Enzymatic removal of inhibitory compounds from lignocellulosic hydrolysates for biomass to bioproducts applications

Abstract

The physicochemical pretreatment is an important step to reduce biomass recalcitrance and facilitate further processing of plant lignocellulose into bioproducts. This process results in soluble and insoluble biomass fractions, and both may contain by-products that inhibit enzymatic biocatalysts and microbial fermentation. These fermentation inhibitory compounds (ICs) are produced during the degradation of lignin and sugars, resulting in phenolic and furanic compounds, and carboxylic acids. Therefore, detoxification steps may be required to improve lignocellulose conversion by microoganisms. Several physical and chemical methods, such as neutralization, use of activated charcoal and organic solvents, have been developed and recommended for removal of ICs. However, biological processes, especially enzyme-based, have been shown to efficiently remove ICs with the advantage of minimizing environmental issues since they are biogenic catalysts and used in low quantities. This review focuses on describing several enzymatic approaches to promote detoxification of lignocellulosic hydrolysates and improve the performance of microbial fermentation for the generation of bioproducts. Novel strategies using classical carbohydrate active enzymes (CAZymes), such as laccases (AA1) and peroxidases (AA2), as well as more advanced strategies using prooxidant, antioxidant and detoxification enzymes (dubbed as PADs), i.e. superoxide dismutases, are discussed as perspectives in the field.

Production of bio-xylitol from D-xylose by an engineered Pichia pastoris expressing a recombinant xylose reductase did not require any auxiliary substrate as electron donor

“…Almost one fth productivity with hemicelluloses hydrolysate compared to the pure xylose, can be attributed to the use of 10 times higher cell concentration and the termination of reaction in 1 hour, for the hydrolysate reaction. Ideally, we can't compare the productivity of pure xylose versus crude hemicellulose hydrolysate because the later contains numerous toxic impurities, such as, furfural, hydroxymethylfurfural, aliphatic acids, and phenolic compounds [33,34]. The application of whole cells in biocatalysis is not uncommon [35][36][37][38][39].…”

Mushroom Ligninolytic Enzymes―Features and Application of Potential Enzymes for Conversion of Lignin into Bio-Based Chemicals and Materials

“…Moreover, the enzymatic process with laccase has already been used for typical delignification and bio-bleaching in the pulp and paper industries instead of chemical oxidation agents [146]. The oxidation of laccase was also used to degrade inhibitory compounds, phenolic and furanic substances, and carboxylic acids, generated in biomass pretreatment processes due to thermal lignin or sugar decompositions [147]. This detoxification could enhance the fermentation productivity or enzymatic conversion yield of biomass hydrolysate for the biorefinery process.…”

A Lignocellulolytic Colletotrichum sp. OH with Broad-Spectrum Tolerance to Lignocellulosic Pretreatment Compounds and Derivatives and the Efficiency to Produce Hydrogen Peroxide and 5-Hydroxymethylfurfural Tolerant Cellulases

“…Moreover, green pretreatment compounds like alkaline hydrogen peroxide (AHP) [17] and ionic liquids (ILs) [18] also affect microbes and enzymes [17,19]. Biological detoxification refers to the employment of biological agents such as natural or engineered enzymes and microorganisms to reduce the toxic impurities originating from the pretreatment step in the fermentation medium [15,[20][21][22]. Biological detoxification is an economical and ecologically friendly method well integrated with bioprocesses, such as separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), and consolidated bioprocessing (CBP) [23,24].…”

“…However, new and novel strains for biorefinery interventions are desirable from abundant fungal biodiversity prevailing in unexplored niches [30]. For plant biomass-based processes, fungal strains from natural or industrial settings preferably exhibit characteristics such as (i) wide-ranging single and multiple lignocellulose-derived inhibitor tolerance [31], (ii) single source of a diverse set of enzymes for lignin and polysaccharide depolymerization [26], (iii) tolerance and stability of the enzyme repertoire toward the end products, physio-chemical parameters, and lignocellulose-derived inhibitors [16,21], (iv) amenable to microbial co-culture and consortium [32][33][34], and (v) genetically tractable for engineering [34,35].…”