Functional properties food protein ingredients

Protein is utilized in many foods for the particular characteristics that it contributes to the final product (1 ). In order for protein products to maintain or enhance the quality and acceptability of a food, the protein ingredients should possess certain functional properties that are compatible with the other ingredients and environmental conditions of the food system. Consequently, an important aspect of the development of new protein additives and their incorporation into food systems is the establishment of their functional properties. Functional properties of proteins are physicochemical properties through which they contribute to the characteristics of food. Study of functionality should provide information as to how a protein additive will perform in a food system (, A). These properties are... 

The whey produced during cheese and casein manufacturing contains approximately 20% of all milk proteins. It represents a rich and varied mixture of secreted proteins with wide-ranging chemical, physical and functional properties (Smithers et al., 1996). Due to their beneficial functional properties, whey proteins are used as ingredients in many industrial food products (Cheftel and Lorient, 1982). According to Kinsella and Whitehead (1989), functional properties of foods can be explained by the relation of the intrinsic properties of the proteins (amino acid composition and disposition, flexibility, net charge, molecular size, conformation, hydrophobicity, etc.), and various extrinsic factors (method of preparation and storage, temperature, pH, modification process, etc.). 

During isolation by conventional methods yeast proteins frequently become denatured, insolubilized and display poor functional properties. These proteins can be rendered more soluble by limited hydrolysis with acid, alkali or proteolytic enzymes. Protein hydrolyzates are most commonly prepared by partial acid hydrolysis and yeast hydrolyzates are popular as food flavorings and ingredients (66). Acid hydrolyzates have flavors resembling cooked meats and are widely used by earners to impart brothy, meaty flavors to soups, gravies, sauces, canned meats. 

Food proteins, especially those of plant origin, often require modification to achieve desirable functional properties for use as food ingredients. For instance, soy protein has limited water solubility at acid pH, which restricts its use in acidic foods such as coffee whitener and acidic beverages. Improved solubility at acid pH for commercial soy protein isolate can generally be achieved by hydrolysis. However, the hydrolysis has to be carefully controlled, because excessive peptide bond hydrolysis may release bitter peptides, resulting in undesirable off-flavors. Scientists are constantly looking for better and safer methods to improve the functional properties of protein to meet the needs of the food industry. 

Many researchers have developed methods for improving the functional properties of proteins by using chemical [1-9] and enzymatic modifications [10-14] to meet the requirement for high-quality proteins in food ingredients. However, most of these methods are not used for food applications because of potential health hazards or the appearance of detrimental products. Therefore approaches different from the conventional ones are desirable for the improvement of the functional properties of proteins in food systems. 

Protein-based ingredients contribute to the enhancement of food texture, flavor, and eye appeal [130], Functionality of protein ingredients can be enhanced also by enzymatic modifications. The factors influencing the choice of an appropriate enzyme for improvement of functional properties of proteins are as follows specificity of the enzyme, conformation of the protein, pH optimum, presence of activators and/or inhibitors, availability, thermostability, and financial causes. 

As stated previously, the functional performance of food proteins as ingredients is dictated by surface characteristics, including hydropho-bicity, electrostatic, and steric parameters [100]. All of these properties can be modified by the processing utilized to provide a concentrated food protein ingredient. Although the process modification that influences the functionality of a food protein will be specific to the type of protein processed, there are some general characteristics that apply equally to all common food proteins. These include... 

Hydrocolloids are high-molecular-weight hydrophihc biopolymers used as functional ingredients in the food industry for the control of viscosity, gelation, microstructure, texture, flavor, and shelf-hfe. The term hydrocolloid encompasses all the polysaccharides that are extracted from plants, seaweeds, and microbial sources, as well as gums derived from plant exudates, and modified biopolymers made by chemical or enzymatic treatment to be soluble or dispersible in water. The general molecular and functional properties of proteins and polysaccharides are compared in Table 5.1. 

Oilseed proteins are used as food ingredients at concentrations of 1—2% to nearly 100%. At low concentrations, the proteins are added primarily for their functional properties, eg, emulsification, fat absorption, water absorption, texture, dough formation, adhesion, cohesion, elasticity, film formation, and aeration (86) (see Food processing). Because of high protein contents, textured flours and concentrates are used as the principal ingredients of some meat substitutes. 

The consumption of dairy products plays a significant role in providing high-quality protein, vitamins, minerals, and other bioactive compounds to the American diet. Dairy products are consumed fresh in the United States in the form of fluid milk, cheese, yogurt, butter, and ice cream. Dried and condensed products such as nonfat dried milk, whey, whey protein concentrates, and isolates are also produced which are used as ingredients to boost the nutritional and functional properties of a host of other food... 

Characteristically, legume seeds are rich in protein and contain intermediate to high levels of lysine and threonine which are important in balancing the deficiencies of these essential amino acids in cereal diets. Certain legume proteins, such as soybean, also exhibit strong functional properties, especially water solubility, water and fat binding and emulsification. Thus soybean flours, protein concentrates and isolates have been used widely as nutritional supplements and functional ingredients in foods. 

The increasing interest in nutritional and functional properties of soybean protein has promoted their use in the manufacturing of foods for human consumption. Soybean products (particularly infant formulas and soybean dairy-like) may also represent an interesting substitute for infants and people allergic to milk proteins. On the other hand, due to their technological properties and low cost, soybean proteins are increasingly employed as ingredients in milk, bakery, and meat products, in which their addition is forbidden or allowed up to a certain limit. 

Nowadays it is well established that the interactions between different macromolecular ingredients (i.e., protein + protein, polysaccharide + polysaccharide, and protein + polysaccharide) are of great importance in determining the texture and shelf-life of multicomponent food colloids. These interactions affect the structure-forming properties of biopolymers in the bulk and at interfaces thermodynamic activity, self-assembly, sin-face loading, thermodynamic compatibility/incompatibility, phase separation, complexation and rheological behaviour. Therefore, one may infer that a knowledge of the key physico-chemical features of such biopolymer-biopolymer interactions, and their impact on stability properties of food colloids, is essential in order to be able to understand and predict the functional properties of mixed biopolymers in product formulations. 

Relationships with other properties. In any food system and possibly in simple systems, the protein ingredient is likely to perform several functions, most of which are being discussed in... 

This book updates and presents new information on the physicochem-istry of functionality, the roles and use of proteins for improving the functional properties of foods, and the application of data from model test systems to actual food ingredients. This volume should be useful to food processors, engineers, chemists, physicists, and others engaged in these or related areas of research. It also is hoped that this book will stimulate its readers to expand research on functionality. 

Morr, C. V. 1982. Functional properties of milk proteins and their use as food ingredients. In Developments in Dairy Chemistry, Vol. 1 Proteins. P. F. Fox (Editor). Applied Science Publishers, New York, p. 375-397. 

For adoption as an ingredient in foods, the isolated protein should have appropriate functional properties (111). Currently we are examining some functional properties of decitraconylated yeast proteins. 

Increasing emphasis is being placed on isolating proteins from various sources and using them as food ingredients. In many applications functional properties are of... 

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