Study of the effects of temperature, pH, NaCl, and a(w) on the proteolyticand lipolytic activities of cheese-related lactic acid bacteria by quadratic response surface methodology

The individual and interactive effects of temperature, pH, NaCI, and a, on the proteolytic and lipolytic activities of Lacrobacillus delbrueckii subsp . bulgaricus B397, Lactococcus lactis subsp. lactis T12, and Lb. plantarum 2739 were studied by quadratic response surface methodology. The effects on enzyme activities depended on the interactions among the independent varia bles, type of activity, substrate and, especially, species. The proteinase activity of strains B397 and T12 was affected differently by pH as individu al or interactive terms depending on the type of substrate alpha(si) or bet a-casein. The increase of NaCI concentration (2.5-7.5%) under cheese-like c onditions had a negative effect on the proteinase activity of strain T12. T he effect of NaCl was related to the corresponding decrease in a(w,) Aminop eptidases N and A, iminopeptidase and endopeptidase of Lc. lactis subsp. la ctis T12 were strongly inhibited by pH 5-6 and NaCl concentration higher th an 3.75%. The negative effects of these independent variables was in severa l cases enhanced by their interaction and/or by the interaction with the lo west temperatures. In contrast, the same peptidases of Lb. plantarum 2739 r etained a high activity under the very hostile environmental conditions. Im inopeptidase and especially endopeptidase activities of strain 2739 were st imulated slightly by NaCl at concentrations up to 5%. Lipase/esterase activ ity of Lb. delbrueckii subsp. bulgaricus B397 was markedly inhibited under cheese-like conditions. (C) 1999 Elsevier Science Inc. All rights reserved.