Enrichment and Identification of Lignin–Carbohydrate Complexes in Softwood Extract

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.

Active role of lignin in anchoring wood-based stabilizers to the emulsion interface

“…[19][20][21][22] In line with this, a systematic study recently confirmed that part of the lignin-carbohydrates association in GGM extracts used as stabilizers has a covalent nature, identified as the so-called lignin-carbohydrate complex (LCC). 15 These findings corroborated with the hypothesis that wood-based stabilizers are naturally amphiphilic, in which the gradient of polarity in the same molecule favors their anchoring to the oil droplet. 1,12 Additionally, specific to the functionality of hemicelluloses as stabilizer agents, recent studies have demonstrated their suitable sensory profile and biocompatibility for application in life science applications, such as food and biomedical products.…”

“…Rich hemicellulose extracts containing galactoglucomannan (GGM) and glucuronoxylan (GX) were extracted from spruce and birch sawdust, respectively, through a pressurized hot water flow-through extraction (PHWE) process according to Kilpeläinen et al 25 Spray-dried galactoglucomannan (sdGGM) and glucuronoxylan (sdGX) were recovered from the resultant water-extract by spray-drying. Chemical and structural compositions of sdGGM and their fractions, i.e., ethanol-precipitated (ep-) GGM and ethanol-soluble (es-) GGM, were previously published, 15 and the fractionation of sdGX was performed as described below.…”

“…In fact, the heterogeneous composition of such extracts has been linked to their enhanced functionality as stabilizers, suggesting the occurrence of a natural combination of beneficial and complementary attributes of their various compounds. 4,10,13,15 Hemicelluloses, including galactoglucomannan (GGM) and glucuronoxylan (GX), promote good steric stabilization of emulsion in varied conditions of pH and ionic strength. 16 However, large amounts of hemicelluloses might be necessary to efficiently cover oil droplets since their structures typically lack hydrophobic sites.…”

“…A simple and efficient method based on liquid-extraction was developed for recovering pure stabilizers from emulsion phases and to enable further structural characterization. Moreover, the nature of lignin-carbohydrate interaction in GX stabilizers (fractionated by antisolvent process) was investigated following a similar approach used previously for GGM stabilizer, 15 in support of the interface study. Results indicated specific structural attributes in wood-based stabilizers associated to the oil droplet stabilization and endorse the value and functionality of using heterogeneous assemblies, supplemented by various lignin structures, rather than purified carbohydrates.…”

Combining cellulose nanofibrils and galactoglucomannans for enhanced stabilization of future food emulsions

“…Spruce galactoglucumannans (GGM) has earlier been shown to stabilize model beverage emulsion systems both against physical destabilization and against lipid oxidation (Lehtonen et al 2016;Mikkonen et al 2009;Mikkonen et al 2016a, b). Phenolic residues from lignin, co-extracted with the hemicelluloses in the PHWE method and partially covalently linked with GGM, are believed to play an important role, both to aid in the adsorption onto the droplet interface and by acting as an antioxidant against lipid oxidation (Carvalho et al 2020;Lahtinen et al 2019;Lehtonen et al 2018). Flocculation of emulsions droplets was observed for dilute emulsions, and contribute to destabilization (Bhattarai et al 2018;Mikkonen et al 2016a, b).…”