Probing covalent and non-covalent interactions between vanillic acid and starch and their effects on digestibility by solid-state NMR

Intermolecular interactions play a significant role on the physicochemical properties and digestibility of starchy foods. This study investigated the covalent and non-covalent interactions between vanillic acid (VA) and porous starch (PS) as well as their effects on digestibility using solid-state NMR. VA-PS conjugates and mixtures were synthesized and characterized using 1H NMR, FT-IR, SEM and XRD. 13C NMR peaks at 163 ppm and FT-IR signals at 1737 cm−1 indicated the formation of ester bond in VA-PS conjugates. While differences between covalent and non-covalent interactions were also probed by solid-state NMR. The specific binding sites between VA and PS were subsequently identified by 1H13C HETCOR spectra before assessing the impact of covalent and non-covalent interactions on digestibility through an in vitro digestion test. The results revealed 13C chemical shifts of about 2.0 ppm, indicating stronger intermolecular interactions, and reduced mobility of the VA-PS conjugate due to its covalent bonding. Overall, the results showed that the VA-PS conjugate, characterized by stronger covalent interactions, exhibited superior effects in inhibiting starch digestibility compared with non-covalent interactions.