McClements Understanding and Controlling the Microstructure of Complex Foods

1. Auflage 2007
ISBN: 978-1-84569-367-1
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 792 Seiten

Reihe: Woodhead Publishing Series in Food Science, Technology and Nutrition

It is widely accepted that the creation of novel foods or improvement of existing foods largely depends on a strong understanding and awareness of the intricate interrelationship between the nanoscopic, microscopic and macroscopic features of foods and their bulk physiochemical properties, sensory attributes and healthfulness. With its distinguished editor and array of international contributors, Understanding and controlling the microstructure of complex foods provides a review of current understanding of significant aspects of food structure and methods for its control.Part one focuses on the fundamental structural elements present in foods such as polysaccharides, proteins and fats and the forces which hold them together. Part two discusses novel analytical techniques which can provide information on the morphology and behaviour of food materials. Chapters cover atomic force microscopy, image analysis, scattering techniques and computer analysis. Chapters in part three examine how the principles of structural design can be employed to improve performance and functionality of foods. The final part of the book discusses how knowledge of structural and physicochemical properties can be implemented to improve properties of specific foods such as ice-cream, spreads, protein-based drinks, chocolate and bread dough.Understanding and controlling the microstructure of complex foods is an essential reference for industry professionals and scientists concerned with improving the performance of existing food products and inventing novel food products. - Reviews the current understanding of significant aspects of food structure and methods for its control - Focuses on the fundamental structural elements present in foods such as proteins and fats and the forces that hold them together - Discusses novel analytical techniques that provide information on the morphology and behaviour of food materials

Autoren/Hrsg.

