Efficient Enzymatic Digestion of Alkali Treated Maize Stover Holocellulose by Developing Balanced Cocktail of Cellulolytic and Hemicellulolytic Enzymes

Abstract

Enzymatic hydrolysis of lignocellulosic biomass is a crucial step for bioethanol production. Highly balanced composition of cellulases and hemicellulases are required for effective bioconversion of lignocellulose into fermentable sugars. As commercial cellulases are often poor in certain hemicellulolytic activities, supplementation of such cellulases with accessory hemicellulolytic enzymes can yield high concentration of fermentable sugars. In the present investigation an attempt was made to develop a balanced cocktail for enzymatic hydrolysis of maize stover. Mild alkali treatment (2% NaOH) of maize stover was found to be beneficial as substrate loss was minimum and holocellulose content was unaffected. Response surface methodology was used for optimization of enzymatic saccharification process using three variables viz. level of crude β-xylosidase, level of commercial cellulases and time. Maximum 601.7 mg/g reducing sugars were obtained with 78.33% saccharification yield using optimum parameters viz 13.0 FPU/g commercial cellulase (MAPs 450), 74.42 U/g crude β-xylosidase and 36 h. Further, the role of accessory hemicellulolytic enzymes was proved by replacing crude β-xylosidase with partially purified β-xylosidase. As compared to crude β-xylosidase, supplementation of partially purified β-xylosidase at the same level, yield of reducing sugars was 536 mg/g which is only 11% lesser than crude enzyme. Moreover, developed enzyme cocktail was equally efficient at low temperature (30 °C) and at high substrate loading (30%). Enzymatic hydrolysate obtained after saccharification was efficiently fermented by ethanologenes.