Abstract
Lignin–carbohydrate complexes (LCCs) are hybrid structures containing covalently linked moieties of lignin and carbohydrates. The structure and behavior of LCCs affect both industrial processes and practical applications of lignocellulosic biomass. However, the identification of phenylglycoside, benzylether, and gamma (γ)-ester LCC bonds in lignocellulosic biomass is limited due to their relatively low abundance compared to plain carbohydrate and lignin structures. Herein, we enriched the LCC bonds in softwood galactoglucomannan (GGM)-rich extract fractionated by (1) a solvent (ethanol), (2) enzymes, and (3) physical techniques. Two-dimensional nuclear magnetic resonance (NMR) spectroscopy analysis was used to identify the LCC bonds. Phenylglycoside and benzylether bonds were concentrated in the ethanol-soluble GGM fractions. A benzylether bond was concentrated into GGM fractions containing larger molecules (>500 Da) through physical techniques. The γ-ester bond was identified in all studied GGM fractions, which is explained by its stability and possible presence in residual xylan. In summary, we demonstrated the potential of the suggested techniques to enrich LCC bonds in softwood extract and improve LCC identification. Such techniques may also enable further studies on the structure and functionality of LCC bonds and open new prospects in the engineering of biomolecules.
Highlights
Lignocellulosic biomass is a renewable and abundant source of natural biomolecules, widely distributed worldwide and the utilization of which is still expanding.[1]
Spruce extract obtained from pressurized hot water flow-through extraction (PHWE) is a heterogeneous mixture containing about 24% of the original spruce wood.[4]
We identified arabinoglucuronoxylan (AGX), the second most abundant hemicellulose in spruce wood, in the GGM samples (11.7%− 13.7%), along with a certain amount of glucuronic acid
Summary
Lignocellulosic biomass is a renewable and abundant source of natural biomolecules, widely distributed worldwide and the utilization of which is still expanding.[1] Sustainable alternatives from natural biomolecules are continually being developed to substitute products traditionally produced from fossil sources.[2]. More sustainable conditions for lignocellulosic biomass deconstruction have been implemented in biorefinery operations. This includes, for example, the use of hot water extraction, where acidic compounds from the lignocellulosic biomass perform autocatalysis.[2] In such extraction, the acetyl groups, involved in acetylation of hemicelluloses, such as softwood galactoglucomannan (GGM), act as catalytic agents.[3]. The existence of physical and chemical interactions between lignocellulosic components, is an unresolved limiting factor impacting the selective separation of pure moieties.[8−10]
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