Esterases of Lactobacillus helveticus and Lactobacillus delbrueckii ssp. bulgaricus

Intracellular esterase activity of Lactobacillus helvetieus CNRZ 32, L. helvetieus ATCC 10797, and Lactobacillus delbrueckii ssp. bulgarieus ATCC 12278 were detennined using chromogenic 0and p-nitrophenyl derivatives of fatty acids as substrates. Each of the three strains of lactobacilli had active esterase, which hydrolyzed p-nitrophenyl derivatives of acetate, butyrate, and caproate. Lactobacillus delbrueekii ssp. bulgaricus ATCC 12278 had the most esterase activity, followed by L. helveticus CNRZ 32, and then by L. helvetieus ATCC 10797. Active esterases in crude cell-free extracts were separated by PAGE; identified by histochemical staining; and their specificities toward (t-and 13-naphthyl esters of acetic, butyric, caproic, and palmitic acids were detennined. Extracts of each of the three lactobacilli exhibited two active esterase bands, but relative mobility values of the enzyme differed among the strains. Esterase activity of L. helvetieus CNRZ 32 increased gradually from the beginning of the log phase until it reached a maximum after 24 h of incubation. The freezing process reduced, when compared with unfrozen cells, the intracellular esterase activity of L. helveticus CNRZ 32 grown in MRS broth or skim milk. Cells of L. helvetieus CNRZ 32 grown in 10% sterile skim milk had slightly less esterase activity (up to 13%), and cells grown in a 7.5% whey-based medium had be-