Polyphenol-Induced Structural Modifications of Potato Starch and Its Effect on Enzyme Inhibition and Digestibility

Abstract

Dietary polyphenols are emerging as promising nutraceuticals for regulating postprandial hyperglycemia by modulating starch digestion and glucose absorption. This study investigated the inhibitory effects of naturally occurring polyphenols - tannic acid (TA) and gallic acid (GA)- towards potato starch digestion from the perspective of starch-polyphenol and enzyme-polyphenol interactions. Native potato starch was complexed with each polyphenol and characterized using X-ray Diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). Enzyme inhibition kinetics against α-amylase and α-glucosidase, along with the digestion kinetics of the starch–polyphenol complexes, were also evaluated. Structural characterization revealed distinct interaction patterns between starch and polyphenols. TA and GA primarily altered the surface morphology of starch granules. They interacted with the helical regions of starch through strong secondary bonding interactions, leading to more stable starch-polyphenol complexes. Enzyme inhibition studies demonstrated pronounced suppression of both α-amylase and α-glucosidase activities. The IC₅₀ values against α-amylase and α-glucosidase were more than 0.6 mg/mL for both GA and TA. Kinetic analyses revealed that TA and GA acted predominantly as competitive inhibitors for the α-amylase and α-glucosidase enzymes. Digestion studies of the starch–polyphenol complexes demonstrated a significant reduction in starch hydrolysis and glucose release compared with starch treated with free polyphenols, indicating that complex formation enhances the resistance of starch to enzymatic degradation. The incorporation of polyphenols within the starch matrix modifies the structural organization of starch, thereby limiting enzyme accessibility to glycosidic linkages and slowing substrate hydrolysis. These results suggest that the nature and strength of starch–polyphenol interactions play a critical role in regulating digestion kinetics and glycemic response. Among the polyphenols investigated, TA and GA exhibited pronounced reduction in starch digestibility, highlighting their potential for developing low-glycemic starch-based functional foods and nutraceutical formulations for dietary management of diabetes.