The role of NADH-oxidation in acetoin and diacetyl production from glucose in Lactococcus lactis subsp. lactis MG1363

Abstract

Product formation from glucose and NADH-oxidase activity from Lactococcus lactis MG1363, a non-citrate fermenter, was studied under aerobic conditions. In continuous cultures constantly aerated to 80% air saturation, the usual homolactic fermentation was almost completely replaced by acetate fermentation (80–90% of the fermented glucose) at low dilution rates. As the dilution rate was increased, the homolactic fermentation was partially restored, however the glucose fermentation profile was pH dependent. Significant production of acetoin and diacetyl was found at low pH and high dilution rates. NADH-oxidase activity was studied under different culture conditions. An up to fivefold increase in NADH-oxidase activity was observed in batch culture when air tension was increased from 0% to 80%. In aerobic continuous cultures at 80% air saturation, the NADH-oxidase activity was directly dependent on dilution rate and growth pH. The observed variations in NADH-oxidase activity played a crucial role in pyruvate flux redistribution and clearly correlated with the observed shifts in end product formation from glucose.