McClements, D. Julian

Leseproben

Introduction
There has been a significant shift in the approach adopted by many scientists working with foods over the past decade or so. In particular, there has been an increasing awareness of the interrelationship between the nanoscopic, microscopic and macroscopic features of foods on the one hand, and the bulk physicochemical properties, sensory attributes and healthfulness of foods on the other hand. It is now widely recognized that the creation of novel foods or the improvement of existing foods largely depends on a better understanding of this complex interrelationship. The objective of this book on understanding and controlling the structure of foods is to provide an overview of the current state of knowledge in this important area. Scientific disciplines often follow an archetypal path as they mature. Firstly, the discipline is largely based on systematic empirical observations of what is happening in the world. For example, when a raw egg is heated in boiling water the transparent viscous liquid surrounding the yolk turns into a white opaque gel. Then, the workers in the discipline design controlled experiments to better understand specific aspects of the subject. Initially, these experiments often treat the system being studied as a ‘black box’ whose behavior is to be understood. Typically, the response (output) of a system when a particular stress (input) is applied to the system is measured, and then correlations between the input and output are sought. For example, researchers may heat an egg white to various well-defined temperatures and measure the change in opacity, water-holding capacity or rheology, thereby establishing the temperature range over which the transition from liquid to gel occurs. Next, scientists may try to understand what is actually causing the observed change in the system based on fundamental physicochemical principles. In this case, conceptual, theoretical and mathematical models are applied to develop a more quantitative description of the system, and to be able to better predict its behavior. For example, one might experimentally determine the chemical composition of egg white and then examine the thermal behavior of the major components, thereby establishing that the changes in the properties of the system upon heating are due to thermal denaturation and aggregation of globular proteins (e.g., ovalbumin). Finally, a detailed understanding of the molecular and physicochemical properties of a system may enable one to design and fabricate properties on a more systematic and rational basis. For example, one may be able to design an egg that gels at a different temperature, or one may be able to design a synthetic egg from other ingredients. I believe that the discipline of food science has undergone this archetypal path, and that we are moving from a period where the emphasis is shifting from understanding food properties to using our knowledge to design and fabricate novel structures. Having said this, one must be aware that foods are a highly diverse and complex group of materials, and that our ability to utilize the principles of structural design for improved performance is currently limited to a few food categories. Nevertheless, as our knowledge of the molecular and physicochemical basis of food structure develops, I anticipate that scientists will be able to use the principles of structural design on a wider range of products. Food architecture: building blocks and forces
The physicochemical, sensory and nutritional properties of foods are largely determined by the type of components present, the interactions amongst them, and their structural organization. A food can be considered to be assembled from a variety of ‘building blocks’ that are held together by the forces acting between them. The type of building blocks and forces involved depend on the structural level of interest, e.g., nano-scale (0.1–100 nm), micro-scale (0.1–100 µm), or macro-scale (0.1–100 mm). Some of the most common building blocks found in foods are listed below: • Nano-scale: atoms, ions (e.g., Na+, Ca2+), molecules (e.g., proteins, polysaccharides, lipids, water), micelles, microemulsions, molecular assemblies. • Micro-scale: lipid droplets, fat crystals, ice crystals, air bubbles, starch granules, cells. • Macro-scale: bulk phases (e.g., oil, water, air). The building blocks on one scale are usually made up from building blocks from a lower scale. Hence, the fat globules in milk are assembled from lipid, protein and phospholipid molecules in water. A variety of forces act between these building blocks, which also depend on the scale (McClements, 2005): • Nano-scale: covalent interactions, physical interactions (i.e., intermolecular van der Waals, electrostatic, and steric overlap). • Micro-scale: physical interactions (i.e., colloidal van der Waals, electrostatic, hydrogen bonding and hydrophobic forces), gravity, electrical forces, mechanical forces. • Macro-scale: gravity, electrical forces, mechanical forces. Identification and characterization of the most important building blocks and forces operating within a particular food product, helps to establish why that food has the particular physicochemical (rheology, optical, stability), sensory (texture, appearance, flavor) and nutritional (bioavailability) properties that it does. Nevertheless, this process is often complicated because most foods are compositionally, structurally and environmentally complex materials. For example, a given food (e.g., ice cream) may contain a wide range of different ingredients (e.g., proteins, carbohydrates, lipids, water, minerals, air), which may form a wide range of different structures at different levels (e.g., micelles, lipid droplets, air bubbles, ice crystals, fat crystals), and may experience a wide range of different environmental conditions during its production, storage, transport and utilization (e.g., thermal processing, chilling, freezing, shearing). Many years of painstaking and systematic work are therefore usually required to be able to understand and predict the properties of most food materials in terms of the basic building blocks and forces involved. A recurring feature of this book is, therefore, the identification and characterization of the various building blocks that occur at different structural levels within foods, and of the forces that act between them. Analytical tools
The depth of our understanding of complex food materials at a particular time is largely determined by the analytical tools that we have available to study their properties. There may be certain features of a system that we cannot (yet) study, because there are no suitable analytical tools available. Alternatively, progress may be slow because there are suitable analytical techniques available, but they are too expensive for widespread and routine application. As existing analytical tools become more affordable and more widely available, or as completely new analytical tools are developed, we are able to ask new questions and to find new answers. For example, the widespread commercial availability of particle-sizing equipment in the 1980s and 1990s saw a great increase in the fundamental study and understanding of colloidal food systems. More recently, the advent of confocal fluorescence microscopy and atomic force microscopy has seen a rapid increase in our understanding of the structural basis of food properties. Another important feature of this book is therefore a discussion of some of the most powerful analytical tools for studying food structure that have recently been developed or become more widely available, e.g., NMR, atomic force, confocal fluorescence, and ultrasonic microscopy. Overview of the structure of the book
This book is roughly divided into four parts. The first part of the book (‘Microstructural elements and their interactions’) focuses on the major structural elements (building blocks) present in foods and the forces (interactions) that hold them together. This section contains chapters on proteins, polysaccharides, lipids, surfactants, water and air, and discusses how these food components assemble into structures that ultimately determine the overall properties of foods. The second part of the book (‘Novel methods to study food microstructure’) focuses on some of the newer analytical techniques that can be used to probe the structural features of food materials and to provide information about their morphology and behavior. This section contains chapters on atomic force microscopy, confocal fluorescent microscopy, ultrasonics, scattering techniques, NMR (Appendix) and computer simulation. It should be recognized that there are many other analytical techniques that are used by food scientists to probe food structure, but that this book has focused on some of the more recent or advanced techniques. The third part of the book (‘Microstructural-based approaches to design of functionality in foods’) demonstrates how the principles of structural design can be used to create improved performance or novel functionalities into foods. The fourth and final part of the book (‘Microstructural approaches to improving food product quality’)...