High and Rapid L-lactic Acid Production by Alkaliphilic Enterococcus sp. by Adding Wheat Bran Hydrolysate

Abstract

Two strains of alkaliphilic lactic acid bacteria, L-120 and AY103, which can produce L-lactic acid extensively, were isolated during trials of L-lactic acid production under unsterilized conditions at pH 9. Strains L-120 and AY103 are similar to Enterococcus casseliflavus and Enterococcus faecalis, respectively, as determined by 16S rRNA gene sequencing. It was found that wheat bran hydrolysate (1.5 or 3.0% dry w/v) strongly stimulates the production of lactic acid in both strains. Strain L-120 produced 149 g L-1 L-lactic acid at 35°C under pH 9 from 180 g L-1 glucose with the production rate of 3.9 g L-1 h-1. Strain AY103 produced 153 g L-1 L-lactic acid from 180 g L-1 glucose with the production rate of 4.2 g L-1 h-1. Both strains produced high-optical-purity (100%) L-lactic acid. In addition, strain L-120 produced 12% (w/v) L-lactic acid from degraded inedible materials, i.e., rice straw and soy bean curd refuse, within 72 h under unsterilized conditions. The obtained results indicate that these two strains are very useful for Llactic acid production with the advantages of high productivity and rapid production with reduced costs of product purification, raw materials and fermenter sterilization.