart and (B) a 3D print of chocolate additive layer manufacturing (ChocALM) logo.

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8.4 OPTIMISATION OF CHOCOLATE 3D PRINTING TECHNOLOGY Based on the development of the Chocolate 3DP technology of the Exeter University team and verification of experimental print parameters, the first 3D chocolate printer was launched in 2012 and registered as Choc Edge Ltd., and then introduced to the market in 2013. In 2014, the Choc Creator secondgeneration machine was created. Compared to the previous originalgeneration machine, this operation was more convenient, the appearance was much more beautiful and humane and it created a brand influence. In 2015, the Choc Creator 2.0 Plus was born and formed a more complete hardware and software. It began to enter the Chinese market and formed a more complete sales system. Throughout the process of chocolate printing, liquid chocolate as the ‘ink’, and in the print nozzle with thermal insulation and cooling system to ensure that the chocolate out of a special viscosity, stacks layer by layer accumulation moulding, depending on the chocolate’s own adhesion. Throughout the manufacturing process, the nozzle will make XeY plane movement and Z-direction movement according to the contour information of the part interface, and undergo cooling bonding to form the interface contour. When a layer of forming is completed, the nozzle along the Z direction will rise up a layer thickness height, and create the next level in the same way and weld together with the previous surface, until the completion of the entire entity manufacturing according to the cycle. Among them, the slicing module is the core of the software control system. The slice-generated documents directly affect the scale, accuracy and complexity of the processing model, thus affecting the efficiency of processing and forming. The current system for chocolate 3DP is based primarily on the fixed slice layer thickness and fixed scan speeds with the best fitting of chocolate’s property. Therefore, we’ll give more details about our experiments and validation of chocolate 3DP to improve the efficiency and quality of chocolate formation.

8.4.1 Adaptive Extrusion Layer Thickness Optimisation Based on Area Change Rate The existing slice mode of 3DP in chocolate is a slice of fixed layer thickness, in which the step effect is easily appeared on the surface of the fixed layer thick section, and the collapse of the chocolate pile occurs when the curvature is too large. Fig. 8.15 shows the step effect. Fig. 8.16 shows the two parts, A and B, of the chocolate model. When the slices are processed under the fixed layer thickness, the thicknesses of the two parts are equal. However, because of the large curvature of the outer surface of part B, the obvious step effect and collapse easily occur. In order to reduce the

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FIGURE 8.15 The step effect.

FIGURE 8.16 The slice model diagram. (A) the thin printing layer thickness for part a and b. (B) the thick printing layer thickness for part a and b. (C) the thick printing thickness for part a and thin printing layer thickness for part b.

risk of step effect and collapsing, thinner slice thicknesses are required. As shown in Fig. 8.16A, this reduces the risk of staircase effects and collapse, but significantly reduces print efficiency. In order to improve the printing efficiency, using a larger slice thickness, the part B of the step effect is obvious, as shown in Fig. 8.16B. The optimised adaptive extrusion layer thickness trades off the printing time and printing accuracy, as shown in Fig. 8.16C; the thickness of sliced layer for part A is larger, while the thickness of slice layer for part B of the shape changes according to the adjusted size.

8.4.1.1 Extruded Layer Thickness Optimisation Calculation In order to reduce the error caused by the shape change and reduce the step effect and improve the efficiency in the process, an adaptive extrusion thickness control was proposed to optimise the rate of change of extrusion cross-sectional area. The principle of adaptive extrusion layer thickness is based on changes in the shape of the chocolate print surface to determine the

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thickness of the extrusion layer. The upper and lower layer area changes more slowly, the layer thickness of the chocolate extrusion thick is large, the thickness of the extrusion layer is small if the area part changes fast. According to the above principles, the optimisation of the extrusion chocolate layer thickness is calculated according to the change rate of two adjacent layers’ area. If the area change rate is greater than the threshold (the threshold is that the chocolate printing is smaller than the threshold value of the occurrence of the staircase effect or the collapse), then the condition is satisfied to obtain the current layer of the appropriate slice layer thickness; otherwise it will not meet the conditions, and it will continuously calculate the appropriate layer thickness. The optimisation calculation method is: l

l

l

l

Step 1: Read the stl file, i ¼ 0, given the initial slice thickness t0, slicing a layer to calculate the 2D cross-sectional area S0. Step 2: Increase an initial layer thickness ti ¼ t0, while the counter i ¼ i þ 1, and calculate the cross-sectional area S1. i 1 Step 3: Determine whether S1SS  c, c is the area change rate if the area i 1 defending rate is greater than the given threshold, ti ¼ ti  tmin, reducing the extrusion layer thickness, recalculating Si. Return back to step 3. If the rate of change after recalculation is less than the given threshold, go to step 4; otherwise, continue to step 3. Step 4: Judge whether ti  tmin, tmin is allowed to extrude minimum layer thickness of chocolate. If so, then record the extrusion layer thickness; otherwise, ti ¼ tmin and record the slice layer thickness data ti.

8.4.1.2 Extruded Layer Thickness Optimisation Experiment The experiments were carried on at 20 C RT, using Cadbury commercial chocolate, melting to constant temperature at 30 C for the printing model. Fig. 8.17A was a fixed extrusion layer thickness of 1.2 mm, resulting in the experimental collapse of the excessive curvature. Fig. 8.17B was the extrusion layer thickness of 0.9 mm; the staircase effect was caused by the neck

FIGURE 8.17 The extruded layer thickness in the optimisation experiment chart.

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TABLE 8.1 A Comparison of the Optimised Extruded Layer Thickness Layer Thickness (mm)

Slice Layers

Scanning Speed (mm/s)

Moulding Time (s)

The minimum layer thickness

0.6

80

4

480

The middle layer thickness

0.9

54

4

320

The maximum thickness

1.2

32

4

190

The collapsed layer thickness

1.5

e

4

e

The adaptive layer thickness

e

43

4

260

Algorithm

curvature. Fig. 8.17C was the chocolate print experimental results of the optimised adaptive base layer thickness.

8.4.1.3 Compression Layer Thickness Optimisation Data Comparison In the experiment, the layer thickness causing the collapse, the minimum layer thickness, the middle layer thickness, the maximum layer thickness (less than the critical value of the collapse layer thickness) and the adaptive optimisation layer thickness were printed separately, and the printing forming time was recorded and compared, as shown in Table 8.1. It can be seen from the data comparison that the movement was based on the change rate of the area to slice print the adaptive extrusion layer thickness; the number of layers was significantly reduced to ensure the quality of the forming and save the chocolate printing time.

8.4.2 Layer Scanning Speed Optimisation Based on Perimeter Change Rate The current chocolate 3D printer usually has a fixed speed, and the printing speed can be set according to the size of the print model at RT, depending on the solidification speed of chocolate after extrusion. If the scanning profile is simple, the faster the speed of filling, the shorter the time of the layer forming, on the contrary, the longer the time. When processing some small crosssection, if a layer of forming time is too short, it will lead to insufficient

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time for the previous layer of chocolate to form the shape. The next layer is then stacked, and it will finally cause the chocolate model collapse and wire drawing phenomenon. Hence, you can use a slower scanning speed or increase the waiting speed between the scanning layers to enhance the forming time of the layer. When processing some sections with a large cross-section, if the forming time of one layer is too long, the previous layer of chocolate will completely solidify and then start to accumulate one layer later, which may easily lead to the phenomenon that the chocolate layer is not firmly bonded. Therefore, the optimisation of the scanning speed during chocolate printing can improve the printing accuracy and the quality of chocolate. In order to improve the processing efficiency to obtain more high-precision moulded parts, the scanning speed and the chocolate extrusion speed also need to be coordinated. Usually, the extrusion speed should be increased accordingly when the scanning speed increases, and vice versa. If the scanning speed is faster than the extrusion speed, the material is insufficiently filled; there will be ‘drawing’ and ‘broken wires’, and even the surface will be vacant and difficult to mould. On the contrary, if the scanning speed is slower than the extrusion speed, the chocolate easily accumulates on the spray head, causing uneven distribution of the chocolate, resulting in chocolate bumps or clogging in the spray head, hindering the next forming and final forming quality. Therefore, in the optimisation of the printing process, the scanning speed and extrusion speed affect each other, and there is a reasonable matching range; the ratio between the two must be in this range to obtain higher printing accuracy. The scanning and extrusion speed matches the reasonable range to meet: vj ˛ ða; bÞ vi where vj is the extrusion speed, vi is the scanning speed, a is the critical value of chocolate breakage of the chocolate wire during the forming and b is the critical value of the appearance of the chocolate accumulation.

8.4.2.1 Speed Optimisation Calculation To reduce the unnecessary print time for each layer and improve the efficiency of the printing process and optimise the print quality of chocolate, one needs to control the adaptive scanning speed of each layer according to the perimeter change. The control principle of the adaptive scanning speed is to determine the layer scanning speed according to the size of the section circumference of the slice. The layer scanning speed of the layer with large contour circumference is large, and vice versa. Based on this principle, the adaptive layer scan rate of perimeter change rate is to optimise the scanning speed of the next layer by calculating the ratio of one-layer perimeter to the smallest perimeter. Firstly, the thickness of extruded layer is calculated by the adaptive layer thickness based on the change rate of the cross-sectional area, the STL file is

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sliced by the layer thickness data and the 2D contour perimeter of all slice sections is calculated to find the minimum perimeter and determine the appropriate minimum scan speed and extrusion speed. The final layer scan speed for each layer is determined by the ratio of the contour perimeter to the minimum contour perimeter for that layer. The optimisation calculation method is: l

l

l

l

l

Step 1: Calculate all layer thickness values ti (i ¼ 0, 1, ., n) based on the layer thickness of the adaptive extrusion based on the change rate of crosssection area in Section 8.4.1.2. Using this layer thickness data, STL file to slice. Step 2: Calculate the 2D contour circumference Pi (i ¼ 0, 1, ., n) of all cross-sections to find the minimum contour circumference Pmin. Step 3: Assign i ¼ 0, set the scanning speed vmin_i and the extrusion speed v j vmin_j and judge whether vmin is within the matching reasonable range (a, min i b). If not, reset vmin_i and vmin_j; if yes, step 4. Step 4: Calculate the scanning speed vi and extrusion speed vj of the ith layer,     Pi Pj vi ¼  vmin i ; vi ¼  vmin j Pmin Pmin wherein the ratio of the scanning speed vi and the extrusion speed vj finally v v j satisfies: vji ¼ vmin ˛ ða; bÞ, that is, always within a reasonable matching min i range; a higher precision of the printing process can be guaranteed. Step 5: Determine whether i  n. If yes, then turn to step 4; if not, the algorithm ends.

8.4.2.2 Speed Optimisation Experiment The experiments were carried out at 20 C RT using a Cadbury commercial chocolate melted at a constant temperature of 30 C. Fig. 8.18A showed that a chocolate model printed at a constant speed of 6 mm/s led to a very small top cross-sectional area because of the relative fast speed of scanning. Chocolate was not well solidified and easily caused the drawing of wire, affecting the print quality. Fig. 8.18B was a chocolate model printed with the optimised scanning speed, and the model quality can be optimised to a certain extent by the adjustment of the adaptive scanning speed according to the size of the cross-section. 8.4.2.3 Scan Speed Optimisation Data Comparison In the experiment, four different printing methods were recorded: the minimum layer thickness, the maximum layer thickness (less than the critical value of collapsed layer thickness), the adaptive extrusion layer thickness and the adaptive scanning speed, and the printing forming times were separately

236 Fundamentals of 3D Food Printing and Applications

FIGURE 8.18 The comparison of the speed optimisation experiment.

recorded for comparison. For example, in Table 8.2, it can be seen that the motion was printed based on the adaptive scanning speed of the perimeter change rate, saving 19.3% of the time compared to that of optimising the extrusion layer thickness printing and saving 56.1% of the time compared to that of the minimum layer thickness print forming.

8.4.3 Conclusions Rapid prototyping and good-quality forming are two of the most important factors in chocolate 3DP and will have a direct impact on the success of chocolate making. Therefore, an optimisation algorithm based on the area change rate of the adaptive slice extrusion thickness with the combination of TABLE 8.2 A Comparison of the Optimised Scan Speed Layer Thickness (mm)

Slice Layers

Scanning Speed (mm/s)

Moulding Time (s)

The minimum layer thickness

0.6

80

4

480

The maximum thickness

1.2

32

4

190

The adaptive layer thickness

e

43

4

260

Adaptive scanning speed

e

43

e

210

Algorithm

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the adaptive scanning speed control based on the rate of perimeter change was proposed. Through calculating the change rate of the contour area to obtain the appropriate layer thickness of each layer and obtain a suitable extrusion layer thickness, and then using the layer thickness data file to slice the model to obtain each layer of 2D polygon contour. Finally, the appropriate layer scan speed for each profile can be determined by using the circumference change rate. The actual chocolate print test results showed that the optimisation of print parameters, to a certain extent, reduce printing time and improve the quality of chocolate print forming. The strength of the tested chocolate model was simple, and the model was small, so the effect on shortening the forming time was not obvious. Conversely, the optimisation of the model quality was more obvious.

8.5 EXTENSION OF CHOCOLATE 3D PRINTING APPLICATION TECHNOLOGY The research and development of chocolate 3DP are mainly used in the production of chocolate retailers and cake shops, etc., which have the demand for personalised chocolate customisation. For example, Fig. 8.19 below shows the rotating chocolate sandwich made by manufacturers using the Choc Creator 2.0 Plus 3D chocolate printer. Fig. 8.20 is a handmade cookie with special print chocolate and biscuit combinations produced by a cake store, which is a creative product developed for Father’s Day using the Choc Creator 2.0 Plus 3D chocolate printer. Fig. 8.21 is a creative cake made by the cake shop using this developed Choc Creator 2.0 Plus 3D chocolate printer, displaying the perfect

FIGURE 8.19

The rotating chocolate sandwich made by chocolate 3D printing.

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FIGURE 8.20

The biscuits printed by chocolate 3D printer for Father’s Day.

FIGURE 8.21

The rabbit cake printed by chocolate 3D printer.

combination of chocolate and candy, etc. Moreover, through the feedback from the cake store, the sale volume of the personalised customised cake is higher than that of the traditional cake. Both the market demand and application of chocolate 3DP is more than just these. In 2016e2017, we have a new application direction and research on food 3DP, which will be elaborated in Chapter 5.

8.5.1 Healthcare Products and Chocolate 3D Printing 8.5.1.1 Healthcare Products and Chocolate Medical Value As health is the first pursuit of mankind in the 21st century, the healthcare industry may become the second-largest industry in the world. There is no

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international term for healthcare products but food, food supplements and medicines. Healthcare products are mainly derived from traditional Chinese healthcare, and their functions are often related to the adjustment of human body. Therefore, to a certain extent, health products are also called as healthcare products. Nowadays, living standards are improving; many people are willing to spend money on healthcare, and gradually it becomes a social fashion; the consumer market is also continuously expanding. However, in the current market, the formula of healthcare products is mainly in the form of pills and capsules, which, in many cases, cannot meet the patient’s compliance with healthcare products. Chocolate is famous as the ‘delicious health product’. Not only does chocolate have a very memorable and unique taste, from a health perspective, it also has a unique healthcare function. Chocolate can increase the body weight of patients with disabilities and excite the spirit of the expression of indifference and extreme weakness in patients, but also calms down overexcited people. In addition, chocolate can also promote gastrointestinal function to help digestion and absorption and has a diuretic effect. As chocolate contains more fat (especially saturated fatty acids) and caffeine, some people worry that chocolate can cause elevated blood lipids and increase the risk of cardiovascular disease in the elderly. An academic researcher at Pennsylvania State University conducted an experiment in which 42 healthy men consumed 46 g of milk chocolate daily. After 27 days, it was found that chocolate had no effect on blood total cholesterol and lowdensity lipoprotein cholesterol, but significantly increased the levels of the high-density lipoprotein cholesterol in favour of the cardiovascular system. Therefore, there is no need to worry about the increase of blood total cholesterol caused by eating chocolate. In addition, the proanthocyanidins (PAC) in chocolate can effectively block the formation of a harmful substance called peroxynitrite to avoid DNA damage and have immunomodulatory effects, reducing the occurrence of cardiovascular diseases and certain cancers.

8.5.1.2 The Combination of Chocolate and Health Products In order to increase customers’ psychological compliance with healthcare products and how to convert the conventional healthcare product forms (usually pills or capsules) into common favourite foods, the market demand for the combination of health products and chocolate has emerged. This will bring three benefits: firstly, to increase the psychological compliance of the consumer to the healthcare product and to appear in the more desirable form of the food, and secondly, to focus on the same piece of chocolate and reduce the psychological pressure of the multiple medicines that need to be taken at the same time (based on the premise that you can mix and take at the same time). Thirdly, through 3D chocolate personalised printing and customisation, you

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can print different colours, shapes, and fonts, playing a reminder of visual effects. To test the feasibility of this method, the addition of vitamin C (white), lutein (yellow) and high-concentration cranberry extract (red) into chocolate, respectively, has been considered in the experiments to better understand the effects of different healthcare additives on chocolate ingredients and the flow performance of chocolate, as described in Section 8.5.2.

8.5.2 Feasibility Experiment of Adding Healthcare Products 8.5.2.1 The Addition of Vitamin C Vitamins are greatly related to human health, in terms of their daily dietary supply, VA, VD, VE, VB12, etc., are calculated in micrograms. VB1, VB2, VC, etc., are calculated in milligrams. For most adults, the RNI (recommended nutrient supply) for most vitamins is below 20 mg/day, whereas the vitamin C RNI is 100 mg/day, one of the largest amounts of vitamins’ recommended daily dietary supplements, which has a number of important roles in maintaining the normal function of the human body. Vitamin C has a series of physiological functions and the historical reputation of ‘universal vitamin’. It has the function of enhancing human immune function, preventing and treating anaemia, promoting collagen formation and steroid metabolism, maintaining the normal functions of bones and teeth and maintaining the integrity of the cell membranes, with detoxification, antiaging and anticancer effects. In daily cooking, 40%e80% of the vitamin C in many vegetables and foods is destroyed and lost. Therefore, normal intake of vitamin C is necessary regardless of the age and sex of the people. If the appropriate vitamin C has been added into the chocolate, people can enjoy the delicious food and intake some essential nutrients. It can not only eliminate the psychological exclusion of consumers of health pills, but also to some extent, chocolate will allow consumers to have some psychological compliance. 8.5.2.1.1 The Experiment of Addition of Vitamin C The body recommends daily intake of vitamin C to be 60 mg, and women in pregnancy and lactation periods require amounts of 70e95 mg. In our chocolate print experiment, 50 g chocolate was mixed with 200 mg oral vitamin C powder. The oral vitamin C powder with 99% purity made up of direct oral granules was purchased from the pharmacy; the colour is white, in line with national GB14754-2010 food requirement standard (Fig. 8.22). The milk chocolate was provided by Cadbury Chocolates. During the experiment, the mixture of 200 mg vitamin C powder and 50 g chocolate was melted and stirred at 40 C. After the chocolate was melted, a little chocolate was added for cooling down to make more stable crystals as

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FIGURE 8.22 Vitamin C powders.

much as possible. The experiments were carried out at 22 C RT; then the mixture was stored at 32 C for 3DP. See the model in Fig. 8.23A, which contained 13 g chocolate and about 52 mg vitamin C. Each chocolate model contains the essential vitamin C content needed by the human body. In the experiment, we will verify that the addition of vitamin C powder will affect the crystallisation process of chocolate and the flowability of chocolate, and we also verify whether the increase of chocolate ingredients will bring discomfort taste. 8.5.2.1.2 The Results Analysis of Addition of Vitamin C The experiments adopted the adaptive layer thickness and the adaptive speed to optimise the chocolate printing (parameter settings can be seen in Chapter 4). The addition of vitamin C has little effect on the colour of the chocolate, in the process of printing, the powder did not affect the chocolate into particles

FIGURE 8.23 (A) The computer model for 3D printing; (B) the 3- printed chocolate of mixed vitamin C and chocolate.

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like the accumulation of the phenomenon, and display good flowability and chocolate printing effect (see Fig. 8.23B). Also, the addition of vitamin C powder did not bring an unpleasant texture and taste to the chocolate.

8.5.2.2 Lutein Addition Lutein is one of the carotenoid pigments widely found in green vegetables and human blood plasma and eyeballs. It not only has antiarteriosclerosis, antioxidation and anticancer effects, but also has an obvious protective effect against vision loss and blindness caused by retinal degeneration. Currently in Europe and the United States, lutein as a functional factor of eye food has been mass commercialisation. The experiments showed that lutein can absorb a large amount of blue light near the ultraviolet light (blue colour is the complementary colour of yellow colour). Blue light, especially the blue visible light wavelength and UV light close, it is the most energetic and potentially harmful light of all visible light reaching the retina. According to the structure of the retina, the light must first pass through the highest concentration region of lutein prior to reaching the retina sensitive rod and cone cells, which can be minimised if the lutein content is abundant at the macula. Children belong to the key protect targets of eye use and protection. From children’s favourite play games to high-intensity learning pressure with the eye and poor habits with the eyes have led to children’s eye myopia and other diseases, which are much higher than those of the previous generation of people. Chocolate belongs to the children’s favourite food; the lutein added to the chocolate can increase children’s psychological compliance of lutein intake, so as to achieve a dual psychological and physical protection. 8.5.2.2.1 Lutein Addition Experiment The human body recommends a daily lutein intake of 12 mg as an additional dietary supplement. Therefore, in our chocolate print experiment, 40 mg oral lutein ester microcapsule powder was blended into 50 g chocolate. Lutein ester microcapsule powder, derived from marigold flower, belongs to the concentrated essence of natural green plant extract. It is molecularly entrapped to prevent the stomach from gastric acid damage, which is more easily absorbed by the small intestine and the colour is yellow, in line with the national Q/ DYN00D6S-2010 food-grade performance standards (Fig. 8.24). The milk chocolate was provided by Cadbury Chocolates. During the experiment, the mixture of 40 mg lutein powder and 50 g chocolate was melted and stirred at 40 C. After the chocolate was melted, a little chocolate was added to cool down to form more stable crystals as much as possible. The experiment was carried out at 22 C RT. The chocolate was stored at 32 C for 3DP; see the printing model in Fig. 8.25A. The model used about 15 g chocolate and 12 mg lutein. Each chocolate model contained the

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FIGURE 8.24 Lutein powders.

FIGURE 8.25 (A) The computer model for 3D printing; (B) the 3D printed chocolate model of mixed lutein and chocolate.

essential lutein for the body’s requirement per day. In the experiment, we will verify that the addition of a lutein extract powder-like item has an impact on the crystallisation process of chocolate and the flowability of chocolate, and verify whether the increase of chocolate ingredients will bring discomforting taste. 8.5.2.2.2 Analysis of Lutein Test Results The experiments adopted the adaptive layer thickness and the adaptive speed to optimise the chocolate printing (parameter settings; see Chapter 4). The addition of lutein has minimal effect on the colour change. During the printing

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process, it did not appear powder effect on the chocolate into granular accumulation, showing good fluidity and chocolate printing effect (Fig. 8.25B). Besides, the addition of lutein powder did not cause unpleasant chocolate taste and texture.

8.5.2.3 The Addition of Cranberry Extract Cranberry, an azalea family, is called the ‘ruby of North America’ and is highly favoured for its nutritional value and health benefits. Its main nutrients have the characteristics of high water, low calorie, high fibre and multiminerals. Botanists have obtained the phytochemicals of PAC, anthocyanins, flavanols and phenolic acids from cranberry extracts, among which PAC can be connected with exogenous agglutinin of bacterial cilia so that the bacteria cannot be combined with the cell receptor and can effectively prevent bacterial adhesion such as urinary tract infection and other diseases through this competitive inhibition. Meanwhile, PAC also have strong anticancer and antiangiogenic properties on the ovary. In addition, anthocyanins, flavanols and phenolic acids in cranberry extract have the ability to protect the cardiovascular system and resist microbial infection. Therefore, cranberry is also known as the ‘ruby’ that cares for the health of women and is favoured by women. A large part of chocolate lovers are women. The blend of high concentration of cranberry extract and chocolate will not only make consumers feel the silky chocolate, but they also take care of women’s health, achieving the delicious and healthy coexistence of chocolate healthcare products. 8.5.2.3.1 Cranberry Addition Experiment The cranberry used in our experiment was high concentration cranberry extract powder granules, produced in Daxing’anling and purchased from the pharmacy, which can be directly taken orally. The colour is pink, and the powder is in line with national Q/SLY0004S-2016 food requirements standard (Fig. 8.26). It has recommended daily consumption of about 5 g. Therefore, in the experiment, 8 g cranberry powder was added into 50 g milk chocolate, of which the chocolate was provided by Cadbury chocolate company. During the experiment, the mixture of 8 g cranberry powder and 50 g chocolate was melted and stirred at 40 C. After the chocolate was melted, a little chocolate was added for cooling down to form more stable crystals as much as possible at 22 C RT. The chocolate was stored at 32 C for 3DP. The print model was as shown in Fig. 8.27. The model used about 14 g chocolate and 2.24 g cranberry powder. In the experiment, we will respectively verify whether the addition of cranberry powder has an impact on the crystallisation process of chocolate and the flowability of chocolate, and verify whether the increase of other chocolate ingredients will bring unpleasant taste and taste.

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FIGURE 8.26 Cranberry powders.

FIGURE 8.27 Mixed cranberry print model.

8.5.2.3.2 Analysis of Cranberry Addition Experiment Result The experiment adopted the optimised chocolate print mode with the adaptive thickness and adaptive speed. After adding the cranberry powder, the colour of the chocolate was slightly reddish. During the printing process, the powder appeared to have no effect on the chocolate granular accumulation, and the chocolate showed fluidity. It was printed according to the parameters set in the

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FIGURE 8.28 The chocolate model with mixed cranberry.

normal experiment (the normal printing calculation parameters can be found in Section 8.5). During the printing and forming process, the chocolate had a slow solidification phenomenon so that the chocolate was too soft and eventually collapsed, as shown in Fig. 8.28. The addition of cranberry powder gave a slightly sour taste in the sweet chocolate but did not affect the taste of the chocolate.

8.5.2.4 Verification of Collapse When adding 8 g cranberry powder to 50 g chocolate, the model showed strong flowability but weak shaping ability. However, the model has both good fluidity and good forming when adding 200 mg vitamin C or 40 mg lutein into 50 g chocolate, respectively. To verify whether the formation of collapse was caused by the properties of chocolate changed by the special ingredients of cranberry powder or added too much amount of cranberry powder, three different formulas were carried out, respectively: (1) adding 100 mg cranberry powder into 50 g chocolate to compare with previous 8 g cranberry powder into 50 g chocolate; (2) adding 8 g vitamin C into 50 g chocolate to compare with 8 g cranberry into 50 g chocolate; and (3) adding 8 g lutein into 50 g chocolate to compare with previous 40 mg lutein into 50 g chocolate. 8.5.2.4.1 Formula 1 Using the same cranberry print model, the mixture of 100 mg cranberry powder and 50 g chocolate was melted and stirred at 40 C. After the chocolate was melted, a little chocolate was added for cooling down to form more stable chocolate crystals as much as possible at 22 C RT. The chocolate was stored at 32 C for 3DP. The print model used the same model as the experiment in Section 8.5.2.3. The model used about 14 g chocolate and 28 mg cranberry powder. The experiments used the adaptive thickness and adaptive speed for the print mode. The colour of chocolate had almost no change when adding 100 mg cranberry powder into 50 g chocolate. During the printing process,

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FIGURE 8.29 The chocolate model mixed with a small amount of cranberry powder.

there was no accumulation of grainy chocolate, showing good liquidity. The chocolate was well printed and formed according to the parameters set in the normal experiment, as shown in Fig. 8.29. From formula 1, it was confirmed that the addition of small amount of external additive material (e.g., health supplement) has little effect on the forming of chocolate moulding during the printing process. In order to further verify this conclusion, the experiments of formula 2 and formula 3 were carried out at the same time. 8.5.2.4.2 Formula 2 Using the same print model in Section 8.5.2.1, the mixture of 8 g vitamin C and 50 g chocolate was melted and stirred at 40 C. After the chocolate was melted, a little chocolate was added for cooling down to form more stable chocolate crystals as much as possible at 22 C RT. The chocolate was stored at 32 C for 3DP. The chocolate model has 13 g chocolate and 2.08 g vitamin C. The experiments used the adaptive thickness and adaptive speed for chocolate print mode. During the printing process, there was no grainy accumulation of chocolate, showing good mobility. The chocolate was printed according to the parameters set in the normal experiment. The first third of printing was good, and the middle part showed a similar phenomenon of slow solidification; finally, the model collapsed, as shown in Fig. 8.30. From formula 2: comparing the addition of 8 g vitamin C or 8 g cranberry powder into 50 g chocolate, respectively, it was confirmed that the adding high proportion of additives extraneous materials will change the fluidity and

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FIGURE 8.30

The chocolate model mixed a large amount of vitamin c.

viscosity of chocolate and have an impact on the forming of printing. The experiment of formula 3 was carried out to further confirm this point. 8.5.2.4.3 Formula 3 Using the same print model as in Section 8.5.2.2, the mixture of 8 g lutein and 50 g chocolate was melted and stirred at 40 C. After the chocolate was melted, a little more chocolate was added for cooling down to form more stable chocolate crystals as much as possible at 22 C RT. The chocolate was stored at 32 C for 3DP. The chocolate model was about 15 g chocolate and 2.4 g lutein. The experiment used the adaptive thickness and adaptive speed for chocolate print mode. During the printing process, the powder did not show grainy accumulation of chocolate, showing good mobility. The chocolate was printed according to the parameters set in the normal experiment. The first third of printing was good, but the middle part showed a similar phenomenon of slow solidification. Finally, the model collapsed, as shown in Fig. 8.31.

FIGURE 8.31 The chocolate model mixed a large amount of lutein.

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From formula 3, comparing the addition of 8 g lutein into 50 g chocolate with the previous addition of 40 mg lutein into 50 g chocolate, it was confirmed that the addition of small amount of extraneous material (health supplement) showed little impact on the printing and forming of chocolate. If adding excessive external additives, the fluidity and viscosity of chocolate will be changed, and the printing and shaping of chocolate will be greatly affected. 8.5.2.4.4 Conclusion After summarising the experimental results of addition of vitamin C, lutein and cranberry powder in chocolate, respectively, for 3DP chocolate, the following two points have been speculated: 1. Fine grinding could make the material reach a certain degree of fineness; people can identify the fineness of more than 25-mm particles. Most of the fineness of vitamin C, lutein and cranberry powder can achieve 15e20 mm, and it will not affect the delicate taste of chocolate lubrication. 2. The composition of chocolate is a dispersion system; the viscosity depends on the ratio of dispersed phase and the dispersion medium (the ratio of dry powder in the fat). The dry particles can be the external additives (i.e., vitamin C, lutein and cranberry powder), sucrose and milk powder. The lower the amount of fat, the higher the viscosity of the chocolate and the worse the flow performance. It also brings some difficulties in the chocolate forming.

8.5.2.5 The Addition of Methyl Cellulose 8.5.2.5.1 Methyl Cellulose Methyl cellulose is made from natural cellulose with white to milk-white colour. It is a tasteless powder (Fig. 8.32). It has multiple functions such as film-forming, emulsifiability, adhesive property and thickening property and is widely used in baked goods, fried foods, desserts, candies and soups as food additives. In order to add additives and to enable normal 3DP of chocolate, a small amount of methyl cellulose was added into the chocolate to perform the 3DP experiment. Since World Health Organisation (WHO) does not specify the daily allowable intake of methyl cellulose because its addition in food is considered harmless to health, 2 and 8 wt.% methyl cellulose were added to verify the impact on the forming and printing of chocolate. 8.5.2.5.2 Methyl Cellulose Addition Experiment Experiment 1: The addition of 2 wt.% methyl cellulose into the mixture of 8 g cranberry and 50 g chocolate (Section 8.5.2.3.2) did enhance the 3DP of

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FIGURE 8.32 Methyl cellulose.

chocolate, as shown in Fig. 8.33A (2% methyl cellulose) and Fig. 8.33B without methyl cellulose (Section 8.5.2.3.2). To a certain extent, methyl cellulose can solve the problem caused by the addition of cranberry powder decreasing the amount of chocolate fat. Experiment 2: When adding 8 wt.% of methyl cellulose into the mixture of 8 g cranberry powder and 50 g chocolate and using the same optimisation parameters for chocolate printing, the chocolate model still collapsed, as shown in Fig. 8.34. The solidification behaviour of the model was not in accordance with increasing methyl cellulose content. It further confirmed the conclusion in Section 8.5.2.5.2 that the addition of extraneous powders (i.e., vitamin C, lutein and cranberry powder) reduces the dispersion ratio of fat; the lower the amount of fat, the less the viscosity and the better the fluidity. It also brings the difficulties in chocolate forming.

FIGURE 8.33 The chocolate model with (A) and without (B) the addition of methyl cellulose.

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FIGURE 8.34 The chocolate model with adding 8 wt.% of methyl cellulose.

8.5.2.5.3 Conclusions The experiments of adding 2 and 8 wt.% of methyl cellulose, respectively, showed that to some extent, methyl cellulose could enhance the ability of chocolate printing. However, the increase of the amount of methyl cellulose is not linear with the enhancement of chocolate printing forming ability. When the addition of methyl cellulose exceeds a certain range of ratio, it will greatly reduce the chocolate’s own fat ratio; the adhesion performance of methyl cellulose will be insignificant and will reduce the ability of chocolate forming. Therefore, adding a small amount of additive (e.g., less than 1%, based on all in-lab experimental experiences) will have little impact on the printing and forming of chocolate. When the external addition (health product) exceeds more than 1%, the chocolate’s own fat ratio will be reduced, and it will affect the forming of chocolate. At this point, one can add a small amount of methyl cellulose to solve the influence of the extra additives (e.g., health products) to optimise of the forming and printing of chocolate.

8.6 SUMMARY AND OUTLOOK With the rapid development and maturity of 3DP technology, its application areas are also fast expanding. Chocolate 3DP is an emerging field of application in recent years. In chocolate 3DP technology, the biggest difficulties mainly lie in the chocolate extrusion parameter design and chocolate special high-viscosity liquid material 3DP technology. The first chocolate 3D printer developed in 2011, and chocolate 3D printers have been available since 2012. With the constant research and development of technology and the improvement of printing parameters, the chocolate 3D

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printer provided by QiaoYI Technology Co Ltd. has been updated to the third generation, realising the desktop, more simplified operation and more moulding efficiency of 3D chocolate printer. In addition, the application of 3D chocolate printing will also achieve cross-industry applications, including 3DP chocolate combined application of drugs now being studied, as well as the realisation of 3DP chocolate and jewellery applications combined in order to achieve the diversity and novelty of 3D chocolate printing. The development of chocolate 3DP is also known as smart food printing. As technology advances, 3DP of smart food will become a ‘private chef’ for homes, hotels and other places, and it will realise the special needs of different people in food and balanced nutrition ratio print, become intelligent ‘nutrition division’ or the most intimate personal food ‘customisation division’, truly ushered in the era of digital food 3DP. At the same time, chocolate 3DP is also facing a huge challenge. From the technical level, our research aims to develop a chocolate 3D printer which is more portable, has more stable shape and overcomes the unique properties of the fluid of chocolate for simple and quantitative addition of chocolate into the machine. We have proposed a portable and quantitative capsule for 3DP chocolate; the shape of this capsule will match the fourth-generation chocolate machine produced by Qiao Yi Technology Co., Ltd. The portable capsule packaging can be heated up with contact of the air while melting the internal chocolate and also can be directly placed in the machine for printing. To some extent, it can facilitate the purchase and transportation and preservation or conversation of the chocolate and guarantee the clean and sanitary process of printing. From the application level, the application of chocolate 3DP will no longer be limited to chocolate makers, chocolate operators, but to achieve more integration between the 3D chocolate printing and across industries in order to realise the intelligent and diversified applications of food 3DP.

REFERENCES Aasted, L., 1998. Method and a System for the Production of Chocolate Articles. Washington, DC: U.S. Patent and Trademark Office. Akutagawa, T., 1983. Process for Molding Chocolate to Make Chocolate Block Having Ornamental Pattern and Internal Hollow Cavity. Washington, DC: U.S. Patent and Trademark Office. Anitha, R., Arunachalam, S., Radhakrishnan, P., 2001. Critical parameters influencing the quality of prototypes in fused deposition modelling. Journal of Materials Processing Technology 118 (1e3), 385e388. Banerjee, S., Golhar, D.Y., 2013. A decision support system for a third-party coordinator managing supply chain with demand uncertainty. Production Planning and Control 24 (6), 521e531. Beckett, S.T., 2008. The Science of Chocolate. Royal. Bellehumeur, C., et al., 2004. Modeling of bond formation between polymer filaments in the fused deposition modeling process. Journal of Manufacturing Processes 6 (2), 170e178.

