A Review of the Role of Amphiphiles in Biomass to Ethanol Conversion

Abstract

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., OPEN ACCESSAppl. Sci. 2013, 3 397 pretreatment, hydrolysis and hydrolysis-fermentation) is reviewed and the proposed mechanisms of actions are described.

Interaction of enzymes with lignocellulosic materials: causes, mechanism and influencing factors

“…Some enzyme and substrate pairs are given in Table 7 with the effect of increasing substrate concentration. The agricultural residues (corn stover, Kumar and Wyman (2008) GC-220 Cellulose Increased with increase in conc Kumar and Wyman (2008) Cellulase Avicel Decreased with increase in conc Eckard et al (2013) Cellulases Pretreated forest wood Increased with increase in conc Matsakas et al (2018) Celluclast 1.5 L T. reesei Corn stover and corn fiber Increased with increase in conc Arantes and Saddler (2011) Cellic CTec 2 High CrI cellulose Increased with increase in conc Li et al (2018) corn fiber, rice husk, wheat straw, etc.) needs considerably lower protein loadings to achieve optimum adsorption than the forestry residues (poplar, Douglas fir and lodgepole pine).…”

Structural changes of lignin in biorefinery pretreatments and consequences to enzyme-lignin interactions - OPEN ACCESS

“…The macromolecular architecture and consequently the accessibility of certain functional groups of insoluble lignin fractions play important roles on the inhibiting effect of lignin. Low molecular weight and hydrophilic/amphipathic fractions of lignin (Leskinen et al 2017) may act in similar fashion as some nonionic surfactants that increase saccharification yields (Eckard et al 2013). Lignin fractions that possess weak interactions with enzymes reduce irreversible binding of enzymes on specific cellulose surfaces.…”

“…Enzymatic saccharification assays should be conducted using "reasonably low" cellulase dosages because excess amount of enzymes can cover lignin and hide detrimental non-productive adsorptive loss of activity (Shen et al 2016). Viable cellulosic bioethanol production likely requires cellulase dosages below 5 FPU/g dry substrate, and it is this range where greatest benefits from process optimization or utilization of lignin blocking additives can be seen (Eckard et al 2013;Leskinen et al 2015b). Better understanding of the interactions that drive enzyme binding to lignin would call for more studies that employ well characterized lignins and pure enzymes with engineered structures that would allow monitoring of binding properties caused by targeted modification of eventually identified binding hotspots.…”

Electrochemical Conversion of the Lignin Model Veratryl Alcohol to Veratryl Aldehyde Using Manganese(III)-Schiff Base Homogeneous Catalysts

“…In addition to lignin disposal in the pulp industry, another major goal in this field is the development of green and efficient methods to transform lignin into fuels and high value-added chemicals [10][11][12]. The polymeric structure of lignin provides an attractive renewable source of aromatic chemicals [13,14]. Catalysis is regarded as a key technology to fulfil the promise of lignin valorization.…”