(138b) Influence of Nutrient Compositions on Optically Pure D-Lactic Acid Production By Sporolactobacillus Terrae SBT-1

D-lactic acid is an important precursor of many chiral chemicals and also a feedstock of polylactic acid (PLA), an attractive versatile biodegradable plastic. PLA is usually produced from optically pure L-lactic acid. However, blending D- and L-lactic acid polymers had higher mechanical performance, thermal resistance, and hydrolysis resistance than the respective single polymers. Thus, poly(D-lactic acid) is also used. Recently, a growing demand for PLA greatly promotes the efficient and environmentally friendly D-lactic acid production from biological process. The most studied wild-type D-lactic acid producer recognizes to the genus Lactobacillus and Sporolactobacillus. So far, the current information of commercial production by fermentation of D-lactic acid is limited. Furthermore, the main obstacles to effective fermentation are being discussed; especially, cost-efficient microbial production of optically pure lactic acid. Although many efforts have been made to enhance the efficiency and cost-effectiveness of D-lactic acid production, less information is available about its underlying regulatory mechanism. Based on the previous reports, several factors, such as medium composition, fermentation conditions, and operation modes influence the enantiomeric purity. This study attempts to explore the effect of nutrient compositions contained in a preculture medium for the seed development step of D-lactic acid production by S. terrae SBT-1. Additionally, the effect of mixing on the fermentation performance was also observed to achieve an efficient D-lactic acid production in 5 L stirred fermenter scale. To study the effect of different medium compositions, all nutrient components (carbon source, nitrogen source, mineral salts, and trace elements) were determined under different types and concentrations. Among the tested fermentation conditions, a favorable preculture media for lactic acid production by SBT-1 was 10 g/L of glucose, 15 g/L yeast extract, 4 g/L NH₄Cl, 0.25 g/L of KH₂PO₄, 0.25 g/L of K₂HPO₄, and 10 mL of salts solution (400 mg of MgSO₄ 7H₂O, 20 mg of MnSO₄ 5H₂O, 20 mg/L FeSO₄ 7H₂O, and 20 mg NaCl per 10 mL of solution). In optimal batch fermentation, complete sugar consumption was investigated at 36 h with maximum lactic acid concentration of 118.36 g/L, the yield of 0.97 g/g and productivity of 3.22 g/L/h. It was further found that the enantiomeric purity of D-lactic acid produced during the fermentation was close to 100% (99.99 %ee). Additionally, the results confirmed that different nutritional fact contained in production medium extremely impact on the production rate and optical purity of lactic acid.