D-lactic acid fermentation platform from oil palm trunk sap by sporolactobacillus terrae SBT-1

Abstract

Lactic acid is an organic acid that contains two enantiomers, L- and D-lactic acid, and is considered the most potential monomer for many industrial products. Lactic acid has versatile applications in the pharmaceutical, food, textile, chemical, and leather industries moreover in poly-lactic acid (PLA) manufacturing. While L-lactic acid is well known in many commercial products and studies, only a few studies on D-lactic acid were found. Lactic acid can be produced either by microbial fermentation or chemical synthesis. Approximately 90 percent of the total lactic acid produced worldwide is via microbial fermentation which provides an optically pure L- or D-lactic acid. To reduce the lactic acid production cost, agricultural waste which is second-generation biomass is applied for lactic acid fermentation. Oil palm trunk sap (OPT sap), the waste from the oil palm trunk recycle process, has the potential as a bacterial culture medium, due to the composition such as sucrose, glucose, fructose, and amino acid. In this study, by applying OPT sap as a carbon substrate together with other commercial sugars (glucose, sucrose, raw sugar, and molasses), fermented by Sporolactobacillus terrae SBT-1, the efficient D-lactic acid producer, the result from the enhancing D-lactic acid fermentation in shake flask provide a high D-lactic acid yield (0.87-0.91 g/g) and productivity (2.42-4.36 g/L·h) and also the high optical purity (96-99% ee). Thus, this platform was optimized in 5L fermenter, the results showed a good fermentation performance. The lactic acid production yield was high (0.84-.1.04 g/g), also the productivity (3.45-6.21 g/L·h), and the optical purity was almost higher than flask culture. In the fermentation using OPT sap supplemented with raw sugar as the carbon substrates, the most effective cost reduction by 14.65% was observed. From the result mentioned above, we can claim that OPT sap is a potential second-generation feedstock for lactic acid fermentation by S. terrae SBT-1.