Food Texture and Viscosity: Concept and Measurement by Malcolm C. Bourne · ISBN: 0121190625 · Publisher: Elsevier Science & Technology Books · Pub. Date: March 2002 Prelims.qxd 1/10/02 3:47 PM Page 15 Preface to the Second Edition Many wonderful advances have been made in understanding what texture is all about and in instrumentation to measure the texture and viscosity of foods since the first edition of this book was published in 1982. Hence the need for a second edition. This book is still intended for those who want to know more about texture and viscosity of food, how these properties are measured and relate to human assessments of textural quality. It draws together literature from many sources including journals in chemistry, dentistry, engineering, food science, food technology, physics, psychology and rheology. Scientific and trade journals dedicated to special food groups, books, proceedings and commercial literature have also been utilized. Journal of Texture Studies has been a major source of information for new developments in the field. The treatment is descriptive and analytical with the minimum of mathe- matics. Equations are given only when they illuminate the discussion and then only in the simplest form. Their derivations, however, are not given, this is not a mathematics text book. Additions have been made to every chapter, and although most of them are small, their cumulative effect is great. Chapter 1 defines texture terms, discusses the importance of textural prop- erties of foods, locates texture in the overall area of food science, gives some interesting general facts about texture, and a brief history of earlier develop- ments in the field. Chapter 2 describes physical interactions between the human body and food – a necessary background for the ensuing chapters. A new section on the hand has been added because gentle squeezing of food is gaining increased attention. Chapter 3, a new chapter, describes the importance of physics in texture measurement. The rigor of the physics approach is needed in our field. However, the limitations of physics to resolve complex practical problems is also noted. Chapter 4 describes the principles of objective methods of texture measurement, including ideas that have yet to evolve into commercial available instruments, and provides a foundation for the following chapter. Prelims.qxd 1/10/02 3:47 PM Page 16 xvi Preface A major goal of this chapter is to move the thinking about texture from a food- by-food basis to general principles that can be applied to all foods. Chapter 5 describes commercial instruments and their use. Although the use of universal testing machines and computer retrieval and analysis of force–time data have become widespread (a great advance in the author’s opinion) there is still a place for the small, simple instruments that are also described. Chapter 6 provides a brief description of commercial viscometers. The description of the various types of viscous flow has been moved to Chapter 3 (physics). There have been a number of great advances in instrumentation, especially for controlled shear stress viscometers. Chapter 7 describes sensory methods for measuring texture and viscosity and is an essential component of this book. Many sensory scientists have no interest in texture. It is hoped this chapter will awaken their interest in texture as a sensory attribute. Chapter 8, a new chapter, covers our present level of understanding of correlations between physical measurements and sensory assessments of texture and viscosity. Chapter 9 outlines a system for selecting a suitable instrument, or a suitable test procedure for a universal testing machine with the minimum of time and cost. Appendix I lists the names and addresses of suppliers of instruments for those who are interested in purchasing equipment. Appendix II gives data on texture–temperature relationships that are too long to fit comfortably into Chapter 8. Appendix III lists test conditions for specific foods in universal testing machines. I have no vested interest in any corporation that sells texture- measuring instruments and have endeavored to be unbiased in describing commercial instruments, and to make the list as complete as possible. Appendix IV gives examples of sensory texture profiles on eleven different foods. Many people will read this book selectively. The practising food technologist and quality controller will concentrate on Chapters 5, 6 and 9. The professor and college student might spend most time on Chapters 3 and 4. The sensory scientist will find Chapters 7 and 8 of greatest interest. The laboratory man- ager wanting to establish a texture laboratory will find Chapter 9 and Appendix I useful. Everybody should find Chapters 1 and 2 of great interest. I have expressed my own opinions and interpretations in this volume because I believe most readers will appreciate some guidance rather than a simple listing of many facts of varying levels of usefulness and accuracy. Even if subsequent reports show the guidance to be wrong at times, I