Whey modification, chemical

The mechanisms of modification are different and depend on the chemical molecules used for the reactions. The anhydride of succinic acid reacts with lysine residues, a-amino groups of proteins and free thiol groups. During succinylation, proteins lose their globular structure and undergo aggregation by disulfide cross-binding with other whey proteins. Acetyl anhydride can modify tyrosine residues. 

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.). 

Although whey protein concentrates possess excellent nutritional and organoleptic properties, they often exhibit only partial solubility and do not function as well as the caseinates for stabilizing aqueous foams and emulsions (19). A number of compositional and processing factors are involved which alter the ability of whey protein concentrates to function in such food formulations. These include pH, redox potential, Ca concentration, heat denaturation, enzymatic modification, residual polyphosphate or other polyvalent ion precipitating agents, residual milk lipids/phospholipids and chemical emulsifiers (22). 

The first soybean protein ingredients made commercially available for food use included full-fat and defatted soy flours and grits (3, 7, 8). These products contain ca. 46-59% protein (NX 6.25) on a moisture-free basis and are available with various heat treatments for specific end-use. Soy protein concentrates and soy protein isolates were introduced into the market about 15 years ago (3, 9, 10, II). By definition soy protein concentrates must contain no less than 70% protein (N X 6.25) and isolates no less than 90% protein (N X 6.25), all on a moisure-free basis. In the past several years there has been much activity in the commercialization of textured soy protein products intended for the extension and replacement of meat. These textured products may be obtained through fiber spinning, shred formation, extrusion, or compaction (12, 13, 14, 15). In addition, soybean milk solids and the heterogeneous proteins in soybean whey might serve as useful substrates in chemical modifications for food use. This short recitation of commercial products illustrates the type of crude protein fractions available for practical modification. Many useful functional properties have been ascribed to these new food proteins. 

It is beyond the scope of this chapter to analyze in detail the various surface interactions and forces that proteins can provide. The number of amphiphilic proteins in the world of proteins is limited, which means that the proteins in use are mainly caseins, whey proteins, P-lactoglobulins (BLGs), egg albumin, bovine semm albumin (BSA), lysozyme, and soy proteins. All other plant proteins have very limited ability to strongly adsorb onto interfaces and reduce interfacial tension to only a minor extent. However, chemical and enzymatic modifications will improve the performance of these proteins (pea, cotton, and cereal proteins), and as a result a few modified proteins can be found in the marketplace that have relatively improved performance. 

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