DEVELOPMENT OF L-LACTATE FERMENTATION USING CHITOSAN AS A NEUTRALIZER

Abstract

 Optically pure lactate is a raw material for biodegradable polylactic resin. Such lactic acid is produced by fermentation, and lime is commonly used as a neutralizing agent. However, gypsum is generated in the process of releasing lactic acid from calcium lactate produced by lactic acid fermentation, and the cost associated with its treatment is expensive and unfriendly to the environment. Thus, it is necessary to establish the new lactate production, for example, by finding alternative neutralizers. Previous research investigated lactic acid fermentation using chitosan as a neutralizer, although the antibacterial activity of chitosan against the lactic acid-producing bacteria inhibited the fermentation. However, the molecular weight of chitosan might influence the antimicrobial activity; therefore, we elucidated the lactic acid fermentation using various molecular weights of chitosan as a neutralizer. In an antibacterial assay, the molecular weight of 3,000~20,000 Da did not present bactericidal activity against the lactate-producing bacteria. In the lactate fermentation, maintaining the pH of the culture medium at not 5.5 but 6.5 decreased chitosan's antibacterial activity and led to chitosan lactate production when using chitosan oligosaccharide as a neutralizer. Additionally, immobilizing lactate-producing bacteria produced chitosan lactate if using a high molecular weight of chitosan that represents the antibacterial activity.