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Berkes, K., Forster, Huth, H., Ritschel, W.G., Schebiella, G., Scholz, N., Thomas, F.G., 1984. Method for Continuous Production of Chocolate Mass. Washington, DC: U.S. Patent and Trademark Office. Boland, M., 2008. Innovation in the food industry: Personalised nutrition and mass customization. Innovation: Management, Policy and Practice 10 (1), 53e60. Chen, Y.W., Mackley, M.R., 2006. Flexible chocolate. Soft Matter 2, 304e309. Childerhouse, P., Aitken, J., Towill, D.R., 2002. Analysis and design of focused demand chains. Journal of Operations Management 20 (6), 675e689. Christopher, M., 2011. Logistics & Supply Chain Management, fourth ed. Financial Times Prentice Hall, Harlow. Cohen, D., Lipton, J., Cutler, M., Coulter, D., Vesco, A., Lipson, H., 2009. Hydrocolloid printing: a novel platform for customized food production. In: Solid Freeform Fabrication Symposium. Austin. Engmann, J., Mackley, M., 2006a. Semi-solid processing of chocolate and cocoa butter: modelling rheology and microstructure changes during extrusion. Food and Bioproducts Processing 84 (2), 102e108. Fitzgerald, B., 1995. Mass customizationeat a profit. World Class Design to Manufacture 2 (1), 43e46. Flint, D.J., Larsson, E., Gammelgaard, B., 2008. Exploring processes for customer value insights, supply chian learning and innovation: an international study. Journal of Business Logistics 29 (1), 257e281. Franke, N., Keinz, P., Steger, C.J., 2009. Testing the value of customization: when do customers really prefer products tailored to their preferences. Journal of Marketing 73 (5), 103e121. Galantucci, L., Lavecchia, F., Percoco, G., 2009. Experimental study aiming to enhance the surface finish of fused deposition modeled parts. CIRP Annals-Manufacturing Technology 58 (1), 189e192. Gilmore, J.H., Pine, B.J., 1997. The four faces of mass customization. Harvard Business Review 75 (1), 91. Hendry, L.C., 2010. Product customisation: an empirical study of competitive advantage and repeat business. International Journal of Production Research 48 (13), 3845e3865. Hopkinson, N., Hague, R., Dickens, P., 2006. Rapid Manufacturing: an Industrial Revolution for the Digital Age. John Wiley, Chichester. Hunter, L.B., 1927. Method of making chocolate products. Washington, DC: U.S. Patent and Trademark Office. Jennings, D., 2005. Thornton’s plc: corporate and business strategy. In: Johnson, Scholes, Whittington (Eds.), Exploring Corporate Strategy. Pearson Education Limited, pp. 293e303. Jeffery, M.S., Glynn, P.A., Khan, M.M.U., 1977. Method of Manufacturing a Chocolate Product. Washington, DC: U.S. Patent and Trademark Office. Khalil, S., Sun, W., 2007. Biopolymer deposition for freeform fabrication of hydrogel tissue constructs. Materials Science and Engineering: C 27 (3), 469e478. Lyons, A.C., Everington, L., Hernandez, J., Li, D., Michaelides, R., Um, J., 2013. The application of a knowledge-based reference framework to support the provision of requisite variety and customisation across collaborative networks. International Journal of Production Research 51 (7), 2019e2033. Martı´nez, J.A., Parra, M.D., Santos, J.L., Moreno-Aliaga, M.J., Marti, A., MartinezGonzalez, M.A., 2008. Genotype-dependent response to energy-restricted diets in obese subjects: towards personalized nutrition. Asia Pacific Journal of Clinic Nutrition 17 (1), 119e122.

254 Fundamentals of 3D Food Printing and Applications Simonson, I., 2005. Determinants of customers’ responses to customized offers: conceptual framework and research propositions. Journal of Marketing 69 (January), 32e45. Sood, A.K., Ohdar, R., Mahapatra, S., 2010. Parametric appraisal of mechanical property of fused deposition modelling processed parts. Materials and Design 31 (1), 287e295. Thrimurthulu, K., Pandey, P.M., Venkata Reddy, N., 2004. Optimum part deposition orientation in fused deposition modeling. International Journal of Machine Tools and Manufacture 44 (6), 585e594. Vorst, J.G.A.J.V.D., 2000. Effective Food Supply Chains: Generating, Modelling and Evaluating Supply Chain Scenarios. Wageningen University, Wageningen. Wang, J., Shaw, L.L., 2005. Rheological and extrusion behavior of dental porcelain slurries for rapid prototyping applications. Materials Science and Engineering A 397 (1e2), 314e321. Wang, S., 2011. An analysis of manufacturers’ supply and demand uncertainty based on the dynamic customisation degree. International Journal of Production Research 49 (10), 3023e3043. Wong, H., Eyers, D., 2011. An analytical framework for evaluating the value of enhanced customisation: An integrated operations-marketing perspective. International Journal of Production Research 49 (19), 5779e5800.

FURTHER READING Afoakwa, E.O., 2010. Chocolate Science and Technology. John Wiley & Sons, Ltd., p. 101 ASTM-International, 2012. Standard terminology for additive manufacturing technologies. In: ASTM F2792e10e1 standard, Vol ASTM F2792-10e1 Standard. ASTM International. Cooper, K.P., Lambrakos, S.G., 2011. Thermal modelling of direct digital melt-deposition processes. Journal of Materials Engineering and Performance 20, 48e56. Geron, M., De Chadarevian, S., 2013. Nutraceutical Chocolate or Compound Chocolate Product.EP. Gibson, I., Rosen, D., Stucker, B., 2010c. Introduction and basic principles. In: Additive Manufacturing Technologies. Springer, New York, U.S. Godoi, F.C., Prakash, S., Bhandari, B.R., 2016. 3d printing technologies applied for food design: status and prospects. Journal of Food Engineering 179, 44e54. Hao, L., Mellor, S., Seaman, O., Henderson, J., Sewell, N., 2010. Material characterisation and process development for chocolate additive layer manufacturing. Virtual and Physical Prototyping 5 (2), 57e64. Jacobs, A.J., 2013. Dinner is printed. New York Times 21 (9). Jia, F., Wang, X., Mustafee, N., Hao, L., 2016. Investigating the feasibility of supply chain-centric business models in 3D chocolate printing: a simulation study. Forecasting and Social Change 102, 202e213. Laudon, R., September October 2010. “In Praise of Fast Food,” Utne Reader. Lipson, H., Kurman, M., 2013. Fabricated the New World of 3D Printing. Wiley Publishing. Lipton, J., Arnold, D., Nigl, F., Lopez, N., Cohen, D., Noren, N., et al., 2010. Multi-material food printing with complex internal structures suitable for conventional post-processing. In: 21st Solid Freeform Fabrication Symposium. Austin. Lipton, J.I., Cutler, M., Nigl, F., Dan, C., Lipson, H., 2015. Additive manufacturing for the food industry. Trends in Food Science and Technology 43 (1), 114e123. Liu, T.Y., Zhou, H.X., Zhang, X., Lan, H.M., Liu, H.B., 2016. Research and application progress of food and soft materials 3D printing technology. Packaging & Food Machinery 5, 59e63.

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Rosales, C.K., Klinkesorn, U., Suwonsichon, S., 2017a. Effect of crystal promoters on viscosity and melting characteristics of compound chocolate. International Journal of Food Science and Technology 20 (1), 119e132. Rosales, C.K., Suwonsichon, S., Klinkesorn, U., 2017b. Ability of crystal promoters to delay fat bloom development in heat-resistant compound chocolate with or without the presence of crystal inhibitor. International Journal of Food Science and Technology 52. Sereno, L., Vallicrosa, G., Delgado, J., Ciurana, J., 2012. A new application for food customization with additive manufacturing technologies. In: AIP Conference Proceedings. AIP Publishing, p. 825e833. Smith, J., 2004. Food Processing: Principles and Applications. Blackwell Publishing Ltd., Oxford. Wegrzyn, T.F., Golding, M., Archer, R.H., 2012. Food Layered Manufacture: a new process for constructing solid foods. Trends in Food Science and Technology 27 (2), 66e72. Yamashita, T., Kitamura, A., Yamamoto, A., Narita, M., 2017. Hydroxypropyl Methyl Cellulose Having High Thermal Gel Strength, Method for the Same, and Food Containing the Same.

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Chapter 9

Creation of Food Structures Through Binder Jetting Sonia Holland1, 2, Tim Foster1, Chris Tuck2 1 Division of Food Science, Sutton Bonington Campus, University of Nottingham, Loughborough, United Kingdom; 23D Printing and Additive Manufacturing Research Group, University Park, University of Nottingham, Nottingham, United Kingdom

Chapter Outline

9.1 Introduction to Binder Jetting 9.2 Powder Characteristics and Interlayer Cohesion 9.3 Powder Binding Mechanisms 9.4 Suggested Analysis 9.5 Formulating a Functional Printing Ink 9.5.1 Ink Jetting Theory 9.5.2 Viscosity Considerations for Ink Jetting 9.5.3 The Effects of Additives to Enhance Viscosity 9.5.4 Surface Tension and Density

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9.6 Controls and Considerations During and Postprinting 9.6.1 Printer Settings 9.6.1.1 Powder Deposition 9.6.1.2 Material Jetting 9.6.2 Combining Powder and Ink During Print 9.7 Postprocessing 9.8 Application and Outlook for Food Materials References

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9.1 INTRODUCTION TO BINDER JETTING In the 21st century, it is commonplace to have one or more inkjet printers within an office environment and in our own homes that are used frequently to record important information in the form of documents or capture moments through printing images. Inkjet printing technology has been around since the 1960s, though the first jetting concept is thought to have been William Thompson’s (Lord Kelvin) siphon recorder, patented in 1867 (Gibson et al., 2009; Thomson, 1870). This was an example of continuous ink jetting (CIJ) whereby ink is continually jetted from a nozzle and deflected toward or away from a chosen substrate, depending on the particulars of the process Fundamentals of 3D Food Printing and Applications. https://doi.org/10.1016/B978-0-12-814564-7.00009-2 Copyright © 2019 Elsevier Inc. All rights reserved.

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employed (Derby, 2015). Within the food industry, CIJ is widely used, particularly in barcoding or in the marking and coding of egg shells (Fellows, 2016), whereas colour labelling and packaging is more likely done with other ink application techniques such as lithography, flexography or gravure (Forrest, 2009). Drop on demand (DoD) inkjet printers can be used to produce images on substrates like icing sheets or edible papers for decorative purposes (Pallottino et al., 2016; Periard et al., 2007). As the name suggests, ink droplets are only produced as and when required through pulse actuation, unlike the constant nature of CIJ. This allows for more complex and highresolution designs to be created with the option of combining a number of nozzles containing inks of varying formulation, for example, with different dye colourants (Le, 1998). Binder jetting was predominantly developed at Massachusetts Institute of Technology (MIT) in 1993, stemming from the use of an inkjet printer to jet a binding ink onto ceramic powder for investment casting processes and was originally termed three-dimensional printing (3DP). A few years later, Z Corp licenced the technology from MIT and launched its first 3D printer and associated materials based on this concept (Wohlers and Gornet, 2014). This type of additive manufacturing (AM) technology is typically lower cost, faster and easier to incorporate multiple material components into, including the option of printing in 24-bit colour, compared with other AM techniques (Gibson et al., 2009). The schematic above (Fig. 9.1) depicts a typical binder jetting process. Once the file for printing has been received, the 2D ‘slices’ of the 3D image are sequentially printed from the inkjet nozzle onto the powdered material on the print bed. After one layer of ink is deposited on the powder below, the X-Y positioning system

Powder spreader

Part

Inkjet print head

Binder droplets

Unused powder

Z

Build platform

FIGURE 9.1 A schematic of the binder jetting process. Reprinted with permission from Gibson et al., (2009).

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printing plate moves down by one ‘z’ unit as the feedstock chamber plate moves up to provide sufficient powder for the next layer. A doctor blade or counterrotating roller and powder leveller carry the raised powder from the feedstock across to fill the build platform with any excess being collected. The next layer of ink can then be printed and the process repeated until the 3D object or group of objects have been created. Powder hoppers on a separate level to the build platform are an alternative to having a feedstock chamber and could facilitate building with multiple materials; however, such systems are not commercially available and are in their research infancy. As with other powder-based processes, such as laser sintering, the presence of loose and unbound powder in the bed throughout printing acts naturally to support the growing 3D object, thus negating the requirement for extra support material as in other AM processes. This also means that structures with added complexity like overhangs are able to be produced. One thing to note when designing structures for binder jetting is that powder must have an exit point if the shape is to be hollow or have voids; for example, if the design is a spherical shell, there will be no exit point for the loose powder, so it will be enclosed within the shape. Further considerations for powder design, ink formulation and combining these in 3D applications will be discussed in subsequent sections of this chapter. Inherently, this process can be categorised as ‘multimaterial’, as it involves combining a powder and ink to form a single component. Thus, many powder and ink combinations capable of producing successful objects exist owing to knowledge in other powderebinder processes and adaptability of inkjet nozzles (within reason). A typical example of how a known process has been translated to use in binder jetting is with ceramics, which is now a relatively mature material feedstock for this type of AM. Yoo et al. (1993), the research group from MIT who pioneered work in this area (see Sachs et al., 1992), describe the adaptation of binder jet printing to produce ceramic parts from MgO powder and a latex binder to initially produce a ‘green part’ for isostatic pressing and sintering as postproduction steps. This work demonstrates the adaptability of binder jetting to different materials and can be a useful guide when thinking of other novel materials. Typically submicron-sized particles, as used in the MIT project, are notoriously difficult to spread due to higher interparticle friction and electrostatic forces, but deliver a higher green part packing density, accuracy and surface finish for this product. Therefore, discovering a way to improve the original binder jet process to gain these advantages has enabled further application in the ceramics area and the ability to translate this knowledge when working with other materials (Gibson et al., 2009; Yoo et al., 1993). In terms of food applications where a liquid binder is introduced to a powder phase, agglomeration in spray drying, and related processes, is an obvious example. Agglomeration involves the accumulation of particulate solids, gradually over time or as a result of processing, resulting in size enlargement of the product clusters. In long-life powdered products, natural

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caking over time is considered a negative effect on product quality, whereas in spray drying, controlled agglomeration, like in a fluidized bed, before packaging can improve qualities such as solubility, wetting, controlled release and flowability of the product (Bhandari et al., 2013; Cuq et al., 2013). Powdered food products tend to lend themselves well to agglomeration due to their stickiness and hygroscopicity. The addition of liquid to powder particles promotes adhesion forces between them. Within agglomeration techniques in the food industry, shear is typically added to promote particle collision, such as high-velocity air or other types of agitation. However, as each layer of the binder jetting process is static once laid down, it is important that packing characteristics of the powder ensure there are enough particles in contact with one another to promote adhesion without the application of an external force, i.e., the powder bed porosity should not be too high. This consideration and other mechanisms of particleeparticle adhesion will be discussed in the following sections along with powder and ink interactions. It is worth noting that agglomeration is not solely reliant on the application of a wet binder. For example, pressure compaction is used in the pharmaceutical industry for tabulation or in food factories to create concentrated stock cubes from bouillon powder. Other external influences such as temperature will further effect the physical or chemical bonding of particulates (Dhanalakshmi et al., 2011; Pietsch, 2003). Binder jetting allows for the inclusion of these in the form of pressure roller systems for spreading powder and also the ability to keep the bulk powder bed at a determined temperature, often just below the glass transition (Tg) of a powder component. The Tg is a second-order phase transition, with both a moisture and temperature dependence, during which an amorphous glassy solid becomes more ‘rubbery’. It occurs over a temperature range which can be determined through thermal analysis and, as will be discussed later, is an important parameter to take into consideration, as it can govern structuring and order within a material (Bhandari and Howes, 1999). Powder and ink formulation design will determine the microstructure of the printed object through the culmination of individual properties and interactions of each component, and macrostructure design is only limited to the imagination of the maker.

9.2 POWDER CHARACTERISTICS AND INTERLAYER COHESION Knowledge of powder material properties is paramount for success in binder jetting; it will allow for the design of an appropriate ink component and also selection of parameters during printing. When using powders in bed processes such as this, there are a number of general considerations: 1. Powder particles must flow freely past one another to allow easy spreading across the powder bed.

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There are a number of powder properties which could potentially cause failure in this respect. It is tempting in powder bed processes to use very fine particulates in the hope of reducing layer size for higher resolution and a better surface finish. However, electrostatic forces between particles increase with a decrease in particle size, causing more interparticle friction and hindering flowability of the powder. Further influencing the friction between particles is their shape (i.e., spherical or irregular) due to the effect on the angle of repose, where irregularly shaped particles can attain a steeper angle which is correlated to lower flowability, though overall powder particle size is more of an influence (Utela et al., 2008). The material coefficient of friction will determine the success of spreading the correct powder without disturbing the layer underneath, as well as ensuring the correct volume of powder is collected and evenly spread, which will differ as a result of the spreading mechanism employed, i.e., using either a counterrotating roller system or doctor blade with or without an integrated hopper system. There exists, too, a dependence on the surface that the powder is being dragged across, with particle size being independent of the resistance to slow if powder is being pulled along a stationary layer made of the same material. Therefore, it is worth noting that flowability and layer success may be different on the first pass over the actual print bed to when the layer underneath is the powder itself (Augenstein and Hogg, 1974; Bhandari et al., 2013; Gibson et al., 2009). Cohesion effects must also be considered at this stage; as well as being crucial for the creation of 3D structures, they can be very detrimental to powder flowability. The surface of glassy food powders can transition to the amorphous, rubbery state over time or through processes such as mechanical milling or spray drying if sufficient time is not allowed to form ordered, more thermodynamically stable, crystalline structures. Thus, identification of conditions exacerbating this for the particular feedstock is crucial, and steps should be taken to limit its occurrence during storage or printing, particularly if the aim is to collect and reuse excess unbound powder from a given printing run (Bhandari et al., 2013; Opali
nski et al., 2012). 2. The maximum particle size should not exceed the intended layer size. This will further help to ensure that layers placed down are smooth, thin and repeatable throughout the process. Equally, if the powder is prone to natural caking and agglomeration, the maximum agglomerate size should not exceed this thickness. Holland et al. (under review) also describe a phenomenon where ink interacts with powder to cause swelling and lifting of a given layer. If, after printing the ink layer, the powder plus ink layer thickness is greater than that which is programmed, then powder being spread across will cause misalignment and movement between layers. Thus, it is important

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that powders and inks are tested for interactive effects in 2D prior to use in a 3D scenario. 3. To enable efficient packing of the powder bed and sufficient ‘green density’ of the printed object, there should be a range of particle sizes within the powder. Green density refers to the relative particle packing density compared to the external volume of a printed object. The minimum required green density of any given part will depend on the powder material properties, binding mechanism (e.g., physical ‘gluing’ versus chemical bonding) and the effect of any postprocessing; for example, Yoo et al. (1993) state a green density of at least 60% is required when printing ceramics that are sintered via solid-state diffusion, whereas Bai et al. (2015) used metal powders in a binder jetting process and worked within a green density range of 44%e57%. The use of bimodal and multimodal powder formulations, whereby smaller particles fall in interstitial voids between coarse particles to provide more available necking sites between particles to improve green and sintered densities, is well documented in literature across a range of powder bed materials and processes (Bai et al., 2015; Brunello et al., 2016; Gibson et al., 2009; Olakanmi et al., 2015; Utela et al., 2008; Xia and Sanjayan, 2016). Apparent bed density and tapped density are simple measurements which can be used to determine the performance of a powder and as a screening tool in formulation development. It is also worth noting that as the surface area-to-volume ratio of a given powder particle increases, its reactivity increases. This introduces the risk of dust formation or risk of explosion as with other fine powders used in the food industry (and others), influencing handling and transportation aspects of the process (Bhandari et al., 2013; Gibson et al., 2009). Importantly for food powders and when thinking ahead to potential powder recycling during processing, higher powder surface area increases susceptibility to oxidation and related compound degradation reactions, depending on the chemical constituents of the powder. With this in mind; controls and monitoring steps should be put in place to ensure the safety and quality of end products, as in all food material processes.

9.3 POWDER BINDING MECHANISMS The powder agglomeration method will depend on the specific material properties of the powder and its interaction with the ink component. Generally, water-soluble materials are best suited to agglomeration. For hydrophobic or water-insoluble materials, the addition of small amounts of a better-suited material can provide sufficient interaction to bind; this should be taken into consideration during material scoping phases for binder jetting.

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Binding can occur physically, chemically or electrostatically. Fig. 9.2 depicts the various adhesion mechanisms that can occur to achieve agglomeration of particles. In nonfood applications, it is common to use heat or UV-curable resins such as acrylic or epoxy-based resins, but due to toxicity of those particular substances and related photoinitiators, they are unsuitable for use in edible products. In some instances, it is the ‘ink’ that provides the full binding effect where the binder cures or hardens around the powder particles to create particulate agglomerates. Of course, the alternative is that interactive effects between the ink and powder components initiate bonding and aggregation; thus, both components would have a part to play in the adhesion. Food powder particles have a tendency to exhibit caking upon addition of moisture; thus, it is likely that for the use of food materials in binder jetting, this is the most likely adhesion scenario. Added moisture will begin to wet the outside of each particle; the degree to which this occurs will depend on the saturation ratio of ink to powder. Ink addition (‘wetting’ stage) will have a number of effects to initiate agglomeration: l

l

l

Polarities and compatibility of both phases will determine the formation of chemical bonds. For food products, this would likely induce the formation of hydrogen bonds if a polar ink (water or ethanol based) is deposited onto a powder with predominantly polar components (the bulk of this would be carbohydrate monosaccharides or polysaccharides and proteins). Facilitation of further low-energy bonding such as van der Waals or ionic interactions and the occurrence of hydrophobic effects, potentially detrimental to adhesion, should be considered, depending on the composition of powder and ink materials. Particle surface viscosity will differ upon ink addition time and volume.

FIGURE 9.2 Agglomeration mechanisms between food particles. Reprinted with permission from Pietsch (1997).

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In the ‘nucleation’ phase of agglomeration, liquid bridges form between particles to initially sinter them to one another, stabilised by capillary forces; over time, soluble components may dissolve and enhance local viscosity to strengthen these sinter bridges. Descamps et al. (2013) state that below a viscosity of 108 Pa s, particles will start to exhibit ‘sticky’ behaviour. The powder bed during binder jetting is static; however, particles with lowviscosity surfaces may plastically deform to create a larger area of contact between them to aid adhesion and reduce porosity which is why a distribution of particle sizes and efficient bed packing is advantageous. In terms of interaction time for layers of a part, the lower layers of a 3D structure will have a longer time to interact due to the nature of the layer-by-layer process and are more likely to exhibit surface solubilisation and deform plastically to create a more viscous sinter bridge between particles. The top layer will experience the process for a shorter time and may not have the chance to absorb the binder, forming a liquid bridge instead which is stabilised primarily by capillary forces unless postprocess resting time or additional steps are factored in. ‘Growth’ interactions are crucial to maintaining cohesion in the z direction, i.e., any given layer interacts with that both above and below it, despite the lack of mixing to promote collision like fluidised beds would provide in conventional food agglomeration processes. Therefore, particle:binder affinity, particle:binder ratio and the thickness of each layer ultimately determine the growth of a 3D structure or of separated 2D slices. ‘Consolidation’, ‘rupture’ and ‘erosion’ effects present in other agglomeration processes are less important here, as there should be minimal perturbation of a given layer once the binder has been added. Subsequently irreversible interactions can be initiated, such as denaturation to covalently bond molecules or state transition may occur between amorphous, semicrystalline or crystalline supramolecular order. Such phenomena are dynamic and subject to not only the plasticization effect of the ink component, but also addition of thermal energy or pressure. This will act as a ‘stabilisation’ step, like in other food powder agglomeration processes. Knowledge of a material’s state diagram and basic chemistry is highly recommended prior to testing in a binder jet printer to be able to select likely ballpark parameters for a successful print, particularly for complex, multicomponent food powders. Fig. 9.3 gives an example of a state diagram of wheat flour, highlighting important areas such as Tg, melting and gelatinization that all need to be considered when using a complex material, particularly a mixed powder system for binder jetting. The state of a material will affect the mechanism and success of adhesion, particularly the ability of ink to penetrate a material if it is highly ordered (crystalline) versus one that is lacking in order (amorphous) and more heterogeneous. Changes to local surface viscosity and the ability for formation and sintering of liquid bridges will be affected by molecular ordering and mobility. Materials with favourable binding properties present in

Temperature (°C)

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220 200 180 ‘Theoretical Tm (starch) 160 flow state’ 140 120 100 Tr (proteins) 80 60 ‘Rubbery state’ 40 ‘Glassy Tgelat, Tg (starch) 20 state’ (starch) 0 Tg (proteins) –20 0 10 20 30 40 50 60 70 80 90 100 Water content (g per 100 g dry matter)

FIGURE 9.3 State diagram for the main constituents of wheat flour (starch and gluten proteins). Tm is the melting point, Tr is the minimum thermosetting temperature for proteins, Tg is the glass transition temperature and Tgelat is the starch gelatinisation; bold labels relate to the gluten proteins. Reproduced with permission from Cuq et al. (2003).

the powder formulation can complement those in the ink; a host of food-grade materials, not only low-molecular-weight carbohydrates, fall into this category. Equally, ‘bridging potential’ of a powder formulation can be negatively affected by the presence of hydrophobic constituents or ionic interactions caused by salts. Inclusion of materials with some water-binding capacity or an ability to form a highly viscous solution or gel upon hydration in the powder component would also be an advantage for creation of food structures by binder jetting. Further, material-specific information on Tg and agglomeration can be found in food science literature (Dhanalakshmi et al., 2011; Hartel et al., 2011; Bhandari et al., 2013; Cuq et al., 2013; Descamps et al., 2013; Roos and Drusch, 2016; Wang and Truong, 2016).

9.4 SUGGESTED ANALYSIS Given that there are many factors to consider in creating a suitable powder for binder jetting, there are a few key analysis techniques to consider undertaking on trial formations. Before any ink is deposited in binder jetting, the powder must first be spread; therefore, it is important to ensure the particles will perform well in this task. It is recommended that visual assessment of powder particles through light microscopy or scanning electron microscopy is undertaken. This will give an indication as to the particle shape and possible particle size distribution; however, it is crucial to conduct some other particle size analysis, such as light scattering, to fully assess the maximum size and distribution of particles. From these data formulation adjustments, further processing, such as milling or sieving, can be conducted if necessary.

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Particle size and shape are linked to the flowability of the powder (Schulze, 2006). Powder behaviour is important, as the powder must spread well over the base plate surface for the initial layer, but also over bound and unbound powder in subsequent layers. A number of methods exist, ranging from quick, crude visual assessments to more advanced setups such as powder flow rheometers. Jenike (1964) described the use of a shear cell to measure powder flow properties in order to design vessels for their transport and deposition which really began research in this area. A number of shear cells are available such as the direct shear cell, Schulze annular ring shear tester (ASTM International Standard D6773) and other devices serving as advances to Jenike’s technique as well as others which incorporate uniaxial compression techniques. Crucially in powder flow analysis, these techniques are undertaken to define the relationship between consolidation stress (s1) of a powder bulk to its unconfined yield stress (sc), yielding a dimensionless ‘flowability’ index value (ffc). ff c ¼

s1 sc

When ffc < 1, the material will not flow, whereas a ffc > 10 indicates a freeflowing material. An index value between 4 and 10 is deemed to be ‘good flow’; thus, this should be the minimum value range to aim for when designing a flowable powder for binder jetting, as any value below 4, which is ‘cohesive’, will be very detrimental to the process, particularly in terms of disturbing lower layers during spreading. In addition, a small angle of repose has been found to confer good flow characteristics of food materials in powder bed processes (Bhandari et al., 2013; Cagli et al., 2007; Descamps et al., 2013; Diaz et al., 2015; Ghosal et al., 2010; Jenike, 1964; Liu et al., 2017; Schulze, 2015). As discussed above, a variety of density measurements may be made to determine how the powder may pack in the powder bed after being spread. The bed porosity, i.e., ratio of the volume of voids to the total bed volume, will greatly determine the ability of particles to adhere to one another to create a cohesive structure, and the porosity of the final printed object. Sorption isotherms of powder formulations measured either through dynamic vapour sorption (as in Holland et al., 2017) or through equilibration over saturated salt solutions, measured by a humidity sensor (described in Descamps et al., 2013), will provide information of how water (or other solvent) molecules bind to the powder particles. In dynamic techniques, desorption can also be measured; thus, any sorption/desorption hysteresis is observed which may be insightful if solvent removal is important in the proposed binder jet process. Finally, thermal analysis through differential scanning calorimetry will provide experimental data to complement state diagram information obtained from literature. Printing parameters such as ink saturation (providing moisture plasticization of transitions) and required temperature settings can be adjusted accordingly to give desired states of order of the material.

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9.5 FORMULATING A FUNCTIONAL PRINTING INK 9.5.1 Ink Jetting Theory DoD inkjet is used in binder jetting; however, the actuation mechanism may vary. Thus, inkjet printheads will inevitably differ between binder jetting machines based on their manufacturer. Actuation mechanisms may be acoustic, thermal, electrostatic or piezo-driven for DoD systems, with the thermal and piezo methods being most commonly employed. In the thermal method, a current pulse is passed through a heating element (located adjacent to or as a ‘roof’ over the nozzle orifice) to locally superheat the ink and nucleate bubble formation. The bubble expands to eject a droplet of ink and then begins to collapse against the heater, triggering droplet break-off and refilling of the ink chamber. Piezo actuation involves deformation of a piezo ceramic, generating waves through the pressure chamber to eject ink droplets, and can be one of four modes: shear, bend, push or squeeze tube (Godoi et al., 2016; Le, 1998; Wijshoff, 2010). Despite variation in actuation mechanisms, the theory behind droplet ejection from the nozzle is universal and can be explained through PlateaueRayleigh instability of liquid jets (Plateau, 1873; Rayleigh, 1878). A volume of liquid is ejected from the nozzle as a jet which is subject to capillary thinning of the liquid bridge between the main droplet and nozzle until this ligament breaks to produce a single droplet, in an ideal scenario, or main droplet and associated satellites (Derby, 2010; McIlroy and Harlen, 2014). As a result, some key analyses can be performed on trial ink formulations before application to the printer to give an idea as to their anticipated success or ‘printability’. The printability parameter (Z) was initially proposed by Fromm (1984) but revised more recently by Reis and Derby (2000) using modelling techniques to better understand the ‘printable’ values of Z. pffiffiffiffiffiffiffiffiffi 1 Re grL Z¼ ¼ pffiffiffiffiffiffiffi ¼ Oh h We The Ohnesorge number (Oh) is a ratio of two dimensionless numbers, the Reynold’s number (Re) and Weber number (We), which are commonly used in fluid dynamics, Re particularly in the food industry when considering product flow through a pipe (Fellows, 2016). Re and We are influenced by velocity; using Oh directly allows for printability characterisation independent of fluid velocity, a parameter which can, of course, be altered in print settings (discussed later). In the liquid jet model, surface tension (g) forces act to destabilise the jet in order to minimise surface energy through breakup into spherical liquid droplets. This action is resisted by the ink’s viscosity (h). Achieving the correct balance between surface tension, viscous and inertial forces is key to developing a functional printing ink. Viscosity is the main driver of printability, determining the amount of thinning the liquid capillary

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undergoes prior to breakup. Surface tension should be sufficient so that the ink does not freely flow from the nozzle in a static state but only to allow breakup to single droplets after actuation. Density (r) and the nozzle diameter (L) of the formulation are also considered in this model. If Z is too low, it is likely that viscous forces are too large, preventing droplet ejection, whereas a high Z number is related to the formation of satellite droplets and potential inaccuracies in droplet positioning if these do not reform with the main droplet before coming into contact with the substrate (Derby, 2010; Hoath et al., 2009; Hoath, 2016; McIlroy and Harlen, 2014). It is worth noting that measurement of these parameters should be undertaken under printing shear rate and temperature conditions to give a Z calculation relevant to conditions the ink will be subjected to. A key figure in Derby (2010) has been converted to an interactive online tool by Abbott which can be used by formulators to estimate printability of trial inks. Measured ink parameters (h, g and r) are selected using the slide bars, along with the set nozzle diameter and projected print speed. The marker moves around the two graphs based on computed values for Z, Oh, Re and We to give an indication of droplet breakup during printing and thus the success of the formulation. It is also useful to hold parameters at given values and then change one at a time to observe the relative effects this would have on the estimated printability, e.g., viscosity fluctuation versus density. Fig. 9.4 is a screenshot of this online tool with values selected within the FujiFilm (2008) guidelines for a Dimatix printer; h ¼ 10e12 cP, g ¼ 32e42 m/Nm and relative r > 1.

Ohnesorge Number 1000

10.00

Splashing Too Viscous

Oh Satellites

Z 10

Sine

0.10 Rayleigh

0.01 Low Energy

1

1 Viscosity cP 10

Oh 0.352

Wave

1.00

100

ρ Density g/cc

Atomization

10

Re

100 1000 Length μm 21

1

10 100 σ dyne/cm Re 32

1000

10000

Velocity m/s 6

1.2 Z=1/Oh 2.8

Re 15.1

We 28.3

FIGURE 9.4 An example of ink properties giving an ideal printing ink, visually represented by the online tool developed by Abbott (2017).

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Water is commonly used in fluid bed agglomeration to adhere amorphous, water-soluble particles to one another, whereas for crystalline particles, more viscous liquids tend to be employed, as water cannot readily migrate through this ordered matrix (Cuq et al., 2013). However, water is not an ideal material for printing, with physical properties being outside those reported as ‘printable’, particularly with regard to its low viscosity and high surface tension; h ¼ 1 cP, g ¼ 72.8 m/Nm and r ¼ 998.2 kg/m at 20 C (Crittenden et al., 2012). Despite this, water has actually been cited as a binding material in a number of food-specific binder jetting applications (Diaz et al., 2015; Von Hasseln et al., 2014). Aqueous-based inks are ideal for food printing due to the majority of food polymers being polar and water-soluble or exhibiting hygroscopicity and tendency to agglomerate in a powdered form when exposed to water. Therefore, such additives may be utilised to create printable, foodgrade inks based on water as a primary solvent.

9.5.2 Viscosity Considerations for Ink Jetting A material’s viscosity describes its resistance to flow when a shear stress is applied. This property of fluids in motion can be described simply by Eqs. 9.1 and 9.2 (below) in which s represents the shear stress as a consequence of a force (F) being applied over a given area (A); the ratio of s to the rate at which _ then gives the material’s shear viscosity (h). the shear is applied (g) F A s h¼ g_ s¼

(9.1) (9.2)

Newton’s law applies to ideally viscous materials, whereby viscosity is directly proportional to the shear stress, independent of the rate at which the shear is applied. Water is one example of a Newtonian fluid. Fluids are termed ‘non-Newtonian’ if the measured viscosity is dependent on the rate shear is applied. Typical non-Newtonian effects are viscosity decreasing with increasing shear rate (shear thinning) and viscosity increasing with increasing shear rate (shear thickening). Flow curves may be constructed by plotting s _ or a viscosity curve replacing s for h on the y-axis to visually depict versus g, a material’s flow behaviour. Fig. 9.5 shows an example of a viscosity curve, where (A) is the expected profile of a Newtonian fluid, (B) a shear-thinning sample and (C) a shear-thickening sample (Mezger, 2014). Food systems are typically composed of multiple materials and exhibit complex flow as a result of high-molecular-weight, multiphase or particulate components. Usually at rest, these components are randomly oriented (for suspended aggregates, anisotropic particles or emulsion droplets) or entangled (in the case of long-chain polymers). Initially, these systems can exhibit high

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FIGURE 9.5 A generalised curve showing the viscosity versus shear rate behaviour of (a) a Newtonian fluid; (b) shear thinning; (c) shear thickening with a dilatancy peak on a logarithmic scale.

resistance to flow when low shear is applied. However, as the shear rate increases, particles or molecules will align or orient in the direction of shear; aggregates are able to be broken up or liquid phase droplets deformed such that the resistance and, therefore, measured viscosity is lower at these high shear rates (shear thinning). The presence of such structures on different length scales can provide a myriad of other rheological effects such as the occurrence of a yield stress or temperature-dependent events that influence flow, such as gelation (Day and Golding, 2016; Dickinson, 2016). Though values used to calculate Z should be accurate under printing conditions (i.e., temperature and shear rate for the reported viscosity), these complex behaviours are not accounted for in the model and thus should only be considered a guide in these instances (Derby, 2010). Non-Newtonian effects can be advantageous depending on the application, particularly in the case of adding low concentrations of shear-thinning polymers which can inhibit the formation of satellite droplets (Derby, 2015; McIlroy et al., 2013). Shear-thinning materials also have the ability to reach a printable viscosity at the high elongational strain rates experienced in the nozzle, but then recover their higher, low shear viscosity after ejection and upon impact with the substrate. A simple viscosity measurement over a range of shear rates should be conducted at the intended ink printing temperature to obtain a flow curve. Generally, viscosity decreases with increasing temperature due to energy input and higher molecular mobility, so selection of an elevated printing temperature could be favourable to achieve a desired viscosity if the ink components are not degraded by such treatments. Rotational rheology in which a sample is contained between a stationary surface and a rotating surface, providing the shear, is a common analysis method for these substances. A number of different geometries exist for taking such measurements, and the best-suited one for analysis will depend on ink components and characteristics. Brookfield viscometers with spindle attachments conforming to International

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Standards Organisation (ISO) and Deutsches Institut fu¨r Normung e.V (DIN) standards may be used to measure low-viscosity liquids. Often, turbulent flow and secondary flow effects are observed when measuring low viscosity liquids, and the ‘Weissenberg effect’, where the liquid ‘climbs’ a rod during shear, can affect the validity of results in the case of a solution consisting of a polymer in water. Concentric cylinder geometries including standard cup and bob, Couette variants or double-gap geometries, which are designed specifically to measure low-viscosity liquids at high shear, can be useful alternatives. Cone and plate as well as parallel plate oscillatory tests using thin film techniques may also provide useful data, again, depending on the ink constituents, as secondary flow effects can result in the material flowing out of the gap at high shear (Davies and Stokes, 2008; Mezger, 2014; Zotek-Tryznowska, 2015).

