Milk-Clotting Enzymes. 1. Proteolysis During Cheese Making in Relation to Estimated Losses of Yield

Abstract

Cheddar cheese was made in beakers (by the process for aged cheese) to compare milkclotting enzymes for their effect on proteolysis during coagulation, cooking, and cheddaring. All enzymes released more N into whey during cooking and cheddaring than calf rennet except the equal mixture of calf rennet and swine pepsin during cheddaring. Levels of true protein were the same in whey during cooking and during cheddaring with all enzymes, except those from Bacillus polymyxa showed proteolysis of whey proteins. Hydrolysis of casein occurred after cooking and during cheddaring with all enzymes including calf rennet. Data were discussed with respect to protein recoveries in cheese from ultrafiltered milk.Probable reductions in yield were estimated using a factor of 27.06 for converting estimated casein reductions in milk to percentage of yield losses. This factor assumes: the prices of milk fat and cheese are equal; cheddar cheese of the same composition is made of .37 moisture and .017 salt; whey contained .065 fat-free, curd-free solids; milk contained .036 fat and .ON64 casein or was standardid to the same casein:fat ratio, considering casein losses; and yield of cheese was 9.834 kg100kg milk. Yield losses (± least significant differences), compared with losses of calf rennet, were estimated as: bovine pepsin, –.14 (± .08); equal mixture of calf rennet and swine pepsin, –.07 (± .08); Mucor pusillus, –.49 (± .11); M. miehei (preparation I), –.63 (± .11); M. miehei, (preparation II), –.68 (± .12); Endothia parasitica, –1.24 (± .32); B. polymyxa, 4.79% (± .32%). These would be economically important losses of concern to cheese makers.Special attention was given to replications and statistical analyses to reduce least significant differences: quadruplicate Kjeldahl analyses, 6 to 12 replicate trials per enzyme, with comparison among enzymes within days.Comparison of levels of N in whey during simulated cheese making in beakers is suggested for comparing milk-clotting enzymes for their effect on yield of different varieties of cheese. This could be considered a basic loss of yield; losses of curd and fat in whey would be additional losses.