Recent advances in understanding the effects of lignin structural characteristics on enzymatic hydrolysis

Abstract

Enzymatic hydrolysis of lignocellulose for bioethanol production shows a great potential to remit the rapid consumption of fossil fuels, given the fact that lignocellulose feedstocks are abundant, cost-efficient, and renewable. Lignin results in low enzymatic saccharification by forming the steric hindrance, non-productive adsorption of cellulase onto lignin, and deactivating the cellulase. In general, the non-productive binding of cellulase on lignin is widely known as the major cause for inhibiting the enzymatic hydrolysis. Pretreatment is an effective way to remove lignin and improve the enzymatic digestibility of lignocellulose. Along with removing lignin, the pretreatment can modify the lignin structure, which significantly affects the non-productive adsorption of cellulase onto lignin. To relieve the inhibitory effect of lignin on enzymatic hydrolysis, enormous efforts have been made to elucidate the correlation of lignin structure with lignin–enzyme interactions but with different views. In addition, contrary to the traditional belief that lignin inhibits enzymatic hydrolysis, in recent years, the addition of water-soluble lignin such as lignosulfonate or low molecular-weight lignin exerts a positive effect on enzymatic hydrolysis, which gives a new insight into the lignin–enzyme interactions. For throwing light on their structure–interaction relationship during enzymatic hydrolysis, the effect of residual lignin in substrate and introduced lignin in hydrolysate on enzymatic hydrolysis are critically reviewed, aiming at realizing the targeted regulation of lignin structure for improving the saccharification of lignocellulose. The review is also focused on exploring the lignin–enzyme interactions to mitigate the negative impact of lignin and reducing the cost of enzymatic hydrolysis of lignocellulose.

Enzymatic Conversion of Different Qualities of Refined Softwood Hemicellulose Recovered from Spent Sulfite Liquor

“…The effect of acetylation on reduced enzymatic hydrolysis of biomass from woods, in general, has been reviewed by Pawar et al [ 53 ], and has specifically been reported for β-mannanases, including Tr Man5A [ 54 , 55 ]. In addition, thermal treatment of lignocellulose may generate lignin-aggregates that bind and inhibit enzymes such as cellulases [ 29 , 35 , 56 ]. However, if this occurred in the present case, it was probably a less pronounced contributing effect with the TMP-AcGGM, since it was purified with SEC [ 40 ], which likely separated such aggregates.…”

“…Softwood-based SSL contains AcGGM and its degradation products, but is also rich in lignin and lignin-derived compounds such as lignosulfonates (LS) [ 25 , 26 , 27 ]. It is known that the presence of lignin results in lower enzymatic cellulose saccharification yields due to steric hindrance, non-productive binding of cellulases onto lignin, and enzyme deactivation [ 28 , 29 ]. The current understanding of the mechanism involved in enzyme-lignin interaction is largely based on the interaction of insoluble lignin with cellulases [ 30 , 31 ].…”

“…The current understanding of the mechanism involved in enzyme-lignin interaction is largely based on the interaction of insoluble lignin with cellulases [ 30 , 31 ]. However, the interaction of water-soluble lignin, particularly LS, with enzyme(s) and their potential enzyme inhibitory role has not been explored in detail [ 29 , 32 ].…”

A review on lignin pyrolysis: pyrolytic behavior, mechanism, and relevant upgrading for improving process efficiency

“…Due to the natural aromatic polystructure, lignin (which can mainly be extracted from softwood, hardwood, and grass, and the model lignin structures is shown in Fig. 1 [ 1 ]) has been regarded as a sustainable alternative to fossil-derived resources to provide valuable biochemicals [ 2 – 7 ]. Interunits of lignin are connected by C–O and C–C bonds (such as β-O-4, β–β, and β-5, Fig.…”

Reduced expression of PRX2/ATPRX1, PRX8, PRX35, and PRX73 affects cell elongation, vegetative growth, and vasculature structures in Arabidopsis thaliana

“…Nevertheless, the development of technologies to solve this problem is expected to reduce the ame retardancy of biomass and increase the yield of extractable cellulose and fermentable sugar for pulp or biofuel production. In recent years, biotechnological approaches to modulate lignin content have been used to optimize plant biomass in various industries (Liu, et al 2020;Yuan, et al 2021). The study of lignin biosynthesis and its function has therefore had signi cant impacts on the industry, agriculture, and other human activities.…”