Effect of acetylation modification on the emulsifying and antioxidant properties of polysaccharide from Millettia speciosa Champ

The highly hydrophilic nature of polysaccharides severely limits their application in oil-in-water emulsion. This work aimed to improve the emulsifying performance of Millettia speciosa Champ polysaccharide (MSCP) by adopting a modification strategy that covalently grafted the acetyl groups to the polysaccharide chains. Three acetylated polysaccharides (AC-MSCP1, AC-MSCP2 and AC-MSCP3) with different degrees of substitution (DS) were successfully prepared and characterized. Acetylation modification led to the degradation of MSCP and decrease in antioxidant ability. Compared with droplet size of MSCP formed emulsion (15.51 μm), a sharp decrease in droplet size of AC-MSCP stabilized emulsion (e.g. 0.24 μm for AC-MSCP2) was observed, which was even smaller than that of gum arabic (GA). Moreover, the emulsifying properties of AC-MSCP was regulated by multi-scale molecular structures. AC-MSCP1, with the lowest DS and molecular weight (MW), formed the largest droplets. AC-MSCP2, with a medium DS and MW, generated the smallest droplets, but droplet size was prone to increase due to low viscosity and electrostatic repulsion. AC-MSCP3, with the highest DS and the largest MW, formed bigger droplets than that of AC-MSCP2, but exhibited better emulsifying stability, owing to strong steric hindrance provided by its highest viscosity and thickest interfacial layer. Altogether, this study confirmed that acetylation modification was a promising method for improving the emulsifying performance of polysaccharide.