Milk proteins enzymatic processing

The earliest commercial milk protein enzymatic modification dates back to the 1940s, when the first formulas for allergenic infants were made. The aims of this process were to reduce allergenicity as well as to change the functional properties of proteins while preserving their nutritional value for clinical use. Unfortunately the hydrolysates thus obtained were characterized by bitter taste, and for mainly this reason proteolysis, as a technological process, enjoyed very little popularity. 

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). 

Methionine-enriched protein was produced also from an enzymatically prehydrolyzed milk protein (SR) by the EPM process, and the methionine contents of SR and the EPM product were determined by a microbiological method. The methionine content in the EPM product was more than twice as high as in the substrate. These protein fractions were separated by thin-layer chromatography [83]. The separated peptides and peptide mixtures were eluted and their molar amino acid contents were determined. The ratio of polar and apolar amino acids in the peptides was found to be influenced basically by transpeptidation taking place in the EPM reaction. The analysis of the peptides of these products showed that methionine was incorporated mainly in peptides with a relatively high ratio of apolar amino acids. 

Allergenicity of proteins of milk and various (heat-treated, fermented, and enzymatically modified) milk products was determined in vitro by ELISA [203]. Food processing like heat treatment or fermentation does not reduce the allergenic character of the proteins. The enzymatic modification, however, showed a significant reduction in the allergenicity of milk proteins (Fig. 7). 

Figure 7 Allergenic character of products obtained from cow s milk proteins by food processing or enzymatic modifications. (1) Cow s milk (2) Na-caseinate (3) kefir (4) yogurt (5) cheese (6,7,8) a-chymotryptic, tryptic, and peptic hydrolysates of casein, respectively (9,10,11) a-chymotryptic tryptic, and peptic EPM products of casein, respectively (12,13) a-chymotryptic and tryptic EPM products of casein, respectively, with methionine enrichment (14,15) fractions of a-chymotryptic EPM products of casein (16,17) fractions of peptic EPM products of casein (18) commercial hypoallergenic formula.

Cheese flavor. C. f. is formed from milk fat, milk protein, lactose during the maturation of cheese mainly through enzymatic and microbial processes. Quantitative and, sometimes, qualitative differences are responsible for the diversity of cheese flavors. Typical aroma substances are the free C4-C,2 fatty acids, C7, C and C, 2-alkanones (also in Roquefort cheese), the butter aroma substances acetoin, 2,3-butanedione, and 5- alkanolides, (-)-(R)-l-octen-3-ol (fungus note in Camembert), 4-alkanolides and alkylpyrazines with nut-like nuances, indole, skatole, and phenols with stable-like odors, as well as numerous sulfur compounds such as methional, methyl mercaptan (moldy, coal-like), dimethyl sulfide and dialkyl polysulfides with, in part, onion- and garlic-like nuances. Furaneol" and homofuraneol (see hydroxyfura-nones) are responsible for the sweetish odor of Em-mental cheese. 

Watanabe and Arai wrote an excellent review on the properties of enzymatically modified proteins and compared the chemical and enzymatic processes of various proteins [135]. Enzymatic processes can normally be carried out under milder and therefore safer experimental conditions than conventional chemical processes. Proteolytic enzymes have been used on proteins to improve their solubility soy protein, leaf protein concentrates, fish protein concentrates, meat proteins, egg proteins, milk proteins, and blood proteins. Special attention was given to caseins, gelatins, egg proteins, and cereals. Partial hydrolysis of these proteins under well-controlled conditions can produce emulsifying and whipping agents... 

Lorenzen, P.C., Mautner, A., and Schlimme, E. 2000. Enzymatic crosslinking of proteins in the production of milk products In Proceedings of the 1st International Symposium on Enzymatic Protein Processing (H. Gruppen and W. van Hartingsveldt eds), pp. 163—169. TNO Nutrition and Food Research Institute, Zeist, The Netherlands. 

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). 

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