Enhancing rice protein dispersibility through pectin complexation and resulting hydrogel formation

In this study, we evaluated whether complexation with pectin improves the dispersibility of rice protein (RP). RP (2% and 5%) was mixed with low-, medium-, and high-methoxyl pectins (LMP, MMP, and HMP, respectively) at pH 2.5 and 7. At pH 2.5, LMP markedly enhanced RP dispersibility, with dispersion beginning at 0.8% LMP and stable gel-like structures forming at ≥2% LMP for 2% RP, whereas MMP and HMP caused phase separation. Notably, zeta potential shifts toward negative values indicated LMP adsorption onto the positively charged RP, and Fourier-transform infrared (FT-IR) spectroscopy showed protonation-related carbonyl changes and strengthened hydrogen bonding. Rheological measurements confirmed that only LMP-containing mixtures met hydrogel criteria (G′ > G″, tan δ < 1). In addition, scanning electron microscopy (SEM) showed a continuous network consistent with hydrogel formation. The RP–LMP hydrogels exhibited >50% curcumin encapsulation efficiency without ethanol. Overall, LMP effectively functionalized RP under acidic conditions, forming weak but stable hydrogels suitable for delivering hydrophobic bioactive compounds. • LMP complexation improved dispersibility of commercial rice protein. • Only LMP enabled complete RP dispersion and hydrogel formation. • RP–LMP hydrogels showed weak yet stable viscoelastic gel properties. • Hydrogels incorporated hydrophobic curcumin under ethanol-free conditions.