Production of lignin monomeric alcohols and lipids from oil palm empty fruit bunch by a combination of alkaline nitrobenzene depolymerization and Lipomyces starkeyi bioconversion

Abstract

The efficient valorization of lignocellulosic biomass into valuable chemicals represents a cornerstone for advancing sustainable bioeconomy practices. This study focuses on the innovative conversion of oil palm empty fruit bunch (OPEFB) into lignin monomeric alcohols and lipids through a novel two-step process combining alkaline nitrobenzene depolymerization and bioconversion by Lipomyces starkeyi. Initially, OPEFB undergoes alkaline nitrobenzene depolymerization to break down complex lignin structures into monomeric aldehydes. The resulting derivates serve as substrates for the bioconversion by L. starkeyi, which is competent at metabolizing lignin-derived compounds into higher-value lignin monomeric alcohols (syringyl, vanillyl, and 4-hydroxybenzyl alcohol) and lipids, simultaneously. The strategy delineates the optimization of depolymerization conditions, sodium hydroxide concentration, nitrobenzene effect, and reaction time to maximize the yield of depolymerized lignin suitable for bioconversion. Subsequently, the bioconversion process toward cell growth, lipid production, and fatty acid profiles in various fermentations by L. starkeyi was explored. The highest syringaldehyde and vanillin obtained reached up to 4.81 mM and 0.64 mM, respectively. Then, it successfully produced 3.57 mM and 0.40 mM of syringyl alcohol and vanillyl alcohol, respectively, with 5.86 g L−1 of the lipid titer. The study demonstrates the potential of this integrated approach to convert OPEFB into valuable lignin-derived biochemicals and lipids, thereby contributing to the development of alternative strategies for biomass utilization efficiently.