Galactoglucomannans (GGM) and glucoronoxylans (GX) are the most abundant hemicelluloses in softwood and hardwood, respectively. Recently, GGM- and GX-rich assemblies obtained through pressurized hot water flow-through extraction (PHWE) of wood saw meal proved to be more efficient emulsifiers than conventional food hydrocolloids, and they also protected emulsified lipids against oxidation. Our hypothesis is that hemicelluloses and phenolic residues in the extracts are covalently linked forming lignin-carbohydrate complexes (LCC). The presence of LCC in the GGM- and GX-rich assemblies likely enhances their functionality in colloidal systems. To confirm this hypothesis, the presence of LCC in GGM- and GX-rich assemblies was investigated. Firstly, GGM- and GX-rich assemblies were recovered from spruce and birch PHWE extracts, respectively, by freeze-drying, spray-drying, ethanol-solubilization and ethanol-precipitation. The chemical structure of the samples was investigated in detail by specialized techniques including high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD), size-exclusion chromatography (SEC) and nuclear magnetic resonance spectroscopy (NMR). Then, further fractionation was performed using the spray-dried (s) GGM sample, which was chosen due to its excellent functionality in emulsions. The sGGM sample was fractionated using anti-solvent precipitation (ethanol/water mixtures), extraction with binary systems (ethyl acetate/water), acid hydrolysis and by a combination of physical (centrifugation and nanofiltration) and enzymatic treatments (sequential and semi-simultaneous) and assessed regarding to the presence of LCC. The presence of phenylglycoside and γ-ester bonds in GGM- and GX-rich assemblies was confirmed, especially in freeze-dried, spray-dried and ethanol-soluble samples. The ethanol-precipitation favored the fractionation of higher-molar mass and more pure GGM and GX fractions. Consequently, the ethanol-soluble samples were concentrated with LCC structures. Among the fractionation methods, the combination of physical and enzymatic treatments resulted in concentration of low molar mass hemicelluloses and LCC structures. Thus, the findings suggest that GGM- and GX-rich extracts are functionalized by the presence of LCCs, which may contribute to their excellent emulsion stabilization capacity.

Analytical insights on lignin-carbohydrate complexes in hardwood and softwood extracts

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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