Information pertaining to enzymatic hydrolysis of cellulose by noncomplexed cellulase enzyme systems is reviewed with a particular emphasis on development of aggregated understanding incorporating substrate features in addition to concentration and multiple cellulase components. Topics considered include properties of cellulose, adsorption, cellulose hydrolysis, and quantitative models. A classification scheme is proposed for quantitative models for enzymatic hydrolysis of cellulose based on the number of solubilizing activities and substrate state variables included. We suggest that it is timely to revisit and reinvigorate functional modeling of cellulose hydrolysis, and that this would be highly beneficial if not necessary in order to bring to bear the large volume of information available on cellulase components on the primary applications that motivate interest in the subject.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/bit.20282

Toward an aggregated understanding of enzymatic hydrolysis of cellulose: noncomplexed cellulase systems.

Cellulases and related enzymes in biotechnology

The structure, function, and biosynthesis of plant cell wall pectic polysaccharides.

The conversion of biomass by thermochemical means is very promising for the substitution of fossil materials in many energy applications. Given the complexity of biomass the main challenge in its use is to obtain products with high yield and purity. For a better understanding of biomass thermochemical conversion, many authors have studied in TG analyzer or at bed scale the individual pyrolysis of its main constituents (i.e. cellulose, hemicelluloses and lignin). Based on these studies, this original work synthesizes the main steps of conversion and the composition of the products obtained from each constituent. Pyrolysis conversion can be described as the superposition of three main pathways (char formation, depolymerization and fragmentation) and secondary reactions. Lignin, which is composed of many benzene rings, gives the highest char yield and its depolymerization leads to various phenols. The depolymerization of the polysaccharides is a source of anhydro-saccharides and furan compounds. The fragmentation of the different constituents and the secondary reactions produce CO, CO2 and small chain compounds. For temperature higher than 500 °C, the residues obtained from the different constituents present a similar structure, which evolves towards a more condensed polyaromatic form by releasing CH4, CO and H2. As the aromatic rings and their substituent composition have a critical influence on the reactivity of pyrolysis products, a particular attention has been given to their formation. Some mechanisms are proposed to explain the formation of the main products. From the results of this study it is possible to predict the reactivity and energy content of the pyrolysis products and evaluate their potential use as biofuels in renewable applications.

A review on pyrolysis of biomass constituents: Mechanisms and composition of the products obtained from the conversion of cellulose, hemicelluloses and lignin

Plants represent a vast, renewable resource and are well suited to provide sustainably for humankind’s transportation fuel needs. To produce infrastructure-compatible fuels from biomass, two challenges remain: overcoming plant cell wall recalcitrance to extract sugar and phenolic intermediates, and reduction of oxygenated intermediates to fuel molecules. To compete with fossil-based fuels, two primary routes to deconstruct cell walls are under development, namely biochemical and thermochemical conversion. Here, we focus on overcoming recalcitrance with biochemical conversion, which uses low-severity thermochemical pretreatment followed by enzymatic hydrolysis to produce soluble sugars. Many challenges remain, including understanding how pretreatments affect the physicochemical nature of heterogeneous cell walls; determination of how enzymes deconstruct the cell wall effectively with the aim of designing superior catalysts; and resolution of issues associated with the co-optimization of pretreatment, enzymatic hydrolysis, and fermentation. Here, we highlight some of the scientific challenges and open questions with a particular focus on problems across multiple length scales.

Deconstruction of lignocellulosic biomass to fuels and chemicals

Characterization of acetylated 4-O-methylglucuronoxylan isolated from aspen employing 1H and 13C NMR spectroscopy.

Characterization of O-acetyl-(4-O-methylglucurono)xylan isolated from birch and beech.

Lors de la cuisson kraft, une grande partie des groupes acides 4-O-methylglycuroniques des xylanes du bois indigene est convertie en groupes d'acides 4-desoxyhex-4-enuroniques (HexA). Nous presentons ici une methode permettant l'extraction selective du HexA a l'aide d'une hydrolyse douce a l'acide des pâtes kraft. La quantite de HexA extraite etait en correlation lineaire avec une diminution de l'indice Kappa. Selon le type de pâte, l'indice Kappa a ete reduit de 2 a 7 unites. L'extraction du HexA a permis de reduire de facon significative la consommation de produits chimiques lors des sequences de blanchiment sans chlore elementaire et sans aucun chlore. La teneur en metal de transition dans les pâtes etait, apres traitement, aussi faible qu'apres un autre traitement avec des agents de complexion. L'hydrolyse selective n'a eu aucun effet marque sur les proprietes du papier des pâtes hautement blanchies, mais elle a ameliore de facon importante la stabilite de la blancheur des pâtes blanchies a l'oxygene et au peroxyde.

Anita Teleman

Papers

Characterization of acetylated 4-O-methylglucuronoxylan isolated from aspen employing 1H and 13C NMR spectroscopy.

Characterization of O-acetyl-(4-O-methylglucurono)xylan isolated from birch and beech.

Selective hydrolysis of hexenuronic acid groups and its application in ECF and TCF bleaching of kraft pulps

Isolation and characterization of galactoglucomannan from spruce (Picea abies)

Effect of cooking and bleaching on the structure of xylan in conventional pine kraft pulp