hope most readers will find useful the methods and yardsticks offered. My personal conviction that empirical tests have been responsible for most of the successes in practical food texture measurement is reflected in the extended discussion of empirical methodology. However, it is a pleasure to report that some of these empirical tests are now being given serious attention by the research community and are on the way to becoming rigorous, fundamental tests. I acknowledge with thanks help from many sources in the preparation of this second edition. A number of individuals and organizations provided figures or compiled tables and their contributions are noted wherever that figure or table Prelims.qxd 1/10/02 3:47 PM Page 17 Preface xvii appears. I particularly thank J. Barnard, O. Campanella, B. R. Heath, M. Peleg, A. S. Szczesniak and Z. M. Vickers, each of whom critically reviewed one or more chapters in the draft stage and made numerous suggestions for improve- ment. I also thank K. C. Diehl, S. A. Brown, J. Faubion, K. M. Hiiemae, G. J. Bourne, T. Gibson and N. Marriott who clarified specific points for me, and B. A. Andersen who typed the many additions and M. M. Walczak who typed the subject index. My colleague, Prof. M. A. Rao has provided encour- agement and fruitful discussions for many years. Representatives from a num- ber of instrument suppliers have been helpful in clarifying details about their instruments. I sincerely thank each one for their contribution. The two pictures on the cover depict the dual nature of food texture meas- urement. Only humans can assess the textural quality of food. In this picture the firm, plump, succulent texture of strawberry is measured sensorially while the firmness is also measured by compression in a machine. Instruments that measure physical properties are widely used and have led to great improve- ments in building and maintaining a high level of textural quality in most of our food supply. Nevertheless, instrument readings are worth little unless cal- ibrated against the human senses. I thank Stable Micro Systems Inc. for pro- viding these cover pictures. Table of Contents Preface to the Second Edition Ch. 1 Texture, Viscosity and Food Ch. 2 Body-Texture Interactions Ch. 3 Physics and Texture Ch. 4 Principles of Objective Texture Measurement Ch. 5 Practice of Objective Texture Measurement Ch. 6 Viscosity Measurement Ch. 7 Sensory Methods of Texture and Viscosity Measurement Correlation Between Physical Measurements and Sensory Ch. 8 Assessments of Texture and Viscosity Ch. 9 Selection of a Suitable Test Procedure App. I Suppliers of Texture and Viscosity Measuring Instruments App. II Effect of Temperature on Texture Measurements App. III Guidelines and Conditions for Testing Foods App. IV Examples of Sensory Texture Profiles References Index Chap-01.qxd 1/10/02 4:11 PM Page 1 Texture, Viscosity, C HAPTER and Food 1 Introduction The four principal quality factors in foods are the following. 1. Appearance, comprising color, shape, size, gloss, uses the optical sense. 2. Flavor, comprising taste (perceived on the tongue) and odor (perceived in the olfactory center in the nose), is the response of receptors in the oral and nasal cavities to chemical stimuli. These are called ‘the chemical senses’. 3. Texture is primarily the response of the tactile senses to physical stimuli that result from contact between some part of the body and the food. The tactile sense (touch) is the primary method for sensing texture but kinesthetics (sense of movement and position) and some- times sight (degree of slump, rate of flow), and sound (associated with crisp, crunchy and crackly textures) are also used to evaluate texture. 4. Nutrition comprises major nutrients (carbohydrates, fat, protein) and minor nutrients (minerals, vitamins, fiber). Other factors, such as cost, convenience, and packaging, are also important but are not considered quality factors of foods. Of the above listed the first three are termed ‘sensory acceptability factors’ because they are perceived by the senses directly. Nutrition is a quality factor that is not perceived by the senses. The sensory acceptability factors of foods are extremely important because people obtain great enjoyment from eating their food and, furthermore, the enjoyment of food is a sensory pleasure that is appreciated from the cradle to the grave. Chap-01.qxd 1/10/02 4:11 PM Page 2 2 Texture, Viscosity, and Food Importance of Texture The importance of texture in the overall acceptability of foods varies widely, depending upon the type of food. We could arbitrarily break it into three groups: 1. Critical: Foods in which texture is the dominant quality characteristic; for example, meat, potato chips, cornflakes and celery. 2. Important: Foods in which texture makes a significant but not a dominant contribution to the overall quality, contributing, more or less equally, with flavor and appearance; for example, most fruits, vegetables, cheeses, bread, most other cereal-based foods and candy fall into this category.