Optimization of pretreatment and enzymatic hydrolysis using commercial and isolated bacterial enzyme cocktail for bioethanol production from corn husk through yeast co-culture batch fermentation

Abstract

This study assesses the impact of physicochemical pretreatment, enzymatic hydrolysis, and co-culture fermentation strategies on bioethanol production from corn husk biomass (CHB). Under optimal alkali pretreatment conditions (1.75% alkali, 4.0 g substrate concentration, 120 °C, 10 h), 35% lignin removal was achieved, with 48% cellulose and 39% hemicellulose recovery. In contrast, acid pretreatment resulted in 30% lignin removal, 45% cellulose recovery, and 34% hemicellulose recovery, showing lower efficiency than alkali pretreatment. During ultrasonication alkali pretreatment enhanced cellulose and hemicellulose exposure up to 51 and 46% and delignification up to 49%. Enzymatic hydrolysis of pretreated corn husk biomass was performed using commercial enzymes [Celluclast 1.5 L (700 EGU or 854 U mL⁻¹) and Viscozyme (13.4 FBG/mL)] and isolated bacterial enzymes, including cellulase from Bacillus licheniformis (9.3 ± 0.3 U mL⁻¹) and xylanase from Enterobacter asburiae PQ396173 (7.0 ± 0.4 U mL⁻¹). The developed enzyme cocktail in ratio 3:2:3:1 (v/v; U mL⁻¹) (Celluclast: Viscozyme: native cellulase: native xylanse) using a cocktail of native and commercial enzymes, yielded total reducing sugar of 740 mg g⁻¹ glucose and 54.6 mg g⁻¹ xylose. Fermentation of hydrolysate prepared with commercial enzymes using monoculture of Saccharomyces cerevisiae and Pichia pastoris yielded 17.6 g L⁻¹ and 12.2 g L⁻¹ bioethanol separately. Co-cultured yeasts produced 26.8 g L⁻¹ ethanol at 96 h of incubation, exceeding monoculture yields. The fermentation with integration of commercial and isolated bacterial enzyme cocktails yielded the highest bioethanol output of 37.3 g L⁻¹ at 96 h incubation, indicating that enzymatic saccharification with a combination of commercial and native enzyme cocktails results in maximum bioethanol production.

Keywords

Corn husk biomass / Ultrasonication pretreatment / Enzymatic hydrolysis / Enzyme cocktail / Fermentation / Bioethanol

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Funding

Siksha 'O' Anusandhan Deemed To Be University

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