Citrate metabolism by Enterococcus faecalis FAIR-E 229

Citrate metabolism by Enterococcus faecalis FAIR-E 229 was studied in vario us growth media containing citrate either in the presence of glucose or lac tose or as the sole carbon source. In skim milk (130 mM lactose, 8 mM citra te), cometabolism of citrate and lactose was observed from the first stages of the growth phase. Lactose was stoichiometrically converted into lactate , while citrate was converted into acetate, formate, and ethanol. When de M an-Rogosa-Sharpe (MRS) broth containing lactose (28 mM) instead of glucose was used, E. faecalis FAIR-E 229 catabolized only the carbohydrate. Lactate was the major end product, and small amounts of ethanol were also detected . Increasing concentrations of citrate (10, 40, 70, and 100 mM) added to MR S broth enhanced both the maximum growth rate of E. faecalis FAIR-E 229 and glucose catabolism. although citrate itself was not catabolized. Glucose w as converted stoichiometrically into lactate, while small amounts of ethano l were produced as well. Finally, when increasing initial concentrations of citrate (10, 40, 70, and 100 mM) were used as the sole carbon sources in M RS broth without glucose, the main end products were acetate and formate. S mall amounts of lactate, ethanol, and acetoin were also detected. This work strongly supports the suggestion that enterococcal strains have the metabo lic potential to metabolize citrate and therefore to actively, contribute t o the flavor development of fermented dairy, products.