Abstract
One of the concerns for economical production of ethanol from biomass is the large volume and high cost of the cellulolytic enzymes used to convert biomass into fermentable sugars. The presence of acetyl groups in hemicellulose and lignin in plant cell walls reduces accessibility of biomass to the enzymes and makes conversion a slow process. In addition to low enzyme accessibility, a rapid deactivation of cellulases during biomass hydrolysis can be another factor contributing to the low sugar recovery. As of now, the economical reduction in lignin content of the biomass is considered a bottleneck, and raises issues for several reasons. The presence of lignin in biomass reduces the swelling of cellulose fibrils and accessibility of enzyme to carbohydrate polymers. It also causes an irreversible adsorption of the cellulolytic enzymes that prevents effective enzyme activity and recycling. Amphiphiles, such as surfactants and proteins have been found to improve enzyme activity by several mechanisms of action that are not yet fully understood. Reduction in irreversible adsorption of enzyme to non-specific sites, reduction in viscosity of liquid and surface tension and consequently reduced contact of enzyme with air-liquid interface, and modifications in biomass chemical structure are some of the benefits derived from surface active molecules. Application of some of these amphiphiles could potentially reduce the capital and operating costs of bioethanol production by reducing fermentation time and the amount of enzyme used for saccharification of biomass. In this review article, the benefit of applying amphiphiles at various stages of ethanol production (i.e., pretreatment, hydrolysis and hydrolysis-fermentation) is reviewed and the proposed mechanisms of actions are described.
Highlights
One of the foremost concerns for economically efficient ethanol production from biomass through the biochemical pathway is the high price and usage rates of cellulolytic enzymes
Pretreatment techniques such as ammonia fiber explosion (AFEX), dilute acid, lime, washed SO2 and Ammonia recycled percolation (ARP) pretreated corn stover, Douglas fir pretreated with SO2 explosion and Avicel were used with prior treatment with bovine serum albumin (BSA) [1,41]
Despite of the intriguing process of converting agricultural residues and herbaceous grasses to fermentable sugars that can be converted to fuel grade ethanol, economical enzymatic hydrolysis of biomass remains a challenge
Summary
One of the foremost concerns for economically efficient ethanol production from biomass through the biochemical pathway is the high price and usage rates of cellulolytic enzymes. Protein-based lignin-blockers such as soybean meal, corn steep liquor, bovine serum albumin (BSA), amylase, chicken egg albumin, and combinations thereof [41], as well as casein [37] have been evaluated during enzymatic saccharification of high lignin containing biomass Pretreatment techniques such as ammonia fiber explosion (AFEX), dilute acid (with Parr reactor), lime, washed SO2 and Ammonia recycled percolation (ARP) pretreated corn stover, Douglas fir pretreated with SO2 explosion and Avicel were used with prior treatment with bovine serum albumin (BSA) [1,41].
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