9.5.3 The Effects of Additives to Enhance Viscosity Soluble sugars, starches, proteins and biopolymers may be used to achieve sufficient ink viscosity and can be selected based on their intended interaction with the powder component based on the binding mechanism. These types of additives affect the viscoelasticity and viscosity of the base solvent (Hoath et al., 2009); therefore, concentrations of these should be selected within a sensible range to confer the required viscosity for printing. Issues mainly arise when ink components are particulate or have a high molecular weight; many food colloids fit into one or other of these categories. Particles in a solution will increase the bulk viscosity by occupying space. In the context of food, this may include suspended granules, milled powders or flavoured flakes which can, in theory, range in size from the nanoscale up through to visible length scales (Dickinson, 2016; McIlroy and Harlen, 2014). It is recommended that the particle’s largest characteristic length is at least 5, if not 10, times lower than the selected test gap in a rheometer (Mezger, 2014) and, of course, should be lower than the intended nozzle diameter of the printhead. In conventional inkjet printing, particulates are often pigments and should not be larger than a few micrometres to avoid particle aggregation and nozzle blocking (Zotek-Tryznowska, 2015); any trapped particle around 15e20 mm can completely block nozzles, contribute to the formation of air bubbles and disrupt proper ink droplet formation (Wijshoff, 2010). Related to this, the challenge of maintaining a stable dispersion through viscosity modulation of the continuous phase could also result in unfavourable printing characteristics as a trade-off when trying to prevent particle aggregation. Droplet size is usually related to the nozzle diameter (Le, 1998; McIlroy et al., 2013). However, Hoath et al. (2009) found that as the concentration of a high-molecular-weight polymer increased, the total droplet volume ejected increased, as well as the proportion of this volume contributing to the trailing ligament rather than the main droplet. The modelled polymer in this work was monodisperse, linear polystyrene, conditions rarely found in the context of

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food materials. Xu et al. (2007) studied the effect of concentration (0.3%e 3.8%) and molecular weight (10.5e46.5 kDa) of cellulose esters in ink formulations. Cellulose esters exhibit weak rod properties, and chains have a random coil conformation in solution, a common characteristic amongst highmolecular-weight food-grade polymers. They show that as concentration remains at or below the coil overlap concentration, the polymer behaves as expected with respect to increasing viscoelasticity and length of the trailing ligament through polymer chain extension. Above this overlap, concentration extended polymers may entangle, with intramolecular H-bonds breaking and reforming as intermolecular H-bonds, greatly increasing the material relaxation time and its elasticity under shear and thus resisting the flow required to print. This was true across the molecular weight range tested. McIlroy et al. (2013) further explored jetting regimes corresponding to molecular weightdependent transitions in DoD printing using polystyrene as a model. It was identified that polymer coils stretch to extended chains as a result of high strain rates in the nozzle during printing as opposed to extensional flow within the extending ligament before break-off. At a critical strain rate, greater than the fracture strain rate (at which carbon-carbon bonds will break), central scission of the molecule may occur. In practical terms, the result of this flow-induced degradation is a reduction in the molecular weight of the polymer ink which could correlate to a loss of functionality. Wheeler et al. (2016) highlighted that polymer conformation also plays a vital role in the success or failure of ink jetting. For polymers of comparable molecular weight, those which were hyperbranched showed a much higher maximum printing concentration than their linear counterparts. This was related to the retention of a stable coil conformation and the longest chain length being smaller, thus resisting degradation during flow through the printhead when using these hyperbranched molecules. Therefore, if high-molecular-weight polymers are used in inks for a food binder jetting process, careful consideration of the balance between molecular weight and their concentration must be considered during the formulation stages; Holland et al. (2017) showed this through the inclusion of xanthan gum in a food-grade ink. Printability was shown to improve as xanthan gum molecular weight was reduced, and a higher effective concentration of xanthan gum was able to be included in the ink whilst maintaining other printable ink properties, which was advantageous for the proposed powder binding mechanism. Yoo and Kim (2013) also investigated the use of xanthan gum in an ink jetting scenario to monitor the impact of extensional properties on capillary breakup. Increases in the extensional viscosity due to the strain hardening of polymers affected ligament detachment from the nozzle; relaxation time of these types of polymers after extension during flow through the nozzle was also found to be an important factor. As a result, concentrations of xanthan gum used in their work were lower than those achieved by Holland et al. (2017) through molecular weight reduction.

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9.5.4 Surface Tension and Density Surface tension drives towards capillary thinning and breakup, whereas other forces act to resist this phenomenon (McKinley, 2005). In the case of water as a good solvent for food-grade materials, high surface tension is a key factor in inhibiting repeatable printing of water droplets, as described above. Some solvents possess lower surface tension than water so can be used as cosolvents to achieve more favourable printing characteristics without surfactants (Soleimani-Gorgani, 2016). Mallinson et al. (2016) describe viscosity and surface tension of aqueous mixtures of glycerol, ethyleneeglycol and 1-propanol at varying mole fractions for the context of inkjet printing. They show how even small additions of glycerol can reduce the surface tension of water, making it a favourable cosolvent for food inkjet printing. Glycerol also has a density greater than 1 (Segur, 1953), which is yet another desired characteristic for production of a repeatable printing ink. Ethanol is another popular cosolvent in edible aqueous ink formulations (Pallottino et al., 2016) and has the advantage of lowering surface tension. Selecting the correct volume fraction of ethanol is important in a formulation, as it has the potential to introduce a number of detrimental effects: its low boiling point can cause solvent evaporation and drying of soluble components at the nozzle, leading to blockages; it may be a less effective solvent for some ink components and cause precipitation of these out of solution. Ethanol and other low-molecular-weight alcohols are lower density than water which could also be detrimental to printing. Another way to control ink surface tension is through the addition of a surfactant. Many surface-active molecules are naturally present in or added to food products; low-molecular-weight molecules such as naturally occurring lecithin or synthesized sorbitan esters to high-molecular-weight components exhibiting surface activity such as proteins and polysaccharides (Kralova and Sjo¨blom, 2009). It has been discussed previously that there are many aspects to consider in terms of ink functionality when adding high-molecular-weight components to a formulation. The low-molecular-weight alternatives also have the advantage of being more mobile towards the interface which could be an important factor when considering timescales within printing processes. It is well documented in literature that temperature can affect the adsorption of surfactants at the interface, as well as their critical micelle concentration and thus the measured interfacial or surface tension (Kralova and Sjo¨blom, 2009; Mohajeri and Noudeh, 2012; Nin˜o and Patino, 1998); therefore, it is again important that surface tension values are measured close to the intended printing temperature. A number of simple surface tension measurement devices are available; the most commonly used techniques are the Du Nou¨y ring method, Wilhelmy plate method or drop shape analysis using a pendant drop approach (Berry et al., 2015). The addition of a surfactant may also affect the contact angle of ink droplets on the powder substrate with the ability to enhance wetting characteristics. A succinct description of contact angle, its

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measurement and relation to food powder wetting can be found in Section 14.4.3 of Gaiani et al. (2013). Ink density, recommended to be above 1, should be taken into consideration, particularly when formulating printing waveforms (discussed in the next section). The density will be affected by the solvent as well as dissolved or suspended constituents. It is likely that inks with suitable rheological and surface tension properties will not be too far off a printable density either; therefore, the two former properties should be fine-tuned preferentially. A final consideration with regard to ink formulation is that trapped air will disrupt droplet formation and ejection mechanisms (FujiFilm, 2008; Hoath et al., 2009).

9.6 CONTROLS AND CONSIDERATIONS DURING AND POSTPRINTING Measurable properties to aim for during powder and ink formulation are useful; however, a number of settings may be altered within a binder jetting machine and can allow leeway for the use of theoretically ‘nonideal’ materials.

9.6.1 Printer Settings 9.6.1.1 Powder Deposition Resolution achieved is, of course, directly related to the layer thickness, independent of the AM process being used (Chen and Zhao, 2016). If able to be varied in a given machine, changing the layer thickness is a process parameter which may be optimised to give a good surface finish and dimensional accuracy. Often, AM is limited in producing truly representative 3D objects based on computer-aided design (CAD) models due to the ‘stair-stepping’ effect; this would occur when 2D slices of the CAD image appear as stacked circles, for example, when considering a sphere. Though the nature of loose powder in binder jetting being able to support an object through printing is an advantage to achieve more complex geometries, the limitations of layer thickness and number of printed layers can oppose this. The smooth, curved edge may not be accurately represented when printing, rendering a printed object whose individual layers are visibly likened to a set of stairs. This is also apparent in other AM processes, particularly extrusion-based techniques (Sun et al., 2017). The powder feed rate, spreading and resulting layer density will largely be affected by the powder physical properties described earlier; the method of deposition will vary the exact parameters that can be changed within the printer. Optimisation of a given machine’s powder delivery should be undertaken to ensure the powder is deposited reliably in a smooth, even layer, and new layers do not drag or distort those underneath them. This will largely affect powder packing and print bed density, contributing to the necessary level of saturation to be set and, ultimately, the density and structural integrity of the printed object.

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9.6.1.2 Material Jetting Printed drops should be a uniform size and shape, thus maintaining a consistent drop volume. Ideally, each nozzle will eject this volume of ink when actuated, which necks and pinches off to allow a single, spherical droplet to fall in a straight line onto the substrate. The presence of longer ligaments is acceptable as long as they thin, pinch off and reform with the main droplet before hitting the substrate. The same is true for any satellite droplets which could be produced by capillary thinning action; satellites and ligaments only pose a problem if they cause the drop to deviate from flight or do not join the main droplet, potentially causing splashing. Sufficient time should be allowed for this merging to occur; thus the printhead is usually situated between 1 and 3 mm above the substrate at all times (Derby, 2015). Different actuation waveforms can be used to control the pulse delivered to each nozzle on the printhead in order to achieve optimal printing characteristics of drop volume, speed and jetting direction from each (Khalate et al., 2012). A waveform is composed of four segments, controlling the chamber filling, droplet ejection, break-off, then recovery and refilling of the chamber. The speed (slew rate), amplitude (voltage) and duration of bending a piezoceramic throughout one printing cycle are all changeable parameters (FujiFilm, 2008). Simple waveforms, such as trapezoidal, are often used successfully, with only small adjustments. Though a number of studies exist describing methods for designing waveforms from scratch based on material behaviour during jetting, manufacturers often include preset waveforms based on common solvents or known material properties for use in specific machines (FujiFilm, 2008; Hoath et al. 2011; Khalate et al., 2012; Kwon, 2009). As a general rule, the more viscous a material under printing conditions, the higher the voltage and steeper the slew rate required, whereas the opposite is true for low-viscosity inks. Hoath et al. (2009) attribute this to the nearlinear extension of a low-viscosity ink ligament until detachment compared with a more rapid deceleration and later detachment of a jet comprised of a higher-viscosity ink. The voltage pulse produces the necessary oscillations to eject ink from a given nozzle; if residual oscillations have not settled before the next pulse, intradrop variation will result (Khalate et al., 2012). Thus, the frequency will be affected if residual oscillations do not dampen within a reasonable time. Ideally, the frequency will be set as fast as possible for economic reasons and to maintain a reasonable print speed, but printing too quickly can be detrimental to the consistency of the print (Cie, 2015). Finally, cartridge ‘purges’ to clean nozzles should be incorporated into printing runs and can usually be set to occur between a given number of print passes. It is very important to include cleaning cycles midprint to clear any temporary blockages caused by dirt, particulates or solvent drying at the nozzle (Cie, 2015; FujiFilm, 2008; Wijshoff, 2010). As mentioned previously, the inclusion of high-molecular-weight polymers or particulates in food inks could be the cause of this issue, so observation during print tests should be undertaken to determine appropriate cleaning cycle intervals.

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9.6.2 Combining Powder and Ink During Print Commonly in inkjet printing, droplet arrays of a test ink are printed on a substrate at a large droplet spacing; assessments of droplet size, drop-to-drop uniformity and spreading behaviour or affinity for that substrate are undertaken. The droplet spacing is then reduced so that individual drops overlap to produce cohesive arrays, and further modification of this will determine the resolution achieved in 2D as desired. As the nozzle diameter is usually on a micron scale, the drop diameter is also within this range; the space between drops should be below an individual droplet diameter to ensure overlap. However, convention is to express drop spacing in ‘drops per inch’ (DPI) rather than as a distance in micrometres. For example, if printing from a 21-mm nozzle with droplet diameter similar to the nozzle size, one may wish to print with a drop spacing of 10 mm to ensure sufficient overlap; this is equivalent to 2540 DPI (Cie, 2015; Creamer, 2012; Wijshoff, 2010). Utela et al. (2008) highlights the importance of testing powders and inks outside of a 3D printer. They suggest observing the interaction between a pile of powder with ink deposited from a syringe to test the absorptive ability of the powder and subsequent cohesion, as well as selectively combining ink and powder in varying ratios to indicate required saturation and potential green strength of parts. Holland et al. (2017) screened food powder and ink formulations in a bespoke system comprised of a recessed plate with powder-containing wells of 100e400 mm thickness which could be used as a substrate in conventional inkjet printing to observe experimental powder and binder interactions in 2D. This enabled quick screening and adaptation of both powder and ink formulations as well as sensible defined parameters for future 3D application. When considering drop spacing in 3D, we tend to refer to the saturation level, which is defined as the ratio of binder to the void space available, calculated by taking into consideration the total print bed volume versus that taken up by solid particles which, of course, is dependent on the packing density (Chen and Zhao, 2016; Goole and Amighi, 2016). Saturation should be at a sufficient level to achieve binder liquid interaction with powder to facilitate liquid bridging between particles. The addition of a binding agent will cause a difference in the rheological behaviour of the particle at the surface compared with its dry core or native state (Cuq et al., 2013). Through achieving wetting on the surface, without excess binder addition causing further migration into the particle and swelling as a result, adjacent wetted particles will be able to bind to one another. If excess solubilising binder is added, the wetted particle may begin to dissolve slowly into single molecules within the liquid phase rather than forming a sticky outer layer to enable binding. Full dissolution of smaller particles may be desirable to ensure filling and solidifying of unwanted porous spaces; however, if all sized particles exhibit this behaviour, the print quality and resolution could be negatively affected.

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Related to the saturation is the timescale on which printing occurs. As with other food powder agglomeration techniques, the time, temperature and physicochemical reactivity of powders and inks for binder jetting will determine the final structure. Particles coated with an aqueous layer on a short timescale will have high surface stickiness compared to the particle centre, as described above. As time progresses, mass transfer of water occurs from the wetted surface to the particle core (either through capillarity in already porous particles or diffusion at rates governed by the crystalline to amorphous ratio in denser particles), and more soluble components may dissolve into the ink. This phenomenon promotes local plasticization, maybe even conversion of the whole particle to the rubbery state, and adhesive contact between neighbouring particles where ink has been deposited (Bhandari et al., 2013). It is obvious that during any print, the top layers of powder ‘see’ the ink for a shorter amount of time compared to the bottom layers; thus, there is a timescale gradient for interaction through the printed object. This could be critical and something to consider, depending on the materials used and any specific physicochemical interactions necessary to have the desired binding effect prior to postprinting treatments. In addition, some binder jetting setups will have options to retain a heated powder bed or to provide overhead heat for a given time to ensure sufficient binder evaporation or drying. With all of these heating steps, exact parameters will depend on what is required by the powder and binder materials to induce the desired crystallization, adhesion or evaporation. Again, the timescale and potential detrimental effects of heating on the native powder or object throughout printing should be considered. Generally, the addition of sufficient thermal energy increases strength; however, it has been shown that insufficient heating will cause brittleness and potentially failure to adhere properly, and excessive heat will contribute to shrinkage and warping phenomena due to thermal expansion and contraction (Chen and Zhao, 2016; Stansbury and Idacavage, 2016). From design to print, there are two major considerations which should also be measured here, accounting for known shrinkage effects and anisotropic effects resulting from print direction. Shrinkage may be due to thermal effects, as mentioned above, as a consequence of polymerization or due to the uneven packing of a powder bed. It is possible to model and account for shrinkage in design if the printing process itself is consistent and the material properties well known and defined (Chen and Zhao, 2016; Stansbury and Idacavage, 2016; Yoo et al., 1993). Shrinkage may occur to different degrees in the x, y and z directions, and reducing shrinkage in one direction may exacerbate the effects in another. This idea is linked to anisotropy in microstructure and structural strength that can occur based on the orientation of a build in the printer. Farzadi et al. (2014) demonstrate this by orienting the same porous scaffold design to print in the x, y and z directions and performing analysis on the resulting structures. They found printing orientation and layer thickness greatly affected the structural integrity and dimensional accuracy of printed

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designs, recommending that the most important dimension of the printed model should be oriented in the x direction, due to coinciding with the movement of the printhead.

9.7 POSTPROCESSING Inducing particle stickiness and adhesion forces through adequate saturation with an ink binding material is ideal so that each particle will be in contact with neighbours potentially on all sides, increasing strength. However, it does mean that particles that have not specifically had binder printed on them may stick to those at the end of a design, resulting in surface roughness and irregularity. Though depowdering via air blowing or vibration mechanisms can dislodge this weakly bound powder at the surface as a postprocessing step, surface roughness is a common phenomenon in powder-based AM processes in all industries and is difficult to avoid. Depending on the desired finish and product volume, a simple soft brush may be used to dust off excess without placing too much stress on the ‘green part’ (printed piece prior to postprocess sintering or firing) if fragility is an issue. In some instances, a wet depowdering mechanism can be employed with sonication or microwaving; however, the fluid used to complete this must not be a good solvent for the printed materials (Farzadi et al., 2014; Gibson et al., 2009; Utela et al., 2008; Wang and Zhao, 2017). For binder jetting of ceramics, the green part density and strength are significantly enhanced after a temperature-induced sintering process, much like in conventional ceramic casting (Derby, 2015; Yoo et al., 1993). In food materials, this could involve conversion of a predominantly amorphous or semicrystalline printed structure to a more thermodynamically and structurally stable crystalline form, demonstrated by Holland et al. (manuscript in preparation) for cellulosic powders. In nonfood applications, acrylate resins, waxes or varnishes are sometimes used to further boost printed part density. The material used to infiltrate remaining void space must have a melting point below that of the printed material, unless a coating step is also employed (Bai et al., 2015; Chen and Zhao, 2016; Utela et al., 2008). Von Hasseln et al. (2014) describe an example of a binder jet-printed structure with a composite powder (comprised of carbohydrate, milk protein, cocoa butter and flavouring) bound by application of water as an edible binder and infiltrated with melted cocoa butter after printing; this is the only example of an infiltration step in food binder jetting, to the authors’ knowledge.

9.8 APPLICATION AND OUTLOOK FOR FOOD MATERIALS Currently, the most widely demonstrated edible feedstock for binder jetting is sugar. 3D Systems have prepared a wide variety of full colour 3D printed sugar structures using the ChefJet printer with collaborators from the culinary world. Geometric complexity ranges from relatively simple cubes to lattice-type

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FIGURE 9.6 A printed sugar creation designed for serving with absinthe in place of the traditional sugar cube (3D Systems).

structures to organic, free-flowing shapes, including Gaudi-inspired chimney toppers for mixologists to serve with absinthe (seen below in Fig. 9.6). Originally based in the Netherlands but recently moved to Sydney, Australia, Julian Sing also uses binder jetting technology to create designs from sugar with the company 3dChef along with offering products created by other 3D methods. Designs range from cake toppers to customised corporate confections, again utilising colours added to the ink formulation to achieve more interesting designs, an example of which is shown below in Fig. 9.7. An interesting food material application has been showcased by Jason Mosbrucker (3Dible.co), printing structures from a number of food powders including cocoa and coffee, as seen below in Fig. 9.8. The materials are all food grade and enjoyable to eat.

FIGURE 9.7 An example of a printed piece by Julian Sing (3dChef) distributed at the 3D Food Printing Conference 2016 in Venlo, the Netherlands, alongside microcomputed tomography scans of the same piece to observe the internal structure (conducted by the authors at The Hounsfield Facility, School of Biosciences, University of Nottingham which received funding from the European Research Council (Futureroots Project), Biotechnology and Biosciences Research Council, Engineering and Science Research Council and the Wolfson Foundation).

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FIGURE 9.8 Left: Coffee cups printed out of ground coffee. Right: Cocoa and coffee printed structures. Kindly provided by Jason Mosbrucker, 3Dible.co.

As with all 3DP technology, many hobbyist printers trial different ink or powder formulations in their homes that often aren’t documented through press releases or on a scientific forum. Many open-source forums exist online where hobbyists share their creations. The RepRap project wiki page is one such forum (http://reprap.org/wiki/Main_Page). Though RepRap is an extrusion-based printer system, there are tried-and-tested powder and ink ‘recipes’ shared for binder jetting. Example inks include sake rice wine and other alcohol-containing formulations with or without colouring and other additives such as glycerol. Powder formulations are relatively limited, with mixtures of sugars to achieve certain particle size distributions, sugars with added meringue powder or salt and maltodextrin mixtures being the only edible examples posted (http://reprap.org/wiki/Powder_Printer_Recipes). The University of Washington also hosts an open-source website, aptly named Open3DP, to encourage sharing of thoughts and expertise of likeminded people. There are a multitude of blog post updates on process or material optimisation with their various 3DP setups. Their recipes generally feature on the RepRap wiki page also, where binder fluids are usually water and alcohol with optional glycerine, colour, flavour and surfactant components. Edible powders tested include sugar mixtures and a rice flour, sugar and maltodextrin mixture. A myriad of nonfood powders have also been trialled; one powder-tobinder ratio shown to be successful when printing with these formulations is 40:1 (https://depts.washington.edu/open3dp/category/formulas/). Southerland et al. (2011) from the University of West England set out to trial three AM processes for food products, including binder jetting. They used a 50:50 blend of caster sugar and icing sugar to give a suitable particle size distribution based on analysis of the original Z Corp powder used in the machine for production of casting moulds e a range between 37 and 149 mm with a minimum of 55% between 37 and 53 mm. At 35% binder saturation, teeth made of sugar were produced successfully, though it was noted that these structures were noticeably more brittle and had more surface roughness compared with a conventional Z Corp powder and binder structure. Though results are not explicitly mentioned in the publication, the researchers also recommend using starch or cornflour as the powder constituents.

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A few researchers have looked into using alternative powder materials in binder jetting techniques. Holland et al. (2017) describe the design and characterisation of cellulose-based powders as a feedstock for binder jetting. The mechanism of adhesion relies on a recrystallization event of the cellulose (amorphous through mechanical attrition) triggered through application of the aqueous ink and necessary thermal energy, to render the printed piece in a semicrystalline form but the surrounding powder unbound and still amorphous. Other stereochemically similar polysaccharides added in the powder or ink component modify this recrystallization temperature, provide additional adhesion and thus vary the resulting mechanical properties. The paper describes observing interactions in 2D; a manuscript is being prepared to show results in 3D from a bespoke, small-scale layering setup used with an inkjet printer. Unlike sugar, cellulose (a plant cell wall structural polysaccharide) cannot be digested by humans nor fermented in the gut, thus is classed as a dietary fibre and does not contribute to calorific intake. Thus, 3DP structures from cellulosic material open up options for reduced calorie structures to be used by both the food manufacturing industry and consumers. There are two main cited patents relating specifically to binder jetting of food materials: Von Hasseln et al. (2014) and Diaz et al. (2015). The former is related to the 3D Systems ChefJet technology covering the production of coloured and flavoured food structures with 25e75%wt maltodextrin and 25e75%wt confectioner’s sugar (similar to those pictured above) as well as a scenario where the product contains 1e25%wt seed crystals, i.e., cocoa butter polymorph V to produce structures similar to Fig. 9.9. They note that combining such powders with a binder containing water, alcohol, glycerine

FIGURE 9.9 A complex binder jet printed design containing chocolate elements. Source: 3D Systems.

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FIGURE 9.10 Top: TNO Powder Binder Printing (PBP) set up (right) and test squares (left). Bottom: Cookie formulation with texture modulation between layers achieved by altering printer settings. Source: TNO, The Netherlands.

and salt will give a harder, ‘candy’-type texture, whereas a binder of milk, alcohol and water would provide a smoother texture, akin to frosting. The latter patent is more detailed in the description of potential feedstock materials (incorporating protein and plant polysaccharides not used by Von Hasseln et al.) and recipes to create products. These range from pasta to cake to cookies and even protein bars. Through varying material composition and relative ratios (particularly of protein and maltodextrin), textures created can range from dry and hard to soft and rubbery. An example of a multitextured cookie produced by this technique can be seen in Fig. 9.10. By varying the printer settings, the top and bottom sections were designed to be more porous, with a dense section between them. After baking in a conventional oven. the material colour changed from white to yellowebrown, and the resulting cookie was multitexture with a soft top and bottom and hard middle (TNO, The Netherlands). Printed products can either be consumed directly after printing, though textural changes may occur on storage, baked in a conventional oven (as for the cookie embodiment), boiled in water immediately or dried for later use (when using pasta materials). The future for binder jetting of food materials is exciting. Through the research which has already been done in the area, it is clear that a variety of materials may be utilised to create structures. With researchers at universities and within companies looking beyond sugar as a feedstock and at the creation of composite powders, a lot of scope exists for the use of this technology, both by consumers at home or companies within the food industry. The technology

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is already creating headlines in the pharmaceutical world with the recent US Food and Drug Administration approval of a binder jet-printed drug ‘Spritam’ manufactured by Aprecia used to prevent epileptic seizures (FDA, 2015; Royal Society of Chemistry, 2015), so it is possible that we could see a parallel breakthrough with food products. Because the unbound powder acts as a support material, binder jetting has an advantage over other 3DP techniques relevant to foods in that it is easier to create more complex geometries than, for example, when using extrusion. A variety of end textures have already been demonstrated. Unlike other 3DP technologies used for foods, the achieved minimum feature size depends on three key aspects: powder particle size, layer thickness and ink nozzle diameter. By optimising materials in these areas, there is great potential not only to develop food macrostructures by binder jetting, but also design microstructures as well.

REFERENCES 3D Systems, November 14, 2017. Private Communication Regarding Figures 6 and 8. Abbott, S., 2017. Private Communication Regarding: Ohnesorge for Inkjet [online]. Available at: http://www.stevenabbott.co.uk/practical-coatings/ohnesorge.php. ASTM International, 2013. F2792-12a - Standard Terminology for Additive Manufacturing Technologies. Rapid Manuf. Assoc., pp. 10e12. https://doi.org/10.1520/F2792-12A.2. Augenstein, D.A., Hogg, R., 1974. Friction factors for powder flow. Powder Technology 10, 43e49. Bai, Y., Wagner, G., Williams, C.B., 2015. Effect of Bimodal Powder Mixture on Powder Packing Density and Sintered Density in Binder Jetting of Metals. https://doi.org/10.1017/CBO9781 107415324.004. Berry, J.D., Neeson, M.J., Dagastine, R.R., Chan, D.Y.C., Tabor, R.F., 2015. Measurement of surface and interfacial tension using pendant drop tensiometry. Journal of Colloid and Interface Science 454, 226e237. https://doi.org/10.1016/j.jcis.2015.05.012. Bhandari, B.R., Howes, T., 1999. Implication of glass transition for the drying and stability of dried foods. Journal of Food Engineering 40, 71e79. https://doi.org/10.1016/S0260-8774(99) 00039-4. Bhandari, B., Bansal, N., Zhang, M., Schuck, P., 2013. Handbook of Food Powders. Processes and Properties. Woodhead Publishing Ltd., UK. Brunello, G., Sivolella, S., Meneghello, R., Ferroni, L., Gardin, C., Piattelli, A., Zavan, B., Bressan, E., 2016. Powder-based 3D printing for bone tissue engineering. Biotechnology Advances 34, 740e753. https://doi.org/10.1016/j.biotechadv.2016.03.009. Cagli, A.S., Deveci, B.N., Okutan, C.H., Sirkeci, D.A.A., Teoman, E.Y., 2007. Flow Property Measurement Using the Jenike Shear Cell for 7 Different Bulk Solids, Proceedings of: European Congress of Chemical Engineering (ECCE-6). Copenhagen, Denmark. Chen, H., Zhao, Y.F., 2016. Process parameters optimization for improving surface quality and manufacturing accuracy of binder jetting additive manufacturing process. Journal of Rapid Prototyping 22, 527e538. https://doi.org/10.1108/RPJ-11-2014-0149. Cie, C., 2015. Ink jet print heads. In: Ink Jet Textile Printing, pp. 73e84. https://doi.org/10.1016/ B978-0-85709-230-4.00006-6.

284 Fundamentals of 3D Food Printing and Applications Creamer, D., 2012. Understanding DPI, PPI, SPI and LPI. Available at: http://www.ideastraining. com/PDFs/UnderstandingResolution.pdf. Crittenden, J.C., Rhodes Trussell, R., Hand, D.W., Howe, K.J., Tchobanoglous, G., 2012. Appendix C: physical properties of water. In: MWH’s Water Treatment: Principles and Design. John Wiley and Sons, Ltd., pp. 1861e1862. https://doi.org/10.1002/9781118131473.app3. Cuq, B., Abecassis, J., Guilbert, S., 2003. State diagrams to help describe wheat bread processing. International Journal of Food Science and Technology 38, 759e766. https://doi.org/10.1046/ j.1365-2621.2003.00748.x. Cuq, B., Mandato, S., Supagro, M., Jeantet, R., Ouest, A., Saleh, K., De, U.T., Ruiz, T., Montpellier, U., 2013. Agglomeration/Granulation in Food Powder Production in Handbook of Food Powders: Processes and Properties. Woodhead Publishing Limited. https://doi.org/ 10.1533/9780857098672.1.150. Davies, G.A., Stokes, J.R., 2008. Thin film and high shear rheology of multiphase complex fluids. Journal of Non-Newtonian Fluid Mechanics 148, 73e87. https://doi.org/10.1016/j.jnnfm. 2007.04.013. Day, L., Golding, M., 2016. Food Structure, Rheology, and Texture, Reference Module in Food Science. Elsevier. https://doi.org/10.1016/B978-0-08-100596-5.03412-0. Derby, B., 2010. Inkjet printing of functional and structural materials: fluid property requirements, feature stability, and resolution. Annual Review of Materials Research 40, 395e414. https:// doi.org/10.1146/annurev-matsci-070909-104502. Derby, B., 2015. Additive manufacture of ceramics components by inkjet printing. Engineering 1, 113e123. https://doi.org/10.15302/J-ENG-2015014. Descamps, N., Palzer, S., Roos, Y.H., Fitzpatrick, J.J., 2013. Glass transition and flowability/caking behaviour of maltodextrin DE 21. Journal of Food Engineering 119, 809e813. https://doi.org/ 10.1016/j.jfoodeng.2013.06.045. Dhanalakshmi, K., Ghosal, S., Bhattacharya, S., 2011. Agglomeration of food powder and applications. Critical Reviews in Food Science and Nutrition 51, 432e441. https://doi.org/ 10.1080/10408391003646270. Diaz, J.V., Noort, M.W.J., van Bommel, K.J.C., 2015. Method for the Production of an Edible Object by Powder Bed (3d) Printing and Food Products Obtainable Therewith. Google Patents. WO2015/115897 A1. Dickinson, E., 2016. Exploring the frontiers of colloidal behaviour where polymers and particles meet. Food Hydrocolloids 52, 497e509. https://doi.org/10.1016/j.foodhyd.2015.07.029. Farzadi, A., Solati-Hashjin, M., Asadi-Eydivand, M., Osman, N.A.A., et al., 2014. Effect of layer thickness and printing orientation on mechanical properties and dimensional accuracy of 3D printed porous samples for bone tissue engineering. PLoS One 9 (9), 1e14. https://doi.org/ 10.1371/journal.pone.0108252. Fellows, P.J., 2016. Food Processing Technology: Principles and Practice. Elsevier Science, Cambridge. Available from: ProQuest Ebook Central. Forrest, M., 2009. Food Contact Materials - Rubbers, Silicones, Coatings and Inks. Smithers Rapra Technology. Online version available at: http://app.knovel.com/hotlink/toc/id:kpFCMRSCI1/ food-contact-materials/food-contact-materials. Fromm, J.E., 1984. Numerical-calculation of the fluid-dynamics of drop-on-demand jets. IBM Journal of Research and Development 28, 322e333. FujiFilm USA, 2008. Dimatix Ink Tutorial [pdf], FujiFilm USA. Available at: http://seeen. spidergraphics.com/cnf5/doc/Ink formulation tutorial.pdf.

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286 Fundamentals of 3D Food Printing and Applications McIlroy, C., Harlen, O.G., Morrison, N.F., 2013. Modelling the jetting of dilute polymer solutions in drop-on-demand inkjet printing. Journal of Non-Newtonian Fluid Mechanics 201, 17e28. https://doi.org/10.1016/j.jnnfm.2013.05.007. McKinley, G.H., 2005. Visco-elasto-capillary thinning and break-up of complex fluids. In: Rheol. Revs., pp. 1e48. Mezger, T.G., 2014. The Rheology Handbook, fourth ed. BWH GmbH, Hanover, Germany. Mohajeri, E., Noudeh, G.D., 2012. Effect of temperature on the critical micelle concentration and micellization thermodynamic of nonionic surfactants: polyoxyethylene sorbitan fatty acid esters. E-Journal of Chemistry 9, 2268e2274. https://doi.org/10.1155/2012/961739. Mosbrucker, J., November 14, 2017. Private Communication Regarding 3Dible.co Powder Binder Printing. Nin˜o, M.R.R., Patino, J.M.R., 1998. Surface tension of bovine serum albumin and tween 20 at the air-aqueous interface. Journal of the American Oil Chemists’ Society 75, 1241e1248. https:// doi.org/10.1007/s11746-998-0169-6. Olakanmi, E.O., Cochrane, R.F., Dalgarno, K.W., 2015. A review on selective laser sintering/ melting (SLS/SLM) of aluminium alloy powders: processing, microstructure, and properties. Progress in Materials Science 74, 401e477. https://doi.org/10.1016/j.pmatsci.2015.03.002. Opali
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Segur, J., 1953. Physical Properties of Glycerol and Its Solutions, pp. 1e27. https://doi.org/ 10.1007/s13398-014-0173-7.2. Aciscience.Org. Sing, J., November 19, 2017. Private Communication Regarding 3dChef Powder Binder Printing. Soleimani-Gorgani, A., 2016. Inkjet printing. In: Izdebska, J., Thomas, S. (Eds.), Printing on Polymers: Fundamentals and Applications. Elsevier Science & Technology Books, pp. 231e246. https://doi.org/10.1016/B978-0-323-37468-2.00014-2. Southerland, D., Walters, P., Huson, D., 2011. Edible 3D printing in technical program and proceedings. In: 27th NIP International Conference on Digital Printing. Society for Imaging Science and Technology. Stansbury, J.W., Idacavage, M.J., 2016. 3D printing with polymers: challenges among expanding options and opportunities. Dental Materials 32, 54e64. https://doi.org/10.1016/j.dental. 2015.09.018. Sun, J., Zhou, W., Yan, L., Huang, D., Lin, L., 2017. Extrusion-based food printing for digitalized food design and nutrition control. Journal of Food Engineering 1e11. https://doi.org/10.1016/ j.jfoodeng.2017.02.028. Thomson, W., 1870. Improvement in Recording Instruments for the Electric Telegraph. UK Patent 2147/1867. TNO, The Netherlands, November 10, 2017. Private Communication Regarding TNO Powder Binder Printing Setup. University of Washington. Open 3DP Recipes. [online] Available at: https://depts.washington.edu/ open3dp/category/formulas/. U.S. Food and Drug Administration (FDA), 2015. SPRITAM (levetiracetam) Tablets [online] Available at: https://www.accessdata.fda.gov/drugsatfda_docs/nda/2015/207958Orig1s000 TOC.cfm. Utela, B., Storti, D., Anderson, R., Ganter, M., 2008. A review of process development steps for new material systems in three dimensional printing (3DP). Journal of Manufacturing Processes 10, 96e104. https://doi.org/10.1016/j.jmapro.2009.03.002. Von Hasseln, K., Von Hasseln, E.M., Williams, D.X., 2014. Apparatus and Method for Producing a Three-dimensional Food Product. 3D Systems Inc. United States Patent US 2014/0154378 A1. Wang, Y., Truong, T., 2016. Glass Transition and Crystallization in Foods, Non-equilibrium States and Glass Transitions in Foods: Processing Effects and Product-specific Implications. Elsevier Ltd. https://doi.org/10.1016/B978-0-08-100309-1.00007-9 Wang, Y., Zhao, Y.F., 2017. Investigation of sintering shrinkage in binder jetting additive manufacturing process. Procedia Manufacturing 10, 779e790. https://doi.org/10.1016/ j.promfg.2017.07.077. Wheeler, J.S.R., Longpre´, A., Sells, D., McManus, D., Lancaster, S., Reynolds, S.W., Yeates, S.G., 2016. Effect of polymer branching on degradation during inkjet printing. Polymer Degradation and Stability 128, 1e7. https://doi.org/10.1016/j.polymdegradstab.2016.02.012. Wijshoff, H., 2010. The dynamics of the piezo inkjet printhead operation. Physics Reports 491, 77e177. https://doi.org/10.1016/j.physrep.2010.03.003. Wohlers, T., Gornet, T., 2014. History of additive manufacturing. Wohlers Rep. 2014-3D print. In: Addit. Manuf. State Ind., pp. 1e34. https://doi.org/10.1017/CBO9781107415324.004. Xia, M., Sanjayan, J., 2016. Method of formulating geopolymer for 3D printing for construction applications. JMADE 110, 382e390. https://doi.org/10.1016/j.matdes.2016.07.136. Xu, D., Sanchez-Romaguera, V., Barbosa, S., Travis, W., de Wit, J., Swan, P., Yeates, S.G., 2007. Inkjet printing of polymer solutions and the role of chain entanglement. Journal of Materials Chemistry 17, 4902e4907. https://doi.org/10.1039/b710879f.

