Improved saccharification of rice straw by removing phenolic compounds using a stable immobilized metagenome-derived laccase on sodium alginate-based hydrogel

Abstract

Laccases can biodegrade lignocellulosic agricultural waste, which has a recalcitrant structure hindering industrial biomass hydrolysis. In the context of biomass decomposition, introduction of a stabilized enzyme with enhanced performance is of critical importance. This study aimed to stabilize laccase, obtained from tannery metagenome (PersiLac2) on sodium alginate-based hydrogels. The immobilized laccase remained stable in the acidic and alkaline pH ranges and preserved over 79.39 % of its initial activity at pH 4.0–9.0. Similarly, immobilized enzyme improved laccase activity at high temperatures, which is crucial in biorefinery processes, and the immobilized enzyme demonstrated 88.35 % activity at 80 ºC. The immobilization of laccase on hydrogels effectively prevented enzyme leaching and rendered it easier to separate and recycle, showing 58.74 % laccase activity after 15 cycles. The efficiency of immobilized PersiLac2 in enzymatic hydrolysis of rice straw was evaluated to enhance the generation of fermentable sugars, saccharification, and phenol reduction. Laccase treatment of rice straw resulted in an excellent saccharification yield and liberation of reducing sugars and removed 77.19 % of phenols during hydrolysis. The depolymerization effect of free and immobilized laccase on rice straw was investigated by FTIR and SEM analyses which confirmed efficient structural disruption by immobilization. The results indicated the potential of immobilized Persilac2 to degrade the compact wrap of lignin–carbohydrate complex in lignocellulosic substrates and its application in biomass-based industries.