Thermoalkaliphilic laccase treatment for enhanced production of high-value benzaldehyde chemicals from lignin

Abstract

Enzymatic conversion of lignin into high-value chemicals is a key step in sustainable and eco-friendly development of lignin valorization strategies. In the present study, a novel thermoalkaliphilic laccase, CtLac, from Caldalkalibacillus thermarum strain TA2.A1 was tested for the depolymerization of lignin and the production of value-added chemicals, using three different lignocellulosic biomass, organosolv lignin (OSL), and Kraft lignin. Seven valuable lignin monomers were identified from the CtLac-treated samples using high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Remarkably, increases of 22.0%, 65.6%, and 27.3% of p-hydroxybenzaldehyde and increases of 111.1%, 93.5%, and 238.1% of vanillin were observed from rice straw, corn stover, and reed, respectively. Comparative analysis of lignin monomers released from rice straw, using Trametes versicolor laccase (TvL) and CtLac indicated efficient depolymerization of lignin by CtLac. CtLac treatment resulted in 2.3 fold and 5.6 fold, and 1.9 fold and 2.8 fold higher amounts of p-hydroxybenzaldehyde and vanillin from OSL and Kraft lignin, respectively, compared to CtLac-treated rice straw samples after 12 h reaction. OSL was the best substrate for the production of benzaldehyde chemicals using CtLac treatment. The results demonstrated potential application of bacterial laccase CtLac for valorization of biomass lignin into high-value benzaldehyde chemicals under thermoalkaliphilic conditions.

Keywords: Laccase; Lignin depolymerization; Lignin valorization; Lignocellulosic biomass; Organosolv lignin; Vanillin.