AMINOPEPTIDASE ACTIVITIES OF STARTER AND NONSTARTER LACTIC-ACID BACTERIA UNDER SIMULATED CHEDDAR CHEESE RIPENING CONDITIONS

The effects of pH, NaCl and CaCl2 concentration on aminopeptidase acti vities of lactic acid bacteria were investigated in order to assess th e potential role of these enzymes on proteolysis during cheese ripenin g. A NaCl concentration of around 4% and a CaCl2 concentration of arou nd 125 mM were selected for study to approximate concentrations presen t in the moisture phase of ripening Cheddar cheese. At pH 5.2, the pH of mature Cheddar cheese, aminopeptidase activities were partially inh ibited in comparison to activities at physiological pH (7.5). However, most of the hydrolysis activities at the lower pH could be either par tially or fully restored by the addition of NaCl and/or CaCl2 at conce ntrations found in the moisture phase of ripening Cheddar cheese. Ther e was a major difference between the Lys p-NA hydrolysis activity of l actococci and lactobacilli in that the activity of lactococci was stim ulated in the presence of salts while the activity of the lactobacilli was inhibited. These results indicate that variations in salt concent ration are important parameters in cheese ripening and flavour develop ment due to their effect on peptidase activities. A decrease in the co ncentration of NaCl, for instance, while perhaps increasing the risk o f growth of contaminating microflora, may reduce bitter flavour develo pment through increased PepN activity of selected non-starter lactobac illi if used as adjuncts. (C) 1998 Elsevier Science Ltd. All rights re served.