Cheese, casein degradation

Fig. 2. Pathway of aSI-casein degradation during Gouda-type cheese ripening.

Fig. 4 Evolution of total casein content together with a- and 13-casein degradation for 30 days of ripening of ewe cheese.

Micrococci comprise approximately 78% of the nonlactic bacteria in raw milk Cheddar cheese (Alford and Frazier 1950). The proteolytic system of Micrococcus freudenreichii functions optimally at 30 °C and at a pH near neutrality (Baribo and Foster 1952). An analysis of pro-teinases present in 1-year-old Cheddar cheese indicates that micrococci may contribute to proteolytic activity (Marth 1963). Proteolytic micrococci also contribute to the ripening of surface-ripened cheeses such as brick and Camembert (Lenoir 1963 Langhus et al. 1945). Micrococcal proteases probably contribute to development of ripened cheese flavor when ripening temperatures are above 10°C (Moreno and Kosikowski 1973). This effect results from degradation of /3-casein. 

Creamer, L. K. and Richardson, B. C. (1974). Identification of the primary degradation product of asl-casein in Cheddar cheese. NZ J. Dairy Sci. Technol. 9,9-13. 

Bitter peptides that have been isolated from cheese are summarized in Table VIII. As expected, bitter peptides originate principally from hydro-phobic regions of the caseins, e.g., sequences 14 to 34, 91 to 101, and 143 to 151 of asi-casein, and 46 to 90 or 190 to 209 of /8-casein. As discussed by McSweeney et al. (1996) the majority of these peptides show evidence of some degradation by lactococcal proteinases and/or peptidases. 

Traditionally fermented dairy products have been used as beverages, meal components, and ingredients for many new products [60], The formation of flavor in fermented dairy products is a result of reactions of milk components lactose, fat, and casein. Particularly, the enzymatic degradation of proteins leads to the formation of key-flavor components that contribute to the sensory perception of the products [55], Methyl ketones are responsible for the fruity, musty, and blue cheese flavors of cheese and other dairy products. Aromatic amino acids, branched-chain amino acids, and methionine are the most relevant substrates for cheese flavor development [55]. Volatile sulfur compounds derived from methionine, such as methanethiol, dimethylsulflde, and dimethyltrisul-fide, are regarded as essential components in many cheese varieties [61], Conversion of tryptophan or phenylalanine can also lead to benzaldehyde formation. This compound, which is found in various hard- and soft-type cheeses, contributes positively to the overall flavor [57,62]. The conversion of caseins is undoubtedly the most important biochemical pathway for flavor formation in several cheese types [62,63]. A good balance between proteolysis and peptidolysis prevents the formation of bitterness in cheese [64,65],... 

Proteolytic enzymes. Proteolytic enzymes produced by starter organisms usually play a key role in the degradation of milk caseins to oligopeptides, smaller peptides and amino acids in fermented dairy products and cheese. Besides being necessary for normal growth of lactococci in milk, this degradation of proteins is important for the development of flavour and texture in cheese. 

The caseins are increasingly degraded during longer ripening. Water-soluble peptides and amino acids are formed which bind a part of the ions. Thus, when chewing a cheese ripened for... 

In stored foods containing natural bixin (9 -ds isomer), in the presence of light, aU-trans-bixin may result and, by its hydrolysis, all-trfl s-norbixin. In cheeses containing bixin, these substances bind to phosphoproteins (e.g. to some caseins), causing pink discoloration of products. In addition to tra s-isomers, some degradation products of bixin may also arise, such as methyl ester of d -trans-4,8-dimethyltetradeca-2,4,6,8,10,12-hexaenoic acid and aromatic hydrocarbons (e.g. m-xylene). 

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