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Chapter 10

3D Food Printing Technology at Home, Domestic Application Estefanı´a Rubio1, So`nia Hurtado2 1 Former Researcher in Food Science and Technology at Natural Machines SL; 2Former Lead Food Technologist at Natural Machines SL

Chapter Outline

10.1 Global Scope 10.2 3D Food Printing Technology 10.2.1 How Does 3D Food Printing Work? 10.2.2 3D Food Printers 10.2.2.1 Hobbyist 10.2.2.2 Industrial Purposes 10.2.2.3 Specialty Stores 10.2.2.4 Research and Education 10.2.2.5 Educational Use 10.2.2.6 Medical Care and Nursing 10.2.2.7 Domestic Purpose 10.2.2.8 Collectivities 10.2.2.9 Permanent and Pop-Up Restaurants 10.2.2.10 Space Missions 10.3 Food Preparations for ExtruderBased 3D Food Printing 10.3.1 Food Preparation Examples Related to Print Purpose

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10.3.2 Rheological Limitations and Technical Considerations 10.3.3 3D Printer DeviceRelated Technical Considerations 10.4 3D Food Printing at Home 10.4.1 A 3D Food Printer Conceived as a ‘Mini Food Factory’ 10.4.2 Versatility: Everyday Cooking and Fine Cuisine, at Home and Hospitality 10.4.3 Traditional Recipes and Adapted Formulations 10.4.4 Reduce, Reuse, Recycle. Environment Friendly and a Potential Contributor to Circular Economy 10.4.5 Domestic Applications with Dietetic Purposes 10.4.5.1 Personalised Nutrition 10.4.5.2 Nutritional Management through 3DFP

Fundamentals of 3D Food Printing and Applications. https://doi.org/10.1016/B978-0-12-814564-7.00010-9 Copyright © 2019 Elsevier Inc. All rights reserved.

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290 Fundamentals of 3D Food Printing and Applications 10.4.5.3 Vegetarian and Vegan 316 10.4.5.4 Allergies and Intolerances 318 10.4.5.5 Toddlers and Children 319

10.4.5.6 Elders and Clinical Nutrition 320 10.5 Limitations, General Considerations and Conclusions 322 References 324

10.1 GLOBAL SCOPE Technology, science, communications, goods production, energy obtention, economy and knowledge transfer: the world itself is continuously adapting toward constant changes from people and societies, all over the world. Household model conception has experienced notable changes nowadays in developed countries. Family models have evolved to many variants besides the married couple with several children. Traditional gender differences in labour and occupation are shortening distances, and single-parent family households have increased all over, making time a highly valuable good to make the most of. All in all, this has led to an increase of technology utilization as a tool to shorten humdrum chores, allowing prioritisation of personal and professional interests. To understand recent changes in lifestyle and human relationships, the internet plays a fundamental role. European data (EUROSTAT, 2016) shows a level of internet access; in households of 87%, in 2017, there was a growth of 58% since 2007. This revolution in information and communication technologies has led to a presence of digital hyperconnected devices at home in response to the consumer need to get everything on demand. According to CNBC (Olick, 2017), in 2016, 80 million smart home devices were delivered worldwide, meaning an increase of 64% from 2015. It seems obvious that a society spending less time at home, with a diversity of consumers’ profiles, most of them highly demanding, completely used to connect utilisation of tools, can altogether lead to a revolution in the kitchen and, probably, a disruption in food industry. In parallel, 21st century main health problems are characterised by an unhealthy lifestyle and wrong dietetic habits, leading to a worldwide obesity pandemic and an increasing prevalence of diabetes and cardiovascular disease (Misra and Khurana, 2008). The food industry has been offering every day more convenient, processed foods, in order to satisfy consumers’ demand (Moodie et al., 2013). However, there is an evident lack in health considerations that should urgently be covered by improving nutritional balance of food products’ formulations. Hopefully, consumers will start to be aware of the problem, and their demand for a healthier choice is becoming a trend (Augustin et al., 2016).

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In addition, passion for food has been transferred from the table to the social media, and sharing the dining experience has become a trend, too (Erlewine, n.d.). It is possible to find foodie contents on TV shows and specialized channels, YouTube, Facebook, Pinterest or Instagram, beneath other media and social platforms. Besides food being used for social self-positioning, keeping healthy through food is still strong enough to condition the way this trending happens. Aside from that, the growth of food allergies and intolerance occurrence (FSA, 2013; Scha¨fer et al., 2001; Wood, 2003), especially in the paediatric population, has made people want to take overall control about what they eat and what it is made from. In parallel, alternatives to the traditional omnivore diet, like vegan or vegetarian ones, are today a growing tendency and lifestyle, rooted in developed countries (Marsh, 2016). Elderly and childhood are also two life stages requiring special attention to new dietetic approaches, where new technologies can definitely make a difference. Considering the evidence, the current situation makes the appearance of a technological kitchen appliance connected to the world through the internet of things suitable, as it is being part of next smart cities generation, taking advantage of big data and allowing complete control and management by the user over self-diet and nutritional status, as well as ensuring food source quality and origin. Three-dimensional food printing (3DFP) technology at home meets all these requirements.

10.2 3D FOOD PRINTING TECHNOLOGY Three-dimensional printing technology has been coexisting aside us longer than it is thought; first development happened in the 1980s, handled by Charles Hull (3D Systems, n.d.-a), and since then, it has exponentially evolved both in technology and applications areas. Even when many large-scale food manufacture processes share basics with 3D technology, it wasn’t until 2010 when it became a reality itself. So far, it can be found around 50 (Venture Radar, n.d.) different companies, all over the world, working to place 3D food printers into the list of everyday used technological gadgets at home.

10.2.1 How Does 3D Food Printing Work? First of all, it requires: l l

A suitable food printing material; A 3DFP or a current 3D printer adapted for food-use purposes. The 3DP or 3DFP will have two basic parts: hardware (HW), that includes all mechanical parts, and firmware (FW), which will be the link between the HW and the software (SW).

292 Fundamentals of 3D Food Printing and Applications

FIGURE 10.1 3DFP process from digital idea to food print. Inspired from Choc Edge (n.d.). l

l

An appropriate SW: there are a lot of open-source good 3D printing SW in the net that can be successfully used for 3DFP; and A proper printing shape design in STL format, which can be easily obtained through many open-source applications from other file formats, such as .jpg, .cad, etc. STL will be translated into G-code through the used SW being ready for the device to start performing the print, as shown in the following illustration (Fig. 10.1).

10.2.2 3D Food Printers There is a wide range of 3D food printers conceived for domestic use (3DigitalCooks, n.d.). It is possible to choose between those ones designed for a very particular use, being able to print specifically powdered goods like sugar, salt or spray-dried foods, or, for example, 3D printers adapted for printing chocolate-based materials with a tempering system included in them or those which allow printing a wide range of ingredients with multiple textures and a variety of viscosities, from smooth sauces to hard doughs. The best option always depends on the needs and expectations of the user. Three-dimensional food printing can be based in different techniques attending to the nature of the food materials that are going to be printed, the same as any other ink or printable material for standard 3D printers. The main 3DFP technologies are described and represented in Tables 10.1 and 10.2. 1. Binder jetting 3D printing or inkjet deposition of binder solutions into powder bed. It is used to print out of powder materials like sugar or starch (Fig. 10.2). This technique belongs to the additive manufacturing category, where a liquid binder solution is injected into a fine powder bed of printed material, following a settle pattern design It is the pattern design chosen before the printing by the user. The rest of powder material that hasn’t been bond works as a supporting material for the 3D structure. Once the entire solid design has been completely made, bond structure is separated from the rest of powder material (Holland et al., 2018).

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TABLE 10.1 Main companies and devices working with binder jetting 3d food printing for domestic and professional kitchen purposes Company name

Device

What does it print?

3D Systems

ChefJet

Sugar-based sweets

What does it look like?

TABLE 10.2 Main companies and devices working with extrusion-based 3D food printing as a kitchen appliance Company name

Device

What does it print?

Natural Machines

Foodini

Wide range of food preparations, open capsules

byFlow

Focus

Wide range of food preparations, open capsules

Choc Edge

Choco Creator

Chocolate, open capsule

Dovetailed

N ufood

Juice liquid into spheres. Ready made flavour boxes.

Print2taste

Procusini

Marzipan and chocolate, branded capsules

How does it look like?

Continued

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TABLE 10.2 Main companies and devices working with extrusion-based 3D food printing as a kitchen appliancedcont’d Company name

Device

What does it print?

XYZprinting

XYZ 3D food printer

Wide range of food preparations. Open capsules

StoreBound

PancakeBot

Pancake dough, open capsule.

How does it look like?

FIGURE 10.2 Sugar-based 3D print by 3D Systems (n.d.). The image was reproduced from the data available at https://es.3dsystems.com/culinary/gallery.

2. Selective sintering 3D printing: There are many subcategories of laserbased 3D printing. However, it is not a commonly used technique for 3DFP at home, although some companies explore it. The principle of the technique is to harden selectively, layer after layer, a fresh powder material through a sintering source which can be laser or hot air following a settled design (Sun et al., 2015), as it is shown in Fig. 10.3. 3. Extrusion-based or fusion deposition modelling (FDM). This technique is the most used for 3DFP because it allows printing a wide range of food materials. It is, as well, an additive manufacturing technique where the printed material, or food, used to be contained in cartridges or capsules.

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FIGURE 10.3 (A) Selective hot air sintering, and (B) selective laser sintering. Inspired from Jie Sun et al. (2015).

There are other systems, such as the use of a peristaltic pump that flows material from an external deposit to the extruder through a pipe circuit, allowing a larger (and longer in time) print, without stopping requirements for cartridge exchanging. Of course, this system has itself a lot of limitations, such as the cleaning and safety assurance, and it might be used for professional purposes, but probably the most recommended option for a domestic intended use is the cartridge/capsule system. In that context, when the print takes place, the cartridge, containing food material, is held by the extruder. The extruder applies a measured pressure over a piston, covering the cartridge content, and it pushes food material to flow through the nozzle, while axes move following a settle pattern, and it keeps printing (extruding and moving) one layer upon the other, until the print is finished, from the bottom to the top. Depending on each device, the extruder can be able to move through the three axes, X, Y and Z, and print over a steady platform or, otherwise, the extruder can be static and print the material over a mobile platform; even both elements could be mobile. In order to print food material, it may be necessary to certainly increase temperature to soften, or melt, the food paste and make it flow through the nozzle; it will depend on the food material nature and its rheology. The majority of 3DFP devices are based in FDM technology: Nufood (n.d.) or Print2taste (n.d.) companies not only develop commercial FDM-based

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FIGURE 10.4 3DP capsules by byFlow (n.d.). The image was reproduced from the data available at https://www.3dbyflow.com/home-en.

devices, but offer their own, optimised cartridges, with food material ready to be printed (Fig. 10.4). It offers the chance to obtain good results without any deep knowledge of food materials; however, the range of food options is weak and limited. There are no possibilities to use your own food recipes, customized or adapted to self needs. Some other companies, like Natural Machines (n.d.), Choc Edge (n.d.), XYZprinting (Doris, 2016), byFlow (n.d.) or PancakeBot (Storebound, n.d.) offer an open-cartridge system, allowing the user to enclose his or her own food preparations. In the particular case of Natural Machines, some food preparation recipes from the company are available for the user, so less inconveniences may be faced during first interactions with the device, and this way, a successful first experience is ensured. Afterwards, when the user gets more familiar with the equipment and SW, possibilities become unlimited. Actually, very little modifications are required to print food out of a conventional 3D printer (RichRap, 2012). Nonetheless, food hygiene and safety are only ensured by those printed exclusively created for a food-intended use; thus, they must be considered closer to kitchen appliances or food processing equipment than to 3D printers. Specific purposes of 3DFP, represented in Fig. 10.5, will determine what requirements of device, environment and whole activity will be. Within 3DFP, it is possible to differentiate between its utilization through specific purposes: hobbyist, industrial, specialty stores, research and education, educational use,

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FIGURE 10.5 Classification of 3D food printing applications.

medical care and nursing, domestic purpose, collectivities, permanent and pop-up restaurants and space missions.

10.2.2.1 Hobbyist This is obviously the first purpose of 3DFP: playing without any other intention than having fun and experimenting. 10.2.2.2 Industrial Purposes Three-dimensional food printers are adapted to an industrial environment, i.e., sequencing a series of extruders performing the same print several times at the same time and thus efficiently producing a fine-tuned product or, for example, using a small 3D food printer as a prepilot test, close to the lab/kitchen scale, in order to test new shapes-deposit of new food product developments, before running them at a larger scale where bigger amounts of food and water will be required. In this last example, a reduction of food waste, energy consumption, washing products and water, as well as time and money saving is evident. There is also the particular case of restaurant chains with a ‘small manufacturing’ workspace behind them, smaller than an industrial production plant but bigger than a restaurant kitchen. They can take benefit of 3D food printers, too. For example, the company BeeHex from Ohio, United States, is particularly focusing in this 3DFP intended use. 10.2.2.3 Specialty Stores The possibility of creating a totally customized design and producing it at the moment brings to 3DFP a special interest from gourmet/cake/candy stores.

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Many companies are willing to include a 3D food printer in their stores for their customers to play, interact and design, themselves, their own productions, at the moment: designs on a cake, candies with a special shape or their selfie in chocolate, in ketchup, on the top of a burger or other possibilities.

10.2.2.4 Research and Education Daniel L. Cohen (Cohen et al., 2009) were the first authors publishing a scientific publication about 3DFP. Later, many food science and technology research groups, designers, architects and different kinds of engineering researchers from universities around the globe became interested in studying further about this new technology and started publishing relevant articles in scientific journals. Thanks to their efforts and work, the knowledge is exponentially growing, permitting a solid, serious treatment and the feasible application of 3DFP into an industrial and business scope. The kitchen intended use, which, at same time, can be used for several purposes: 10.2.2.5 Educational Use l

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Cooking and haute cuisine academies: Endless projects around 3DFP could be born from chef students at top cooking academies. There is still a lot to do, a lot to explore in terms of food textures; processing, cooling, and cooking combinations and 3D printing possibilities. A 3D food printer can be conceived as a tool for teaching about electronics at schools and high schools; it is a friendly smart device with a lot to learn from. There is an example of this purpose, a project that started in July 2017: Sue’s tech kitchen (Yurieff, 2017), from Randi Zuckerberg. Its approach consists of encouraging kids to experiment with new technologies, and 3DFP is one of the tools they are using in this purpose.

10.2.2.6 Medical Care and Nursing Three-dimensional food printing can help people with dysphagia, or diseases that don’t allow swallowing properly, improve their eating experience. Researchers from several fields are already working on it (CORDIS, 2015; NASA, 2013; Rushton, 2017). Nutritional information and overall intake could be monitored and directly reported to the medical team taking care of the user/ patient who could be at home. 10.2.2.7 Domestic Purpose After the hobbyist, this is surely the first and the last objective. Thinking of a 3D food printer as a kitchen appliance widened the scope of possibilities of many companies, research groups and technical centres, but, at the same time, they came across a raw reality: before settling down in a domestic kitchen, its

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capabilities and versatility have to be tested in a professional kitchen (lab, restaurant, school, hospital kitchen). Once this will happen with honours, everyone will have their personal 3D food printer at home. It is inevitable to happen in a second stage; thus, it will take its time to be tested and perfected for home usage. It is expected that the invention, in parallel, of other innovative technologies that could be combined with 3D printing in order to improve and perfect its capabilities as a kitchen appliance and, also, upcoming new food products will be a good match for these new devices, for example, lab-grown meat, fish and dairy or biomass goods.

10.2.2.8 Collectivities Three-dimensional food printers as vending machines at schools, colleges, libraries, nursing homes, hospitals, railway stations, shopping centres, etc., could mean the possibility of getting ready fresh-made foods completely personalized at the same moment of consumption. Customized according to personal needs and preferences and, being directly ordered from an internet user account, from any connected device. 10.2.2.9 Permanent and Pop-Up Restaurants Examples of this are food trucks and caterings for events: Naturally, there is a huge interest in this area. From one side, Michelin-starred restaurants are interested in using 3D food printers in an attempt to emphasise new designs and spectacular dishes, but also, there is an interest in using them in order to fasten some dish preparations, for example, repeating exactly the same dish decoration as many times as required in a short time. Catering companies are probably the most interested in it. 10.2.2.10 Space Missions Since 2003, NASA (National Aeronautics and Space Administration) (NASA, 2013) is investing in research around 3DP and, specifically, 3DFP. Apparently, it could be used in order to improve quality of life of astronauts participating in long space missions. 3DFP should be adapted to nongravity conditions and probably provided by an apparatus for powdered foods preparation while/before printing. This would help them keep nourished at the same time they enjoy their meals in a more interactive and varied way, also through gamification and thus strengthening their emotional and psychological state. The European Food Safety Authority (EFSA) is also foreseeing to take advantage of 3DP in general (for fixing broken devices with several materials, etc.) as an exploitation of this new technology in space stations. It is important to highlight that the same device can be used with several purposes. It is not always required to adapt it according to its destination.

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10.3 FOOD PREPARATIONS FOR EXTRUDER-BASED 3D FOOD PRINTING Most food industry professionals, chefs and researchers in food science and technology tend to think there might be strong limitations about using simple foods as a printing material, requiring the indispensable help of texturizers, gelling agents, emulsifiers or other additives. Quite the opposite, naturally, simple food preparations can be satisfactorily 3D printed. In general, raw food is a perfect symphony, created by nature, with complex molecular structures combined and linked forming a single and efficient matrix. All these compounds in the food net will be fundamental in food preparation that later will be 3D printed. Fibres and starch which are naturally found in vegetable-sourced foods can give the needed structure to stand up to a more-or-less homogeneous matrix in space; in muscle fibres from meat or fish, it is also observed a space configuration that brings a determined shape and texture, where proteins efficiently link all the compounds and retain the water in the net, keeping the food structure unified in a determined shape and volume. Even when food is physically changed due to processing, blending, heating up or freezing, bearing enzymatic and/or microbial activity, experimenting with pH changes for other chemical causes or whatever other circumstance, leading to a notorious physical change in the food structure in space, it will be transformed, but still, it will keep in some way unified, in most case scenarios. The extrusion process in 3D printing can change mechanical properties of food material, but it doesn’t usually produce space configuration transformation itself. It’s true that before 3D printing, most foods will require a previous treatment to homogenize and diminish the particles’ size in order to easily flow through the nozzle; yet the transformed food can naturally keep the ‘standing up in space’ required properties for 3DFP. Fats, in the food matrix, will also be key factors to smoothen and lubricate while extruding. Their nature and space configuration can be crucial, though temperature and room conditions will be determinant in most 3DFP cases. Some carbohydrates, such as hydrocolloids, contribute to the overall texture. There is a clear example in natural, simple, fruit jams and confitures. As seen in Fig. 10.6, it is possible to obtain a thick-enough cherry jam as a successful 3D printing material. No extra thickeners or gellifiers are required. Limitation occurs within print requirements. A wide variety of basic foods preparations with simple ingredients can be used, going from simple vegetable purees to traditional food recipes such as colcannon from Ireland, marzipan, meat or fish loaf, beans or other legume pastes, cereal flour-based doughs, eggbased cream, cheese, yoghurt, etc.; only a certain e soft but hard enough to stand e consistency, allowing a range of viscosities, going from a standard tomato sauce (w103e104 cP) to a ready-to-bake bread dough (>105 cP), of course, subjected to many other rheological parameters related to the food

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FIGURE 10.6 Fruit based 3D print.

material behaviour (i.e., plasticity, elasticity, stickiness) when it is being printed: extruded and deposited at a certain temperature in certain overall room and surface conditions. Requirements of the print, determined by the user, will delimit suitability of every food material. An intricate flat design could be made with caramel sauce, butter or chocolate sauce, but a high-height print should be made with mashed potatoes, hummus, chocolate or sugar fondant.

10.3.1 Food Preparation Examples Related to Print Purpose 3D Food printing offer multiple possibilities in terms of printing pattern designs and dimensions: 1. flat decorations on a plate, cake, slice, cookie, extended dough or liquid based dishes (i.e., soup) 2. thin, low-heighted objects conceived as a snack (Fig. 10.7) a. printed before baking/frying/steaming b. printed and ready to eat 3. tall, high-height objects a. solidification of deposited material will allow holding next layers b. printed at room temperature c. food material heat requirement d. food material cool down requirement e. special conditions (i.e., tempering chocolate) f. cooking while printing 4. preparations conceived as a filling (Fig. 10.8)

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FIGURE 10.7 3D printed thin cookies by byFlow (n.d.). The image was reproduced from the data available at https://www.3dbyflow.com/gallery.

FIGURE 10.8 3D printed filled appetizer.

10.3.2 Rheological Limitations and Technical Considerations Texture is one of the most valuable attributes in food acceptance. However, in 3DFP technology, it won’t only contribute to the sensorial profile; mechanical properties of the food material will also define most of the printing considerations, illustrated in Fig. 10.9. The most important element of texture to be

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FIGURE 10.9

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Key elements in fused deposition modelling (FDM) 3D food printing.

considered in this field is rheology, defined as ‘the study of the deformation of flow of matter’ (Bourne, 2002). Probably the biggest challenge in 3DFP is properly adjusting printing parameters according to mechanical behaviour variations in each food material at determined room conditions. Moreover, in the majority of food recipes and formulations, every single batch has its own differences related to external parameters and conditions, i.e., raw materials’ origin can determine significant proximate composition differences, and preparation methods are not always reproducible enough, especially when they’re carried out at a home kitchen by different users who don’t necessarily know each other or haven’t created the recipe themselves. Providing detailed information when creating recipes, and using proper tools, is some important general advice to be considered, i.e., using a good food processor with temperature, power and time monitoring. Some interesting research in food technology (Kim et al., 2017; Liu et al., 2017; Severini et al., 2016; Yang et al., 2018) has already been done in order to frame the scope of possibilities and look for ways of improvement in formulation, processes and treatments before, during and after the printing process. Furthermore, being aware that ‘changing rheology trick’ could be one of the most frustrating issues for the user, many companies are working to widen databases, using big data sources and creating SW tools in which printing parameters setting of most food materials have already been implemented. Other possible and more precise solutions to this ‘trick’ would be to incorporate a probe, or infrared, sensor that could determine mechanical properties of food material and, automatically, calibrate the device for a highprecision adjustment that would bring an excellent print result. A handicap to this solution is the substantial device cost increase that makes it suitable for a professional use but probably not for a domestic one. Main considerations according to food materials’ rheology in FDM 3DFP at home are: Viscosity, defined as fluid’s resistance to flow, is one of the main food features to watch out for in 3DFP. Fluids have classically been classified as Newtonian in which viscosity is independent to shearing forces at a steady

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temperature, and non-Newtonian, in which viscosity varies under shearing forces. Variation of viscosity in non-Newtonian fluids will be different depending on the composition of ingredients, shearing force, temperature and stress duration (Bourne, 2002). Three-dimensional printing optimal food material behaviour would probably be ‘pseudoplastic’ or ‘shear thinning’, in which viscosity decreases as the shearing forces are increased, and it would come back to its initial viscosity when the shearing force stops. Examples of shear-thinning food materials are mashed potato, guacamole or hummus. Those ingredients allow printing of several layers, overlapping one after the other and creating a tridimensional structure without any temperature modification required. By the other hand, ‘threshold effort fluids’ demand a certain shearing effort to flow, and after that, they behave as Newtonian fluids. Some examples are ketchup, French mustard or mayonnaise (Corte´s et al., 2016). These foods can be printed in 2D at home, but they require being mixed with other ingredients or additives to be printed in 3D, because by themselves, they don’t generally hold the shape. Hardness is defined as required strength amount to deform. It is possible to print certainly hard doughs, such as fresh Italian pasta. Obviously, a powerful extruder will be required if good results are expected. If a hard food material is able to be printed with a current 3D food printer extruder, it is possible to do it with a wide-nozzle diameter, being aware that a precise result can’t be expected. Barilla and TNO launched their first pasta 3D printer in 2016, conceived more for an industrial, rather than a domestic, purpose. Elasticity is a key feature in many food preparations. It is defined as the ability of mass to recover its shape after being stretched. Generally, it is not a desirable property in 3D printing, and it represents a challenge to the user. Most traditional doughs are based on water and wheat flour mix, which contain gluten, and more concretely, gliadin and glutenin, wheat proteins responsible for elasticity that characterise this product and that, after being baked, will bring its characteristic and desired texture (Fig. 10.10). A slower printing speed and a closer distance from nozzle to tray will improve print results of elastic food materials. Referring to the food formulation, the big challenge comes from printing something that afterward will have a nice texture and flavour at mouth; for example, adjusting water proportion in wheat-based doughs will reduce hardness and elasticity, allowing a nice print. However, disappointment will arrive at first bite. Gluten-free doughs are an alternative that generally improve printability, obtaining very interesting results in both 2D and 3D prints. Melting point is described as temperature for a solid to change its state to liquid at 1 atm. Several foods and ingredients can be found naturally solid at room temperature, but they melt when temperature is increased; i.e., butter and other fats from different sources, chocolate, some

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FIGURE 10.10 3D printed bread rolls.

hydrocolloids and gelatine. Heating an ingredient over the melting point will lead to a difficult-to-control flow, and, thus an imprecise result will happen. An accurate temperature management will ensure getting an optimum print. Glass transition temperature: Is the Phenomena observed when glass state is changed into a supercooled and melts during heating, or to reverse transformations, during cooling. Both states are noncrystalline states, but while glass is a rigid solid, supercooled melt, being observed between Tg (glass transition temperature) and Tm (melting point temperature) (Meste et al., 2002). At this stage, it is able to be successfully printed, being reversible, which is what makes these materials very interesting from the 3DFP point of view. Only glass-structure food matrices have this property. Among these materials, one of the most relevant in 3DFP is chocolate, followed by cocoa fat, compound chocolate, several sourced fats (animal and vegetal, hydrolysed oils) or some commonly used hydrocolloids. It is a very interesting food feature because once food material is extruded into a shape, at a certain room temperature, it rapidly cools down and recovers its solid glass state, allowing intricate printing. Stickiness: It is understood, from a substance as the capability to adhere on a surface. It is possible to find this property in a large amount of food ingredients present at every home, such as many kinds of rice or wheat-based doughs, candies, chewing gum, cheese, jellies, hydrogels, etc. It is generally a desirable feature in 3D printing because it is indispensable to have the ability to stick and keep on the tray from first layer and stick layer after layer until the last one. It requires a deep understanding of each food matrix to set up all the

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FIGURE 10.11 3D printed dextrose-based fondant cube.

parameters correlated with stickiness: temperature before, during and after printing, deposition and printing speed, distance to tray from nozzle, layer height and distance from layer to layer (Fig. 10.11). Homogeneity refers to the state of whole food printing material, along the capsule or cartridge, which needs to be homogeneous enough and behave as a constant fluid that will change uniformly when temperature or pressure are applied. Therefore, external factors, conditions and printing parameters should have the same effect in all food material areas, from top to centre of the cartridge, and exactly the same in the farthest extreme of the nozzle, leading to a progressive, stable flow without notorious differences, having, as a result, an even print. Air bubbles, or air spaces in a food material’s cartridge, are one of the most disturbing phenomena in 3DFP, and they are absolutely related to the homogeneity requirement. To ensure homogeneity of material, several treatments, before and during the printing process, may be considered: treatments carrying out food material vacuuming, agitation or stirring, or even vibration, which will be helpful and efficient for air bubble removal. Also blending, mashing and straining could be taken into consideration, also regarding the following issue. Particles’ diameter and nozzle size: Inner diameter of the nozzle should be, at least, equal to or bigger than the particle diameter of food material. Homogeneity should not be confused with small particle mix requirement; for instance, it is possible to successfully print with couscous (Fig. 10.12), whole grains or minced meat at home. It is a matter of using a proper nozzle diameter size, but it should not be a limitation.

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FIGURE 10.12 3D printed coarse couscous star by Natural Machines (Natural Machines, n.d.). Was reproduced from data available at https://www.naturalmachines.com/press-kit/#.

By the other hand, smaller-diameter nozzles allow printing more intricate designs with the suitable food material, being aware that the smaller diameter you use, the longer the printing process will take to be completed. Therefore, from a domestic point of view, it is advantageous to use different nozzle diameters. It widens food printing materials possibilities, allowing a variation of textures in 3D printed meals.

10.3.3 3D Printer Device-Related Technical Considerations Main considerations depend on every device (HW, FW and SW). However, there are some related general features: l l

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Deposit speed: Time to extrude a volume of food paste through the nozzle. Printing speed: Time to print from one point of the design to another in the same deposition layer. Material container heating system: This allows temperature management and heating of food paste contained in the cartridge. Distance between layers: This is closely related to nozzle diameter size. Usually, a lower distance between layers and nozzle diameter size leads to higher print accuracy. Precision of the print is directly determined by nozzle diameter. Material container volume capability: A smaller cartridge diameter requires lower power to extrude the food paste. A bigger container allows a larger print without capsule exchanging, but a smaller container seems to lead to more accurate results, avoiding any flow turbulence while extruding. Extrusion power: Power required to make food paste flow through the nozzle. Depending on the food paste rheological properties, a higher or

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lower extrusion power may be required. Printing wheat pasta, for instance, is one of the traditional food pastes that demands a powerful extruder. Scanning: Capability to analyse and collect data of a real object and digitise it to obtain a 3D digital model to be 3D printed afterwards. It allows replicating an existing object and, also, to have a reference of the object’s shape inside the device, allowing, for example, to scan the shape of a cake and decorate its top, printing over it. Sequencing: Capability to connect other devices such as smartphones, computers, other 3D printers or sequenced kitchen appliances, and using internet data to share and download contents. Internet of things. Tray heating/tray cooling: Capability to heat or cool down the printing surface in order to cook, reduce temperature or simply keep the print warm. It is especially relevant in those devices aimed to print ready-to-eat flat designs as pancakes or to print with ice cream, regarding tray cooling. Cooking: Capability to rise the inner temperature of food material high and long enough to cook it. Novel technologies and sous-vide are being considered by many companies. Cooling down: Capability to cool down the food paste during printing process. Particularly interesting are its applications in ice cream, butter, chocolate and high-melted sugar solutions, such as caramel. Preblending/tempering: Capability to blend and homogenise food paste in the cartridge or in an external deposit, immediately before printing. It is specially required for chocolate, tempering-required fats and food mixes that need fine homogenization before being printed. It is a very useful tool for ensuring a homogeneous temperature and air bubbles’ removal. Automatic setup of printing parameters: Capability of the device to automatically self-calibrate the printing parameters, attending to the mechanical properties of the food material. Filling system or apparatus: In order to improve homogeneity and avoid air bubbles’ presence, some companies have already developed tools or systems for a better, easier filling of food material container.

10.4 3D FOOD PRINTING AT HOME 10.4.1 A 3D Food Printer Conceived as a ‘Mini Food Factory’ Processed food, illustrated in Table 10.3, is defined by the Food and Agriculture Organization of the United Nations (FAO) (Fellows, 2004) as ‘any change that is made to a food to alter its eating quality or shelf-life’. Ultraprocessed food represents the main source of energy in diet of most people in developed countries (Monteiro et al., 2010, 2018; Moubarac et al., 2013). In general, a high-quality assurance and control level regarding hygiene and food safety has been reached by the food industry. However, nutritional value of the outcoming products has been generally left aside

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TABLE 10.3 Food processing level classification (Moubarac et al., 2013) Group 1: Unprocessed or minimally processed food

Group 2: Processed culinary ingredients

Group 3: Ultraprocessed food

(Martı´nez et al., 2017; Monteiro et al., 2010, 2018; Moubarac et al., 2013) in favour of offering cheaper and profitable options to consumers, leading, after decades, to an exponential rise of obesity prevalence (Monteiro et al., 2018), cardiovascular disease, (Moreira et al., 2018) and other-diet related illnesses and, as a consequence, the loss of trust from the consumers’ side, who realise the goodness of a homemade, traditional diet, returning to the self-made concept also seen in the agriculture field where self-harvesting is becoming a trend. But also, there is an emergence of new, healthier food concepts, with a more balanced nutritional profile, demanded by consumers. In parallel, but sometimes found all together, ‘clean label trends’ are kicking up high in food marketing, especially in demand for ‘natural’, ‘organic’ and/or ‘free from’ products (Asioli et al., 2017). There is also an increasing requirement for animal well-being warranty, as well as for locally grown, environmentally caring products. Still, consumers keep demand up for convenience: snacking trends and fast food consumption as a way of being quickly nourished while they follow through with their busy lives, almost without stopping and sitting down for a bite. Attending to all these considerations, the food industry should meet new consumer demands, at the same time ensuring general food safety and quality, and shelf-life and logistics are improved for these balanced and ‘free from’ new products. In some cases, this can appear to be a real big deal. Threedimensional printing at home could offer practical solutions to these challenges.

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Most foods from group 1 and 2, from Table 10.3 food processing level classification (Moubarac et al., 2013), can be 3D printed, with a major advantage of not needing any preservative, because they will immediately be consumed after printing. Users are able to use their own raw food to prepare and print any fresh, balanced, full-of-nutrients snack: crackers, veggie patties, biscuits, pastries, dairy, meat and fish dishes, etc., knowing exactly what the meal is made of. And, of course, 3DP adds value, customizing shape, portions and size according user preferences. In the future, the food industry could also satisfy the commodity advantages of on-site produced, ultraprocessed food. Consumers could take advantage of convenient, ready-to-print products without the current self-preparation requirements. In fact, some small companies are already offering some 3DP commercial food products. Sustainability and circular economy are also being planned through 3DFP. New packaging systems and food containers are able to be designed and developed; previous commercial product concepts, failures and successes should be considered, i.e., coffee aluminium capsules, edible packaging and wrapping or zero-waste, biodegradable ones. Packaging is a clear and determinant innovation challenge in terms of food safety, stability, compatibility with production and conservation processes, shelf-life and logistics, but also in terms of marketing, economy and sustainability. So far, some food global companies are already investing in research in 3DFP field: Nestle´, Hellmann’s, PepsiCo, Hershey’s in collaboration with 3D systems, Barilla in collaboration with TNO, or Barry Callebaut, in collaboration with byFlow, among many others.

10.4.2 Versatility: Everyday Cooking and Fine Cuisine, at Home and Hospitality The eating experience can be considered as a lens of multiple colours, turning to a determined tone, depending on each person’s priorities. Main colours in this lens are social interaction, nourishment, health, pleasure, tradition, ethics and emotion. Three-dimensional food printers can be adapted to each user’s lens, satisfying his or her expected eating experience. They can be used to reproduce traditional, everyday meals: self-made bread, cereal bars, pizza, burgers, fresh pasta, dairy desserts or mashed vegetables. However, it is necessary to highlight the potential 3DFP has in fine cuisine due to its ability to perform in shape what would be impossible, or extremely difficult, to do by hand and, what is still more difficult, exactly repeat the same dish, as many times as required, in any place of the world, at the same time, if desired. These abilities and possibilities place 3D printers in the spotlight among new food trends that satisfy consumer eager for innovative experiences in the gastronomic area.

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FIGURE 10.13 Mei Lin’s passionfruit flower by 3D Systems (n.d.-a,b). The image was reproduced from the data available at https://www.3dsystems.com/culinary/collaborations.

This innovative path in food performance has been taken by many well-known chefs, and 3D printing dishes are astonishing customers in fine restaurants all over the world. For instance, Paco Pe´rez, the Spanish Michelinstar chef, has incorporated 3DFP technology to some of his creations (Koenig, 2016) using the Foodini 3D food printer by Natural Machines. Another example of 3DFP technology, through fine cuisine, are the collaborations between the companies Modernist Cuisine and 3D systems’ sugar lab using ChefJet Pro (Caren, 2015) (Fig. 10.13). 3D food printer N ufood, by Dovetailed, drops liquid content into a waterbased solution, obtaining a similar product to Ferran Adria`’s ‘spherification’. ByFlow, the developers of Focus 3D printer, have also mixed the concept of molecular cuisine with 3D printing (Cuthbertson, 2015); at the same time, they collaborated with Food Ink project (Food Ink, n.d.), bringing their 3D-printed creation to costumers’ tables at restaurants in 2016. Main advantages for chefs using 3DFP are (Koenig, 2016): l l l l l

customization use of mathematical patterns accuracy automatization reproducibility

A limitation in this field is technical knowledge required by the chef’s side to create their own designs, although it could be resolved by developing specific chef-use SW.

10.4.3 Traditional Recipes and Adapted Formulations Three-dimensional food printing for domestic purposes has a huge potential in the way people will interact with food in the future (Fig. 10.14), reinventing

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FIGURE 10.14 3D printing possibilities at home.

traditional recipes, using self-harvested foods for snacks’ preparation or, in the contrary, buying ready-to-print nutritionally enriched food products. Raw foods: Printable ingredients and raw foods are found within all food groups, and usually, they only require an easy preparation. Some examples are mashed potatoes (Fig. 10.15), mashed beans, fish and meat paste, sugar syrup (Vancauwenberghe et al., 2017), butter, fresh cheese or avocado.

FIGURE 10.15 Honeycomb design 3D printed with homemade mashed potatoes.

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Food products: Formulations specially tailored for 3DFP usually include gellyfiers or other texturizers such as LM and HM pectins, several-sourced starches, fibres and other hydrocolloids and gelatine, among many other additives. Some literature in food technology referred to 3DFP has been reported in the last years, with interesting results. In general, two major areas are being investigated: l

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Study of the relation between 3DFP and food materials’ mechanical properties and rheological behaviour. Results confirm some additives, ingredients and food products such as surimi gel (Wang et al., 2018), potato starch (Liu et al., 2018; Yang et al., 2018), mashed potatoes (Liu et al., 2018), LM pectin or collagen (Severini et al., 2018) as good contributors to a ‘printable’ texture. Formulation and development of 3DFP food products. Some healthy formulations are suggested, with good 3DFP results: snacks for children (Derossi et al., 2018), vegetable-based smoothies and other edible food materials (Severini et al., 2018). A study carried by VTT Technical Research Centre of Finland aimed to assess on the applicability of extrusion-based 3D printing technology for food materials as a starting point in the development of healthy, customized snack products, concluding the best printing results were achieved with pastes containing 10% cold swelling starch, 15% skimmed milk protein, 60% semiskimmed milk protein, 30% rye bran, 35% oat protein concentrate or 45% fava bean protein concentrate (Lille et al., 2018).

