Recalcitrant carbohydrates after enzymatic hydrolysis of pretreated lignocellulosic biomass

Abstract

BackgroundTo reduce the cost of the enzymes for the hydrolysis of lignocellulosic biomass, two main strategies have been followed: one, the reduction of enzyme dosing by the use of more efficient and stable enzymatic cocktails; another, to include accessory enzymes in the cocktails to increase yields by reducing the recalcitrant carbohydrate fraction remaining at the end of the process. To guide this second strategy, we have explored the chemical bond composition of different fractions of recalcitrant carbohydrates after enzymatic hydrolysis.ResultsTwo lignocellulosic feedstocks of relevance for the biofuels industry have been analyzed, corn stover and sugarcane straw. On comparing the composition of chemical bonds of the starting pretreated material with samples after standard and forced hydrolysis (with enzyme overdosing), we obtained similar sugar and chemical bond composition.ConclusionsThis suggests that the current enzymatic cocktails bear the set of enzymes needed to hydrolyze these feedstocks. From our point of view, the results show the need for a parallel fine-tuning of the enzymatic cocktails with the pretreatment process to maximize sugar release yield.

Coupling the pretreatment and hydrolysis of lignocellulosic biomass by the expression of beta‐xylosidases

“…Under these conditions, endo‐acting xylanase activity does not seem to be a limitation, because the final xylose released is higher than the sum of starting xylose plus xylobiose. This means that the residual insoluble xylan in this material is subject to efficient degradation, leading to the conclusion that for the release of a similar hemicellulose potential of the softly pretreated material the only limitation would be a strong beta‐xylosidase activity to drag all the soluble oligomers to monomeric xylose The recalcitrant xylan percentage resulted in both cases similar, near 20%, and matched with the amount previously characterized by Alcántara et al () at high enzyme loadings. These authors concluded that the recalcitrant hemicellulose was mostly formed by xylose molecules linked by beta‐1‐4 bonds, corresponding to xylan.…”

Production of Cellulases by Bacillus cellulosilyticus Using Lignocellulosic Material

“…For the sake of efficient and rapid hydrolysis of carbohydrates the lignocellulosic material or raw material must be pretreated [9,22]. Lignin should be removed before enzymatic hydrolysis because it acts as a protective physical barrier for cellulose to degrade in sugars and for removal of lignin alkali-pretreatment is carried out because it effectively retains most of the cellulose and removes the major portion of lignin [9,23].…”

Effect of steam-pretreatment combined with hydrogen peroxide on lignocellulosic agricultural wastes for bioethanol production: Analysis of derived sugars and other by-products

“…However, the compact and rigid structure of lignocellulosic matrix acts as a physical barrier able to prevent cellulase-catalysed hydrolysis, fermentable sugars release, and subsequent ethanolic fermentation. This complex and heterogeneous architecture is the cause of biomass recalcitrance to microbial and enzymatic deconstruction [18] . Thus, a physical and chemical pretreatment process of SCB is required to reduce recalcitrance biomass and increase the reactive surface area [19] .…”