An Electrophoretic Study of Peptidases in Starter Streptococci and in Cheddar Cheese

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A modified electrophoretic starch gel technique was developed and applied to the detection of peptidase activity in zymograms of crude extracts of Group N streptococci and extracts of cheese made with these organisms. The method required only 0–36 mg of peptide substrate for each test. Dipeptidase, tripeptidase and aminopeptidase activities were detected in strains of Streptococcus cremoris and Strep, lactis and in curds and cheeses made with these organisms. Intracellular and extracellular fractions of Strep, lactis showed similar peptidase activity but with Strep , cremoris there were fewer peptidases in extracellular fractions. The peptidase composition of curd and cheese extracts of different ages was dependent upon the strain and species of starter streptococcus used in making the cheese.