Novel ingredients: In order to ensure sustainable food resources, especially protein, that nowadays mainly come from livestock, many approaches are being studied (Forum for the Future, 2016), and one of the most relevant is the overall reduction of animal meat production. In this direction, researchers and institutions are studying alternative ingredients (Alexander et al., 2017) that could provide same or better nutritional profile to the consumer. In many cases, these new foods require an effort on ensuring a visual and overall sensorial positive perception from the consumer. It is required to be identified as edible, appealing and appetizing, because in some cases, it is something completely new that might be rejected. Three-dimensional food printing offers a solution approaching the consumer as an interactive, and attractive, way of acceptance of these novel foods and technologies (Schouteten et al., 2016). Some alternative ingredients being considered are flours based in insects (Schouteten et al., 2016), algal (Bleakley and Hayes, 2017) and microbial protein (Matassa et al., 2016) that could be easily introduced in the printable formulations, while cultured meat and meat analogues from beans (Alexander et al., 2017) could constitute the printable material for 3D printing themselves.

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10.4.4 Reduce, Reuse, Recycle. Environment Friendly and a Potential Contributor to Circular Economy As the FAO pointed out, population is growing, resources are decreasing and environmental impact is reaching historical levels; an urgent change in our productive system is needed (FAO, n.d.-a). Globally, it is estimated that every year, 1.3 billion tonnes of food are lost or wasted; that means a third of all food produced for human consumption (FAO, n.d.-a). It doesn’t only increase food insecurity, but it costs massive financial losses while squandering natural resources (FAO, n.d.-b). According to the Netherlands Environmental Assessment Agency, turning the current system into a more circular economy could be the right approach to answer the problem (Rood et al., 2017). The circular economy is based on optimising natural resources’ use, raw materials and products, reusing and giving them a second commercial life. The aim of a circular economy is to make the most of natural resources and, as far as possible, avoid waste and environmental pollution (Rood et al., 2017). It distinguishes three basic challenges: l l l

sustainably managing resources limiting food waste optimising residual streams

At this stage, 3D printing has a role to play as a sustainable new model of manufacturing: l

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Reducing food lost with domestic 3DFP: 3DFP offers food producers and directly, farmers, the chance to use fresh fruit or vegetables that don’t meet quality standard requirements to be displayed at the supermarket by producing a food paste suitable for 3DFP, minimising food lost. This could also be applied to other food fields like cereals, legumes, nuts or also to excess of, or not directly valuable, parts of fish, dairy and meat that are thrown away every day. Reducing food waste with domestic 3DFP. Major food waste in developed countries is coming from consumers (Bourguignon, 2015). Threedimensional food printing is proposed as a sustainable solution to reduce unconsumed food amounts (Thyberg and Tonjes, 2016). Dosage and portion sizes can be monitored and controlled through SW, and also, food overstock and leftovers (for example, banana and carrots) can be transformed at home into a food paste, bringing them a second chance to be eaten, resulting, at the end of the day, in a more efficient management of food resources (Lupton, 2017).

Most leftovers and fruits, going to waste, have lost their good colour and can have overmaturation flavours that some people can reject, but simple culinary tricks like adding lemon juice could be helpful.

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10.4.5 Domestic Applications with Dietetic Purposes 10.4.5.1 Personalised Nutrition First aim of eating food is being nourished, to stay healthy through nutrition, and thus, it should be placed in the centre of any other approach and further development of 3DFP technology in order to make it meaningful. Wrong dietetic habits and lifestyle are one of main problems in developed countries, and, at the same time, interindividual differences among people are gaining relevance against traditional standardisations of dietary recommendations in each country. Motivations to personalise diets are linked to interindividual needs’ differences, health conditions and preferences, and 3DFP could help provide the ability to give a personal use for each device, registering individual information details (anthropometry, general conditions, allergies, preferences, etc.) that could be updated anytime and followed by a nutritionist, if desired (Lipton, 2017). Each country designs and determines its dietetic guidelines according to its population characteristics. The classical populations’ groups attending to nutritional needs are based on gender, physical activity, age stage and physiological state. For every group, different nutritional recommendation intakes of total energy amount, protein, carbohydrates, fats, vitamins and minerals have been tailored. However, it becomes a challenge for the majority of the population to follow guidelines, and that doesn’t always suit the real needs of each person. Tailoring diets per person, instead of determining generic standards, would be a key factor in improving dietetic inhabits. In Fig. 10.16, 3DFP is placed as a helpful tool for users to meet their specific nutritional requirements.

FIGURE 10.16 3D food printing (3DFP) management in personalised nutrition.

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10.4.5.2 Nutritional Management through 3DFP X(g)/Y(g/mm2) ¼ Z(mm2) A 3D-printed meal in a nutritionist viewpoint would first require settling all nutrients’ amount requirements. X(nutrient requirement) ¼ nutrient grams In parallel, energy and nutrients’ amount in each material must be known. It can easily be calculated from nutritional databases and food composition tables, translated from grams to millimetres squared of food paste. Y(nutrient in food) ¼ nutrient grams/mm2 food Finally, food paste volume is determined to meet user nutrient intake requirements. Z(food material) ¼ mm2 Although this would be a professional intended use tool for medical doctors, nutritionists and nurses, this approach could be useful for anyone interested in keeping healthy, ensuring a proper nutritional intake or users with special diets, required to avoid, reduce or increase the dietary amount of some specific nutrients, for example, in people with chronic diseases, sports people, vegans and vegetarians or any other special condition that requires a nutritional control amongst the general users. Furthermore, 3DFP nutritional management SW tools could be a good complement to nutrigenomic sciences, because it would allow personalisation of food nutrients’ profile, as well as to control consumed amounts according to user characteristics. Allowance of nonprofessional users to use nutritional control tools should be ensured to avoid an incorrect, dangerous use of them.

10.4.5.3 Vegetarian and Vegan The veggie movement, involving veganism, vegetarianism and flexitarianism, based on the reduction or complete removal of animal products from the diet, principally emerged due to environmental, health and animal welfare concerns and has grown stronger than ever in the last decade, and it is expected to continue exponentially growing globally in the next years (Lantern, 2017). According to Mintel data, the launch of new food products with veggie claim labels increased 257% between 2013 and 2016 worldwide (Pe´rez, 2016). Another characteristic of the veggie lifestyle choice is the preference towards clean label products because many additives come from animal sources

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(Vegan easy, n.d.). It is also seen a preference for local, raw, fresh ingredients and products. Three-dimensional food printing can be useful in the monitoring and ensuring of the food source and its origin. Raw foods can be chosen for printing, and the user can strictly control every ingredient and every food in the final meal or product of the ‘minifactory’. A practical recipe example is shown in Fig. 10.17. Although expectations are seriously high, vegetal alternative to animal sourced foods offered is still limited. A 3DFP device, combined with a current blender and a cooking appliance, allows reproduction of many of the basic processes used in a regular factory, so most traditional dishes: burgers, sausages, cheese, pizza, tacos, waffles, cookies, etc., could be totally customized

FIGURE 10.17 Adapted meat pie to 3DFP Vegetarian version.

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with a 3D food printer in a conventional kitchen. A preconception of ‘unnatural’ towards 3DFP could be a handicap in this particular social sector (Lupton and Turner, 2016).

10.4.5.4 Allergies and Intolerances Food intolerances and allergies are in the focus, not only of health agencies, but also of the food industry (Hefle and Taylor, 2004). Although prevalence varies between countries, it is considered a global issue. Food allergy affects the 6% of population, children at the age of 2 and younger being the most sensitive (FSA, 2013; Scha¨fer et al., 2001). Food intolerances, by the other hand, affect, in a wider grade, adults, and they are assumed to represent the 20% of prevalence in the population (Wood, 2003). There are multiple large studies in several directions to find out why these disorders are exponentially increasing. Some results and relevant conclusions are often controversial and not always aligned, but there are some evidences pointing to an ‘hyperhygienic’ world that is nonselectively killing microbiota in soils, food, human body and everywhere, positively leading to lessening the occurrence of general infections but negatively affecting immunologic response (Lambrecht and Hammad, 2017). Also stress and anxiety, such extended disorders nowadays, seem to be tightly related to them (Patel et al., 2017). Besides research willing to prevention ¼ Besides private industry and institutions individual efforts to prevent food allergen cross contamination between food product and meals, current reality is driving public institutions’ efforts to ensure food industry’s adaptation to regularize and control food allergens’ presence in their manufacturing facilities and declare their potential presence in their commercial products. Food ingredients declared as potential allergens or able to cause adverse reactions to sensitive consumers are, according to the EFSA: cereals containing gluten, milk, eggs, nuts, peanuts, soybeans, fish, crustaceans, molluscs, celery, lupin, sesame, mustard and sulphites (EFSA NDA Panel, 2014). A 3D food printer can be conceived as a personal device, independently used by every person owning his capsules or food material containers (the only part in contact with food) and thus avoiding cross-contaminations. Threedimensional food printing appears on the stage as an innovative and creative tool in the field of food allergens management. Ensuring problematic allergens will not be in the meal seems an easy measure; however, it becomes a daily challenge for many people. Three-dimensional food printing in domestic, clinical and hospitality scenarios can help managing diet and controlling meal preparation. The application of 3DFP in celiac diet calls for special attention because gluten-free doughs are a printable material with great results. WASP Company (World’s Advanced Saving Project), in collaboration with Zeroinpiu`,

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developed ‘DeltaWASP 20 40 printer’ dedicated to the celiac food preparation for kitchen which works for collectivities (big group of people, as in schools or hospitals) (WASP, 2017).

10.4.5.5 Toddlers and Children Nutrition plays a fundamental role in every step of life. Especially at early stages, it has a strong influence over developing obesity and other diet-related illnesses. In the last two decades, an effort has been shown from public health institutions and governments to improve children and teenagers’ diets and lifestyle habits. However, a significant success hasn’t still been shown; on the contrary, obesity prevalence seems to keep growing. A new approach is required, perhaps in other directions, different influential vehicles or, directly, in the very first life stages (Anzman et al., 2010). Three-dimensional food printing can help to catch the interest of the youngest members of the family, creating natural, balanced and inviting snacks and main courses, adapted to their needs in size and texture, that can be shaped according to the kid’s preference: from dinosaurs or fairies to a pirate boat. Legumes, vegetables and fruits that some kids tend to struggle with will gain familiarity and attraction if the presentation is improved; in this purpose, 3DFP can be useful. When it comes to kids from the age of 4 and older, a tendency to selfdetermination appears. Suddenly, they want to do everything on their own and feel in control. This moment can be a great opportunity to involve children in meal preparation with 3DFP, allowing them to customise their creations and enhance the contact with fresh ingredients and their transformation into palatable dishes in a safe environment, free from the kitchen-associated risks like fire, blades and hot surfaces. Moreover, an adapted user interface can let kids autonomously draw and design their creations, combining technology, art, writing, creativity and autonomy, as well as cooking skills. A study driven by Nestle´ Research Centre compared the intake of vegetables, pasta and chicken between two groups of kids. It revealed how the group of kids involved in the preparation of food with their parents’ help had a higher intake of vegetables, as cauliflower and salad, as well as a higher intake of chicken and overall calories, compared to the group of kids in which only the parents cooked. Furthermore, they reported a significantly increased valiance and dominance after the cooking experience (Van der Horst et al., 2014). Three-dimensional food printing as an interactive kitchen appliance is, therefore, a useful tool for parents to spend time with their kids in a stimulating environment that enhances a positive attitude towards healthy food, and, at the end of the day, it contributes to healthier diet habits. At the same time, it gives a chance to learn while having a fun experience. A real example of a meal made for one of the authors’ daughters is shown in Fig. 10.18.

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FIGURE 10.18 3D printed spinach and cheese little house.

We foresee, as a first step, introducing 3DFP devices at schools and high schools, with adapted interfaces for later to spread them to domestic scenarios.

10.4.5.6 Elders and Clinical Nutrition Nowadays, developed countries’ citizens’ lives are longer than ever, and predictions follow that tendency, too. According to the World Health Organisation, 2 billion people will be aged 60 and older by 2050 (WHO, 2017). The facts are obvious; the average population is ageing. However, as life expectancy rises, health related with ageing must be strengthened. Dysphagia, or swallowing difficulties, as a consequence of diverse health conditions, is one of the most common disorders in elders. Reported prevalence of dysphagia in nursing home residents varies between 38% and 69.6% (Hollaar et al., 2017). Dysphagia is a physiological state that leads to many other clinical conditions as malnutrition and weight loss, malnutrition and weight loss, ought to a low caloric intake, notoriously lowering life expectancy (Norman and Pirlich, 2013), but also, it means a handicap in the social interactions, as well as a risk for self-confidence (Oeppen and Vaupel, 2002), quality of life and life desire. The current approach to this situation is offering a semisolid, puree-based diet, consisting of a pharmaceutical, clinical nutrition formula product and/or a traditional, nutritionally complete meal, blended as a plain puree that could also be fortified or supplemented with micronutrients. An exclusive semisolid diet can be maintained for months, years or for the rest of life, even when physiological disorders come. Lack of appetite and eating willingness can

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completely disable oral feeding, leading to probe feeding or, finally, parenteral nutrition. A recent review (Verdonschot et al., 2017) reported a relation between anxiety and depression with oropharyngeal dysphagia patients. Years ago, another interesting study reported that 45%, of patients with dysphagia affirmed not to enjoy mealtime, 41% reported to feel anxiety or panic at mealtime and 36% reported to avoid eating in public, due to their difficulty swallowing (Ekberg et al., 2002). Due to the problem’s severity, scientists from several disciplines, public organizations and private companies are working together to find new alternatives, and 3DFP stands as an interesting one. This option is currently being studied in detail by Australia’s Commonwealth Scientific and Industrial Research Organisation (Tyers, 2017). The objective of the team, led by Dr Amy Logan, is developing a mini food factory system that could create ‘tailored diets’ based on a person’s genetic information, physiological state and lifestyle (Archer et al., 2017). At the same time, the European commission, through the H2020 program, funded the PERFORMANCE project, conducted in Germany, from 2012 to 2015 (CORDIS, 2015), which aimed to develop and validate a holistic, personalized food supply chain for frail elderly in nursing homes, ambient assisted living facilities or at home (Norman and Pirlich, 2013). In parallel, some university hospitals are already driving pilot trials with 3D food printers in order to improve life quality of their patients. Some examples are University of Utah Hospital (Rushton, 2017) (United States), using Foodini from Natural Machines (Fig. 10.19), and the University of Copenhagen and Aalborg University Hospital in Denmark, using its own prototype.

FIGURE 10.19 3D food printed at University Hospital of Utah. The image was reproduced from the data available at https://it.utah.edu/node4/news/april_2017/food-printer.php.

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Another example is in Singapore, the Khoo Teck Puat Hospital, led by Ms. Gladys Wong, Chief Dietitian, using Foodini from Natural Machines (Cheong, 2017). Advantages of 3DFP in clinical nutrition include: l

l

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Offering a palatable and inviting meal. 3DFP keeps same flavour and taste of original food, only adapting its texture and shape. Increasing overall food intake. Improvement in visual meals’ presentation, variety, traditional meals’ resemblance (i.e., visual imitation of a steak with French fries and baby carrots) causes patients to increase overall food intake, promoting health maintenance. Avoiding accidents during mealtime. Transition from solid and liquid to soft, pureed meals, notoriously avoids accidents, like pneumonia or choking episodes (Ekberg et al., 2002). Personalising the food matrix to every patient, sizing their needs. Sticking a microchip, Radio Frequency Identification (RFID), QR code or similar, on the food container, including dietetic needs and preferences of the user. Multilocation. 3DFP technology is able to work in different environments as clinical, nursing homes, or in a domestic context. Printing on-site would be the best way to avoid logistics’ inconvenient. Improving social life of patients. The mealtime experience doesn’t become a risk for them, both physically and emotionally, empowering them to take part in the social life and bringing dignity back. Allowance of pharmacologic supplementation. Printed food can also be fortified or supplemented with any medical treatment required by the user, with a precise control over the quantity of the food matrix dropped amount control SW that some devices already offer, in order to exactly measure the nutrients amount in each print or the possible administration of a pharmacologic treatment mixed inside food. Medical and nutritional control follow-up. SW can be specially designed in order to report all the printed and eaten meals, their nutritional information and also, the satisfaction grade of the user towards every meal.

A limitation in this field is the difficulty to change traditional models of hospitals and nursing homes’ kitchens to embrace 3DFP. Next steps in research and pilot experiences should incorporate 3DFP devices in the kitchen, or even in a small, clean room in every floor, avoiding inconvenient logistics. On the other hand, keeping storage in cold or warm temperatures before serving must be ensured (Cheong, 2017).

10.5 LIMITATIONS, GENERAL CONSIDERATIONS AND CONCLUSIONS Considering all the possible applications of 3DFP as a domestic kitchen appliance, the main limitations are related to devices’ technical improvement

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and the still undefined legal regulations. Three-dimensional food printers are being designed following general standards of both kitchen appliances and industrial food machinery. Three-dimensional food printing companies should also consider food safety framework regulations. The US Food and Drug Administration published, in May 2016, a draft guidance named ‘Technical Considerations for Additive Manufactured Devices’ (FDA, 2017), even though a solid legal framework is not reached yet and further cooperation between regulatory agencies, public organisations, food manufacturers and 3DFP companies is needed in order to develop specific guidance and evaluation protocols for devices’ design, development and commercialization and also in reference to labelling of commercial food paste products (Gowling WLG, 2016). On the other hand, 3DFP technology is still a novel field for developers, with a long way ahead to become an everyday-use, handy device. Main challenges to overcome in order to size consumers’ needs are: l l

l l

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automatic printing parameters’ setup capability for each food material; printing path optimization in order to shorten the printing process time and improve accuracy; improvement of incorporated scanning technology; incorporation of other technologies, such as artificial intelligence and virtual reality, to widen the scope of possibilities and improve the overall experience; integration of powerful extruders or improvement of current extruding systems and apparatus for example using robotic arms; food materials’ heating system optimization; cooking capability, becoming oven-like or similar; creation of complementary, standalone tools, such as filling system, blending system, homogenising system (Hurtado et al., 2016), specialized SW, etc.; optimization of size, design and materials of the device, according to sustainability; and affordability.

Besides technical improvement considerations, consumer acceptance has to be addressed (Lupton and Turner, 2016) and considered a priority. In this chapter, different educative proposals have been discussed, and this approach is foreseen as a determinant tool to normalize and increase familiarity with the technology, discarding the unnatural preconception of 3D printed food. At a first stage, a proof of acceptance is required from professional chefs and food business people to later arrive at every home, like it happened with microwaves, computers or TV, long time ago. Three-dimensional food printing technology has become, in the last years, an exponentially trending topic, catching the attention of worldwide journalists and being massively spread in all media: TV, scientific, specialized and

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financial journals, technological and social websites and blogs, etc. Despite this undeniable media phenomenon, arising interest and curiosity in many areas, it will only be time that will determine whether it has been a trend that everybody speculated and talked about, or, otherwise, it will become an everyday-used device, present in every kitchen. As discussed, there are many interesting applications of 3DFP, not only in a food business purpose, but in a social, medical and educational motivation, that makes this technology something highly valuable for society. The same way it happens with every new tool, people will decide what they make of it and how they use it, and their practice will drive 3DFP in one or another direction. In our opinion, it probably will not have success itself, but, combined with other novel technologies, it will become one of the next basics in many areas, included domestic usage.

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326 Fundamentals of 3D Food Printing and Applications Food and Drug Administration, 2017. Technical Considerations for Additive Manufactured Devices, Draft Guidance for Industry and Food and Drug Administration Staff, p. 28. Retrieved from: https://www.fda.gov/downloads/MedicalDevices/DeviceRegulationand Guidance/GuidanceDocuments/UCM499809.pdf. Food Standards Agency, September 2013. An Overview of Our Research and Work the Agency’s Role in Food Allergy and Intolerance. Retrieved from: https://www.food.gov.uk/sites/default/ files/multimedia/pdfs/publication/allergy_fsa_overview.pdf. Forum for the Future, 2016. The Future of Protein - the Protein Challenge 2040: Shaping the Future of Food, p. 40. Gowling, W.L.G., September 12, 2016. 3D Printed Food, When Will the Laws Take Shape? Retrieved from: https://gowlingwlg.com/en/insights-resources/articles/2016/3d-printed-food%E2%80%94-when-will-the-laws-take-shape. Hefle, S.L., Taylor, S.L., 2004. Food allergy and the food industry. Current Allergy and Asthma Reports 4 (1), 55e59. https://www.ncbi.nlm.nih.gov/pubmed/14680623. Hollaar, V.R.Y., van der Putten, G.J., van der Maarel-Wierink, C.D., Bronkhorst, E.M., de Swart, B.J.M., de Baat, C., Creugers, N.H.J., 2017. Nursing home-acquired pneumonia, dysphagia and associated diseases in nursing home residents: a retrospective, cross-sectional study. Geriatric Nursing 38 (5), 437e441. https://doi.org/10.1016/j.gerinurse.2017.02.007. Holland, S., Foster, T., MacNaughtan, W., Tuck, C., 2018. Design and characterisation of food grade powders and inks for microstructure control using 3D printing. Journal of Food Engineering 220, 12e19. https://doi.org/10.1016/j.jfoodeng.2017.06.008. Hurtado, S., Delgado, V., Sepu´lveda, E., inventors. Natural Machines, assignee, 2016-11-24. Apparatus and Method for Preparing Food Mixtures Using Ultrasounds before 3d Printing. International patent 2016186815. Food Ink, n.d. Food Ink. Press kit. Retrieved from: http://foodink.io/press-kit/. Kim, H.W., Bae, H., Park, H.J., 2017. Classification of the printability of selected food for 3D printing: development of an assessment method using hydrocolloids as reference material. Journal of Food Engineering 215. Elsevier B.V. https://doi.org/10.1016/j.jfoodeng.2017. 07.017. Koenig, N., March 1, 2016. How 3D printing is shaking up high end dining. BBC News. Retrieved from: http://www.bbc.com/news/business-35631265. Lambrecht, B., Hammad, H., 2017. The immunology of the allergy epidemic and the hygiene hypothesis. Nature Immunology 18 (10), 1076e1083. Lantern, 2017. The Green Revolution, entendiendo el auge del movimiento veggie. In: Lantern Papers, p. 26. Lille, M., Nurmela, A., Nordlund, E., Metsa¨-Kortelainen, S., Sozer, N., 2018. Applicability of protein and fiber-rich food materials in extrusion-based 3D printing. Journal of Food Engineering 220, 20e27. https://doi.org/10.1016/j.jfoodeng.2017.04.034. Lipton, J.I., 2017. Printable food: the technology and its application in human health. Current Opinion in Biotechnology 44, 198e201. https://doi.org/10.1016/j.copbio.2016.11.015. Liu, Z., Zhang, M., Bhandari, B., Wang, Y., 2017. 3D printing: printing precision and application in food sector. Trends in Food Science and Technology 69, 83e94. https://doi.org/10.1016/j. tifs.2017.08.018. Liu, Z., Zhang, M., Bhandari, B., Yang, C., 2018. Impact of rheological properties of mashed potatoes on 3D printing. Journal of Food Engineering 220, 76e82. https://doi.org/10.1016/j. jfoodeng.2017.04.017.

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328 Fundamentals of 3D Food Printing and Applications Norman, K., Pirlich, M., 2013. Handbook of Food Fortification and Health, vol. 2, pp. 171e177. https://doi.org/10.1007/978-1-4614-7110-3. Nufood, n.d. About n ufood. Retrieved from: http://www.nufood.io/about.html. Oeppen, J., Vaupel, J.W., 2002. Broken limits to life expectancy. Science 296 (5570), 1029e1031. Olick, D., January 4, 2017. Why 2017 Will Finally Be the Year of the Smart Home: Consumers Figure it Out. Reality Check. CNBC. Retrieved from: http://www.cnbc.com/2017/01/04/why2017-will-finally-be-the-year-of-the-smart-home-consumers-figure-it-out.html. Storebound, n.d. PancakeBot. Retrieved from: http://www.pancakebot.com/. Patel, N., Herbert, L., Green, T.D., 2017. The emotional, social, and financial burden of food allergies on children and their families. Allergy and Asthma Proceedings 38 (2), 88e91. https://doi.org/10.2500/aap.2017.38.4028. Pe´rez, B., 2016. Vegetariano, vegano, flexitariano. los vegetales son tendencia en el desarrollo de nuevos productos. AINIA. Retrieved from: http://www.ainia.es/tecnoalimentalia/consumidor/ vegetales-tendencia-nuevos-productos/. Print2taste, n.d. Procusini Foods. Retrieved from: https://www.procusini.com/procusini-foods/. Venture Radar, n.d. 3D and Food and Printing. VentureRadar. Retrieved from: https://www. ventureradar.com/search/ranked/3DANDFoodANDPrinting/. RichRap, April 6, 2012. Universal Paste Extruder for 3D Printers. Thinguiverse. Retrieved from: https://www.thingiverse.com/thing:20733. Rood, T., Muilwijk, H., Westhoek, H., 2017. Food for the Circular Economy. PBL Netherlands Environmental Assessment Agency, The Hague. Retrieved from: http://www.pbl.nl/sites/ default/files/cms/publicaties/PBL-2017-Food-for-the-circular-economy-2878.pdf. Rushton, E., April 2017. University Hospital Now Printing e Yes, Printing e Real Food. UNIVERSITY INFORMATION TECHNOLOGY, THE UNIVERSITY OF UTAH. Retrieved from: https://it.utah.edu/node4/news/april_2017/food-printer.php#. Scha¨fer, T., Bo¨hler, E., Ruhdorfer, S., Weigl, L., Wessner, D., Heinrich, J., et al., 2001. Epidemiology of food allergy/food intolerance in adults: associations with other manifestations of atopy. Allergy: European Journal of Allergy and Clinical Immunology 56 (12), 1172e1179. https://doi.org/10.1034/j.1398-9995.2001.00196.x. Schouteten, J.J., De Steur, H., De Pelsmaeker, S., Lagast, S., Juvinal, J.G., De Bourdeaudhuij, I., et al., 2016. Emotional and sensory profiling of insect-, plant- and meat-based burgers under blind, expected and informed conditions. Food Quality and Preference 52, 27e31. https://doi. org/10.1016/j.foodqual.2016.03.011. Severini, C., Derossi, A., Azzollini, D., 2016. Variables affecting the printability of foods: preliminary tests on cereal-based products. Innovative Food Science and Emerging Technologies 38, 281e291. https://doi.org/10.1016/j.ifset.2016.10.001. Severini, C., Derossi, A., Ricci, I., Caporizzi, R., Fiore, A., 2018. Printing a blend of fruit and vegetables. New advances on critical variables and shelf life of 3D edible objects. Journal of Food Engineering 220, 89e100. https://doi.org/10.1016/j.jfoodeng.2017.08.025. Sun, J., Peng, Z., Yan, L., Fuh, J., Hong, G.S., 2015. 3D food printingdan innovative way of mass customization in food fabrication. International Journal of Bioprinting 27e38. https://doi.org/ 10.18063/IJB.2015.01.006. Thyberg, K.L., Tonjes, D.J., 2016. Drivers of food waste and their implications for sustainable policy development. Resources. Conservation and Recycling 106, 110e123. https://doi.org/ 10.1016/j.resconrec.2015.11.016.

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Tyers, P., May 30, 2017. Dysphagia No Longer a Bitter Pill to Swallow with 3D Printed Food. CSIRO. Retrieved from: https://blog.csiro.au/dysphagia-no-longer-bitter-pill-to-swallow-3dprinted-food/. Van der Horst, K., Ferrage, A., Rytz, A., 2014. Involving children in meal preparation. Effects on food intake. Appetite 79, 18e24. https://doi.org/10.1016/j.appet.2014.03.030. Vancauwenberghe, V., Katalagarianakis, L., Wang, Z., Meerts, M., Hertog, M., Verboven, P., Nicolaı¨, B., 2017. Pectin based food-ink formulations for 3-D printing of customizable porous food simulants. Innovative Food Science and Emerging Technologies 42 (June), 138e150. https://doi.org/10.1016/j.ifset.2017.06.011. Verdonschot, R.J.C.G., Baijens, L.W.J., van de Kolk, I., Kremer, B., Leue, C., 2017. Affective symptoms in patients with oropharyngeal dysphagia: a systematic review. Journal of Psychosomatic Research 97 (March), 102e110. https://doi.org/10.1016/j.jpsychores.2017.04.006. Wang, L., Zhang, M., Bhandari, B., Yang, C., 2018. Investigation on fish surimi gel as promising food material for 3D printing. Journal of Food Engineering 220, 101e108. https://doi.org/10. 1016/j.jfoodeng.2017.02.029. Wood, R., 2003. The natural history of food allergy. American Academy of Pediatrics 111 (3), 1631e1637. https://doi.org/10.1016/j.jaip.2015.11.024. World Health Organization, September 2017. Ageing and Health. Fact Sheet No 404. Retrieved from: http://www.who.int/mediacentre/factsheets/fs404/en/. World’s Advanced Saving Project, January 19, 2017. The 3D Printer for the Future Kitchen. Retrieved from: http://www.wasproject.it/w/en/the-3d-printer-for-the-future-kitchen/. Yang, F., Zhang, M., Bhandari, B., Liu, Y., 2018. Investigation on lemon juice gel as food material for 3D printing and optimization of printing parameters. Lebensmittel-Wissenschaft und Technologie- Food Science and Technology 87, 67e76. https://doi.org/10.1016/j.lwt.2017. 08.054. Yurieff, K., December 6, 2017. Randi Zuckerberg’s Pop-up Kitchen Serves up Tech for Kids. CNNMoney, New York. Retrieved from: http://money.cnn.com/2017/12/06/technology/randizuckerberg-tech-kitchen/index.html.

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Chapter 11

Prosumer-Driven 3D Food Printing: Role of Digital Platforms in Future 3D Food Printing Systems Siddharth Jayaprakash, In˜igo Flores Ituarte, Jouni Partanen Department of Mechanical Engineering, Aalto University, Espoo, Finland

Chapter Outline 11.1 11.2 11.3 11.4

Introduction What Is Prosumption? Evolution of Prosumption Current State of 3D Food Printing 11.4.1 Market Segmentation 11.4.2 3D Food Printing Ecosystem and Associated Value Chains 11.4.3 Ingredient Portfolio 11.4.4 Machine Concepts

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11.5 Food Prosumption With 3D Food Printing 11.5.1 Change Drivers 11.5.2 Future of Food 11.5.3 Digital Platform for 3D Food Printing 11.5.4 Futuristic Application Areas 11.5.5 Example Use Cases 11.5.6 The Impact 11.6 Conclusions References

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11.1 INTRODUCTION Three-dimensional printing is a collective term used to refer to a variety of technologies that allow layer-by-layer construction of 3D objects from a computer-aided design model. The whole process is controlled by a computer program and requires minimal human interaction. Also known as additive manufacturing, this technology has evolved considerably over the last couple of decades. It is currently at the peak of inflated expectation and is predicted to achieve mainstream adaptation between 2019 and 2024 (Gartner Inc., 2014). Present-day 3D printing technology allows for the utilisation of a broad range Fundamentals of 3D Food Printing and Applications. https://doi.org/10.1016/B978-0-12-814564-7.00011-0 Copyright © 2019 Elsevier Inc. All rights reserved.

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of materials including both natural and synthetic polymers, metals and a variety of food ingredients. As the technology is still being refined and new value chain models are being innovated, its applications and impact will continue thrusting out to areas like the food sector. Three-dimensional printing systems that accept food ingredients as printing materials are known as 3D food printers. Here, food structure designs in the form of additive manufacturing file formats are translated to individualised edible structures through layer-by-layer deposition of food ingredients. The process is also known as food layered manufacturing (Wegrzyn et al., 2012), and is technically referred to as additive food manufacturing (Pinna et al., 2016). This technology is made possible by effectively combining additive manufacturing knowhow with food science and digital gastronomy (Sun et al., 2015a). Unlike food robots that simply automate the traditional cooking process, 3D food printers facilitate creation of fully individualised edible structures from unique food designs. The relevance of this technology in academia and industry has increased significantly since the inception of first 3D food printer prototype (Periard et al., 2007; Cohen et al., 2009; Lipton et al., 2010) at Cornell University in 2007. According to Frost and Sullivan, there has been a drastic increase in 3D food printing-related patents since 2013 (Sullivan and Frost, 2015). The identified applications range all the way from use in home and restaurant kitchen (Van Bommel, 2014) to that in spacecrafts (Hall, 2013). It is interesting to note that even though a lot of application areas are identified for 3D food printing, its innovation potential is highly underutilised. Scientific literature on the associated value chains as well as the service implications are still scarce. The current state of 3D food printing can be compared to the conventional 3D printing technology of the last decade. According to Janne Kytannen, 3D printing, which was then utilised as industrial systems was just a ‘fascinating technology with very little consumer knowledge’ (Kytannen, 2005). With the arrival of desktop 3D printers and digital platforms in the mainstream market, the level of consumer involvement in production activities has increased considerably (Rayna et al., 2015). For example, a combination of digital platforms and advanced production technologies like 3D printing could help translating consumer creativity in the form of 3D designs into personalised physical objects. This in turn is blurring the line between production and consumption activities. American futurist Alvin Toffler has predicted this ongoing paradigm change in manufacturing sector as early as in 1980. In his 1981 book, The Third Wave (Toffler, 1981), Toffler introduced the word prosumer to address people who produce goods for their own consumption. With the arrival of 3D food printing technology and advanced Information and Communications Technology (ICT) platforms, similar changes are highly anticipated in the food production sector.

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11.2 WHAT IS PROSUMPTION? Prosumption, or prosumerism, is a business term that refers to a meld of production and consumption. It is an activity that involves production of goods by its own consumers. Even though the term was introduced in the 1980s, the concept of prosumption has existed since the preindustrial era (Toffler, 1981; Kotler, 1986; Ritzer et al., 2012). According to Ritzer and Jurgenson (2010), even Karl Marx, who is considered as the supreme scholar of industrial production, has realised how people took turns in their roles as producers and consumers. He has also understood the impact of this interplay much before Toffler. The book The Third Wave (Toffler, 1981) by Alvin Toffler describes the interrelations of production and consumption through three stages of societal history, namely, preindustrial era, era of industrial revolution, and postindustrial era (see Fig. 11.1). He called these three stages as three waves of human history. Phillip Kotler added on to Toffler’s work, where he emphasised on the difference between production for use and production for exchange (Kotler, 1986). During the preindustrial era, people grew crops and vegetables for their own consumption. Much of the economy was dependent on agricultural activities. This means that most of the people were prosumers during that time and age. A small section of population did fishing, hunting, carpentry and other specialised trades. They exchanged their competency for food, clothing and other goods. This situation has changed significantly once we reached the industrial era. During the time of the industrial revolution, factories became the core establishments, and people started producing goods merely for exchange. The prosumer population has marginalised drastically during this era which gave rise to pure consumers and producers. Ritzer and Jurgenson argue that even during the era of factory economy, the roles of producers and consumers were not mutually exclusive, since producers consumed goods made at their factories, and consumers made meals for their own consumption. Currently, the society is moving towards an age of individualisation from that of centralised production and mass consumption. Toffler and Kotler were very much ahead of their times as they predicted this paradigm change as early as in the 1980s. Toffler termed this upcoming era as the third wave of human history (Toffler, 1981). This third wave is characterised by advancement in technology, high level of education, waning market dependency and demassification (Toffler, 1981; Kotler, 1986). There has been a gradual decline in the acceptance rate of boring repetitive tasks, and the trend is toward working

FIGURE 11.1 Three waves of human history according to Toffler (1981).

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smart rather than working hard. Instead of relying entirely on the market, people are using latest ICT and production technologies to create quality goods for their own use. This also means that the size of the prosumer population is increasing gradually, while the number of pure consumers is decreasing.

11.3 EVOLUTION OF PROSUMPTION Even though the term prosumption was introduced in the early 1980s, the concept remained underresearched until the outset of 21st century. Its academic relevance started to increase because of the societal change (Ritzer et al., 2012) associated with the mainstreaming of digital platforms and technology innovations like 3D printing (Rayna et al., 2015). In the beginning, prosumption was mostly limited to do-it-yourself activities like home painting and cooking. With the arrival of computers and web 2.0, prosumption opened up to incorporate various customisation tasks. This, along with e-commerce platforms, continues to provide consumers with mass customisation possibilities. The highest level of prosumption occurs when the consumer invests in software and equipment such as cameras, 3D printers and scanners. Investing in 3D printers, for example, allows consumers to produce customised speciality products at home. These equipment act as complementary assets for the associated enterprises and are pivotal in creating, delivering and capturing value. With the rise of prosumers, the concept of value co-creation is gaining prominence on an industrial level. Increasingly, businesses are considering consumers for more active and creative roles, rather than just workforce replacement. The latest ICT infrastructure and advanced production technologies allow consumers to participate effortlessly in idea development, design, production, testing, as well as distribution activities (Prahalad and Ramaswamy, 2004; Tapscott and Williams, 2006). Working closely with consumers allows businesses to create products with high desirability value. This will, in turn, minimise the chances of failure at market entry. Since mass production is gradually giving way for mass customisation, companies are shifting their business strategy to service-dominant logic (Lusch et al., 2008) and customer-dominant logic (Heinonen et al., 2010) from the traditional goods-dominant logic. In addition to this, branding and marketing activities of firms are increasingly focusing on aspects like production efficiency, personalisation and skill development. This ongoing, inevitable transition of business logic was predicted by Toffler (1981) and Kotler (1986) in their early research works related to prosumption. All these changes are paving the way toward experience innovation (IDEO, 2009), which can be seen as an amalgamation of products, services and user environments. This new model of innovation is already becoming visible in the 3D printing industry for specialised goods.

