Abstract: A strain of Lactobacillus lactis highly capable of producing diacetyl, named as DX, was screened out of 6 lactic acid bacterial isolates and the fermentation conditions for diacetyl production by strain DX were optimized. The 16S rDNA sequence analysis and phylogenetic tree indicated that the 16S rDNA gene sequence of strain DX revealed 99% homology with Lactococcus lctis. Therefore, this strain was identified as Lactococcus lctis. Using central composite experimental design combined with response surface methodology, the optimal fermentation conditions for diacetyl production by strain DX were determined as follows: skim milk concentration 10 g/100 mL, inoculum amount 2%, fermentation medium initial pH 6.5, and fermentation temperature 37 ℃. Under these conditions, the diacetyl production was up to 22.383 mg/L.

Key words: lactic acid bacteria, diacetyl production, screening, fermentation conditions, optimization