Microbial D-lactic acid production, In Situ separation and recovery from mature and young coconut husk hydrolysate fermentation broth

Abstract

The bioplastic industry's demand for D-lactic acid is increasing due to the widespread use of polylactic acid (PLA). Presently, D-lactic acid production exploits lignocellulosic biomass as carbon sources for fermentation gaining major attention. Mature coconut husk (MCH) and young coconut husk (YCH) hydrolysates were used as fermentation broth for D-lactic acid production by Lactobacillus coryniformis subsp. torquens. Yeast extract was added and broth pH was controlled by NaOH in both hydrolysates to facilitate the D-lactic acid production. A significant increase in D-lactic acid production with 14.93 and 19.88 g/L, in MCH and YCH was observed, respectively. However, the D-lactic acid produced existed in the form of lactate salt, which requires multiple separation and purification steps. In situD-lactic acid separation and recovery using ion exchange resin (IRA-67) of 0.4–1.0 g was investigated, and the result showed that 0.6 g of resin effectively separate D-lactic acid while maintaining broth pH in the optimum range. The total recovery of D-lactic acid from IRA-67 resin was 0.67 g for MCH and 0.90 g for YCH hydrolysate broth, with 90% recovering efficiency. The recovered D-lactic acid was considered to have the least fermentation impurities and potentially be used in PLA synthesis.