Utilization of oil palm frond for enzyme and renewable feedstock production using solid state fermentation

Abstract

Oil palm frond (OPF) is the largest agro-residue and lignocellulose biomass in Malaysia amounting to 56 million tons every year. At present, it is mainly utilized as soil fertilizer and animal feed, whereas excess fronds are commonly burned to save up plantation space and to avoid contamination. Such practices undermine the economic value of OPF and contribute to environmental pollution. Tapping into its rich lignocellulose content, the study investigated bioconversion potential of frond petiole for lignocellulolytic enzyme production. Six locally isolated fungi A. awamori MMS4, A. niger EFB1, A. fumigatus SK1, T. virens UKM1, T. viride MM3, and T. asperellum MR1 were screened for their enzyme production capability under solid state fermentation. The fermentation was carried out in petri dish using OPF fibre (0.125 mm) at 60% moisture content and 35°C for 7 days. The fermentation produced enzyme mixture high in lignin peroxidase (20-222 Ug-1), endoxylanase (6-109 Ug-1) and endoglucanase (2-9 Ug-1), alongside exolgucanase, ß-glucosidase, manganese peroxidase and laccase. The multi-enzyme mixture was suitable for technical application and when tested for the enzymatic deinking of old newspaper achieved a pulp brightness of up to 51.5% and tensile strength of 34.0 Nm/g. To avoid generation of secondary waste, the remaining fermented OPF (post enzyme extraction) was re-fermented up to three cycles. This further increased enzyme production by 26-79% and fibre utilization by 14-26%. Such repeated fermentation also proved favourable in improving the sustainability and cost of enzyme production at each cycle. Fermented OPF that were no longer fermentable after three cycles was subjected to nutrient regeneration by enzymatic hydrolysis and autolysis. The process generated a nutrient rich hydrolysate containing carbon (1.79 gL-1), nitrogen (0.11 gL-1) and phosphorus (0.36 gL-1) that were useable as growth medium and supported both bacterial and fungal growth. Overall, the study showed the potential bioconversion of OPF into valuable enzymes and the significance of re-fermentation and hydrolysis process to maximise usage of fermented waste as renewable feedstock.