Insights into pH-modulated interactions between native potato starch and cyanidin-3-O-glucoside: Electrostatic interaction-dependent binding

Abstract

Potato starch (PS), a natural and structured semicrystalline polymer, exhibits a distinct capacity to bind cyanidin-3-O-glucoside (C3G) at different pH values (3, 5, and 7). In this study, levels of NaCl (0.05%, 0.5%, and 5%, w/v) were introduced as electrostatic disturbing agents to the PS-C3G complexes to quantitatively reveal the role electrostatic interactions played in the binding at different pH conditions. The binding rate dropped from 31.60% to 2.19% as the pH value shifted from 3 to 7, indicating a decreasing affinity from C3G to PS. Further zeta potentials showed the possibility of electrostatic interactions in the PS-C3G complexes at pH 3 as well as screened charges in the presence of NaCl. The binding rate at pH 3 then exhibited a progressive decline to a final approximate one-third as the concentration of NaCl increased, which implied that the electrostatic interactions constituted the primary two-thirds of the driving forces involving complex stability at pH 3. The results of attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, however, showed that hydrogen bonds had a negligible effect on the binding of C3G to PS at all pH conditions. Finally, the confocal laser scanning microscopy (CLSM) images, particle size and color differences were consistent with the change in the binding rate. Overall, electrostatic interactions were considered the key pH-modulated interactions between PS and C3G at different pH conditions.