Citrate Utilization and Diacetyl Production by Various Strains of Leuconostoc mesenteroides ssp. cremoris

Abstract

Sixty Leuconostoc strains from different culture collections were studied for taxonomic identification. Based on morphological and biochemical tests, 21 strains, including 1 from the American Type Culture Collection, were typed as Leuconostoc mesenteroides ssp. cremoris. The objective of this identification and of an additional phenotypic characterization of Leu. mesenteroides ssp. cremoris strains was to select the strains that were most useful for producing flavor compounds in dairy fermentations. Strains were examined for citrate utilization, production of diacetyl and acetoin under neutral and acidic conditions, diacetyl reductase activity, and plasmid profiles. Considerable variability within strains was observed. Most strains utilized citrate under neutral conditions, pH 6.5, without a concomitant production of diacetyl or acetoin. Although addition of yeast extract to milk stimulated bacterial growth and citrate utilization, no diacetyl or acetoin was detected in these cultures. Only the addition of citric acid after a preincubation period resulted in significant production of diacetyl and acetoin by pure cultures of Leu. mesenteroides ssp. cremoris. Strains were found that utilized citrate to produce diacetyl and acetoin with low diacetyl reductase activity, and these strains were compatible with acid-producing lactococci. Such strains are most valuable for use as starters for cultured dairy products that rely on the presence of diacetyl for maximum quality.