Structure-driven interactions between indica rice starch and tea polyphenols during thermally induced phase transition

Despite the extensive use of tea polyphenols (TP) in starch-based functional foods, the role of the starch fine structure in the efficient formation of starch-TP complexes is not well understood. This study investigated the interactions between indica rice starches (Hly 16, Ly 6176, Zz 83) and TP at various phase transition temperatures (T o , T p , T c ). Microstructural characterization confirmed progressive gelatinization: T o (intact granules), T p (partial swelling), and T c (complete gel network formation). Meanwhile, crystalline structures of all three starch-TP mixtures underwent a transformation from A-type to V-type. Notably, the Zz 83-TP-T c complex exhibited the highest V-type crystallinity, which may be attributed to its amylose content (highest) and amylose chain length (longest); consequently, these characteristics promoted more effective starch-TP interactions. Correspondingly, Zz 83-TP-T c also showed the highest resistant starch (RS) content (40.86%) compared to Ly 6176-TP-T c (36.25%) and Hly 16-TP-T c (36.33%). Furthermore, a significant positive correlation was observed between RS content and V-type crystallinity, indicating that the formation of V-type complexes effectively reduced starch digestibility. These results elucidate that the fine structure of indica rice starch plays a crucial role in the formation of the starch-TP complex, providing a molecular basis for precise health food design. • Starch fine structures significantly affected its molecular interaction with TP. • The phase transition temperature of starch decreased upon incorporation of TP. • Starch-TP mixture readily forms a V-type crystal under T c condition. • The formation of V-type complexes effectively reduced starch digestibility.