Studies on the Cellulase Inhibition by Phenols from Hydrothermal Pretreated Soybean Wastes

Abstract

Biofuels can be generated through the processing of lignocellulosic plant material. Chemical and biological processes known as pretreatment are utilized to process plant material. Pretreatment contributes to the breakdown of the crystalline structure of lignocellulosic materials. A method of pretreatment is hydrothermal pretreatment with various acids and bases. This study addresses the effect of hydrothermal pretreatment with sodium hydroxide (NaOH) or hydrogen peroxide (H2O2) on enzymatic hydrolysis of soybean straw. Hydrothermal pretreatment of soybean straws (10% w/v) was carried out with either sodium hydroxide (1% v/v, NaOH) or hydrogen peroxide (1% v/v, H2O2) at 121°C for 60 min to evaluate the effect of water-soluble inhibitors (released during the pretreatment) on cellulolytic enzymes. The cellulose in pretreated solids (1% w/v glucan) was enzymatically hydrolyzed for 72 h with 25 mg enzyme protein/g glucan in the presence of either buffer or pretreated liquor (rich in phenols and lignin-derived molecules). The hydrolysis of NaOH treated solids in buffer gave a 57% cellulose conversion to glucose versus a 39% glucose yield from the H2O2 treated solids. When pretreated liquor was applied, NaOH and H2O2 treated solids had a 20% and 30% glucose yield, respectively, indicating the suppression of enzyme activity by non-productive bindings between enzyme proteins and inhibitors.