Milk proteins chemical modification

The following factors appear to control the emulsification properties of milk proteins in food product applications 1) the physico-chemical state of the proteins as influenced by pH, Ca and other polyvalent ions, denaturation, aggregation, enzyme modification, and conditions used to produce the emulsion 2) composition and processing conditions with respect to lipid-protein ratio, chemical emulsifiers, physical state of the fat phase, ionic activities, pH, and viscosity of the dispersion phase surrounding the fat globules and 3) the sequence and process for incorporating the respective components of the emulsion and for forming the emulsion. 

Elimination of Immunoreactive Properties of Milk Proteins in Chemical Modifications (1 g of Modifying Agent/g Protein)... 

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.). 

The chemical modifications of the tryptophan residues lead to a decrease in the nutritive value of proteins as observed in autoclaved soja meals (124), heated meats (125), heated casein (126), and heated skim milk (122) this last reference is probably the most reliable work published in this field. The nutritional effects and the metabolic transit of heat-treated and oxidized tripeptide (gly-try—gly) have been investigated (123,132,137) recently only the metabolic transit study is related here. 

Both the protein and fat components in milk influence the properties of food, but the ability of the milk to impart desirable properties to food is mostly influenced by the physical functional properties of the milk protein components (Kinsella, 1984 Mulvihill and Fox, 1989). The inherent functionality of milk proteins is related to the structural/ conformational properties of protein, which is influenced by both the intrinsic properties of the protein and extrinsic factors. Modification of the protein composition or structure and the organization of the proteins within the dairy ingredient through the application of physical, chemical, or enzymatic processes, alone or in combination, enable the differentiation of the functionality of the ingredient and designing the required functionality for specific applications (Chobert, 2003 Foegeding et al., 2002). 

Most chemical agents used for studying the chemical modification of proteins are not suitable for food applications. These studies nevertheless demonstrate how changes in amino acid side chains, and both the structure and conformation of proteins can impact on functionality. A comprehensive review of chemical modification of milk proteins has been carried out (Chobert, 2003). Only some highlights and more recent work on modification with chemical agents are covered here. 

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 now evident that acylation with anhydrides (such as acetic and succinic anhydrides) and with lactones (such as -propiolactone) is being proposed (< ) for improving the solubility of soy protein isolates at acidic pH, particularly for the preparation of coffee whiteners. Moreover, this chemical modification has been evaluated for altering the food-use properties of several milk proteins (40), egg protein (41), wheat protein (42), fish protein (43), and single-cell protein (44). 

The spectrum of surface active behavior displayed by food proteins directly reflects differences in structural and physicochemical properties among the proteins originating from various sources i.e. meat, milk, legumes. Chemical or enzymatic modification of model food proteins has indicated that alteration of specific structural features e.g. net charge, disulfide bonding, size, does influence film formation, foaming and emulsifying properties. 

Lastly, synthetic varieties of textiles are present primarily in apparel and are either petroleum-based or blends with natural fibers. Polyester fibers, aramid fibers, acrylics, nylon, polyurethane, olefins (hydrophobic), polylactide (hydrophilic), milk protein-based fibers, and carbonization-based fibers all constitute synthetics which require some level of surface-modification. This includes nonwovens, structures bonded together by entangling fiber or filaments mechanically, thermally, or chemically. 

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). 

Despite the proven occurrence of relatively large quantities of D-fructosamine derivatives in some common dehydrated foods, such as tomato or milk powders, no official or even recommended methods for their routine analysis in foods have thus far been offered. The situation is somewhat better with the fructosamine assay introduced into clinical practice however, the assay is not particularly selective and evaluates total fructosamine modification on circulating proteins, peptides, and other biomolecules combined. Difficulties with development of universal, fast, and reliable analytical methods for fiuctosamine derivatives originate Irom the chemical nature of this carbohydrate structure, which is unstable at elevated temperatures and in the presence of nucleophilic and oxidation agents. It does not absorb appreciably in the UV-Vis range, is highly hydrophilic, and is not readily modified into analytically useful derivatives. 

Polymers from nature may be used as isolated or modified. Modification was generally used in the past and continues to produce protein, starch and cellulose derivatives for many applications. New opportunities are becoming apparent for surplus by-products from the food industry such as the proteins from wheat, com, soy and milk. Lignin continues to be a cheap resource from the paper industry. All of these polymers may be chemically modified or blended with plastics from fossil or renewable origin to produce promising new materials. 

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