Study of the effects of temperature, pH and NaCl on the peptidase activities of non-starter lactic acid bacteria (NSLAB) by quadratic response surface methodology

The individual and interactive effects of temperature, pH and NaCl on the a minopeptidase-types N and A and proline iminopeptidase activities of severa l strains of non-starter lactic acid bacteria (NSLAB) were studied by quadr atic response surface methodology. The effects on enzyme activities depende d on the interactions among the independent variables, species, strains wit hin species and type of activity. With few exceptions, the aminopeptidases N and A and proline iminopeptidase activities of Lactobacillus casei sap. p seudoplantarum and Lb. curvatus were strongly inhibited by the hostile chee se-like conditions, while the peptidases of Lb. casei ssp. casei and especi ally Lb. plantarum were tolerant or not affected by variations in pH and sh owed the least sensitivity to NaCl or even a requirement for NaCl for the o ptimal activity. Strains which maintained relatively high activity under ch eese-like conditions were selected within the species. The proline iminopep tidase of Lb. casei ssp, casei 2107 as well as Lb. plantarum 2788 and 2789 greatly tolerated the interactions among the independent variables. At 10 d egrees C in the presence of 3.750% NaCl and independent of the pH, the PepN activity of Lb. plantarum 2788 and 2789 was at least 33% of the maximum de termined at pH 7.5 and 35 degrees C. Proline iminopeptidase activity was mo st sensitive to the individual and interactive variations in temperature, p H and NaCl. On the other hand, aminopeptidase-type A activity seemed to be least sensitive to cheese-like conditions. (C) 2000 Elsevier Science Ltd. A ll rights reserved.