Bioconversion of Oil Palm Trunk Residues Hydrolyzed by Enzymes from Newly Isolated Fungi and Use for Ethanol and Acetic Acid Production Under Two-Stage and Simultaneous Fermentation

Abstract

Oil palm trunk (OPT) is one of the richest biomass in Southern Thailand. The OPT residues (OPTr), obtained after separation of the sap, was hydrolyzed by the crude enzymes of the selected fungal isolates under solid-state fermentation (SSF) and submerged fermentation (SmF). From screening and identification studies, Ceratocystis paradoxa TT1 produced the highest CMCase activity (18.16 Unit gds−1) from SmF while Trichoderma koningiopsis TM3 exhibited the highest xylanase and FPase activities (56.46 and 2.13 Unit gds−1, respectively) from SSF. Enzymatic hydrolysis of OPTr using the crude enzymes of T. koningiopsis TM3 (25 Unit gds−1) at 50 °C for 15 h revealed the maximum reducing sugars of 11.92 g L−1 with the yield of 0.48 gg−1. Bioconversion of the OPTr hydrolysate to ethanol by Saccharomyces cerevisiae TISTR5055 could be increased (2.13-fold) by supplementation of YM nutrients. The effects of co-cultures (S. cerevisiae TISTR5055 and Acetobacter aceti) for production of co-products (ethanol and acetic acid) from the OPTr hydrolysate with and without YM nutrients addition was conducted under two-stage fermentation and simultaneous fermentation. Both fermentation types gave similar ethanol production (4.15 and 4.01 g L−1) but the ethanol productivity (0.34 g L−1 h−1) from two-stage fermentation was 1.55-fold higher than that from simultaneous fermentation. On the other hand, the maximum acetic acid production (2.12 g L−1) and productivity (0.09 g L−1 h−1) were achieved from the simultaneous fermentation of the co-cultures without nutrient addition. These two values were 1.7-fold higher acetic acid concentration and 4.4-folds higher productivity than the two-stage fermentation.