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

Hemicellulose-rich wood extracts show efficient capacity to adsorb at emulsion interfaces and stabilize them. Their functionality is enhanced by lignin moieties accompanying the hemicellulose structures, in the form of lignin-carbohydrate complexes (LCCs) and, potentially, other non-covalent associations. The formation and stability of emulsions is determined by their interfacial regions. These are largely unexplored assemblies when formed from natural stabilizers with a complex chemical composition. Understanding the structure of the interfacial region could facilitate both designing the extraction processes of abundant biomasses and unraveling a valuable industrial application potential for the extracts. Herein, we characterized the LCCs from the interface of oil-in-water emulsions stabilized by galactoglucomannan (GGM) or glucuronoxylan (GX)-rich wood extracts, using two-dimensional nuclear magnetic resonance (NMR) spectroscopy analysis. The type of covalent linkage between residual lignin and hemicelluloses determined their partitioning between the continuous and interfacial emulsion phases. Benzylether structures, only found in the interface, were suggested to participate in the physical stabilization of the emulsion droplets. In turn, the phenylglycosides, preferentially observed in the continuous phase, were suggested to interact with adsorbed stabilizers by electrostatic interaction. More hydrophobic lignin structures, such as guaiacyl lignin type, dibenzodioxocin substructures, and certain end groups also contributed to droplet stabilization. The elucidation of such attributes is of paramount importance for the biorefinery industry, enabling the optimization of extraction processes for the preparation of wood-based stabilizers and designed interfaces for novel and sustainable emulsion systems.