Use of agroindustrial biomass for biofuel and enzyme discovery and production

Abstract

Biomass is all biologically produced matter and means a biological reservoir of energy. The list of biomass wastes is large, for example, agriculture, horticulture, forest residues, food processing, and municipal solid wastes, among others. Biomass is widely available; its use reduces the amount of wastes and the biofuels obtained from it are considered renewable energy. Crop cultivation activities (e.g., rice, banana, maize, and sugarcane) produce large quantities of agricultural wastes. These (lignocellulosic) materials are composed of cellulose, hemicellulose, and lignin, and cellulose is the most abundant organic polymer on Earth, but the conversion of lignocellulose into reducing sugars is more difficult than the conversion of starch. Microorganisms play an important role in the global carbon cycle, and microbial decomposers have been isolated from raw materials as reported in many publications. These microbes secrete, among other enzymes, ligninases, hemicellulases, and cellulases, which hydrolyze the polymers present in the agroindustrial wastes. The search for microbes with good performance on lignocellulosic materials is expanding to other niches and currently many extremophiles are under characterization. Microbial enzymes are produced by different approaches: solid state fermentation, liquid submerged fermentation, or by genetic engineering of the lignocellulolytic microorganism or by heterologous expression in model microorganisms. Biological treatment of lignocellulose improves the efficiency of hydrolysis, and compared to other pretreatments, it does not require handling chemical substances. Other challenges to overcome in biofuel production are the presence of inhibitors, mainly furan derivatives, which are generated during physical and chemical pretreatment of lignocellulosic biomass. Research is now focused on developing methods for detoxification and identification or the development of much more tolerant fermentative microbes. Current efforts are paying attention to the consolidation of processes for biofuel conversion in order to make them more efficient and economically feasible. This chapter reviews the state of the art for valorization of biomass to produce enzymes and biofuels.