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Three-dimensional printing technology has been predicted to be most transformative during the period between 2015 and 2025 (Karlgaard, 2011). As mentioned earlier, a combination of 3D printing and digital platforms has the power to take prosumption to a higher level, disrupting the existing manufacturing paradigm. Digital platforms for 3D printing allow consumers to intervene at any given stage in a production process, giving them a more prominent role in the 3D printing business. These changes which are clearly visible in the speciality goods sector are much anticipated in other areas like the food production industry. The associated model of co-creation results in a stronger customer relationship and helps businesses to reach distant markets effectively.

11.4 CURRENT STATE OF 3D FOOD PRINTING Three-dimensional food printing technology is still in its nascent form, and only limited business models and value chains have been identified so far. Also, 3D food printing cannot compete with conventional food production technologies in terms of price at present. Under these circumstances, a prime value for businesses investing in this technology is in differentiating themselves from their competitors. Early adaptation of 3D food printing technology allows the businesses to be on par with the latest food technology trends. Another advantage for early adopters is to get the associated R&D tailored to their own product offerings. For example, Hershey’s collaboration with 3D Systems (Molitch-Hou, 2015), and Barilla’s collaboration with the Netherlands Organisation for Applied Scientific Research (TNO) (Van Bommel, 2014; Van Der Linden, 2015), means that their recipes have been tried and tested throughout the R&D process of the respective 3D food printers. Unlike their competitors, the abovementioned food brands don’t have to reformulate their recipes to get the most out of the technology. Most of the available publications in the field of 3D food printing are related to the innovation of printable food raw materials, its rheology optimisation, sustainable and healthy food ingredients, and adapting the existing 3D printing technology for food printing. In addition to this, research organisations like TNO of the Netherlands and VTT Technical Research Centre of Finland have identified interesting application areas and scenarios for 3D food printing (Van Bommel, 2014; Van Der Linden, 2015; Poutanen et al., 2017). Even though the technology is continuously being refined, and increasingly, application areas are being identified, there is still an insufficiency of scientific knowledge on how 3D food printing technology can be taken to the people. In other words, service implications of 3D food printing is an area that is still unexplored.

11.4.1 Market Segmentation The 3D food printing market is predicted to reach $400 million by 2024, with a compound annual growth rate of 50% between 2017 and 2024

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(Research Nester, 2018). The market is steered by factors such as the demand for customised food products, potential impact of 3D printed food on health and well-being, sustainability and advancing ICT. Based on existing literature and reports by future foresight experts, 3D food printing market segments can be classified into five clusters (see Fig. 11.2). The first cluster represents the home and domestic kitchen, where 3D food printers could serve individuals for producing personalised meals. The second cluster is a group of small enterprises including bakeries and restaurants. The third cluster includes large enterprises like food brands and sports/fitness centres. The airline industry is another identified market under this cluster. NGOs, including nursing homes and disaster relief centres, fall into the fourth cluster, whereas conferences, festivals and other events are grouped together in the final cluster. Three-dimensional food printing businesses could also utilise various events as platforms for marketing their innovation and offering. Europe is spearheading the 3D food printing market, with multiple players from Spain and Netherlands being active in the household and restaurant sectors. It is interesting to note that most of the microwave pancakes sold in Netherlands are produced using the extrusion process. There are also some significant developments being made by businesses, universities and research organisations in the United States, Australia and New Zealand. In the United States, 3D Systems and the Culinary Institute of America are on the forefront

FIGURE 11.2 3D food printing market segmentation.

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of 3D food printing-related innovation activities. In Asia, most of the related research and business activities are cramped within Japan, Korea, Taiwan and China. Since 3D food printing is a novel innovation with a dynamic scope of application, its market segmentation and research scope are expected to expand and evolve in the upcoming years (Sullivan and Frost, 2015; Research Nester, 2018).

11.4.2 3D Food Printing Ecosystem and Associated Value Chains The current 3D food printing ecosystem can be viewed as a nexus of various entities (see Fig. 11.3) including universities and research centres, consumers, 3D food printer manufacturers, food ingredients producers, food ingredients distributers, food brands and restaurants, digital platforms, software developers and marketplaces including e-commerce. The nature of interaction between these actors of the ecosystem is crucial in creating, delivering and capturing value within the associated food economy. In other words, individual 3D food printing value chains are determined by the nature of interactions between various entities of the ecosystem.

FIGURE 11.3 Various entities of the 3D food printing ecosystem.

338 Fundamentals of 3D Food Printing and Applications Markets and Purchase

Distribution

Food Production

Consumption

Food Processing & Packaging

Restaurant/ Catering

FIGURE 11.4 A simple, traditional food value chain.

A food value chain in general is a network of value-adding activities of actors involved at various stages of the food product life cycle. A traditional value chain (see Fig. 11.4) in its simplest form often starts with research, development and production of food ingredients. The second key activity would be the distribution of food ingredients to processing plants. In most cases, these processing plants are present within large food brands. These enterprises convert the raw ingredients into palatable food products that are ready for the markets. Different preservation processes like pasteurisation, canning, refrigeration, freezing, etc., are carried out during this stage if necessary. Packaging is one important activity involved during this stage of the food value chain. Processed and packaged food products are marketed and distributed to outlets including supermarkets, restaurants, smaller groceries, cafes and bakeries. Consumers buy food products from these marketplaces for consumption, which may often involve further cooking at home. Waste management is another activity which is critical to food value chains, and it should ideally be taken care of by all the actors involved. In case of traditional food value chains, the interaction and co-creation possibilities between consumers and businesses are very minimal, making the business logic highly product centric. This situation is slowly changing with the arrival of 3D food printers. The identified 3D food printing value chains (Figs 11.5 and 11.6) show that consumers are having a more central role in the value creation process, enabling food prosumption to a considerable extent. Fig. 11.5 illustrates the value chain associated with the industrial use of 3D food printing, whereas Fig. 11.6 represents the value chain associated with desktop 3D food printers for the domestic kitchen. In case of the former

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3D Printer Manufacturer– Hardware + Software

Food Enterprise

Ingredients Producer

Consumer

Web Service

FIGURE 11.5 3D food printing value chain: consumer buys 3D printed food.

(Fig. 11.5), food enterprises, including restaurants and food brands, buy 3D food printer hardware and software through a B2B channel. These brands will then use their recipes to 3D print food products that are to be sold to consumers. In some cases, consumers can select the food ingredients and designs to be printed before making the order through the web platform. In case of the latter value chain (see Fig. 11.6), 3D food printers are sold directly to the consumers as kitchen equipment. Consumers then use the food raw materials purchased from marketplaces to create food designs for their consumption. Most of the existing desktop 3D food printers come with a web service or a digital platform that helps consumers to download food designs and recipes. The term prosumer is not used with respect to these value chains because the associated level of prosumption is still minimal. Even though consumers can create food structure designs and recipes using the online platform, personalisation in terms of food textures, ingredient composition and nutrition is still not feasible. On the other hand, these value chains highlight the more central role that consumers could play in food production, as well as the co-creation possibilities. When combined with an effective digital service model, these consumer-centric value chains can take food prosumption to a higher level.

340 Fundamentals of 3D Food Printing and Applications 3D Food Printer Brand – Software + Hardware

Ingredients Producer

Markets & Purchase

3D Food Printer Purchase

Web Service

Consumer

FIGURE 11.6 3D food printing value chain: consumer buys 3D food printer.

11.4.3 Ingredient Portfolio Initially, the ingredient portfolio for 3D food printing was limited to naturally printable food raw materials like chocolate, sugar, hummus and cheese (Yang et al., 2001; Periard et al., 2007). This has expanded gradually and currently includes food materials like cereals, fruits and vegetables (Lipton et al., 2010; Tanaka et al., 2015). Since 3D food printing is still an emerging technology, there are a lot of challenges associated with the selection and optimisation of ingredients for printing. Food raw materials that can be utilised by existing 3D food printing systems can be classified into natively printable ingredients, traditional nonprintable ingredients and alternate food ingredients (Sun et al., 2015b; Izdebska and Zolek-Tryznowska, 2016; Pinna et al., 2016). The nature of food ingredients being used will have a significant impact on printing parameters like printing speed, mixing efficiency and geometrical accuracy. The nature of ingredients being used will also determine whether the printed food structure is compatible with conventional postprocessing techniques. In order to create high-quality food structures, the ingredients should hold their form upon deposition; allow easy customisation of shape, texture and nutrients

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and maintain nutritional and geometrical stability during postprocessing operations (Godoi et al., 2016). Natively printable food materials exist either as pastes or as powders. Natively printable food pastes include chocolate, hummus, mashed potatoes, dough, batter, icing and cheese. Sugar and starch, on the other hand, fall under the category of natively printable food powders. These ingredients can easily be mixed and customised. Also, natively printable food materials other than batter and dough seldom require postprocessing. The second category of food ingredients, i.e., traditional nonprintable food materials, can be made printable by mixing simple additives like hydrocolloids (Cohen et al., 2009; Lipton et al., 2010; Sun et al., 2015b; Godoi et al., 2016; Izdebska and Zolek-Tryznowska, 2016). Some examples of these ingredients are fruits, vegetables, meat and rice. The third and final category includes sustainable and innovative ingredients like insect protein, protein from algae, protein from broad beans and oats, etc. These are considered as the food ingredients of the future, as they can tackle challenges related to food sustainability and security. As demonstrated in the ‘Insect Au Gratin’ project (Soares, 2011), these alternate ingredients can also be mixed with natively printable ingredients for creating food products which are tasty and healthy at the same time.

11.4.4 Machine Concepts Even though Nanotek Instruments Inc. filed the first 3D food printer patent (Yang et al., 2001) in 2001, no physical prototypes were made until 2007. The most significant development in 3D food printing took place between 2007 and 2010 at Cornell University (Periard et al., 2007; Cohen et al., 2009; Lipton et al., 2010). During the same time, Windell Oskay and Lenore Edman of Evil Mad Scientist Labs (CandyFab, 2006) have developed the first 3D sugar printer that utilises selective hot air sintering and melting technology. Before this period, printing of personalised food was just an idea associated with sci-fi series like Star Trek (Star Trek Replicator, 1987). Three-dimensional food printing and digital gastronomy concepts developed by the Massachusetts Institute of Technology (Zoran and Coelho, 2011) and Nestle (Begley, 2014) point out that real-world food replicators are not far away from becoming a reality. By 2010, the 3D food printing scene in Europe started evolving as TNO of Netherlands came up with a selective laser sintering printer for creating food structures from powdered ingredients with added flavours and nutrients. Choc Creator, a chocolate 3D printer that works on a fused deposition modelling platform was commercialised by Choc Edge in 2011. In 2013, TNO collaborated with Italian pasta manufacturing giant Barilla to develop a 3D food printer capable of producing customised pasta shapes. During the same year, Barcelona-based Natural Machines introduced Foodini

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3D food printer which utilises fresh and raw food ingredients. Foodini is based on the soft material extrusion process, and it can print using multiple ingredients with the help of reusable metal capsules. It comes with a digital platform that allows users to import designs, download recipes and control the printing process (Natural Machines, 2013). During this period in the United States, the ChefJet series of 3D food printers were introduced to the market by 3D Systems and Culinary Labs. These printers are based on liquid binding technology. 3D Systems then collaborated with Hershey to develop an extrusion-based chocolate 3D printer called ChocJet. Another development in the United States was the collaboration between NASA and Systems & Materials Research Corporation to innovate a pizza printer that produces nutritious meals for astronauts on extended space expeditions. After 2014, a lot of new players have entered the market, including Dutch company byFlow with their Focus 3D food printers, German enterprise Print2Taste with Bocusini 3D food printers, Katjes Magic Candy Factory and NuFood Robot.

11.5 FOOD PROSUMPTION WITH 3D FOOD PRINTING It is important to note that the prosumer value offered by most of the current 3D food printing systems is still limited. This is primarily due to the absence of an effective digital platform that connects the 3D food printers with prosumers. The potential interactions between 3D food printers, digital platforms, and prosumers are not well researched at present. A thorough qualitative research has been conducted to understand how digital platforms could be best combined with 3D food printers to facilitate a higher degree of food prosumption. Qualitative data was collected using semistructured interviews with experts from four different countries. Knowledge gathered from the literature review process was used to plan the semistructured interviews, and the interviewee pool was kept diverse given the interdisciplinary nature of the topic. Interviewees included experts from academia, research organisations, future foresight consultancy, food brands, 3D food printing start-ups, food distributers, software providers, and service providers. The diverse background and varied expertise of the interviewees helped in gaining fresh data from multiple perspectives.

11.5.1 Change Drivers From the interview data, various change drivers for prosumer-driven 3D food printing were collected and grouped in to four categories, i.e., technology, well-being, market megatrends, and sustainability (see Fig. 11.7). Within the first category, digital revolution and advancements in 3D printing technology

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FIGURE 11.7 Change drivers for prosumer driven 3D food printing.

are two of the most significant drivers for change. Latest ICT allows knowledge to be shared digitally regardless of the geographical location. This, when viewed together with advancing 3D food printing technology, calls for a shift from centralised factory-based food production towards localised production. Three-dimensional food printing technology is found to be an excellent facilitator of personalised nutrition. It will be of great value to fitness enthusiasts when coupled with a digital platform that supports health and nutrition monitoring. Changing eating habits and consumer convenience are also significant drivers within the second category. Megatrends, including dynamic markets associated with globalisation, shift toward on-demand food production, growing global food demand, and call for transparent supply chains, are all drivers for the mainstreaming of prosumer-driven 3D food printing. Under the current market conditions, enterprises should strive for consumer-centric and sustainable business models to differentiate themselves from the competition. Key change drivers within the category of sustainability includes global climate change, concerns regarding food miles, and food wastage. There is also an emerging trend of buying and consuming food made with locally produced ingredients. This, as well as the recent innovations in sustainable alternate food ingredients, nicely complements prosumer-driven 3D food printing.

11.5.2 Future of Food It is clear from the interviews that future of food is not only dependent on technology but also on the ongoing societal changes. One of the most significant ongoing change is the growing population worldwide. This will

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directly lead to an increase in global food demand. The Food and Agriculture Organization of the United Nations predicts a 70% increase in food demand by 2050 (FAO, 2017). Consumption patterns in developing countries are being altered by the ongoing changes in income distribution. Consumers in those countries are slowly transitioning towards a nutrient-rich diet from a primarily cereal-based diet. If these changes are not addressed properly, it will lead to an overexploitation of natural resources in those food-insecure regions. These identified trends underline the importance of timely investments for developing a sustainable food system. The food system of the future should feed the growing population with nutrient-rich food while being able to check overexploitation of natural resources. Development of sustainable food ingredients is one research avenue that is very relevant at present. These alternate food materials would play an important role in curbing the high carbon footprint associated with the meat and dairy industry. Examples for these food materials include artificial meat and protein powders from algae, insects, oats, and broad beans. Insect protein, for example, is found to be nutritious, highly sustainable, and economically viable. Farming of insects and algae requires only a limited supply of natural resources, whereas their food conversion efficiency is significantly higher than that of traditionally produced meat. Another key research avenue is the further development of powder-based and liquid-based meals. These food products have comparatively higher nutrients-to-weight ratio and can condense a wide variety of nutrients within them. Scaling up the research and development activities related to the above-discussed alternate ingredients will help addressing the problems of food security, malnutrition, and sustainability. On the flipside, consumer desirability of these alternate ingredients is still uncertain. Prosumer-driven 3D food printing could bring in an added value here by converting these ingredients into palatable, desirable, and personalised food products. Food of the future will be a means to personal well-being rather than just a source of nutrition. Hence, food personalisation and food convenience are two avenues that need to be looked upon seriously. Facilitating a personalised shopping and eating experience might be game changing in the food sector. This is where ICT innovations and advanced food production technologies like 3D food printing would play a significant role. Internet of things (IoT) and advanced machine learning could facilitate on-demand, decision-free ordering of food products. Consumer convenience will drive distribution channels of the future. According to VTT Technical Research Centre of Finland, next-generation vending machines have a potential to disrupt food distribution when coupled with advanced production technologies and latest ICT. In addition to food convenience, satisfaction in eating is another factor that determines the future food systems. For instance, a combination of latest

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technologies like artificial intelligence and virtual reality could be used to hack and manipulate human senses to create a more enjoyable eating experience.

11.5.3 Digital Platform for 3D Food Printing Qualitative data from the interviews shows that the nature of prosumer platforms will have a huge impact on the desirability of future 3D food printers. In this context, desirability is a combination of usability and prosumer experience. An ideal digital platform for 3D food printing is one that has a simple and intuitive user interface. While being simple, it should provide an optimal amount of customisation options for prosumers. This is very important because overabundance of these features could create a cognitive overload amongst users. The platform should also be scalable, i.e., it should be easy for the service provider to add on additional features to the interface later. The user should be able to monitor available food ingredients in real time. Similarly, monitoring of the printing process as well as the total calories and nutrients consumed is also found to be important. Users should be able to create 3D designs with ease. This can be made sure by giving access to predesigned templates that can easily be modified. They should also be able to smoothly upload food structure designs made with any independent software. Another good-to-have feature is the ability to take the user’s medical data and personal preferences into consideration during the printing process. Last but not the least, the user should be able to share their recipes and 3D food structure designs with fellow prosumers.

11.5.4 Futuristic Application Areas The most potential application areas of prosumer-driven 3D food printing have been identified from the qualitative data gathered from interviews (see Figs. 11.8e11.10). It has been found that combining next-generation vending machines with 3D food printing technology and advanced ICT could disrupt the existing food distribution chains. Three-dimensional food printing-enabled vending machines offer consumers personalised snacks to support their individual efforts related to health and well-being. The concept is targeted at daily commuters and office workers so as to redefine on-the-go food convenience. Three-dimensional food printing vending machines could be located in coffee shops, universities, office spaces, and in other public places such as train stations or metro stations. The second concept is aimed at fine diners. It brings together 3D printing technology and digital gastronomy to create unique dining experiences. In other words, digital recipes (e.g., by star chefs) could be converted into personalised meals using a 3D food printer. This way, the same food product (e.g., dessert) could be designed differently for different individuals.

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FIGURE 11.8 Future application areas of prosumer driven 3D food printing; 1.

Here the key personalisation parameter is design, i.e., shape, texture and portion size. It is clear from the research that 3D food printing is an enabler of personalised nutrition. Also, the concept of self-quantification has gained mainstream attention with the arrival of personal tracking applications in smart devices. A combination of these two technologies can facilitate the creation of personalised healthy snacks in fitness centres and sports clubs. Here, the personalisation will mainly be for nutrient content, portion size, ingredients, texture, and flavour. The concept of utilising 3D food printers in the home kitchen is not a new one. There are already 3D food printers in the market that are targeted at home cooks. On the other hand, these printers offer limited functional value in terms of customisation possibilities and design freedom. This is mainly due to the absence of an innovative prosumer platform. In the future, the IoT, artificial intelligence and machine learning would allow home cooks with 3D food printers to create personalised healthy meals by just using their smart devices. This could help them in reducing the total time spent in kitchen. It is clear from the research data that personalised nutrition is one domain where 3D food printing has a huge scope. One application area associated with personalised nutrition is the utilisation of prosumer-driven 3D food printing in senior homes. With the help of an intuitive digital platform, senior citizens would be able to easily customise nutrients and food textures of meals they consume. This would enhance their overall eating experience without compromising on convenience, health, and well-being. Hospitals are another application area where next-generation 3D food printers could be employed. A 3D food printer coupled with a smart digital platform has the ability to redefine the hospital meal experience of inpatients.

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FIGURE 11.9 Future application areas of prosumer-driven 3D food printing; 2.

Similar to that of hospital meals, onboard meals in airplanes are often bland. With the help of a playful and user-friendly mobile platform for 3D food printing, passengers could create personalised food designs whilst flying. This might also impact their overall flying experience in a positive way. Universities are another application area where prosumerdriven 3D food printers could create an added value. Eating habits are changing gradually, and there is an increasing demand for food convenience and personalised nutrition. Combining next-generation ICT with 3D food printing would help in redefining student meals at university campuses. Students could turn their personal 3D designs into healthy snacks or meals based on their nutritional requirements. It is clear from the interviews that there is an ongoing inevitable shift from factory-based food production to localised production. Prosumer-driven 3D food printing could potentially play a significant role in decentralising food production. For example, autonomous food trucks with prosumer-driven 3D food printers could produce and distribute personalised meals made with locally grown food ingredients. This disruption in food production and distribution systems will help in minimising food miles as well as food wastage. In other words, localised food production utilising prosumer-driven 3D food printing will positively impact the overall sustainability of our food system.

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FIGURE 11.10 Future application areas of prosumer driven 3D food printing; 3.

11.5.5 Example Use Cases Example workflow diagrams for three selected application areas are described in this section to better communicate how food prosumers could utilise future 3D food printing systems. The first workflow model is associated with the role of prosumer-driven 3D food printing in next-generation food vending. Conventional vending machines are automated systems that sell and deliver convenience goods to impulse buyers. It should be noted that 3D food printingenabled vending machines, on the other hand, won’t be targeted at impulse buyers. These next-generation food vending systems would disrupt the existing food distribution chains by making the best use of digital revolution and advancements in 3D food printing technology. Using a smartphone application, the user could select the 3D food vending machine at the most convenient location. They would then select the recipe and place the order. During ordering, the selection will be personalised either by the user or the vending machine based on the user’s health and well-being targets. The personalisation might be related to portion size, flavour, nutrition, and design. Also, food properties such as crunchiness, creaminess, or saltiness could be customised. The printing process will be initiated once the user confirms the order and the collection time. Fig. 11.11 gives a detailed step-by-step illustration of the whole process. Prosumer-driven 3D food printing in fine dining is all about facilitating a smooth transition from molecular gastronomy to digital gastronomy. Here, molecular gastronomy refers to the idea of creating a unique relationship

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FIGURE 11.11 An example of prosumer workflow for 3D food printing-enabled vending machines.

between food and its consumers via different taste experiences. Digital gastronomy, on the other hand, is a culinary vision where molecular gastronomy is further enhanced by digital technologies. In fine dining, the overall eating experience is far more important than just the food product. A 3D food printer coupled with a playful digital interface has the potential to create unique food experiences. Fig. 11.12 illustrates a prosumer workflow for the fine dining use case of 3D food printing. The user (fine diner) could filter available recipes in the web platform of restaurant based on popularity, price,

FIGURE 11.12 An example of prosumer workflow for 3D food printing in fine dining restaurants.

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FIGURE 11.13 An example of prosumer workflow for 3D food printing in fitness centres.

season, allergies, etc. These recipes would then be customised based on individual preferences. User could either upload designs or create them using the intuitive interface and available templates. The printing process will take place in front of the user, for example, on the table. This would allow the user to follow the process live. The concept of 3D food printing for fitness enthusiasts is driven by a growing need for personalised nutrition. These 3D food printing systems could replace the conventional food vending machines present in fitness centres. This use case also offers an opportunity to utilise sustainable alternate food ingredients that are currently being innovated. An example prosumer workflow for this use case is illustrated in Fig. 11.13. Personalised snack designs could be created by the user, or predesigned recipes could be selected. Once the user confirms the order, the 3D food printer will optimise the printing process in such a way that the personalised snack can be collected soon after the workout session.

11.5.6 The Impact Three-dimensional food printing technology has been found to have a huge eco-innovative potential. It is also a great enabler of food prosumption when paired with an effective digital service model. Research data shows that 3D food printing systems of the future will be able to facilitate personal wellbeing through the creation of individualised food products, reduce food wastage, and disrupt the food distribution channels. There will be a gradual

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shift from factory-based mass production of food products to decentralised production utilising locally grown ingredients, 3D food printing technology, and digital platforms. This will, in turn, minimise the food miles and the associated carbon footprint. The above-mentioned points highlight the potential of prosumer-driven 3D food printing in generating a sustainable food system with a circular economy, i.e., a regenerative model that optimises resource utilisation and minimises emissions and wastage of raw materials. With the help of a prosumer platform based on the latest ICT, nextgeneration 3D food printing systems offer interesting possibilities in terms of food customisation. These food systems also nurture consumer convenience and add an interaction and fun aspect to food preparation. This fun and interaction aspect is crucial when it comes to certain application areas like fine dining. Prosumer-driven 3D food printing also provides a platform for food brands to connect and co-create with consumers. Co-innovation with consumers would result in the creation of food products with a higher desirability value and market potential. By leveraging innovations like Artificial Intelligence (AI), Internet of Things (IoT) and Quantified Self, future 3D food printing value chains could become collaborative, data driven, transparent, and connected. This in turn translates to the creation of mutually beneficial outcomes for all the associated actors.

11.6 CONCLUSIONS Digital platforms have become an indispensable part of user experience innovation over a short period of time. The nature of these platforms has a strong co-relation with the consumer acceptance of a product or technology. Along with 3D printing technology, digital platforms have played an important role in facilitating a high degree of prosumption in the specialty goods sector. The food production sector, on the other hand, is still highly centralised, and the current level of food prosumption is very minimal. Increasingly consumers are anticipating a transition from mass production toward an on-demand personalised production of food products. This could be made possible by leveraging the latest ICT and the budding 3D food printing technology. This chapter is aimed at creating an understanding on how digital platforms could be used together with future 3D food printing systems to facilitate food prosumption. First, the concepts of 3D food printing and prosumption are introduced, along with their relevance in today’s world. Next, a detailed literature review on the evolution of prosumption and the state of the art of 3D food printing is carried out. The state-of-the-art section is focused on the market segmentation of 3D food printing, identified value chains, current ingredient portfolio, and existing machine concepts. A qualitative study has been conducted in order to understand the change drivers for prosumer-driven 3D food printing, key characteristics of a prosumer platform for 3D food

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printing, and the most potential application areas. The research involved semistructured interviews of 15 experts from four different countries. The identified key drivers for prosumer-driven 3D food printing falls well within the categories of technology, well-being, sustainability and market megatrends, respectively. The two key technology drivers are the ongoing 3D printing revolution and advancements in ICT. The most important change driver under well-being is the forthcoming call for personalised nutrition. Food convenience and changing eating habits of consumers are also significant drivers within this category. Key drivers related to sustainability includes the quest for alternate food ingredients, local buying and consumption, and the global challenge of food wastage. Important drivers identified under market megatrends includes call for consumer-oriented innovation, growing food demand, shift towards localised food production, and the call for a pellucid supply chain. The most relevant characteristics identified for the digital prosumer platform includes simplicity, scalability, ready access to recipes, intuitive 3D designing capability, real-time monitoring of ingredients, and compliance with personal preferences and medical data. Qualitative data also highlights the importance of having an optimal number of customisation options. This is critical because excess customisation possibilities might create a cognitive overload among prosumers. It is also clear from the interviews that in addition to just being a source of nutrition, future food will also be a source of personal well-being. Future of food is found to be dependent on associated technology innovations, changing social behaviour of consumers, and government policies. Sustainability, convenience, and satisfaction are three key parameters associated with the future of food production, distribution, and consumption. Finally, nine different prosumer architypes and use cases for future 3D food printing systems are identified and illustrated in this chapter. Also, prosumer workflow diagrams of three use cases, namely, 3D food printing-enabled vending machines, 3D food printing in fine dining, and 3D food printing in fitness centres, are made. This is done in order to give a better picture on how prosumers would utilise digital platforms associated with future 3D food printing systems. Technology feasibility and economic viability of most of the identified use cases are still uncertain. But once these use cases are adopted, food production value chains would be a lot more connected, collaborative, transparent, and sustainable.

REFERENCES Begley, S., 2014. Nestle´ Is Developing an Instant-Nutrient Food Machine, TIME Health. Available at: http://time.com/2912509/nestle-is-developing-an-instant-nutrient-food-machine/. CandyFab, 2006. The CandyFab Project. Available at: http://candyfab.org/. Cohen, D.L., Lipton, J.I., Cutler, M., Coulter, D., Vesco, A., Lipson, H., 2009. Hydrocolloid printing: a novel platform for customized food production. In: 20th Annual International Solid Freeform Fabrication Symposium. Austin, Texas, pp. 807e817.

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FAO, 2017. The Future of Food and Agriculture: Trends and Challenges. Rome. Available at: http://www.fao.org/publications/card/en/c/d24d2507-41d9-4ec2-a3f8-88a489bfe1ad/. Godoi, F.C., Prakash, S., Bhandari, B.R., 2016. 3D printing technologies applied for food design: status and prospects. Journal of Food Engineering 179, 44e54. https://doi.org/10.1016/ j.jfoodeng.2016.01.025. Elsevier Ltd. Hall, L., 2013. 3D Printing: Food in Space. Brian Dunbar. Available at: https://www.nasa.gov/ directorates/spacetech/home/feature_3D_food.html. Heinonen, K., Strandvik, T., Mickelsson, K., Edvardsson, B., Sundstro¨m, E., Andersson, P., 2010. A customer-dominant logic of service. Journal of Service Management 21 (4), 531e548. https://doi.org/10.1108/09564231011066088. IDEO, 2009. Design Kit: The Human-Centered Design Toolkit, IDEO.org. Available at: http:// www.designkit.org/. Gartner Inc., 2014. Gartner’s 2014 Hype Cycle for Emerging Technologies Maps the Journey to Digital Business. Hype Cycle for Emerging Technologies. Available at: http://www.gartner. com/newsroom/id/2819918. Izdebska, J., Zolek-Tryznowska, Z., 2016. 3D Food Printing - Facts and Future. Agro Food Industry Hi-Tech. Karlgaard, R., 2011. 3D Printing Will Revive American Manufacturing. Forbes. Available at: https://www.forbes.com/sites/richkarlgaard/2011/06/23/3D-printing-will-revive-americanmanufacturing/#619d20e12548. Kotler, P., 1986. The prosumer Movement : a new challenge for marketers. Advances in Consumer Research 13, 510e513. Available at: http://www.acrwebsite.org/search/view-conference-proceedings.aspx?Id¼6542. Kytannen, J., 2005. Rapid Manufacture for the Retail Industry, in Rapid Manufacturing. John Wiley & Sons, Ltd., pp. 275e282. https://doi.org/10.1002/0470033991.ch18 Lipton, J., Arnold, D., Nigl, F., Lopez, N., Cohen, D., Nore´n, N., Lipson, H., 2010. Multi-material Food Printing with Complex Internal Structure Suitable for Conventional Post-processing. Lusch, R.F., Vargo, S.L., Wessels, G., 2008. Toward a conceptual foundation for service science: contributions from service-dominant logic. IBM Systems Journal 47 (1), 5e14. https://doi.org/ 10.1147/sj.471.0005. Molitch-Hou, M., 2015. Hershey & 3D Systems Unveil New Cutting-Edge Chocolate 3D Printer at CES. 3D Printing Industry. Available at: https://3Dprintingindustry.com/news/hershey-3Dsystems-unveil-new-cutting-edge-chocolate-3D-printer-ces-39279/. Natural Machines, 2013. Foodini. Available at: https://www.naturalmachines.com/. Periard, D., Schaal, N., Schaal, M., Malone, E., Lipson, H., 2007. Printing food. In: Proceedings of the 18th Solid Freeform Fabrication Symposium, pp. 564e574. https://doi.org/10.1007/ s00216-007-1293-0. Pinna, C., Ramundo, L., Sisca, F.G., Angioletti, C.M., Taisch, M., Terzi, S., 2016. Additive manufacturing applications within food industry: an actual overview and future opportunities. In: XXI Summer School Francesco Turco - Industry 4.0 Creating New Waves. ˚ kerman, M., 2017. Food Economy 4.0. VTT’s Poutanen, K., Emilia, N., Jaakko, P., Kaisa, V., A Vision of an Era of Smart Consumer-Centric Food Production. VTT Technical Research Centre of Finland Ltd. Prahalad, C.K., Ramaswamy, V., 2004. Co-creating unique value with customers. Strategy and Leadership 32 (3), 4e9. Rayna, T., Striukova, L., Darlington, J., 2015. Co-creation and user innovation: the role of online 3D printing platforms. Journal of Engineering and Technology Management. https://doi.org/ 10.1016/j.jengtecman.2015.07.002.

354 Fundamentals of 3D Food Printing and Applications Research Nester, 2018. 3D Food Printing Market: Global Demand Analysis & Opportunity Outlook 2024. Research Nester Reports on ICT & Electronics. Available at: https://www. researchnester.com/reports/3D-food-printing-market-global-demand-analysis-opportunityoutlook-2024/272. Ritzer, G., Jurgenson, N., 2010. Production, consumption, prosumption: the nature of capitalism in the age of the digital “prosumer”. Journal of Consumer Culture 10 (1), 13e36. https://doi.org/ 10.1177/1469540509354673. Ritzer, G., Dean, P., Jurgenson, N., 2012. The Coming of Age of the Prosumer. https://doi.org/ 10.1177/0002764211429368. Soares, S., 2011. Insects Au Gratin/Project. Available at: http://www.susanasoares.com/index.php? id¼82. Star Trek Replicator, 1987. Star Trek. Available at: http://www.startrek.com/database_article/ replicator. Sullivan, Frost, 2015. Industrial Bioprocessing Alert: 3D Food Printing. TechVision. Sun, J., Peng, Z., Yan, L., Fuh, J., Hong, G.S., 2015a. 3D food printingdan innovative way of mass customization in food fabrication. International Journal of Bioprinting. https://doi.org/ 10.18063/IJB.2015.01.006. Sun, J., Peng, Z., Zhou, W., Fuh, J.Y.H., Hong, G.S., Chiu, A., 2015b. A review on 3D printing for customized food fabrication. Procedia Manufacturing 1, 308e319. https://doi.org/10.1016/ j.promfg.2015.09.057. Elsevier B.V. Tanaka, H., Asano, Y., Watanabe, M., Masumori, A., 2015. Food Printing technologies out of white rice. In: International Conference on Digital Printing Technologies, pp. 289e292. Available at: http://www.scopus.com/inward/record.url?eid¼2-s2.0-84952941349&partnerID¼tZOtx3y1. Tapscott, D., Williams, A.D., 2006. Wikinomics: How Mass Collaboration Changes Everything. Penguin Books, New York. Toffler, A., 1981. The Third Wave. Van Bommel, K., 2014. 3D Food Printing. TNO. Van Der Linden, D., 2015. 3D Food Printing: Creating Shapes and Textures. TNO, pp. 1e36. Wegrzyn, T.F., Golding, M., Archer, R.H., 2012. Food layered manufacture: a new process for constructing solid foods. Trends in Food Science and Technology 27 (2), 66e72. https:// doi.org/10.1016/j.tifs.2012.04.006. Elsevier Ltd. Yang, J., Wu, L., Liu, J., 2001. Rapid Prototyping and Fabrication Method for 3-D Food Objects. US. Patent. doi: US6280785 B1. Zoran, A., Coelho, M., 2011. Cornucopia: the concept of digital gastronomy. Leonardo 44 (5), 425e431. https://doi.org/10.1162/LEON_a_00243. The MIT Press.

Chapter 12

Safety and Labelling of 3D Printed Food Jasper L. Tran University of Minnesota, San Francisco, United States

Chapter Outline

12.1 Introduction 12.2 3D Printed Food’s Possibilities and Implications 12.2.1 3D Printed Food’s Endless Possibilities 12.2.2 Implications of 3D Printed Food 12.2.2.1 Solving the Food Scarcity Problem 12.2.2.2 Eliminating Malnutrition 12.2.2.3 Reducing Climate Change 12.2.2.4 Eliminating No-LongerNecessary Businesses 12.2.2.5 Solving the Problem of Supplying ‘Food on the Go’ 12.3 3D Printed Food’s Safety and Labelling Issues 12.3.1 Safety Issues 12.3.1.1 Short Term: Food Poisoning

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12.3.1.2 Scenario 1: Food Allergy 12.3.1.3 Scenario 2: Batches of Ingredients Containing Contaminations 12.3.1.4 Long Term: Changes to the Human Body 12.3.2 Labelling Issues 12.3.2.1 Scenario 1: Food Printing the Majority of the Package Food to Sell to the Mass Population 12.3.2.2 Scenario 2: Food Printing a Small Portion of the Package Food to Sell to the Mass Population 12.3.2.3 Scenario 3: Food Printing in Front of the Customers Before Selling

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12.1 INTRODUCTION In recent years, controversies regarding 3D printing have been on the rise, with broad questions raised over its regulation and intellectual property (Tran, 2015a). Yet legal scholars have overlooked the legal issues arising specifically from 3D printed food. This chapter fills that gap as the first to look at the issues surrounding 3D printed food. The 3D printer will soon be another kitchen appliance (Kurutz, 2013; Lemley, 2015). Three-dimensional printers can now print food, ranging from ordinary meals to personalised nutrition and edible growth (i.e., growable food). But with all the new possibilities that food printing presents, it also brings along many new challenges. Two of the major challenges to 3D printed food include safety and labelling. Under the issue of safety, short-term consumption of 3D printed food can cause food poisoning or similar harm, whereas long-term consumption can result in permanent changes within the human body. In the short term, there are two food-poisoning scenarios: (1) one or a few individuals are poisoned from consuming 3D printed food, or (2) a large number of people are poisoned. Furthermore, long-term modification of eating habits could lead to necessarily permanent changes within the human body in order to adapt to a new diet of consuming strictly 3D printed food. Labelling will likely face issues similar to the current genetically modified organism (GMO) labelling debate (Nauheim, 2009). For instance, regardless of whether 3D printed food is safe or not, and assuming consumers cannot easily discern their food’s origin, do consumers have the right to know where their food comes from? Other labelling issues could include imitation food and economic adulteration (i.e., misleading consumers). This chapter fleshes out such labelling issues through four hypothetical scenarios: (1) a big corporation that food prints the majority of the package or the entire food package to sell to the mass population, (2) a big corporation that food prints only a small portion of the packaged food to sell to the mass population, (3) a grocery store that food prints sushi on sight before packaging it and selling to the local community, or (4) an individual who food prints a meal at home.

