DIACETYL PRODUCTION BY DIFFERENT STRAINS OF LACTOCOCCUS-LACTIS SUBSP LACTIS VAR DIACETYLACTIS AND LEUCONOSTOC SPP

Several strains of Lactococcus lactis subsp. lactis var. diacetylactis and Leuconostoc spp. were compared for product formation from citrate in milk cultures. Most strains produced acetoin and butanediol. Some strains derived from buffer starter cultures produced, in addition, alpha-acetolactate. Lactococcus lactis strain C17, which produced acetoin and butanediol but no alpha-acetolactate in culture, was compared physiologically with L. lactis strain Ru4, which produced only alpha-acetolactate. Activities of enzymes involved in citrate metabolism were almost identical in both strains, with the exception of alpha-acetolactate decarboxylase, which was missing in strain Ru4. The formation of alpha-acetolactate, acetoin and diacetyl was further analysed in cell-free extracts. Alpha-Acetolactate synthase activity saturated at a high pyruvate concentration (100 mm). This is in agreement with the observed accumulation of pyruvate externally, and probably internally, during alpha-acetolactate, acetoin and butanediol production by L. lactis cells.