ENGINEERING OF CAMEL CHYMOSIN FOR IMPROVED CHEESE PROPERTIES

摘要

More than 20 Mio tons of cheese are produced world-wide per year. By improving cheese yield and quality through process optimization, the amount of milk needed for manufacturing can be reduced significantly. Chymosin, an aspartic acid protease, is initiating milk coagulation in cheese manufacturing by cleaving off the glycomacropeptide (GMP) from the surface of casein micelles. Non-specific proteolysis of casein molecules by chymosin during this milk clotting process releases soluble peptides into the whey, resulting in protein losses from the cheese. The ratio between specific clotting activity (C) and non-specific proteolysis (P) of a coagulant can therefore be used as predictor for cheese yield. During ripening of the cheese, remaining coagulant continues proteolytic break-down of the caseins with significant impact on cheese properties. While the main proteolytic activity, the release of N-terminal peptides from alphaS1 casein (alphaS1-N), is associated with cheese softening and loss of firmness, cleavage of the C-terminal end of beta casein (beta-C) contributes to unwanted bitterness of the cheese [1]. The chymosin from Bos taurus (bovine chymosin) is traditionally used as milk coagulant in cheese manufacture. However, the homologous enzyme from Camelus dromedarius (camel chymosin) has been shown to be a superior alternative for various cheese types, since it reveals higher specific activity (C) and specificity (C/P) for the milk clotting reaction [2], as well as lower alphaS1 and beta casein proteolysis during ripening (Fig. 1).