Abstract
Optically pure lactic acid has recently received increased attention as a key intermediate of biodegradable plastics. Many researchers have been studying production of L-lactic acid by lactic acid bacteria and fungi from biomass. However, little attention has been given to microbial production of D-lactic acid. We studied production of D-lactic acid from rice bran, one of the most agricultural by-products in Japan. Lactobacillus delbrueckii subsp. delbrueckii IFO3202 was used for the production of D-lactic acid. Since rice bran contains sugars as starch and cellulose, we applied simultaneous saccharification to lactic acid fermentation with amylase and cellulase; 37 kg m-3 soluble sugar was obtained from 100 kg m-3 defatted rice bran powder by enzymatic hydrolysis at 37°C and pH 5.0 with 6.7 g m-3 amylase and 3.3 g m-3 cellulase. L. delbrueckii IFO3202 was inoculated into MRS medium without glucose after the addition of unsterilized defatted rice bran powder and enzyme solution. The bacterium produced 28 kg m-3 lactic acid from 100 kg m-3 rice bran after 36 h at 37°C and pH 5.0, where the growth of microorganisms contaminated in the bran was suppressed. The optical purity of produced D-lactic acid was 95% e.e.
