Insights into the effects of phenolic acids on rice starch properties via noncovalent interactions

The development of advanced starch-based materials is hindered by limited understanding of structure-dependent phenolic acid (PA) binding mechanisms. This study employed a multi-technique approach (Fourier-transform infrared, x-ray diffraction, rheology, molecular docking) to investigate 16 PAs with varying hydroxylation patterns and methoxy substitutions. Three distinct binding modes were identified: (1) Polyhydroxylated acids (e.g., gallic acid [GA]) formed bridge-structured complexes with amylose helices (ΔH: 13.68 J/g; binding energy: -3.17 kcal/mol), increasing relative crystallinity (RC) by 18%-22% and reducing digestibility by 31%-35%; (2) methoxylated derivatives (e.g., syringic acid) bound helical cavities via hydrophobic interactions (ΔH: 9.21 J/g; binding energy: -2.86 kcal/mol), enhancing thermal stability without altering RC; (3) cinnamic acids preferentially interacted with amorphous regions through hydrogen-bonding networks. These findings establish two fundamental principles for starch modification: (a) Phenolic architecture dictates supramolecular assembly pathways, and (b) binding site selection governs functional specificity. The acquired knowledge enables targeted design of starch materials for diabetic-friendly foods (controlled digestibility) and biodegradable packaging (enhanced thermomechanical properties), advancing beyond empirical modification approaches. Future research should investigate dynamic binding behaviors during thermal processing and storage. PRACTICAL APPLICATION: This study guides next-gen PA-starch functional foods: (a) Selecting PAs with polyhydroxy/methoxy groups enables precise resistant starch design for rice-based staples with tailored digestibility. (b) Heat-stable polyhydroxy PA-starch complexes (GA, HCA, 4HA) suit high-temperature-sterilized products like instant noodles, while phenolic acid derivatives (cinnamic acid) form amorphous networks for dual encapsulation of hydrophilic (B12) and lipophilic (D3) nutrients in low-temperature pasty foods, overcoming fortification challenges.