Acid-Assisted Organosolv Pre-Treatment and Enzymatic Hydrolysis of Cynara cardunculus L. for Glucose Production

Abstract

Lignocellulosic biomass is a non-edible feedstock that can be used in integrated biorefinery for the production of biochemicals and biofuel. Among lignocellulosic biomass, Cynara cardunculus L. (cardoon) is a promising crop thanks to its low water and fertilizer demand. Organosolv is a chemical treatment that uses numerous organic or aqueous solvent mixtures, and a small amount of acid catalyst, in order to solubilize the lignin and hemicellulose fractions, making the cellulose accessible to hydrolytic enzymes. Lignocellulosic residues of cardoon underwent a two-step treatment process to obtain fermentable glucose. In the first step, the milled biomass was subjected to microwave-assisted extraction using an acidified γ-valerolactone (GVL)/water mixture, yielding a solid cellulose pulp. In the second step, the pre-treated material was hydrolyzed by cellulolytic enzymes to glucose. The first step was optimized by means of a two-level full factorial design. The investigated factors were process temperature, acid catalyst concentration, and GVL/water ratio. A glucose production equal to 30.17 g per 100 g of raw material (89% of the maximum theoretical yield) was achieved after conducting the first step at 150 °C using an acidified water solution (1.96% H2SO4w/w).

Fractionation of Cynara cardunculus L. by Acidified Organosolv Treatment for the Extraction of Highly Digestible Cellulose and Technical Lignin

“…The HY Equation (5) shows that the enzymatic hydrolysis is independent from the GVL/water ratio, confirming what was observed and discussed in previous research work performed by the same authors [31].…”

“…The investigated factors were process temperature, catalyst concentration, and GVL/water ratio. The combination of microwave-assisted GVL organosolv treatment and enzymatic hydrolysis of lignocellulosic cardoon has not yet been reported, except for a preliminary work performed by Gelosia et al [31]. This study may pave the way to novel fractionation processes in cardoon-based biorefinery, enabling the development of sustainable biofuels and biochemicals.…”

“…The design comprised of 20 runs (Table 1) and it was built on a previous factorial experiment [31] by adding axial (α = 1.633) and center points. Experimental data were analyzed by Analysis of Variance (ANOVA) to determine the contribution of each factor to the model and the correlation between them.…”

“…The HY performance is influenced by the presence of lignin, since it has been reported that high lignin content hinders enzymatic hydrolysis through physical inhibition and non-specific adsorption in enzymes [51,52]. However, other works on enzymatic hydrolysis using pre-treated material with a high lignin content have shown a high saccharification rate [31,53]. Therefore, changes and modifications of lignin operated by organosolv pretreatment could play an important role in HY.…”

Fractionation of Oil Palm Fiber Using Green Solvent for Lignin Separation

“…The solvent/water mixture contributes two integral roles in an organosolv process; (1) the impregnation of plant tissue, which is the process of catalyst or reagents transfer to the lignin through polysaccharide matrix, and (2) the transport of the soluble lignin fragments from the matrix to the bulk solution. The process results in higher solids surface area and pore volume which shortens hemicellulose hydrolysis time and reduces enzyme consumption which lead to an extensive removal of lignin with minimum loss of cellulose (<2%) (Borand & Karaosmanoǧlu, 2018;Gelosia et al, 2020;Mathew et al, 2018). Organosolv operating parameters that determine efficiency (delignification, cellulose recovery) include solvent type and concentration, temperature, and L/S ratio.…”