Esterases of Lactobacillus helveticus and Lactobacillus delbrueckii ssp. bulgaricus

Abstract

Intracellular esterase activity of Lactobacillus helveticus CNRZ 32, L. helveticus ATCC 10797, and Lactobacillus delbrueckii ssp. bulgaricus ATCC 12278 were determined using chromogenic o- and 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 delbrueckii ssp. bulgaricus ATCC 12278 had the most esterase activity, followed by L. helveticus CNRZ 32, and then by L. helveticus ATCC 10797. Active esterases in crude cell-free extracts were separated by PAGE; identified by histochemical staining; and their specificities toward α- and β-naphthyl esters of acetic, butyric, caproic, and palmitic acids were determined. 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. helveticus CNRZ 32 increased gradually from the beginning of the log phase until it reached a maximum after 24h 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. helveticus 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 between 1.3- and 1.7-fold more activity, depending on which test substrate was hydrolyzed, than did MRS-grown cells.