12.2 3D PRINTED FOOD’S POSSIBILITIES AND IMPLICATIONS 12.2.1 3D Printed Food’s Endless Possibilities To fully raise a cow for meat, ‘you have to feed a cow 20,000 gallons of water and 10,000 pounds of grain in its lifetime. Then there’s the cost

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of slaughtering, shipping and packaging. Our grandkids will say, “that was insane”’ (Federico-O’Murchu, 2014). Instead, imagine the possibility of going to one’s kitchen to have a 3D printer print out a customised burger (Rawstorne, 2013). That will soon be the future, where 3D printed foods are widely available. Three-dimensional printers resemble the Star Trek Replicator e a machine that can constitute any physical matter out of thin air. (In Star Trek, the Replicators originally synthesised meals on demand, but took on other uses in the later series.) Current 3D printers function ‘by setting raw materials into two-dimensional patterns on a platform and gradually raising to stack each layer on top of the next until completion’ (Desai and Magliocca, 2014; Tran, 2015b). Similar to the traditional 2D printers, 3D printers need to follow an electronic blueprint to print, called a computer-aided design file (CAD file). ‘Users can create CAD files by designing them from scratch or scanning an object. [and then] edit and share CAD files with others through the Internet’ (Tran, 2015b). Three-dimensional printers can print out anything, from a lithium-ion microbattery to a human kidney, and can print in materials like ‘extruded or powdered plastic, metal, ceramic, food, cement, wood, and even human cells’ (Sun et al., 2013; Osborn, 2014). Three-dimensional printers can print nearly any type of food (hereinafter, ‘food printing’) imaginable including: (1) food that we currently eat, like fruit, pasta, chocolate, cookies, lollipops and chewing gum; (2) food that is not found in nature, like ‘edible growth’ (i.e., self-contained multiingredient bite-size food with living edible plants growing from them); and (3) personalised nutritional food (Grunewald, 2014; Li et al., 2014; Molitch-Hou, 2014a,b; Sher, 2015). Food printing has advanced so far that it can now treat a renowned chef to a 3D printed 50-course meal (Molitch-Hou, 2014c). Food printing fundamentally changes the way we think about food manufacturing and preparation, as it could eliminate the entire process, from grocery shopping for ingredients to preparing the ingredients and cooking. In the future, an individual could potentially have a readymade meal in an instant. No food manufacturing and preparation means: (1) less labour involved, resulting in cheaper food cost, and (2) food becomes more portable e an individual can now make any kind of food in the comfort of their own home rather than depending on the food manufacturer or restaurants to make a certain type of food. (Of course, any kind of liquid food, for example, juice or soup, might still require preparation, as current 3D printing technology can only print solid food.) At first, people might be hesitant to eat 3D printed food due to their perception that it does not taste as good as traditional food (to distinguish from 3D printed food). After a while, most people would likely become desensitised to the new taste so as to not notice the difference. However, unless the choice of access to traditional food has been completely eliminated, the opposite could also hold true: people might get tired of eating only 3D printed food and revert back to traditional food.

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12.2.2 Implications of 3D Printed Food In addition to endless possibilities of food printing, 3D printed foods bring about many emostly positive e implications, including: (1) solving food scarcity problems, (2) eliminating malnutrition, (3) reducing climate change, (4) eliminating no-longer-necessary businesses, and (5) solving the problem of supplying ‘food on the go’ to astronauts and military personnel. More in-depth details of food printing’s five implications and ramifications are discussed below.

12.2.2.1 Solving the Food Scarcity Problem Soon, the world will face a food scarcity problem (Koba, 2014). The population is growing at an exponential rate, and larger populations need more food to sustain their living (Krier and Gillette, 1985). While the world’s population continues to grow, the available space on Earth remains constant. Unless humans can start living on another planet (as Tesla’s CEO, Elon Musk, is working on this with SpaceX), agriculture and traditional farming will likely take a huge environmental toll on the planet (Davenport, 2015). According to Dr. Jason Clay, Senior Vice President for Market Transformation at the World Wildlife Fund: We have to produce as much food in the next 40 years as we have in the last 8000. . . . By 2050 we’re going to have to produce twice as much food as we do today. We need to find a way to do this more sustainably. The biggest threat to the planet is to continue producing food in a business-as-usual fashion. (Phillips, 2013).

In other words, the world needs a solution to the soon-to-be global food scarcity problem, and tackling such a large-scale problem takes time. Luckily, food printing is showing strong promise, and it could potentially be part of the solution to this global problem. Three-dimensional printing makes it easier and faster to produce food. Eliminating the entire manufacturing process of a variety of foods allows the manufacturing system to focus more on making ingredients. Once the food production process focusses simply on making the food ingredients that go into the 3D food printer, the challenge of making enough to feed the exponentially growing population shifts to the forefront. Yet solving the food scarcity problem is just the most obvious effect of 3D printed food; food printing brings along many more promises.

12.2.2.2 Eliminating Malnutrition At his 2015 State of the Union Address, President Barack Obama discussed the availability of personalised medicine in the near future (Handelsman, 2015). But how about personalised nutritional food? Avi Reichental, CEO of 3D Systems, and others are working on 3D printed ‘personalised nutritional food’, although ‘[i]t may start with simple structures like bars that will include our required daily nutrients and vitamins’. Imagine the day when an individual

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can customise and print each healthy meal in the comfort of their own kitchen without the need for grocery shopping or looking at nutritional labels or logging each of their meals; that day is not too far from now. Individual autonomy in combination with 3D printing nutritious, personalised food menus creates the potential for significant health benefits. This is especially true with the overwhelming prevalence of malnutrition in society today. According to the World Health Organization, malnutrition means ‘undernutrition and overnutrition’ or simply ‘a deficiency of nutrition’. (Blo¨ssner et al., 2005). Malnutrition can result in obesity, stunted growth, decreased energy levels (e.g., anaemia is one form of malnutrition common in women between 15 and 49 years old), weak immune systems and susceptibility to many other diseases (e.g., 1 in 12 adults worldwide have type 2 diabetes). Currently, obesity is one of the most alarming problems related to malnutrition (Gostin, 1995; Diller, 2013; Yang, 2015). The United States is the most obese industrialised country in the world, with an obesity rate of 33.9%, according to the World Health Organization’s most recent data (Kaplin, 2011). This rate is substantially higher as compared to approximately 14% in the mid-1970s (Gorman, 2006). The impacts of such a high rate are dramatic; ‘obesity accounted for 18% of deaths among Black and White Americans between the ages of 40 and 85’, and healthcare spending on obesity currently ‘range[s] from $147 billion to nearly $210 billion per year’ (Danaei, 2009). While obesity is one of the most prevalent issues, malnutrition as a general matter is becoming more prevalent. In 2014, Global Nutrition Report released a warning that the world is crossing a ‘malnutrition red line’, suffering from too much or too little nutrition. Currently, malnutrition leads to ‘11% of GDP being squandered as a result of lives lost, less learning, less earning and days lost to illness’. Malnutrition affects both poor and developed countries, and many countries are struggling to keep the ‘obesity epidemic’ under control (Kaplin, 2011; Kinver, 2014; Yang, 2015). But fear no more, personalised food holds the promise of fixing all malnutrition problems, assuming no access problem (i.e., everybody has access to adequate supplies of personalised food). Long-term investment in researching personalised food can lead to the possibility of providing each person exactly the nutrition they need, with the nice addition of taste being easily customised to fit each person’s desire. That is, each individual would be able to obtain the nutrients they need from 3D printed food. This would curb the increasing obesity rate currently facing the American population. Another solution to the malnutrition problem is to print nutrient-rich food that would meet most individual’s needs, i.e., meet his or her suggested daily value (Phillips, 2013). Additionally, food printing skips the cooking and/or microwaving steps, which reduces human exposure carcinogens from charring and toxic radio waves, respectively, when consuming 3D printed food. Consequently, humans’ consumption would become healthier. In short, food printing can reduce and possibly eliminate malnutrition once and for all.

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12.2.2.3 Reducing Climate Change When everyone begins to 3D print his or her own food, the process of food production will change drastically. Instead of growing different varieties of food, the agriculture sector will shift its focus to producing different ingredients (and there are not that many required to supply 3D food printers). Consequently, agriculture would need to compensate for this change and transform drastically as well. This transformation would result in a very limited human footprint on the planet and would, in effect, reduce climate change (Phillips, 2013). For example, producing enough chicken, beef and pork to feed the current population is taking a significant toll on the planet, as these animals consume large quantities of resources and create substantial amounts of waste. Replacing these major food sources with more sustainable options that require much fewer inputs reduces the environmental impact (Foster, 2013). This transformation, unfortunately, comes with a downside as well. If agricultural practices are completely changed or replaced altogether by food printers, it will cause a dramatic impact on entire ecosystems. For instance, many species adapted to human’s agricultural activities and are heavily dependent on an environment where these activities occur. A change in the current agricultural model would eliminate these dependent species’ usual habits, alter the food chain and, in effect, endanger certain animal species. However, in order to shift to food printing, change is inevitable, and other animals would likely continue to evolve and adapt in the new agricultural model. Fortunately, history indicates that equilibrium will eventually return, and the strong will survive in the new agricultural landscape to supply ingredients for food printing (Darwin, 1864). 12.2.2.4 Eliminating No-Longer-Necessary Businesses Once everyone begins to food print in the comfort of their own home, it removes the need for grocery stores, chefs or associated jobs. (In order for everyone to have the ability to food print at home, presumably each person will have a 3D food printer at his or her home. Once this happens, people will no longer need to go out to buy food or to restaurants if they can print food at home instead. Obviously, stores can still sell products and chefs can still cook, but once the need for them is removed, they would eventually cease to exist. Interestingly, this reduction of labour has nothing to do with robots or artificial intelligence. But the additions of robots and artificial intelligence would further effectuate this reduction of labour.) (Nilsson, 1984). Given the ease of ordering goods online and the finite nature of the ingredients needed for food printing, people can start ordering food printing ingredients in the comfort of their own homes. Once this is the case, grocery stores are no longer needed.

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Eventually, when people can prepare their food easily, the culinary profession, including chefs, could go out of business as well. (Note that eating out is not a necessity, but rather it is something people do as a special activity. When every home and office has a food printer, where people can select which food they want every day, their need [and likely desire] to go out and spend money on prepared food would eventually cease to exist.) During and after the complete transition to a world where every house and office has a 3D printer readily available for food printing uses, going out to eat food cooked by a chef would be a luxury activity for people with extra time and money (Koenig, 2016).

12.2.2.5 Solving the Problem of Supplying ‘Food on the Go’ Food is an everyday need for humans to not only survive but also have enough nutrients and energy to function (Benforado et al., 2004). Some professions require ‘food on the go’, which requires a supply of food for people when they are away from permanent structures that would easily supply food. For instance, astronauts need food to survive in space, and military personnel need food when they are deployed. Additionally, hikers and backpackers need to bring meals and snacks on their trips. Moreover, other recreationalists, families and people who travel frequently for work may also want their food readily available without having to packing heavily. Food printing also solves this ‘food on the go’ problem. To produce food, all an individual needs are food ingredients, a 3D food printer and energy. (These are not difficult for a team to carry. Furthermore, the energy for a 3D printer to be used in space can presumably be powered in the same way as other appliances that are used on a spacecraft.) Astronauts and military personnel would benefit the most from this invention (King et al., 2014). (Of course, food printing would likely face a few problems before being readily available for space use. Current research on battery-powered 3D printers would help the effective implementation of food printers for uses in space. Furthermore, although both astronauts and military personnel have specific needs, what their needs have in common is food supply, which the technology of food printing could solve completely.) Thus, the National Aeronautics and Space Administration and the military are currently investing heavily in food printing (Hall and Dunbar, 2013). The ability to print food on demand would reduce cost, eliminate food waste (by food printing only what a person needs to eat) and provide nutrient-rich food with longer expiration dates than the current 3-year shelf-life of a Meal, Ready-to-Eat (Benson, 2014).

12.3 3D PRINTED FOOD’S SAFETY AND LABELLING ISSUES Once 3D printed food is nicely integrated into the US economy, two major issues will soon face food printing: safety and labelling.

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12.3.1 Safety Issues In terms of safety, 3D printed food would likely raise both short-term and long-term issues. It is natural for people to be wary about such a dramatic change in food production. For instance, one expert in 3D printing, Tim Shinbara from the Association of Manufacturing Technology, echoes these concerns, particularly in terms of 3D printed food: Even if it technically works, should we be doing it? If we start creating food instead of growing or harvesting it e that gets a little scary. At a molecular level, does your body accept something that’s been artificially and genetically manufactured? Even if it looks the same under a microscope, what will it do to you over 10, 20 years? (Federico-O’Murchu, 2014). While the timeline for widespread 3D printed food is unknown, safety concerns like Shinbara’s are already prevalent. Some of these main concerns are discussed below.

12.3.1.1 Short Term: Food Poisoning 3D printed food, though new, is still food after all. Thus, relevant statutes will still apply and presumably govern 3D printed food unless the government implements new statutes in the future that specifically regulate 3D printed food. 21 U.S.C. x 321(f) (2012). Historically, legislation always progressed slower than technologies, so, unsurprisingly, there is currently no statute directly regulating 3D printed food (Tran, 2016). Short-term consumption of 3D printed food could give rise to adulterated food, which is prohibited, and could result in food poisoning issues. 21 U.S.C. x 331 (listing prohibited acts); x 334 (providing for seizure); x 332 (providing for injunctions); x 333(f) (providing for criminal penalties); x 335b (providing for civil penalties). On the regulatory end, adulterated food is typically regulated under food safety inspection, falling under the shared jurisdiction of the US Department of Agriculture and the Food and Drug Administration (FDA) (Goetz, 2010). 21 U.S.C. x 374 (authorising FDA inspections). The relevant statute for adulterated food is the Federal Food, Drug, and Cosmetic Act of 1938, 21 U.S.C. xx 301e92 (2015), which prohibits both the adulteration of food and the sale of adulterated food. 21 U.S.C. x 346 (including a safe harbour for food additives that could otherwise cause a food to be adulterated, but such an analysis would not be relevant to 3D printed food unless FDA provides by regulation a tolerance level for poisonous or deleterious additives that might occur in 3D printed food); 21 U.S.C. x 331(a)e(c). A food is ‘adulterated’ if: (1) ‘it bears or contains any poisonous or deleterious substance which may render it injurious to health’, or (2) ‘it bears or contains any added poisonous or added deleterious substance. that is unsafe’. Food poisoning, excluding food allergies, must necessarily result from either definition (a) or (b), containing ‘poisonous or added deleterious substance’. 21 U.S.C. xx 342(a)(1); 342(a)(2)(A) (2015).

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In the event of food poisoning, the FDA would prosecute the food production companies, and if food poisoning resulted in deaths, the case could become a criminal prosecution. The FDA enjoys complete discretion in deciding whether to prosecute or not; its decision is not subject to judicial review as the statute precludes it. For instance, Heckler v. Chaney stated: ‘The [Federal Food, Drug, and Cosmetic] Act’s enforcement provisions thus commit complete discretion to the Secretary to decide how and when they should be exercised’; 470 U.S. 821, 835 (1985). In any event, there are two possible food poisoning scenarios from the perspective of the victim(s): (1) one or a few individuals are poisoned from consuming 3D printed food, or (2) a large number of people are poisoned. As both scenarios involve liability for different actors, each is discussed in detail below.

12.3.1.2 Scenario 1: Food Allergy Scenario 1 covers the situation when one or only a few individuals were poisoned from consuming 3D printed food. Scenario 1 is very unlikely and would only happen in the case of specific individual’s food allergy. The FDA currently enforces food allergy issues by requiring the disclosure of major food allergens on labels or labelling, with the failure to do so enforceable as a misbranded article, rather than an adulterated article. Food Allergen Labelling and Consumer Protection Act of 2004, Pub. L. 108-282, 118 Stat. 905 (2004) (codified principally at 21 U.S.C. x 343[w]). Current law only requires labelling or disclosure of eight major food allergens (milk, egg, fish, shellfish, tree nuts, wheat, peanuts, soybeans). In the case of an allergy from 3D printing ingredients, labelling of all traces of ingredients should be mandated to shift the responsibility to each individual consumer. This way, other parties involved in the food printing process could disclaim liability. (That is because government agencies enjoy total discretion in deciding to prosecute cases of food poisoning, thus are immune from liability.) Each individual is presumably responsible for selectively not consuming food to which they are allergic. Once all the ingredients are clearly labelled, allergic reactions can be prevented. In the event of mislabelling that results in food poisoning from allergies, the party responsible for the mislabelling would take the blame for the damages stemming from food poisoning, as the damages were foreseeable. 12.3.1.3 Scenario 2: Batches of Ingredients Containing Contaminations Scenario 2 occurs when one or more batches of food printing ingredients contain contaminated substances. Scenario 2 is the more likely occurrence of the two scenarios. In the event this happens, the parties responsible for the

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contamination bear the liability. If the parties lack incentive to do a nationwide recall e for example, to avoid reputational harm to the corporation’s business e the government should intervene and mandate a recall of the ingredients containing poisonous or deleterious substances. (FDA’s authority to issue a recall is broad.). 21 U.S.C. x 350l. There are only a few parties involved in the food printing process: the food printer manufacturer, the ingredient manufacturer e which could be one or more parties e and the shipping company or retailer that sold the food printer/ ingredients to each individual. Given the limited number of players in the food printing process, the chance of food poisoning decreases with fewer parties, meaning fewer chances for error. Depending on if the contamination occurs either early or late in the process, the number of food poisoning cases would likely be either very large or very small, respectively. Based on the specifics of the food printing process, health insurance could easily handle food poisoning in the event of either a small or a large number of food poisoning cases. For instance, Hot Stuff Foods, LLC v. Houston Casualty Co. denied coverage under an ‘Accidental Product Contamination’ policy for a food company’s voluntary recall due to mislabelling that did not pose a public health hazard but noting arguendo a recall that did pose a public health hazard would be covered. 771 F.3d 1071, 1075e76 (8th c.2014). However, a recall protocol must be in place or significant class action product liability lawsuits against the responsible party (i.e., food printer manufacturer or ingredients manufacturer) are possible. In the event it is impossible to identify the party responsible for the contamination, strict liability can apply to the makers, either the food printer manufacturer or ingredients manufacturer or the retailer e all of which are product providers, not service providers e via res ipsa loquitur. (The doctrine of res ipsa loquitur is generally applied in situations where negligence clearly occurred, and (1) the defendant had exclusive control of the instrumentality during the relevant time, and (2) the plaintiff shows that he was not responsible for the injury. The court is not required to infer negligence and a presumption is not created; res ipsa loquitur merely permits the fact finder to infer negligence from the facts. RESTATEMENT [SECOND] OF TORTS x 328D [1965].) Thus, the defendants would be jointly and severally liable to the poisoned plaintiff(s), as the manufacturers, rather than the victim(s), should bear the burden of apportionment in terms of blame and compensation.

12.3.1.4 Long Term: Changes to the Human Body There is a high possibility that long-term modification of eating habits to strictly consuming 3D printed food could result in permanent changes to the human body. The interesting question becomes: Who is responsible for this change? If the change is ‘good’ e for example, the human body readily

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accepts 3D printed food and, over time, rejects traditional food because of human’s adaptation and evolution process e there is no harm done (Darwin, 1864). However, if the change is ‘bad’ e for instance, the human body rejects all 3D printed food e there is a legal safety issue. (Of course, ‘good’ or ‘bad’ here are subjective, as some might argue that it is actually not ‘good’ if the human body rejects traditional food because, for instance, ingredients for 3D printed food may become scarce.) Given the relative novelty of 3D printed food, there have not been any long-term, well-controlled population studies of the food printing industry. Without such a study, it is hard to make a legal conclusion. (Note that the absence of evidence does not imply a lack of consequences; it merely means that no conclusion can yet be drawn.) Currently, no foreseeable legal issues with long-term consumption of 3D printed food exist, at least not yet. Although no one knows the answer without anecdotal evidence, preventative measures and a well-defined compensation scheme for the injured victims e in the event that only some, not all, people who have consumed 3D printed food develop health complications e are needed. But assuming there is a problem with modification of eating habits e for instance, if everyone who has consumed 3D printed food developed cancer e then similar guidance as above could apply (i.e., holding the responsible parties strictly liable), which in this case is likely the ingredients’ manufacturer. Otherwise, to prove negligence, the causation element would be impossible to prove, given a long time has passed, and many variables (in addition to the long-term dietary adaption of consuming only 3D printed food) could cause the change. For instance, Univ. of Texas Sw. Med. Ctr. v. Nassar states: ‘In the usual course, this standard requires the plaintiff to show “that the harm would not have occurred” in the absence ofdthat is, but fordthe defendant’s conduct’. Because of the lack of research in this area e besides the legal issues discussed in the preceding paragraphs e many of the potential legal issues in terms of the safety of consuming 3D printed food are still unclear.

12.3.2 Labelling Issues The more interesting legal issue comes from the labelling aspect of selling 3D printed food. This issue would likely end up before the US Supreme Court if government agencies like the FDA do not have clear guidelines for labelling 3D printed food. For instance, in POM Wonderful LLC v. Coca-Cola Co., a recent case about whether the name, label, marketing and advertising of CocaCola’s juice blend misled consumers as to its actual content, the Supreme Court held that a statutory private right of action under the Lanham Act is not precluded by regulatory provisions of the Food, Drug, and Cosmetic Act. 134 S. Ct. 2228, 2241 (2014).

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Three-dimensional printed food will likely face the same labelling challenges as GMO food. GMO food faces the same problem as food printing with respect to unknown long-term effects (Endres, 2000). As a result, people are scared of consuming GMO food and demand clear labelling, arguing for the right to know (Nauheim, 2009). Although people might be sceptical of consuming 3D printed food at first, once it is proven safe and is an appealing (i.e., tasty) food alternative, it might be the future of our food supply. Assuming current law applies to 3D printed food, two current provisions of the Federal Food, Drug, and Cosmetic Act of 1938 favour clear labelling. First, 3D printed food could qualify as imitation food. 21 U.S.C. x 343(c) (2015) (on imitation [misbranded] food). For instance, in the case of processed apple juice versus real apple juice, processed apple juice must be labelled ‘concentrated’, which itself is an imitation of freshly squeezed apple juice. Labelling otherwise would be misleading. Second, there might also be an issue of economic adulteration (i.e., food fraud) for 3D printed food. 21 U.S.C. x 342(b) (2015) (on economic adulteration). When real food would likely cost more to produce than 3D printed food, selling 3D printed food without clear labelling would be cheating the consumers of their money if both naturally produced food and 3D printed food are sold at the same price. This analysis is more applicable to cases where a large portion of (or a majority of) the packaged food was 3D printed. For instance, without clear labelling, consumers who presumably cannot tell the difference between real food and 3D printed food e by taste or sight e might initially think they were purchasing real food when in fact what they got was 3D printed food. On the other hand, this analysis is less applicable to the cases where only traces of 3D printed food (as ingredients) were used to prepare food. (This view presumes that consumers accept traces of 3D printed food [as ingredients] in their food overall; thus, clear labelling is not required. Obviously, those who called themselves ‘purists’ would have a problem with this.) The labelling requirement based on the current law will be demonstrated through four hypothetical scenarios. Note that the labelling issue is only relevant during the transition time from a society with no 3D printed food to one with exclusively 3D printed food. The point of being able to food print is that eventually the world resembles Scenario 4, where everyone can simply food print a meal at home without buying any packaged food from the grocery store. But until then, the labelling issue is relevant in the transition period where Scenarios 1e4 are applicable. All scenarios assume that 3D printed food is not recognizable to the average individual who cannot discern from its appearance that the food was 3D printed. If 3D printed food were obvious from its looks, there would be no need for labelling and the call for labelling 3D printed food would be moot. Even if the 3D printed food was only obvious to some people but not others, labelling would still be an issue.

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12.3.2.1 Scenario 1: Food Printing the Majority of the Package Food to Sell to the Mass Population Scenario 1 covers the situation when a big corporation food prints the majority of the package or the entire food package to sell to the mass population. This scenario is a strong case for labelling, given the majority (or the entire amount) of food was food printed. A similar argument for the consumers in the GMO debate applies here: the consumers have the right to know what type of food they are eating (Nauheim, 2009). 12.3.2.2 Scenario 2: Food Printing a Small Portion of the Package Food to Sell to the Mass Population Scenario 2 covers the situation when a big corporation food prints only a small portion of the packaged food to sell to the mass population. This is a weaker case for labelling, as the results can go either way, depending on the proportion of 3D printed food in each package. If the amount of 3D printed food were too small, say, less than 1%, labelling would not be necessary. But if the amount of 3D printed food was larger but not large enough to be considered the majority under Scenario 1 (i.e., 30% labelling), labelling is warranted. In short, a certain threshold would need to be set as the labelling cut-off. This is similar to labelling trans fat in food nutritional value, where less than 0.5 g of trans fat needs not be labelled (i.e., leaving trans fat value at 0%). 21 C.F.R. x 101.9(c)(2) (2015). However, traces of 3D printed food (less than 1%) could still scare ‘purists’, i.e., those who prefer to consume wholly natural food (Thierer, 2013). Ethically, labelling is still needed for these health-conscious people, a similar requirement in the ongoing ‘organic’ versus ‘regular’ food debate (Czarnezki, 2011). (The debate is similar because, for example, (1) some people are allergic to even just a trace amount of ingredients that can cause them allergy, such as gluten; and (2) people should feel safe with the food they consume, not scared of unknown ingredients they might not know about.) Furthermore, as discussed above, to avoid liability for causing allergic reactions in some people, best practice would be to label all 3D printed food as ‘3D printed’ and shift the responsibility to the consumers to determine what food to put in their bodies. Thus, when in doubt, it is better to label as ‘3D printed’. 12.3.2.3 Scenario 3: Food Printing in Front of the Customers Before Selling Scenario 3 covers the situation where, for example, a grocery store food prints sushi on sight before packaging it and selling to the local community. This is a weaker case than Scenario 2, where some of the consumers saw the food was 3D printed, and the rest of the consumers know e from common knowledge e that the food was 3D printed. However, a small amount of customers might not

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know that the food was 3D printed if it was their first time trying the food, or they bought the food after business hours when the food printing was over. This case is a toss-up, with arguments leaning strongly to the side of no labelling. The customers with actual knowledge of seeing the food printing process would not need any labelling, as they would already be on notice. However, the customers without actual knowledge would arguably want labelling. Given how the scenario portrays how the food printing process is done in front of most customers, Scenario 3, on balance, favours no labelling.

12.3.2.4 Scenario 4: Food Printing a Meal at Home Scenario 4 covers a situation where an individual food prints a meal at home. This is a clear case for no labelling because the individual did not even buy packaged food; thus, there is no package to label.

12.4 CONCLUSION At the 2016 Minnesota Journal of Law, Science & Technology symposium, the keynote speaker, Candice Ciresi, described the 3D printing of food as ‘a first world problem, not a third world solution’. This characterisation notes that the current food printing technology is using food-based e not chemical e materials to assemble food products in novel shapes rather than generating new food as a potential solution for solving famines or food scarcity. However, she also mentioned that scientists are working on the possibility of creating food from chemical compounds, which could enable food printing to generate new food where scarcity exists, thus serving as a potential ‘third world solution’. (Ciresi, 2016). This chapter discusses both the first-world legal problems that will arise during attempts to commercialise 3D printed food and also looks to the future when 3D printed food may become part of a third-world solution. This chapter analysed these first-world legal issues by starting with the premise that the 3D printer may become the fundamental daily appliance in every household, where people can food print and customise each meal in the comfort of their own homes. Safety issues will require legal professionals to creatively adapt existing FDA regulations over food safety and food allergens to a world where food manufacturers and food consumers are one in the same. Labelling issues are currently in flux, and lawyers should watch the litigation over GMO foods to understand how the courts will consider freedom to label and freedom from labelling issues surrounding 3D printed food. Although these two big legal issues will soon face the food printing technology e and are the primary focus of this chapter e they are not the only issues associated with 3D printed food. Other issues will likely include, but are not limited to, intellectual property, policy and ethics that will arise as 3D printed food rolls out in larger commercial settings.

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REFERENCES Benforado, A., et al., 2004. Broken scales: obesity and justice in America. Emory Law Journal 53, 1645. Benson, J., JulyeAugust 2014. Chow from a 3-D Printer? Natick researchers are working on it. Army Tech 2, 22. www.dodmantech.com/ManTechPrograms/Files/Army/Army_Technology_ Mag_3D_Printing.pdf. Blo¨ssner, M., et al., 2005. World Health Org., Envtl. Burden of Disease Series, No. 12, Malnutrition: Quantifying the Health Impact at National and Local Levels 1. www.who.int/ quantifying_ehimpacts/publications/MalnutritionEBD12.pdf. Ciresi, C., March 4, 2016. Former General Counsel, Stratasys, Keynote Address at the University of Minnesota Law School Journal of Law, Science & Technology Symposium: Disruptive Innovation: Legal Concerns in 3D Printing. Video available at: www.youtube.com/watch? v¼znAhzZxwDwk. Czarnezki, J.J., 2011. The future of food eco-labeling: organic, carbon footprint, and environmental life-cycle analysis. Stanford Environmental Law Journal 30, 3. Danaei, G., et al., April 28, 2009. The preventable causes of death in the United States: comparative risk assessment of dietary, lifestyle, and metabolic risk factors. PLoS Medicine 6 (4). http://journals.plos.org/plosmedicine/article?id¼10.1371/journal.pmed.1000058. Darwin, C., 1864. The Origin of Species. Davenport, C., December 21, 2015. Elon Musk’s SpaceX returns to flight and pulls off dramatic, historic landing. The Washington Post. www.washingtonpost.com/news/the-switch/wp/2015/ 12/21/elon-musks-spacex-pulls-off-dramatic-historic-landing/. Desai, D.R., Magliocca, G.N., 2014. Patents, meet napster: 3D printing and the digitization of things. Geological Journal 102, 1691. Diller, P.A., 2013. Combating obesity with a right to nutrition. Geological Journal 101, 969. Endres, B.A., 2000. “GMO:” genetically modified organism or gigantic monetary obligation? The liability schemes for GMO damage in the United States and the European Union. Loyola of Los Angeles International and Comparative Law Review 22, 453. Federico-O’Murchu, L., May 11, 2014. How 3-D Printing Will Radically Change the World. CNBC. www.cnbc.com/id/101638702#. Foster, T., November 18, 2013. Can artificial meat save the world. Popular Science. www.popsci. com/article/science/can-artificial-meat-save-world. Goetz, G., December 16, 2010. Who Inspects What? A Food Safety Scramble. Food Safety News. www.foodsafetynews.com/2010/12/who-inspects-what-a-food-safety-scramble/#.Vnw0YhorJZ0. Gorman, L., 2006. Economic explanations of increased obesity. The National Bureau of Economic Research. www.nber.org/digest/apr06/w11584.html. Gostin, L.O., 1995. The resurgent tuberculosis epidemic in the era of AIDS: reflections on public health, law, and society. Maryland Law Review 54, 1. Grunewald, S.J., October 11, 2014. Edible Growth Puts the Fun in 3D Printed Fungus Food. 3D Printing Industry. http://3dprintingindustry.com/2014/10/11/edible-growth-puts-fun-3dprinted-fungus-food. Hall, L., Dunbar, B., July 28, 2013. 3D Printing: Food in Space. NASA. www.nasa.gov/ directorates/spacetech/home/feature_3d_food.html. Handelsman, J., January 21, 2015. Precision Medicine: Improving Health and Treating Disease. White House Blog. www.whitehouse.gov/blog/2015/01/21/precision-medicine-improvinghealth-and-treating-disease.

370 Fundamentals of 3D Food Printing and Applications Kaplin, L., 2011. A national strategy to combat the childhood obesity epidemic. UC Davis Journal of Juvenile Law and Policy 15, 345. King, D.L., et al., 2014. Mobile open-source solar-powered 3-d printers for distributed manufacturing in off-grid communities. Challenges in Sustainability 2, 18. Kinver, M., November 13, 2014. World is crossing malnutrition red line, Report warns. BBC News. www.bbc.com/news/science-environment-30005268. Koba, M., October 15, 2014. World May Not Have Enough Food by 2050: Report. CNBC. www. cnbc.com/2014/10/15/world-may-not-have-enough-food-to-eat-by-2050-report.html. Koenig, N., March 1, 2016. How 3D printing is shaking up high end dining. BCC News. www.bbc. com/news/business-35631265. Krier, J.E., Gillette, C.P., 1985. The un-easy case for technological optimism. Michigan Law Review 84, 405. Kurutz, S., February 20, 2013. A factory on your kitchen counter. The New York Times. www. nytimes.com/2013/02/21/garden/the-3-d-printer-may-be-the-home-appliance-of-the-future. html. Lemley, M.A., 2015. IP in a world without scarcity. New York University Law Review 90, 460. Li, P., et al., 2014. Intellectual property and 3D printing: a case study on 3D chocolate printing. Journal of Intellectual Property Law 9, 322. Molitch-Hou, M., May 27, 2014a. The 3D Fruit Printer and the Raspberry that Tasted like a Strawberry. 3D Printing Industry. http://3dprintingindustry.com/2014/05/27/3d-fruit-printerraspberry-tasted-like-strawberry/. Molitch-Hou, M., August 22, 2014b. Barilla Launches 3D Printed Pasta Contest with Thingarage. 3D Printing Industry. http://3dprintingindustry.com/2014/08/22/barilla-launches-3d-printedpasta-contest-thingarage/. Molitch-Hou, M., August 25, 2014c. 3D Systems Treats Renowned Chef to 3D Printed Absinthe Treat in 50 Course Modernist Meal. 3D Printing Industry. http://3dprintingindustry.com/2014/ 08/25/3d-systems-treats-renowned-chef-3d-printed-absinthe-treat-50-course-modernist-meal/. Nauheim, D.A., 2009. Comment, food labeling and the consumer’s right to know: give the people what they want. Liberty University Law Review 4, 97. Nilsson, N.J., 1984. Artificial intelligence, employment and income. AI Magazine. Summer. Osborn, L.S., 2014. Of PhDs, pirates and the public: three-dimensional printing technology and the arts. Texas A&M Law Review 1, 811. Phillips, A., October 9, 2013. What Does 3D Printing Have to Do with Food Scarcity and Climate Change? Think Progress. http://thinkprogress.org/climate/2013/10/09/2757331/3d-printingfood/. Rawstorne, T., December 27, 2013. The Future of Cooking? PRINT Your Dinner: Don’t Scoff But Now 3D Printers Can Make Food. Daily Mail. www.dailymail.co.uk/sciencetech/article2530195/The-future-cooking-PRINT-dinner-Dont-scoff-3D-printers-make-food.html. Sher, D., February 13, 2015. Don’t Burst My Bubble: 3D Printed Chewing Gum Is Coming. 3D Printing Industry. http://3dprintingindustry.com/2015/02/13/dont-burst-bubble-3d-printedchewing-gum-coming/. Sun, K., et al., 2013. 3D printing of interdigitated Li-ion microbattery architectures. Advanced Materials 25, 4539. Thierer, A., 2013. Technopanics, threat inflation, and the danger of an information technology precautionary principle. Minnesota Journal of Law, Science and Technology 14, 309. Tran, J.L., 2015a. The law and 3D printing. The John Marshall Journal of Information Technology and Privacy Law 31, 505.

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Tran, J.L., 2015b. To bioprint or not to bioprint. The North Carolina Journal of Law and Technology 17, 123. Tran, J.L., 2016. Press clause and 3D printing. Northwestern Journal of Technology and Intellectual Property 14, 75. Yang, J., September 16, 2015. Malnutrition Not Just a Problem Affecting Poor Countries, Report Shows. Star. www.thestar.com/news/world/2015/09/16/malnutrition-not-just-a-problem-affectingpoor-countries-report-shows.html.

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Chapter 13

Future Outlook of 3D Food Printing Sangeeta Prakash1, Bhesh R. Bhandari1, Fernanda C. Godoi2, Min Zhang3 1

School of Agriculture and Food Sciences, The University of Queensland, Brisbane, QLD, Australia; 2Tessenderlo Innovation Center e Tessenderlo Group, Tessenderlo, Belgium; 3 State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, China

Chapter Outline

13.1 Introduction 13.2 Future of 3D Printing 13.2.1 Constructs with Varying Microstructure Leading to Novel Food Textures 13.2.2 Improved TextureModified Food for People with Swallowing and Chewing Difficulties 13.2.3 Increased Fruit and Vegetable Intake Among Children

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13.2.4 Healthy Foods With Reduced Fat, Sugar and Salt 13.2.5 Preventing Wastage of Perishables and Sustainability 13.3 What to Expect in the Next 5 Years? References

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13.1 INTRODUCTION Three-dimensional (3D) food printing is the technology of the future, capable of presenting creative, unique and intricate food items in an attractive format. The 3D food printer is potentially a print-and-eat technology for the future generations. Food technologists have just embraced 3D printing technology since 2006, when the first food printer was developed at Cornell University by Professor Hod Lipson (Lipton et al., 2015). Within a short span, researchers worldwide have printed a variety of foods using a range of 3D printers available to them or in-house built printers. This book compiles the developments in the area of 3D food printing in the last few years. Fundamentals of 3D Food Printing and Applications. https://doi.org/10.1016/B978-0-12-814564-7.00013-4 Copyright © 2019 Elsevier Inc. All rights reserved.

