Impact mechanism of methylation degree on structure and emulsifying ability of soy hull polysaccharides

Abstract

As a chemical modification method, methylation may enhance the emulsification of polysaccharides. In this study, we methylated soy hull polysaccharide (SHP) at 60 °C for 0–8 h and analyzed the degree of methylation (DM), crystallinity, surface hydrophobicity, interfacial adsorption, and emulsification capacity of methylation-modified SHP (MSHP). Fourier infrared spectroscopy results showed that the DM changed from 41.48% ± 1.46%–58.30% ± 2.63% after 8 h of methylation (MSHP-8h). The polysaccharide residues were analyzed by 1H NMR. Increasing the DM improved the surface hydrophobicity of SHP, which effectively reduced the interfacial tension (IFT) of SHP at the O/W interface. At equilibration, the IFT was the lowest for MSHP-8h (15.40 mN/m). However, interface thickness was negatively correlated with the DM. Methylation promotes the migration of SHP to the oil side; therefore, the polysaccharide layer remaining in the aqueous phase decreases with an increasing DM at low and fixed SHP concentration. A reduction in hydrophilicity weakens the hydrogen bonds between polysaccharides to cause the polysaccharide layer to be easily destroyed during the dilution process of the droplet size measurement. However, thin adsorption or hydration layers can adversely affect the stability of the interfacial layer; consequently, emulsions prepared with MSHP-4h were the most stable. Our findings provide a practical and theoretical reference for improving emulsification ability of polysaccharides.