Review Article
Vijaya Rani, Saritha Mohanr
Abstract
Overall economics of the biomass to ethanol process is largely determined by the efficiency of biomass hydrolysis. Performance of cellulase cocktails used for saccharification of cellulose in biomass is often limited by lower amounts of β-glucosidases present, which catalyse hydrolysis of cellobiose, the product of endo and exocellulases to glucose. Inappropriate ratio of these enzymes in commercial cocktails leads to accumulation of cellobiose which inhibits the activity of cellulases. Thus, this rate limiting enzyme is of crucial importance in determining the efficiency of commercial cellulases. The saprophytic fungus Trichoderma sp., exploited for production of commercial cellulases, produces very minute quantities of β-glucosidases as compared to endo and exocellulases. However, several other organisms are known to produce β-glucosidases in higher quantities, over a broader substrate range. Strategies to get optimal ratio of exocellulases, endocellulases and β-glucosidases to enhance saccharification yields are, therefore, discussed. Appropriate levels of β-glucosidase activity in commercial cocktails have been obtained by supplementing with accessory β-glucosidases, transgenic approaches and by optimizing β-glucosidase production through manipulation of culture conditions. These approaches have resulted in achieving higher β-glucosidase activity in cellulase cocktails, facilitating higher sugar yields and thereby potentially improving enzymatic saccharification of biomass and eventually ethanol production.