Microwave assisted alkali treated wheat straw as a substrate for co-production of (hemi)cellulolytic enzymes and development of balanced enzyme cocktail for its enhanced saccharification

Abstract

Abstract In-house production of saccharifying enzymes using lignocellulosic biomass as inducer of enzyme production can yield (hemi)cellulolytic enzymes with more specificity and efficiency for hydrolyzing the same lignocellulosic substrates. In the present study, production of (hemi)cellulolytic enzymes was carried out using microwave assisted alkali (MAA) treated wheat straw and the crude enzyme was evaluated for hydrolysis of the same substrate. Co-production of cellulolytic and hemicellulolytic enzymes by Aspergillus niger ADH-11 was optimized using MAA treated wheat straw as a substrate and corn steep liquor (CSL) as moistening medium under solid state fermentation employing response surface methodology. Under optimized conditions viz. inoculum 30% (v/v of moistening agent), CSL 7.1% and incubation time of 4.99 days, 2.34 U/g of FP activity, 308.16 U/g endo-glucanase, 96.61 U/g of β-glucosidase, 3815.96 U/g of xylanase and 174.42 U/g of β-xylosidase activity were produced. By statistical optimization, FP activity and xylanase yield were enhanced by 2.0 and 14.22 fold respectively and time for production was reduced significantly. It was found that supplementation of in-house produced enzyme to commercial cellulase can improve the levels of xylanase, β-glucosidase and β-xylosidase significantly. Enzyme cocktail containing 5 FPU/g of SIGMA cellulase and 5 FPU/g in-house produced enzyme yielded 610.35 mg/g of reducing sugars in 72 h with 68.41% saccharification and released more glucose as FP activity: β-glucosidase ratio was enhanced. The cocktail was also assessed for its efficacy at high substrate loading and lower temperature for its use in simultaneous saccharification and fermentation (SSF) process for bioethanol production.