Optimization of Nutrients in Fermentative Lactic Acid Production Using Oil Palm Trunk Juice as Substrate

Complex nutrients e.g. carbon, nitrogen, peptides, vitamin and salts significantly play important roles in lactic acid production efficiency depending on types of microorganism and sources of raw material. In this study oil palm trunk juice and Lactobacillus rhamnosus TISTR 108 (ATTC 10863) were utilized for lactic acid production. Additional nutrients including peptone, yeast extract and mixed salts were tested. Response surface methodology involving Box Behkhen Design (BBD) was applied to examine the optimal condition. Prediction of optimization was performed using full quadratic regression equation. The predicted maximum lactic acid concentration was obtained at 64.05 g·l-1 within a period of 48 h under an optimal condition of 10 g·l-1 peptone with mixed salts containing 0.4 g·l-1 MgSO4·7H2O, 0.1 g·l-1 MnSO4·4H2O, 3 g·l-1 K2HPO4, 3 g·l-1 KH2PO4 and 3 g·l-1 CH3COONa·3H2O in 250 ml shake flask using CaCO3 as a titrant. Verification of optimization condition was performed in 2 l fermenter using Ca(OH)2 as neutralizing agent. Increase in lactic acid fermentation was achieved at 92.81 g·l-1 at 48 h cultivation. The lactic acid yield and volumetric productivity were 0.94 g·g-1 and 1.91 g l-1·h-1, respectively. This suggests that OPT juice is potentially used as carbon and nutrient sources for lactic acid production.