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Three-dimensional printing is based on the additive manufacturing (AM) process, which consists of a layer-by-layer deposition with predetermined thickness to create complex freeform structures. There are different 3D printing technologies that can be used based on the food types, e.g., inkjet printer for low-viscosity pizza sauce, while extrusion-based printing is more suited for soft materials such as cheese and chocolate. There are also other 3D printers based on laser sintering and binder jetting technology. However, the extrusion technique, based on fused deposition modelling, is the most suited for 3D food printing due to the semisolid nature of most food materials. To achieve a high-quality 3D printed food, it is important for food researchers to understand the properties and composition of food materials. The main basics to achieve 3D food printing are: 1. flowability of the food materials while extruding through the nozzle; and 2. holding structure to maintain shape during and after printing process. Fig. 13.1 presents the various rheological, physicochemical, structural and mechanical characteristics of the food material that aid in 3D food printability (Godoi et al., 2016).

13.2 FUTURE OF 3D PRINTING It’s a very exciting time for AM food that provides a platform to experience food in a whole new way. There are many advantages of 3D food printing in creating new textures and consistent soft-textured food for elderly and dysphagia patients, promoting consumption of fruits and vegetables among

FIGURE 13.1 Materials’ properties and factors to consider for the rational design of 3D food structures. Adapted from Godoi, F.C., Prakash, S., Bhandari, B.R., 2016. 3d printing technologies applied for food design: status and prospects. Journal of Food Engineering 179, 44e54.

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kids and also solving some problems we are currently facing, like lifestylerelated diseases and to reduce food wastages, etc. The next few years will see a rise in the use of AM in food, and some of the potential areas of development are discussed below.

13.2.1 Constructs with Varying Microstructure Leading to Novel Food Textures In other manufacturing sectors, 3D printing is mainly used for prototyping. However, with food, 3D printing gives the freedom to construct various food structures. The layer-by-layer 3D printing technique has the ability to change the internal structure of printed objects by varying infill patterns and infill percentages in order to control the density of the raw materials to fabricate freeform geometries with variable textural properties. Fig. 13.2 presents the cross-section and longitudinal-section micrographs of mashed potatoes printed with 100% and 70% infill percentages, respectively, and the mould or cast sample of mashed potato which shows a uniform internal structure for the cast sample. In comparison, an obvious layered (longitudinal section) and porous structure was obtained with 3D printed samples regardless of infill levels. Interestingly, 3D printed samples, even at 100% infill, were significantly less hard (Fig. 13.3) compared to cast samples due to an internal structure created by layer-by-layer deposition (Liu et al., 2018).

13.2.2 Improved Texture-Modified Food for People with Swallowing and Chewing Difficulties Dysphagia, or swallowing disorders, is a medical condition where patients experience difficulty or discomfort chewing and swallowing the food. There are various texture-modified foods available in the market that are soft and easy to swallow, like thickened drinks, smooth pureed fruit/vegetable meals and soft bite-sized moist food. Providing patients with the right-consistency food is critical, as otherwise it could put patients at greater risk of choking and aspiration. However, often the texture-modified foods are less appealing in appearance, texture and taste; hence they are poorly consumed. Threedimensional printed food has the ability to address some of the challenges associated with dysphagia. Three-dimensional printing technology that uses a software to digitally extrude material in a layering pattern can potentially improve the visual appeal, supplement essential nutrients in between layers, create novel soft texture and, most importantly, maintain the consistency that is critical for the patient. This will ensure patients look forward to their mealtimes, ensuring proper nutrition and better quality of life (Fig. 13.4). In a European Union project which is headed by a food company in Germany, some aged care facilities have positively rated the 3D printing technology that prints purees vegetables like carrots and broccoli into their

376 Fundamentals of 3D Food Printing and Applications FIGURE 13.2 Microstructure of mashed potatoes made using a mould and samples printed at 100% and 70% infill viewed from cross-sectional directions at magnification 300 times; longitudinal section: magnification 160 times. Red lines (grey lines in print version) mean the observed layered structure. Adapted from Liu, Z., Bhandari, B., Prakash, S., Zhang, M., 2018. Creation of internal structure of mashed potato construct by 3D printing and its textural properties. Food Research International 111, 534e543.

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FIGURE 13.3 Texture difference between different infill levels of 3D printed samples and mould sample. Means with different subscript within the same series are significantly different (p < .05).

FIGURE 13.4 3D printing of puree meat with (A) and without glycerol filling (B) as a potential food for elderly and patients with dysphagia. Adapted from Zawada, B., Ukpai, G., Powell-Palm, M.J., Rubinsky, B., 2018. Multi-layer cryolithography for additive manufacturing. https://doi-org. ezproxy.library.uq.edu.au/10.1007/s40964-018-0045-3. Progress in Additive Manufacturing.

original shape with similar nutritional profile and a soft, moist and easy-tochew form. The report also project that 3D printed beef burgers could be sold in supermarkets in the Netherlands by the year 2020 (http://www.3ders.org/ articles/20151026-eu-develops-performance-3d-printed-food-for-elderly-andpatients-with-dysphagia.html).

13.2.3 Increased Fruit and Vegetable Intake Among Children Children are often fussy about eating fruits and vegetables, and pick the colour, taste, texture and shape of the food. Fruits and vegetables are essential for growing children, as these foods provide them with energy, vitamins, antioxidants, fibre and other essential nutrients. Three-dimensional printing has the ability to create novel texturised foods printed from horticulture ingredients, entrapping other additional components (not present in fruits and

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FIGURE 13.5 3D printed foods in attractive format that will appeal to children. Adapted from Sun, J., Zhou, W., Yan, L., Huang, D., Lin, L.Y., 2018. Extrusion-based food printing for digitalised food design and nutrition control. Journal of Food Engineering 220, 1e11.

vegetables) between layers and presenting attractive, kid-friendly shapes that will ensure increased fruit and vegetable intake by children (Fig. 13.5).

13.2.4 Healthy Foods With Reduced Fat, Sugar and Salt Cutting down fat, sugar and salt from the diet and the associated health benefits is quite well known. Three-dimensional food printing is capable of making a significant contribution toward healthy food manufacturing. The technology will allow localised use of ingredients in between layers (Fig. 13.6A) without having to mix them with the whole raw material, thereby reducing the amounts of salt, sugar and fat, as is the current practice. The location of the ingredients in the layered pattern of food will be such that consumers perceive it in the first bite (Fig. 13.6B) that lingers as the oral processing continues. Fat is a key ingredient in many foods. Lipid oxidation causes deteriorative changes in chemical, sensory and nutritional food properties. AM will not only cut down the amount of fat, but also prevent its oxidation, as the fat is hidden in between the layers of printed food with no exposure to light or air. Three-

FIGURE 13.6 (A) Transparent view of a 3D printed cookie with a layer of localised sugar/salt/fat entrapped between the top and bottom layers. (B) First bite of the cookie, transparent view.

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dimensional printing technology also opens up the possibility of incorporating functional ingredients that are more susceptible to oxidation. Another example of entrapping localised ingredients is the use of the faster-dissolving pyramid-shaped salt crystals developed by Cargill, providing a greater rush of salty taste (https://www.forbes.com/sites/nadiaarumugam/ 2011/07/28/tasty-ways-manufacturers-can-reduce-salt-but-keep-the-flavor/ #1fb2005e4602). The pyramid-shaped crystals claim to reduce the amount of salt used in products, and when used in 3D printed food as a localised ingredient in between the layers, they will further reduce the amount of salt to be used. The technology will also allow the use of seaweed (proven to be an effective salt replacer) that can be entrapped in between layers of printed food, thereby avoiding oxidation of the seaweeds. Traditional sweets are very popular in Middle East, India and other countries. The sweet manufacturing process in these countries is very labour intense and yields different results with each batch. Sugar that is used in making sweets is a unique 3D material in the sense that it can be used as a 3D printing ink and to build innovative structures without requiring any support from any other ingredient. The melting and crystallising property of sugar together with proper control of crystal particle size (for the crystalline form of sugar), temperature, nozzle diameter and speed will allow 3D printing of sweets with unique texture through fused deposition modelling. In terms of unique texture, the amorphous sugar regions tend to be more mobile and flexible, giving the sweet increased ability to stretch while the crystalline regions impart greater strength and density. Every year in the Middle East, tonnes of date palm fruit go to waste despite being used quite a lot to make many delicacies, including sweets. Date palm fruit has enormous potential for use as food ingredient for printing valueadded product foods. The 3D printing technology provides ample scope toward utilisation of the date palm fruit with other functional ingredients, the natural sugar in the fruit acting as an aid for 3D printing. The challenge will be to experiment with various ingredients that are able to form a printable ink with the sticky date palm fruit. This will allow efficient and effective date palm fruit waste management. Three-dimensional food printing has the potential to cut down the excess fat and sugar used in the dairy-based sweets commonly consumed in South Asian countries, and it will help reduce diseases like diabetes, cardiovascular diseases, obesity etc., that are associated with excess fat/sugar consumption and are on the rise.

13.2.5 Preventing Wastage of Perishables and Sustainability Three-dimensional printing technology has the capacity to reduce food waste by utilising low-value food products such as meat off-cuts, distorted fruits and vegetables and fish and seafood by-products which would otherwise be discarded. The perishables can be processed and converted into forms that can be used for printing at a later stage.

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There is a growing interest in the use of renewable food sources such as insects, algae, duckweed, grass, lupine seeds and beet leaves to construct foods that are sensorially acceptable to consumers. The consumption of the algae and insects is a sustainable and nutritious source of ingredients that can be made more appealing through 3D printing.

13.3 WHAT TO EXPECT IN THE NEXT 5 YEARS? The last few years saw a rapid rise in research related to 3D printing of food, and it is expected that this trend will continue in the coming 5e10 years with greater integration between professional 3D printers, novel food materials, designing and 3D printing processes. The world’s population will hit 9.8 billion by 2050 (United Nations, 2017). The increasing global population, climate change, shortage of water and food waste pose a serious threat to food security. There is a growing concern as to how to feed the extra mouths, and 3D food printing could be the key future food creator. The technology prevents food wastage by utilising perishable fruits and vegetables and low-value byproducts such as meat off-cuts (which traditionally goes to waste) to create palatable, wholesome food products. In fact, it is predicted that in the future, 3D bioprinting will print seafood and meat from cells with comparable taste and texture to the real thing, which will help eliminate the world food crisis without animal cruelty, wasting water or emitting carbon into the environment, thereby saving the environment. There will be a rise in research related to using layer-by-layer printing for customising food with low salt, fat and sugar that ensures less lifestyle-related diseases. The technology has the ability to serve personalised food and control the potion size but, in combination with nutrigenomics, can potentially create meals based on an individual’s genetic information. Food will normally need to be processed postprinting to improve nutritional property, taste and safety. The retention of the shape and structure during the stages of further processing, such as freezing, thermal treatment or radiation, are also important subjects of research and development. The design of the food prior to printing can consider all these possibilities. In other disciplines of AM, expected postprinting changes of materials are contemplated as 4D printing when the 3D construct is not actually a final product. Despite many advantages offered by 3D food printing technology, the industry faces a number of challenges e both from technological and social perspectives. From a technological perspective, 3D printing requires scaling up with increased speed that would get the attention of the food industry. Further, depending on the food being printed, precise control of temperature at the feeding system, the hopper, the nozzle (single or multiple) and the platform of the 3D printer system may be necessitated. Microbial stability and food safety will also need to be addressed during printing of foods.

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REFERENCES 3ders. EU Develops PERFORMANCE 3D Printed Food for Elderly and Patients with Dysphagia. http://www.3ders.org/articles/20151026-eu-develops-performance-3d-printed-food-for-elderly-andpatients-with-dysphagia.html. Arumugam, N., 2011. Tasty Ways Manufacturers Can Reduce Salt but Keep the Flavor. https:// www.forbes.com/sites/nadiaarumugam/2011/07/28/tasty-ways-manufacturers-can-reduce-saltbut-keep-the-flavor/#1fb2005e4602. Godoi, F.C., Prakash, S., Bhandari, B.R., 2016. 3d printing technologies applied for food design: status and prospects. Journal of Food Engineering 179, 44e54. Lipton, J.I., Cutler, M., Nigl, F., Cohen, D., Lipson, H., 2015. Additive manufacturing for the food industry. Trends in Food Science and Technology 43 (1), 114e123. Liu, Z., Bhandari, B., Prakash, S., Zhang, M., 2018. Creation of internal structure of mashed potato construct by 3D printing and its textural properties. Food Research International 111, 534e543. Sun, J., Zhou, W., Yan, L., Huang, D., Lin, L.Y., 2018. Extrusion-based food printing for digitalized food design and nutrition control. Journal of Food Engineering 220, 1e11. United Nations, 2017. World population projected to reach 9.8 billion in 2050, and 11.2 billion in 2100. Zawada, B., Ukpai, G., Powell-Palm, M.J., Rubinsky, B., 2018. Multi-layer cryolithography for additive manufacturing. Progress in Additive Manufacturing. https://doi-org.ezproxy.library. uq.edu.au/10.1007/s40964-018-0045-3.

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Index Note: ‘Page numbers followed by “f ” indicate figures, “t” indicate tables.’

A N-Acetylglucosamine, 110 Acid-induced gelation, 183 Adaptive extrusion layer thickness optimisation compression layer thickness optimisation data comparison, 233, 233t extruded layer thickness optimisation calculation, 231e232 experiment, 232e233, 232f slice model diagram, 230e231, 231f step effect, 230, 231f Additive layer manufacturing (ALM), 219e221 Additive manufacturing (AM) process, 41e42, 93e94, 95f, 258, 274, 374 for food products, 280 powder-based, 278 Additives to enhance viscosity, effects of, 271e272 Agglomeration techniques, 259e260, 263e264, 263f fluid bed, 269 food powder, 277 Air pressure-based extrusion, 24e25 Antibrowning agents, 130 Anti-oxidant activity, 140 Aqueous-based inks, 269 Artificial cocoa butter, 217 AutoCAD, 59 Autodesk, 54e55

B Bilayer tablets, 179 Binder jetting printing, 32e34, 257e260, 292, 293te294t application and outlook for food materials, 278e283 companies and devices, 292e294, 293t controls and considerations during and postprinting, 274e278 in food creation, 33e34

formulating functional printing ink, 267e274 materials’ properties on, 33, 35 postprocessing, 278 powder binding mechanisms, 262e265 powder characteristics and interlayer cohesion, 260e262 suggested analysis, 265e266 Blender, 56e59 Butter, 184 Buttermilk, 184 By-product ingredients, 142

C Calcium phosphate, 180 CandyFab, 14e15, 31e32 Cartesian 3D printers, 47e48, 47f Caseins acid-induced gelation, 183 micelles, 183 oleogels, 183e184 subtypes, 183 Cellulose esters, 271e272 Cellulose nanofiber, 101 Ceramics, binder jetting of, 278 Cereal-based food formula, 78, 94e97 Cereal-based products, 94 enriched with edible insects, 108e113 printing variables affecting quality of, 107e108 Change drivers, 342e343, 343f ChefJet printer, 169, 278e279, 281e282 Chemical cross-linking, 10 Chitin, 110 Choc Creator 2.0 Plus 3D chocolate printer handmade cookie bakery, Father’s Day, 237, 238f rabbit cake, 237e238, 238f rotating chocolate sandwich, 237, 237f Chocolate additive layer manufacture (ChocALM), 221, 221f, 229, 229f Chocolate extrusion printing, 24

383

384 Index Chocolate forms and melting points, 155, 156t Chocolates. See also 3D chocolate printing additive layer manufacturing (ALM), 219e221 background, 210 cocoa flavanol, 209 crystallisation and tempering, 218e219, 219f customisation of, 210e211 formulations common chocolate products, 158e160 specialty chocolate products, 160e161 and health products, 239e240 medical value, 238e239 rheological behaviour of, 223, 223f state and texture of, 216e217 structure, 155e157 traditional chocolate making, 212e213 viscosity and flow properties, 217e218 CIJ. See Continuous ink jetting (CIJ) C-IJP. See Continuously inkjet printing (C-IJP) Clear labelling, 366 Cocoa beans, 210 cocoa butter, 217 production, 217 Cocoa butter alternatives, 217 melting point of, 218 triglycerides composition, 217 X-ray diffraction analysis of, 218 CocoaJet, 151e152 Coextrusion printing, 179 ‘Cold extrusion’, 163 Collectivities, 299 Commercial RepRap printer model, 50e51 Commercial XZ head printer model, 50e51 Common chocolate products enrobing, 159 moulding, 158, 159f one shot, 160 panning, 159e160 Complex coacervate formation, 11 Computer-aided design (CAD) system, 46, 54e61, 57te58t, 59f, 83 Concentric cylinder geometries, 270e271 Conching, 155 Conductive inks, printing of, 6 Confocal scanning laser microscopy (CSLM), 191e192 Contaminations, 363e364

Continuous ink jetting (CIJ), 257e258 operations, 169e170 Continuous jet printer, 34 Continuously inkjet printing (C-IJP), 3e4 Controlled fusion, 44 Conventional food extrusion process, 95e96 Conventional food supply chain, 20 Conventional inkjet printing, 271 Cooking cereal-based products, 94 Corn dough, 106e107 Cranberry extract analysis of, 245e246, 246f experiment, 244, 245f proanthocyanidins (PAC), 244 women’s health, 244 Create 3D virtual models of food, 54e60 Crystal polymorphs, 8 CuraEngine, 177e178 Cura software, 62, 82

D 3D cereal-based products, 96 textural properties of, 104e107 3D chocolate printing, 73e74, 152 additive layer manufacturing (ALM), 219e221 application handmade cookie bakery, Father’s Day, 237, 238f healthcare products, 238e251 rabbit cake, 237e238, 238f rotating chocolate sandwich, 237, 237f ChocALM, 229, 229f commercial feasibility study business model, research, 211e216 chocolate background, 210 chocolate status quo, 210e211 computational simulation, 215e216 customised production, 214 development of, 216e229 earlier printing works, 209e210 experimental chocolate additive layer manufacturing (ChocALM), 221e222, 221f extrudate geometry, 222e223 subsystems, 221e222 extrusion, 163e167 extrusion optimisation, multilayer components, 228, 228f extrusion rate and nozzle moving speed line testing and measurement, 225, 225f

Index software extrusion rate vs. resulting bead diameter, 226e227, 226f software setting vs. mass of chocolate extruded over period, 226e227, 226f volumetric material flow rate of, 227 and y-axis movement rate, 227, 227f features, 216 crystallisation and tempering, 218e219 state and texture of, 216e217 viscosity and flow properties, 217e218 food supply chain (FSC) business model, 211e212 formulations, 158e161 inkjet, 169e171 manufacturer-led production model, 213, 213f manufacturer’s inventory cost, 214 manufacturer’s profit (MP), 214 nozzle aperture size, 224, 224fe225f nozzle height, 224 optimisation of adaptive extrusion layer thickness, 230e233 Choc Creator, 230 layer scanning speed optimisation, 233e236 rapid prototyping and good-quality, 236e237 properties, 152e158 retailer-led production model, 213, 215f rheological behaviour, 223, 223f sintering and binding, 168e169 traditional production and management model, 212e213 3D edible objects, 63e80 Default axis step per unit, 81 Default_max_accelleration, 81e82 Default_max_feedrate, 81 Delta configuration printer, 53e54 Delta 3D printer configuration, 48, 49f Delta printer, 50e51 Desirability, 345 Dietetic approaches allergies and intolerances, 318e319 elders and clinical nutrition, 320e322 nutritional management, 316 personalised nutrition, 315 toddlers and children, 319e320 vegetarian and vegan, 316e318, 317f Differential scanning calorimetry (DSC) analysis, 219, 219f ‘Digital Chocolatier’, 24

385

Digital gastronomy, 348e350 Digital platform, 345 Digital recipes, 345e346 DoD-IJP. See Drop-on-demand inkjet printing (DoD-IJP) Domestic purpose, 3D food printers, 298e299 Dough, factors affecting printability of, 97e102 3D printed chocolate samples, 75e77, 77f 3D printed construct, mechanical properties of, 13e14 3D printed dairy applications accuracy and consistency, 190e191 flowability, 190 linear viscoelastic region (LVR), 189e190 melting properties, 189e190 microscopy, 191e192 particle size, 190 porosity, 192e193 rheometers, 189 rotational viscometer, 189 shape stability, 193 snap quality, 191, 192f texture analysis, 191 uniaxial compression, 191 wettability, 190 3D printed food samples, 136, 138f 3D-printed fruit-based snack, 72e73, 74f 3D-printed insect foods, prototypes of, 112, 112f 3D printed lemon juice gel, 75, 76f 3D printed structures, 128, 129t 3D printing (3DP). See also 3D chocolate printing chocolate filament, 69e70, 71f commercial market, 208 cultural creativity, 209 extrusion process, 130 forum community, 68 platform, 161e162 structural configuration of, 47e54 techniques, 3e14 Droplet jetting behaviour, 4 Drop-on-demand inkjet printing (DoD-IJP), 3e4, 257e258 ‘Drops per inch’ (DPI), 276 3D slicing software programs, 62, 63t 3D System’s ChefJet printer, 6, 45e46 Dual-responsive hydrogels, 29 Du Nou¨y ring method, 273e274 Dynamic YS, 6e7

386 Index

E Ecosystem, 337e339, 337f Edible insect-based products, 112e113 cereal-based products enriched with, 108e113 Educational use, 3D food printers, 298 Elasticity, 304, 305f Emulsifiers, 157e158 ‘Engineered comestible meat’, 45e46 Enzymatic crosslinking, 11 E-step calibration, 71e72 Ethanol, 273 EU school fruit scheme, 118e119 Extrusion-based three-dimensional food printing (3DFP), 1e2, 20, 27e29, 36f, 95e96 companies and devices, 292e294, 293te294t device-related technical consideration, 307e308 examples, 301 gel-forming extrusion, 9e11 filled appetizer 3D print, 302f food preparations, 300e308 fruit based 3D print, 300, 301f fused deposition modelling (FDM), 303f limitation, 300e301 melting, 23e24 melting extrusion, 7e9 pre- and post treatment methods, 29e30 printed thin cookies 3D print, 301, 302f rheological limitations, 302e307 soft materials, 24e29 technical considerations, 302e307 vegetable-sourced foods, 300 Extrusion cooking technology, 107

F Fab@home system, 8, 24, 44e45, 152 FDM. See Fused deposition modelling (FDM) Feed rate. See Print speed FFF printer. See Free-form fabrication (FFF) printer ‘Filament diameter’, 79 Fill density. See Infill Firmware of the 3D printer, 80e83 ‘Five a Day’, 118e119 Flowability, 190 Food allergy, 363 Food creation binder jetting in, 33e34 melting extrusion-based printing in, 24

FoodJet printer, 5, 35, 170 Food materials application and outlook for, 278e283 implementation of 3DP technology for, 2 Food object, internal structure of, 2 ‘Food on the go’ supplying problem, 361 Food poisoning, 362e363 Food powders agglomeration of, 168 particles, 263 Food printing process, 20, 23 Food products, 1e2, 313 Food safety and acceptance, 197 Food scarcity problem, 358 Food sector, 41e47 Food’s possibilities, 356e357 Food supply chain (FSC) business model challenges of, 211e212 manufacturers vs. customers, 212 steps and operations, 211e212 Food texture testing, 104e105 Food vending machine, 348 FreeCAD, 55e59 Free-form fabrication (FFF) printer, 162e163 Freeze-drying process, 104 Fruit and vegetables 3D printing potential nutritional and healthy properties of, 119e123 processing steps for, 123e134 settings of conditions for, 134e139 intake among children, 377e378, 378f nutritional composition of, 119, 120te122t seasonality of, 123, 124t waste, use of, 141e142 Functional printing ink, formulating, 267e274 Fused deposition modelling (FDM), 95, 162e163, 178, 178f, 293te294t, 294, 303f. See also Extrusion-based three-dimensional food printing (3DFP) advantage of, 179 calcium phosphate, 180 coextrusion printing, 179 elasticity, 304, 305f glass transition temperature, 305 hardness, 304 homogeneity, 306 melting point, 304e305

Index nozzle size, 306, 307f particles’ diameter, 306 stickiness, 305e306 technology, 44e45 viscosity, 303e304

G G-codes, 55, 60e61, 83e86, 161e162, 177e178 Gelatin, 10e11, 13, 130e131 Gel-forming extrusion, 9e11 Gellan gum, 13, 130 Geometric software model, 167 Ghee, 184 Glass transition temperature, 305 Glycerol, 273 Graphical decoration, 5 Green density, 262

H Healthcare products, 378e379, 378f chocolate, combination of, 239e240 chocolate medical value, 238e239 cranberry extract analysis of, 245e246, 246f experiment, 244, 245f proanthocyanidins (PAC), 244 women’s health, 244 lutein addition analysis of, 243e244 blue light, 242 experiment, 242e243, 243f eye food, 242 methyl cellulose addition adhesion performance, 251 experiment, 249e250, 250fe251f multiple functions, 249, 250f verification of collapse composition of, 249 fine grinding, 249 formula 1, 246e247, 247f formula 2, 247e248, 248f formula 3, 248e249, 248f vitamin C addition experiment of, 240e241, 241f physiological functions, 240 results analysis of, 241e242 Heat resistance, 160e161 Hershey’s shell topping, 170 ‘High-fat insects’, 110 High-molecular-weight polymers, 272

387

Hobbyist, 297 Home, 3D food printers at adapted formulations and traditional recipes, 311e313 circular economy, 314 domestic applications with dietetic purposes, 315e322 mini food factory, 308e310 reduce/reuse and recycle, 314 versatility, 310e311 Homogeneous food formulation, 130e131 Hot air sintering 3D printer, 168, 168f Hydrocolloids, 65e66, 69e70, 100e102, 130e131 formulations and mouthfeel of foods, comparison between, 130e131, 131t Hydrogelforming materials, 45

I Ice cream chocolate, 160 Implications, 3D printed food ‘food on the go’ supplying problem, 361 food scarcity problem solving, 358 malnutrition eliminating, 358e359 no-longer-necessary businesses eliminating, 360e361 nutrition deficiency, 359 obesity, 359 overnutrition, 359 reducing climate change, 360 undernutrition, 359 Industrial advantages/disadvantages, 3D printing, 197e198 Industrial ecology concepts, 141 Industrial purposes, 297 Infill, 75 speed, 80 Ingredient portfolio, 340e341 Ingredients in 3D printing process, effect of, 98e100 Inkjet printing (IJ), 3e6, 34e35. See also Binder jetting printing food creation, 35 technology, 257e258 3D printing chocolate, 169e171 Ink jetting theory, 267e269 viscosity considerations for, 269e271 Innovative food formulations in 3D printing, 44, 108e113 Innovative ingredients, 50 ‘Insect Au Gratin’, 112

388 Index Insect-enriched products, 94 research in 3D printing for obtaining, 110e113 Insect powder, 112 Ionotropic cross-linking, 10

J Jenike’s technique, 266

L Labelling issues, 365e368 clear labelling, 366 Federal Food, Drug, and Cosmetic Act, 1938, 366 food printing a meal at home, 368 food printing in front of customers before selling, 367e368 majority of food package to sell, to mass population, 367 small portion food package to sell, to mass population, 367 Lactose, 185e186 Laser-based printing in food creation, 32 implications of materials’ properties on, 31e32 Laser sintering, 180e181, 180f, 259 Layer height, 66e67 Layer scanning speed optimisation calculation, 234e235 data comparison, 235e236, 236t experiment, 235, 236f processing efficiency, 234 Lectin, 157e158 Linear viscoelastic region (LVR), 189e190 Liquid-based 3D printing technologies, 130 Liquid binding (LB), 45e46, 181 Liquid jet model, 267e268 Lutein analysis of, 243e244 blue light, 242 experiment, 242e243, 243f eye food, 242

M Machine concepts, 341e342 Malnutrition, 358e359 Manufacturer-led production model, 213, 213f Manufacturer’s profit (MP), 214

Market segmentation, 335e337, 336f Mass customisation, 334 MC. See Methylcellulose (MC) Mechanical (piston or screw) methods, 7 Mechanical properties of 3D printed construct, 13e14 Medical care, 298 Melting extrusion-based printing, 7e9, 23e24 in food creation, 24 materials’ thermal properties on, 24 Methylcellulose (MC), 100e101 adhesion performance, 251 concentration levels, 131, 132f experiment, 249e250, 250fe251f gel, 45 multiple functions, 249, 250f Micellar casein concentrate (MCC), 188 Microdispensing system, 75e77 Microencapsulation processes, 5e6 Microscale dispensing system, 50e51 Milk components fat, 184e185 lactose, 185e186 physicochemistry, 181 proteins, 181e184 Milk fat butter, 184 milk fat globule membrane (MFGM), 184 structure of, 185 triglycerides (TG), 184 Milk fat globule membrane (MFGM), 184 Milk proteins caseins acid-induced gelation, 183 micelles, 183 oleogels, 183e184 subtypes, 183 whey products cold-set gelling mechanism, 182e183 fine-stranded gels, 181e182 gelation of, 181e183 physiochemical property, 181e182, 182f Mini food factory, 308e310, 309t Motor-driven plunger, 163e165 Moulding, chocolate, 158, 159f Mouthfeel of foods, comparison between hydrocolloid formulations and, 130e131, 131t Multiaxis robots with 3D tools (MX3D) technology, 41e42, 42f Multicomponent food system, 7

Index

N Natively printable food materials, 341 NaviereStokes equation, 4 Nesquik, 169 Nonfood applications, 263, 278 Non-Newtonian effects, 269e270 Novel food textures, 375 Novel ingredients, 313 Nozzle height. See Layer height Nursing, 298 Nutritional composition of fruits and vegetables, 119, 120te122t Nutritional compounds in 3D printing process, effect of, 98e100 Nutritional properties of edible insects, 108e110

O Ohnesorge number (Oh), 267e268 Oil-in-water emulsion, 184 Oleogels, 183e184 Onshape Inc., 56 OpenSCAD, 56 ORD Bot hadron, 50e51 Overnutrition, 359

P Path planning, 46 PBP. See Powder Binder Printing (PBP) Pectin solution, 130e131 Permanent and pop-up restaurants, 299 Personalised food formulas, designing of, 126e129 Personalised nutrition, 176, 315, 315f Piezoelectric inkjet printers, 3e4 Piezo techniques, 169e170 Piston-driven configuration, 7 PLA. See Polylactic acid (PLA) Plastic materials, common printing of, 71e72 PlateaueRayleigh instability of liquid jets, 267 Pneumatic (piston or screw) methods, 7 Polylactic acid (PLA), 117e118 Polysaccharides, 281 Polyvinylpyrrolidone, 8e9 Post-deposition cooking process, 102e103 Postprocessing method, 36, 102e104 Powder and ink during print, combining, 276e278 Powder-based three-dimensional food printing (3DFP), 1e2, 130

389

Powder bed printing (PBP), 6, 180e181 Powder Binder Printing (PBP), 282f Powder binding mechanisms, 262e265 Powder formulations, sorption isotherms of, 266 Powder layer binding, 14e15 Printability, 272 of dough, binding agents to improve, 100e102 Printable dairy structures micellar casein concentrate (MCC), 188 processed cheese, 188 semiskimmed milk powder (SSMP), 186e187 skimmed milk powder (SMP), 187 sodium caseinate (NaCas), 187e188 Printable food formulations, 98 Printable fresh fruits, composition of, 128, 128t Printable fruit-based formula, 135e136 composition of, 127, 127t Printable pastes, composition of, 128, 129t Print-and-eat technology, 373 Printed products, 282 Printer settings material jetting, 275 powder deposition, 274 Printing behaviour materials’ properties, soft materials on, 27e29 parameters on, 23e24, 26e27, 31e34 Printing chocolate, 45 Printing precision, factors affecting, 20 binder jetting printing, 32e34 extrusion-based printing, 23e30 inkjet printing, 34e35 selective laser sintering, 30e32 Printing quality, assessment of, 11e14 Printing variables, 105e106, 108 affecting quality of cereal-based products, 107e108 Print speed, 64e65 Proanthocyanidins (PAC), 244 Processed cheese, 188 comparable difference, 196 confocal laser scanning micrographs of, 195, 195f sample delivery system, 193e194 texture profile analysis (TPA) profiles, 194, 194f

390 Index Process parameter, 31, 36 Prosumption, 342e351 additive manufacturing, 331e332 change drivers, 342e343, 343f current state, 335e342 definition, 333e334 digital gastronomy, 332, 348e350 digital platforms, 335, 345 ecosystem, 337e339, 337f evolution, 334e335 example use cases, 348e350, 349fe350f food layered manufacturing, 332 food value chain, 337e339, 338f domestic kitchen, 338e339, 340f industrial use, 338e339, 339f future of food, 343e347, 346fe348f impact, 350e351 Information and Communications Technology (ICT) platforms, 332 ingredient portfolio, 340e341 ‘Insect Au Gratin’ project, 341 Internet of things (IoT), 344e345 machine concepts, 341e342 market segmentation, 335e337, 336f mass customisation, 334 natively printable food materials, 341 The Third Wave, Toffler, Alvin, 333 three waves, 333e334, 333f TNO, Netherlands, 335 value co-creation, 334 Pythagorean theorem, 48, 81

R Raw foods, 312 Raw fruits and vegetables, selection of, 126e129 Reduced fat food, 378e379 Reduced salt food, 378e379 Reduced sugar food, 378e379 Repetier firmware, 80 RepRap project, 80, 280 Research and education, 3D printing, 298 Research challenges, 3D printing, 197e198 Retailer-led production model, 213, 215f Retraction variables, 78 Rheometers, 189 Rotational rheology, 270e271 Rotational viscometer, 189 ‘Ruby of North America’, 244. See also Cranberry extract

S Safe rule of thumb, 26e27 Safety issues contaminations, 363e364 food allergy, 363 food poisoning, 362e363 food printer manufacturer, 364 human body changes, 364e365 ingredients manufacturer, 364 short term, 362e363 Screw-based extrusion process, 24e25, 52e53 Screw-driven system, 7 Selective Compliant Assembly Robot Arm (SCARA), 48e49 Selective hot air sintering and melting (SHASAM) technology, 14e15 Selective laser melting, 180e181 Selective laser sintering (SLS), 30e32, 44, 96e97, 180e181 Selective sintering 3D printing, 294 Self-supporting layers, mechanism of formation of, 23, 26 Semiskimmed milk powder (SSMP), 98e99, 186e187 Shape fidelity, 11e13 SHASAM technology. See Selective hot air sintering and melting (SHASAM) technology Shear-thinning materials, 269e270 SketchUp, 55, 60 Skimmed milk powder (SMP), 98e99, 186e187 Slic3D software, 69e70 Slicing software, 62 basic principles of, 62 Slic3R, 62, 177e178 SLS. See Selective laser sintering (SLS) Smart foods, 211 Smoothed-particle hydrodynamic modelling, 167 Smoothies, 125 SMP. See Skimmed milk powder (SMP) Snap quality, 191, 192f Sodium caseinate (NaCas), 187e188 Soft materials extrusion-based printing, 24e29 in food creation, 30 Solid polymorph crystals, 156e157 SolidWorks 2016, 60 SOLIDWORKS solutions, 55 Space missions, 299

Index Specialty stores, 297e298 Spiral printing pattern, 79f SSMP. See Semiskimmed milk powder (SSMP) ‘Stair-stepping’ effect, 274 Standard Tessellation Language (STL), 177e178 Static YS, 6e7 Stepper motors drive, 51e54 Submicron-sized particles, 259 Sugar-based 3D print, 294f Surface-active agents, 157e158 Surface tension and density, 273e274 Synergism, 7 Syringe-based extrusion, 24e25, 52e53 Syringe-based printer, 24e25, 25f

T Tempering process, 156 Tenebrio molitor, 110e112, 111f Texture-modified food, swallowing/chewing difficulties, 375e377, 377f Texture profile analysis (TPA), 13 Thermalegelation, 10 Thermal inkjet printer, 3e4 Thermoplastic materials, 117e118 Three-dimensional cylinders of lemon juice gel, 68e69, 69f Three-dimensional (3D) food printers characteristics, 374, 374f future expectations, 374e380 microstructure, 375, 376f perishables/sustainability wastages prevention, 379e380 Tinkercad software, 55e56, 59e60 TNO’s encapsulation printer, 5e6, 5f Tomato by-products, 141e142 TPA. See Texture profile analysis (TPA) Traditional step motor, 51, 52f Transglutaminase, 102 Triglycerides (TG), 184 composition, 100

391

U Undernutrition, 359

V Vegetable-based products, 118e123 Vegetable 3D printed foods, 139e140 Vegetable-sourced foods, 300 Vegetables smoothie, composition of, 128, 128t Virtual pyramid model, 136, 137f Viscosity, 303e304 Visual PathBuilder, 60 Vitamin C experiment of, 240e241, 241f physiological functions, 240 results analysis of, 241e242

W Water-in-oil emulsion, 184 ‘Weissenberg effect’, 270e271 Wettability, 190 Wheat flour, 264e265 Whey products cold-set gelling mechanism, 182e183 fine-stranded gels, 181e182 gelation of, 181e183 physiochemical property, 181e182, 182f

X Xanthan gum, 11, 101, 130e131

Y Yield stress (YS), 6e7

Z Z-Corp inkjet process, 6 ‘Zero waste economy’, 141 Zigzag printing pattern, 79f

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