Abstract:

Calcium carbonate added as the neutralizer during Rhizopus oryzae fermentation for L-lactic acid production would cause membrane fouling and environmental pressure during the downstream separation. As a consequence, ammonia and sodium hydroxide were separately used as a substitute for calcium carbonate in this study, and the fermentation conditions for L-lactic acid production and the fermentation kinetics were dealt with. Added calcium carbonate during during Rhizopus oryzae fermentation resulted in an average 7.3-fold increase in L-lactic acid production. The optimal concentrations of added ammonia and sodium hydroxide were 10 mol/L and 25%, respectively. Mycelial pellets in diameter ranges between 0.2 mm and 1.2 mm and between 1.2 mm and 2.2 mm were formed after 72 h fermentation under these concentration conditions, and the residual sugar amounts were 2.58g/L and 1.37 g/L and the L-lactic acid concentrations in the fermentation broths were 74.34 g/L and 80.61 g/L, respectively.

Key words: Rhizopus oryzae, L-lactic acid, neutralizer, fermentation kinetics