Gallic acid forms V-amylose complex structure with starch through hydrophobic interaction.

This study aimed to investigate the role of amylose and amylopectin in the formation of starch-polyphenol complex and elucidate the interaction mechanisms. Gallic acid (GA) was used to complex with maize starch with various amylose contents. Results showed GA formed V-type crystals with normal maize starch (NMS) and high amylose maize starch (HAMS), while higher relative crystallinity was exhibited in HAMS-GA complexes than NMS counterparts. Molecular structure analysis revealed more amylose in GA-starch complexes than in treated starch counterparts without GA, and this was more apparent in HAMS than NMS, implying amylose is preferred to complex with GA than amylopectin. FTIR detected higher R1047/1022 value in starch-GA complexes than their starch counterparts without GA, suggesting increased short-range ordered structrure of complexes. Typical signatures of hydrophobic interactions were further revealed by isothermal titration calorimetry, indicating the complexation of GA to starch is mainly through hydrophobic bonds. More binding sites were observed for HAMS (72.50) than NMS (11.33), which proves the preferences of amylose to bind with GA. Molecular dynamics simulated the complexation of GA to amylose, and confirmed hydrophobic bond is the main interaction force. These findings would provide guidance for precise design and utilization of starch-polyphenol complexes in functional foods.