Exploiting Self-Immobilized Fungi for Biovalorization of Oil Palm Sap to Organic Acids Through Repeated-Batch Fermentation.

This study focused on utilizing agricultural waste, oil palm sap (OPS) as a sole nutrient source for organic acid production by self-immobilized fungi. Among the fungi cultured in OPS, Rhizopus oryzae TISTR 3336 was selected as it could form compact and adequate-size pellets (3-5 mm) and gave the highest total acid production yield of 0.31 ± 0.02 g/g-sugar under pH control. The optimal conditions were as follows: inoculum size of 10⁶ spores/mL and shaking speed of 120 rpm. Using concentrated OPS gave higher final concentration of organic acids but reduced the production yield. The repeated-batch fermentation of OPS by self-immobilized fungi was successfully carried out for four cycles. The optimal initial sugar concentration was 40 g/L, giving the organic acid productions ranging of 19 to 35 g/L, with yields ranging of 0.47 to 0.87 g/g-sugar. This study has shown the efficient bioconversion of agricultural wastes into organic acids using self-immobilized fungi in the repeated-batch fermentation.