Protein in food systems

Sikorski, Z.E. (2002). Chemical reactions of proteins in food systems, in Sikorski, Z.E., ed.. Chemical and Functional Properties of Food Proteins, CRC Press, Boca Raton, 191-216. 

The most important feature affecting the functional and organoleptic properties of a protein is its surface structure. Surface structures affect the interaction of a protein with water or other proteins. By modifying the structure of the protein, particular functional and organoleptic properties are obtained. Functional properties of a protein are physicochemical characteristics that affect the processing and behavior of protein in food systems (Kinsella, 1976). These properties are related to the appearance, taste, texture, and nutritional value of a food system. Hydrolysis is one of the most important protein structure modification processes in the food industry. Proteins are hydrolyzed to a limited extent and in a controlled manner to improve the functional properties of a foodstuff. 

Table 2 Functional Roles of Food Proteins in Food Systems...

The effective utilization of proteins in food systems is dependent on tailoring the protein s functional characteristics to meet the complex needs of the manufactured food products. Many food proteins require modification to improve such functional properties as solubility, foaming and emulsifying activity (EA). Reviews on classical food protein modifications for improved functionality are available in the literature (Means and Feeney, 1971 Feeney and Whitaker, 1977, 1982, 1986). 

One of the most important factors that determine whether or not a protein is usable in the fabrication of a food product is its functionality. The functionality results from a combination of physico-chemical properties that define the behavior of the food protein in food systems. It is evident that a detailed understanding of food protein functionality requires an intimate knowledge of the protein structure. The bovine milk protein system has been studied in great detail. Although providing useful structure-function... 

A third approach, very commonly practiced, has been the study of specific properties in model systems of protein-nonprotein components of different but similar known proteins. The statistical correlation of the results to the behavior of the proteins in food systems throws some light on the effect of particular structural features on this behavior. 

The functional properties of food proteins is a subject of considerable interest and importance. For example, in the last two decades much effort has gone into the development of various nonconventional sources of protein. The vast majority of this effort, however, has been concentrated on various aspects of production of economical protein resources and not on the actual utilization of these resources. The result is that many nonconventional protein resources, while they can now be produced fairly easily, can in many cases be produced only in a form lacking desirable functional properties. The point is simply that a protein, even though it may have excellent amino acid balance and all other prerequisites for a nutritionally superior protein, will have no impact on human nutrition unless it has the functional properties necessary for its incorporation into food systems. A specific example of this problem is the case of fish protein concentrate, the utilization of which is severely restricted by its very limited solubility in water. There are, of course, many other examples, but for present purposes it is sufficient to emphasize that there is a real need for the development of chemical, physical, or enzymatic methods that increase the usefulness of proteins in food systems. 

Table I. Some Functional Properties of Proteins in Food Systems (1)...

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. 

Skills in separation of grain components and their analysis are needed to address these problems. Some examples of naturally occurring antinutritional compounds are phytates (already mentioned), phenols, tannins, and trypsin- and a-amylase inhibitors. Phenols and tannins bind with and precipitate proteins in food systems, thus decreasing digestibility. Minimizahon of these compounds in cereals is an objective. 

Quaternary structure of proteins in food systems is important for a number of reasons. Firstly, many food proteins are large and oligomeric in nature, composed of either identical or heterogeneous subunits. Examples include p-lactoglobulin (dimer), avidin... 

Interaction between proteins and other amphiphilic substances has been shown to influence technical properties of proteins in food systems. Since proteins and low molecular weight amphiphiles often coexist in systems where formation and properties of inter-facial films are of fundamental importance (e.g. dairy products, dough, meat emulsions), influence of the mode of interaction between proteins and amphiphiles in the bulk solution on the surface behaviour is of interest. 

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