Optimization of laccase production and its application in delignification of biomass

Abstract

Purpose Current research focuses on the biological delignification of biomass by microbial laccase which is an environmentally friendly process. Methods Various statistical approaches were designed for optimization of laccase production like Plackett–Burman design as well as response surface methodology (RSM). A laccase mediator system was designed for the delignification of saw dust which was molecularly characterized by high-performance liquid chromatography (HPLC), Fourier transformation infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Results The present study reveals wheat bran is a potential substrate for the production of laccase (63 U/g and 9.6 mg/ g protein) under solid-state fermentation by Trichoderma harzianum strain HZN10. Statistical optimization by RSM using central composite design (CCD) revealed that wheat bran contributed maximally to the overall laccase production followed by yeast extract. Laccase production under optimized conditions yielded 510 U/g with 8.09-fold increase. HPLC peaks representing 4-hydroxy-3-methoxybenzoic (vanillic) acid and 4-hydroxy-3,5-dimethoxybenzoic (syringic) acid showed drastic reduction in laccasetreated saw dust sample indicating the elimination of toxic inhibitors, thereby signifying the detoxification of sample. The laccase-treated saw dust showed 1.6-fold increase in reducing sugars after enzymatic (cellulase) hydrolysis. The FTIR analysis revealed the structural alterations occurring during the delignification process. SEM of biologically treated saw dust revealed the morphological alterations during the delignification process targeting the fiber cell walls rich in lignin. Conclusion The delignification of saw dust was effective by laccase mediator system and was evidenced by HPLC, FTIR and SEM analysis. Hence, laccase can be a powerful tool in biomass to biofuel conversions.