High sugar yields from sugarcane (Saccharum officinarum) bagasse using low-temperature aqueous ammonia pretreatment and laccase-mediator assisted enzymatic hydrolysis

Sugarcane (Saccharum officinarum) bagasse (SCB) is a promising feedstock for cellulosic ethanol production. Combination of low energy pretreatments with efficient enzymatic saccharification is desirable to reduce process cost. SCB was converted into fermentable sugars with high yield by aqueous ammonia soaking (AAS) pretreatment and laccase-mediator assisted enzymatic hydrolysis. The optimal process conditions for AAS were determined as 20% aqueous ammonia, 50 °C, 48 h residence time and 1.2 mm particle size by employing response surface method. Hydrolysis of pretreated SCB by cellulases resulted in release of 57.30% of total sugars in the raw SCB. Addition of laccase to cellulase enzyme mixture enhanced the total sugar yield to 68.2%. When the mediator 1-hydroxybenzotriazole was added to the cellulase-laccase cocktail, the total sugar yield was improved to 78.4%. The mediator also reduced the amount of laccase required for maximum sugar yield. The glucan conversion of pretreated SCB with cellulase-laccase-mediator cocktail was 86%, which is higher than the reported levels of glucan conversion for SCB pretreated by AAS at high temperature. Therefore, the combination of low-temperature AAS and laccase-mediator assisted enzymatic hydrolysis would be useful to develop low-energy biomass conversion process.