Proteins in Food Processing

Rickey Y. Yada

• Publisher: Woodhead Publishing
• Year: 2004
• eBook ISBN: 9781855738379
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

Proteins are essential dietary components and have a significant effect on food quality. Edited by a leading expert in the field and with a distinguished international team of contributors Proteins in food processing reviews how proteins may be used to enhance the nutritional, textural and other qualities of food products.After two introductory chapters, the book discusses sources of proteins, examining the caseins, whey, muscle and soy proteins and proteins from oil-producing plants, cereals and seaweed. Part two illustrates the analysis and modification of proteins, with chapters on testing protein functionality, modelling protein behaviour, extracting and purifying proteins and reducing their allergenicity. A final group of chapters are devoted to the functional value of proteins and how they are used as additives in foods.Proteins in food processing is a comprehensive and authoritative reference for the food processing industry. - Reviews the wide range of protein sources available - Examines ways of modifying protein sources - Discusses the use of proteins to enhance the nutritional, textural and other qualities of food products

1

Introduction

R.Y. Yada    University of Guelph, Canada

Through their provision of amino acids, proteins are essential to human growth, but they also have a range of structural and functional properties which have a profound impact on food quality. Proteins in food processing reviews the growing body of research on understanding protein structure and developing proteins as multi-functional ingredients for the food industry.

Chapter 2 describes what we know about the common chemical and physical properties of proteins and the range of factors that influence how these properties are expressed in particular food systems. It provides a context for Part I which discusses the diverse sources of proteins, whether from milk, meat or plants. Individual chapters review the structure and properties of these groups of proteins and ways of improving their functionality as food ingredients.

Part II builds on Part I by summarising the range of recent research on analysing and modifying proteins. A first group of chapters reviews ways of testing and modelling protein behaviour, understanding enzyme activity and detecting allergenic proteins. They are followed by chapters reviewing the range of techniques for extracting, purifying and modifying proteins. The book concludes by analysing the many applications of proteins as ingredients, from their use as edible films to their role in modifying textural properties and improving the nutritional quality of food.

The financial support from the Natural Sciences and Engineering Research Council of Canada is gratefully acknowledged.

2

Properties of proteins in food systems: an introduction

E.C.Y. Li-Chan The University of British Columbia, Canada

2.1 Introduction

The word ‘protein’ is defined as

any of a group of complex organic compounds, consisting essentially of combinations of amino acids in peptide linkages, that contain carbon, hydrogen, oxygen, nitrogen, and usually, sulfur. Widely distributed in plants and animals, proteins are the principal constituent of the protoplasm of all cells and are essential to life. (‘Protein’ is derived from a Greek word meaning ‘first’ or ‘primary,’ because of the fundamental role of proteins in sustaining life.) (Morris, 1992)

Proteins play a fundamental role not only in sustaining life, but also in foods derived from plants and animals. Foods vary in their protein content (Table 2.1), and even more so in the properties of those proteins. In addition to their contribution to the nutritional properties of foods through provision of amino acids that are essential to human growth and maintenance, proteins impart the structural basis for various functional properties of foods.

Table 2.1

Total protein contents of the edible portion of some foods and beverages^a

Food	Total protein (%)
Almonds	21.1
Apples (raw, eating)	0.4
Bananas	1.2
Beans (canned, baked)	5.2
Beer (bitter)	0.3
Beef (lean, raw)	20.3
Beansprouts (raw)	2.9
Bread (white)	8.4
Cabbage (raw)	1.7
Cheese (Cheddar)	25.5
Cheese (Parmesan)	39.4
Chicken (lean, raw)	20.5
Chocolate (milk chocolate)	8.4
Chocolate (plain chocolate)	4.7
Cod fillet (raw)	17.4
Cornflakes	7.9
Egg (whole)	12.5
Ice cream	3.6
Lentils (dried)	24.3
Milk (cow's whole)	3.2
Milk (human)	1.3
Pasta	3.6
Potatoes (new)	1.7
Rice	2.6
Sweetcorn (canned)	2.9
Soya milk	2.9
Tofu (steamed)	8.1
Tuna (canned)	27.5
Yogurt (plain)	5.7

^a Adapted from Table 5.1 of Coultate (2002).

The objective of this chapter is to provide an introduction to the chemical and physical properties of food proteins that form the basis for their structural and functional properties. However, food scientists wishing to study proteins in food systems must be cognizant of the complexity of such systems in terms of composition and spatial organization. Food systems are usually heterogeneous with respect to (a) protein composition (foods usually do not contain a single protein entity, but multiple proteins); (b) other constituents (most foods contain not only water and other proteins, but also lipids, carbohydrates as major components, and various other minor components such as salt, sugars, micronutrients, minerals, phenolic compounds, flavour compounds, etc.); and (c) structural or spatial organization (proteins exist in foods as tissue systems, gels, coagula, films, emulsions, foams, etc., and not usually as the dilute solutions or crystalline forms that are typically investigated in model systems). Furthermore, significant changes in the properties of the proteins are induced by environmental factors and processing conditions that are typical of food systems.

Lluch et al. (2001) have written an excellent chapter describing the complexity of food protein structures. The diversity of the structural role of proteins in various food raw materials is illustrated by comparing protein structures in the muscle tissues of meat, fish and squid, the protein bodies of plant tissues such as cereals, legumes, oilseeds and shell (nut) fruits, and the casein micelle structure of bovine milk. Interactions of proteins with other components are exemplified in protein-starch interactions observed during dough processing and baking, protein-hydrocolloid interactions in dairy products, protein-fat interactions in comminuted meat emulsions, mayonnaise and cheese, protein-water as well as protein-protein matrix interactions in fish surimi gels, yogurt and cheese (Lluch et al., 2001).

With this complexity in mind, in addition to describing the basic chemical and physical properties of proteins and their amino acid building blocks, this chapter provides an overview of the factors that can influence the properties of proteins in food systems, and suggests approaches that may be useful to elucidate the structure-function relationships of food proteins.

2.2 Chemical and physical properties of food proteins

2.2.1 Amino acids commonly found in proteins

It is commonly recognized that 20 amino acids form the building blocks of most proteins, being linked by peptide (amide) bonds formed between α-amino and α-carboxylic acid groups of neighbouring amino acids in the polypeptide sequence. Nineteen of these 20 amino acids have the general structure of H₂N-C_αH (R)-CO₂H, differing only in R, which is referred to as the side chain, while the 20th amino acid is in fact an ‘imino’ acid, in which the side chain is bonded to the nitrogen atom. With the exception of the amino acid glycine, in which the side chain is a hydrogen atom, the α-carbon atom exhibits chirality. Typically, only the L-form of the amino acids is found in proteins, bein...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Contributor contact details
• 1: Introduction
• 2: Properties of proteins in food systems: an introduction
• Part I: Sources of proteins
• Part II: Analysing and modifying proteins
• Part III: Applications
• Index