Integrated sustainable enzymatic hydrolysis and fermentation pathways for enhanced PHA synthesis from oil palm fronds biomass

Abstract

This study aims to fine-tune the combination of pretreatment, enzymatic hydrolysis, and fermentation to improve the conversion of oil palm fronds (OPF) into polyhydroxyalkanoates (PHA). It is based on the premise that optimising the sequential stages of pretreatment, enzymatic hydrolysis, and microbial fermentation will enhance cellulose accessibility, glucose release, and PHA production from oil palm fronds, providing an efficient and economically viable alternative to non-biodegradable, petroleum-based plastics. The objectives are to investigate the effects of alkaline and bleaching pretreatments on lignin removal and cellulose-enrichment, to assess enzymatic hydrolysis efficiency under optimized conditions, and to compare the PHA production potential of Bacillus cereus and Escherichia coli using OPF-derived hydrolysates. OPF was pretreated at 40, 80, and 120 °C for 2, 4, and 6 h. The optimal condition, 120 °C for 4 h, yielded 89.07 % enriched cellulose and reduced lignin to 6.43 %. Enzymatic hydrolysis using Aspergillus niger cellulase for 48 h released 36.23 g/L of glucose. Fermentation results showed that Bacillus cereus produced the highest PHA yield of 54.46 % after four days. FTIR confirmed the presence of ester carbonyl groups characteristic of PHA, while UV–Vis and HPLC analyses were used to monitor lignin removal and glucose concentration. These findings demonstrate the feasibility of an integrated bioprocess for PHA production from OPF, with a clear interdependence between pretreatment severity, enzymatic efficiency, and microbial performance. This work supports the advancement of circular bioeconomy strategies and highlights OPF as a sustainable resource for bioplastic production with strong economic and environmental potential.