(448a) Relationship of Different Cultivation Conditions to the Efficacy of D-Lactic Acid Fermentation By Sporolactobacillus Terraesbt-1

Lactic acid is a versatile organic acid which contains the chiral properties, including L-isomer and D-isomer. Recently, lactic acid is emerged in the variety of applications; in particular, its demand is driven by rapid expansion of poly(lactic acid) (PLA) market. PLA is synthesized by polymerization of lactic acid and employed for various applications including packaging, cosmetic, and pharmaceutical industries due to its biodegradability nature. The lactic acid molecule has a chiral carbon that confers optical purity. It can be found in two different optical isomers including L(+)-lactic acid and D(-)-lactic acid. Highly optically pure lactic acid is required for the synthesis of high-quality plastic, and poly-L-lactic acid (PLLA) and poly-D-lactic acid (PDLA) are produced from L-lactic acid and D-lactic acid, respectively. Microbial fermentation has been extensively used as the major route for the synthesis of optically pure lactic acid. In comparison of L-lactic acid, the production of optically pure D-lactic acid has attracted to develop due to the demand for producing thermostable PLA, but large-scale production of D-lactic acid has not yet been commercialized. The main obstacle to produce optically pure D-lactic acid is the market price that their cost should be competitive. Several limitations, including the use of alternative substrates, sensitivity to decrease lactic acid yield and productivity, and decreased optical purity of lactic acid have been being discussed. Furthermore, more cost-effective production of optically pure lactic acid is needed to meet the current huge demand. In addition, fermentation conditions might influence the optical purity of lactic acid. Two optically pure isomers of lactate were produced from pyruvate through reactions catalyzed by either the chiral-specific D-lactate dehydrogenase (D-LDH) or L-lactate dehydrogenase (L-LDH). However, studies on the associations of L- and D-LDH with the optical purity of lactate are limited. In this study aims to investigate the associations of L- and D-lactate dehydrogenase with the optical purity of lactate under different cultivation conditions. Comparison of D-lactic acid fermentation performance by S. terrae SBT-1 was carried out in flask culture. Different nitrogen sources, including yeast extract and corn steep liquor (CSL) could influence the optical purity of lactic acid as well as enzymes responsible for L- and D-lactic acid production. Decreasing optical purity of D-lactic acid was observed in fermentation medium containing CSL as the nitrogen source. Consistently, lower L-LDH and D-LDH were also found. This indicated that the proper nitrogen source could impact the correlation between the optical purity of D-lactate and enzyme activities in S. terrae SBT-1.