CONTRIBUTION OF RENNET AND STARTER PROTEASES TO PROTEOLYSIS IN CHEDDAR CHEESE

Proteolysis in aseptic, chemically acidified (GDL) cheese and in starter cheese made under controlled bacteriological conditions (i.e., free of non-starter micro-organisms) was measured by gel electrophoresis, the formation of pH 4.6- and 12% trichloroacetic acid-soluble N, gel filtration and the liberation of free amino acids. Rennet was mainly responsible for the level of proteolysis detected by gel electrophoresis, pH 4.6-soluble N and gel filtration, i.e., large, medium and small peptides. Rennet alone was capable of producing only a limited range of free amino acids; only methionine, histidine, glycine, serine and glutamic acid were produced at quantifiable levels (> 0.2 .mu.mol/g) in GDL cheese. Free amino acids in cheddar cheese are mainly the result of microbial peptidase activity. The levels of free amino acids in the starter cheese were considerably lower than values reported for commercial cheddar.