Diacetyl and alpha-acetolactate overproduction by Lactococcus lactis subsp. lactis biovar diacetylactis mutants that are deficient in alpha-acetolactate decarboxylase and have a low lactate dehydrogenase activity.

Lactococcus lactis subsp. lactis biovar diacetylactis strains are utilized in several industrial processes for producing the flavoring compound diacetyl or its precursor alpha-acetolactate. Using random mutagenesis with nitrosoguanidine, we selected mutants that were deficient in alpha-acetolactate decarboxylase and had low lactate dehydrogenase activity. The mutants produced large amounts of alpha-acetolactate in anaerobic milk cultures but not in aerobic cultures, except when the medium was supplemented with catalase, yeast extract, or hemoglobin.