Fungal pretreatment of sweet sorghum bagasse with supplements: improvement in lignin degradation, selectivity and enzymatic saccharification

Abstract

Sweet sorghum bagasse (SSB) from food processing and agricultural industry has attracted the attention for uses in production of biofuel, enzymes and other products. The alteration in lignocellulolytic enzymes by use of supplements in fungal pretreatment of SSB to achieve higher lignin degradation, selectivity value and enzymatic hydrolysis to fermentable sugar was studied. Fungal strain Coriolus versicolor was selected for pretreatment due to high ligninolytic and low cellulolytic enzyme production resulting in high lignin degradation and selectivity value. SSB was pretreated with supplements of veratryl alcohol, syringic acid, catechol, gallic acid, vanillin, guaiacol, CuSO 4 and MnSO 4 . The best results were obtained with CuSO 4 , gallic acid and syringic acid supplements. CuSO 4 increased the activities of laccase (4.9-fold) and polyphenol oxidase (1.9-fold); gallic acid increased laccase (3.5-fold) and manganese peroxidase (2.5-fold); and syringic acid increased laccase (5.6-fold), lignin peroxidase (13-fold) and arylalcohol oxidase (2.8-fold) resulting in enhanced lignin degradations and selectivity values than the control. Reduced cellulolytic enzyme activities resulted in high cellulose recovery. Enzymatic hydrolysis of pretreated SSB yielded higher sugar due to degradation of lignin and reduced the crystallinity of cellulose. The study showed that supplements could be used to improve the pretreatment process. The results were confirmed by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetric/differential thermogravimetric analysis of SSB.

Fungal Laccase Production from Lignocellulosic Agricultural Wastes by Solid-State Fermentation: A Review

“…An obstacle to the utilization of lignocellulosic waste is the stubbornness of lignin, in which cellulose fibrils are embedded, prevent the conversion of structural polysaccharides into fermentable sugars [109]. In recent reports, physical and chemical pretreatments have been reported to degrade lignin into lignocellulosic biomass within a short time (10-40 min) [110,111].…”

“…It was reported that Fe 2+ had a stimulating effect on the lignin degradation of wheat straw by Trametes gibbosa and kept the cellulose degradation rate low when the Fe 2+ concentration was 0.5 mM, providing better selectivity in lignin degradation [119]. To achieve a high lignin breakdown and low cellulolytic enzyme production, the fungal strain C. versicolor was selected for biological pretreatment of sweet sorghum bagasse, resulting in excellent cellulose recovery [109]. The biological pretreatment of lignocellulosic biomass by SSF is selective, energy-saving, and effective under mild environmental conditions [114].…”

Agrowaste bioconversion and microbial fortification have prospects for soil health, crop productivity, and eco-enterprising

“…Likewise, fungal treatments in which fungi and actinomycetes directly colonize with the residues or enzymatic treatments using lignolytic enzymes help improving biodelignification process (Ilyin et al 2004;Moreno et al 2015). It further needs exposure of suitable mesophilic and thermophilic conditions that may include combined organic and inorganic complexes like CuSO 4 -gallic acid supplement for aggravating high functional bioconversion activities (Mishra and Jana 2017). The bioconversion process can be fastened with the use of such functionally characterized microbial inoculants that possess high enzymatic activities for lignocellulosic degradation (Choudhary et al 2016).…”

Effects of wheat straw solid contents in fermentation media on utilization of soluble/insoluble nutrient, fungal growth and laccase production

“…Reducing sugar in biomass and its consumption in fermentation was measured using glucose as standard by HPLC (Agilent 1200 series, MN, USA), equipped with refractive index detector (RID) and Hi-Plex H column (300 × 7.7 mm, PL1170-6830, Agilent) maintained at 55 °C and 80 °C, respectively. HPLC grade water was used as the mobile phase eluting at 0.6 mL min −1 (Mishra et al 2017). Consumption of insoluble nutrients was measured by loss of dry weight of biomass in fermentation.…”