D-lactic acid production by Sporolactobacillus inulinus Y2-8 immobilized in fibrous bed bioreactor using corn flour hydrolyzate.

Abstract

In this study, a fibrous bed bioreactor (FBB) was used for D-lactic acid (D-LA) production by Sporolactobacillus inulinus Y2-8. Corn flour hydrolyzed with α-amylase and saccharifying enzyme was used as a cost-efficient and nutrient-rich substrate for D-LA production. A maximal starch conversion rate of 93.78% was obtained. The optimum pH for D-LA production was determined to be 6.5. Ammonia water was determined to be an ideal neutralizing agent, which improved the D-LA production and purification processes. Batch fermentation and fedbatch fermentation, with both free cells and immobilized cells, were compared to highlight the advantages of FBB fermentation. In batch mode, the D-LA production rate of FBB fermentation was 1.62 g/l/h, which was 37.29% higher than that of free-cell fermentation, and the D-LA optical purities of the two fermentation methods were above 99.00%. In fed-batch mode, the maximum D-LA concentration attained by FBB fermentation was 218.8 g/l, which was 37.67% higher than that of free-cell fermentation. Repeated-batch fermentation was performed to determine the long-term performance of the FBB system, and the data indicated that the average D-LA production rate was 1.62 g/l/h and the average yield was 0.98 g/g. Thus, hydrolyzed corn flour fermented by S. inulinus Y2-8 in a FBB may be used for improving D-LA fermentation by using ammonia water as the neutralizing agent.