Abstract
PurposeCurrent research focuses on the biological delignification of biomass by microbial laccase which is an environmentally friendly process.MethodsVarious 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).ResultsThe 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 laccase-treated 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.ConclusionThe 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.
Highlights
The rising concerns on the scarcity and exhaustion of fossils fuels and their related environmental impacts have forced the research toward the development of sustainable alternatives such as conversion of lignocellulosic biomass to biofuels (Sun and Cheng 2002)
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)
Wheat bran was found to be a potential substrate among the various agricultural waste residues screened for laccase production by Trichoderma harzianum strain HZN10 under solid-state fermentation (SSF)
Summary
The rising concerns on the scarcity and exhaustion of fossils fuels and their related environmental impacts have forced the research toward the development of sustainable alternatives such as conversion of lignocellulosic biomass to biofuels (Sun and Cheng 2002). Production of biofuels such as cellulosic bioethanol is a challenging task due to the bottle necks related to the saccharification process (Taha et al 2015). Lignin is a highly complex irregular branched three-dimensional polyphenolic polymer consisting of different functional entities like phenyl propanoid units of coniferyl, sinapyl and p-coumaryl alcohols. Functional groups such as phenolic hydroxyl, benzylic hydroxyl and carbonyl moieties were linked to lignin backbone and phenyl propanoid, thereby making them more complex (Vivekanand et al 2008).
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