Hydroxyl position of 3 flavonoid isomers modulate gelatin structure-properties relationship: Structural rearrangement, non-covalent binding mechanism and function regulation.

Flavonoid modification is an effective method to improve protein properties. Non-covalent complexes of gelatin and flavonoid isomers with same hydroxyl number but different hydroxyl position (kaempferol-KA, luteolin-LUT and fisetin-FIS) were fabricated. Binding mechanism and their properties were elucidated. Results showed that the ordered α-helix of gelatin was transferred to disordered structures after the addition of flavonoids by lowering the content of hydrogen bonds and enhancing the contents of ionic bonds and hydrophobic interactions. The conformation change of gelatin was correlated with hydroxyl position of flavonoid. KA (3-5-4' OH) endowed gelatin with small particle size. LUT (5-3'-4' OH) endowed gelatin with good emulsifying properties due to high hydrophobic interactions (0.42 ± 0.07) and random coil (39.2%). FIS (3-3'-4' OH) endowed gelatin with optimal foaming capacity and gel properties due to high surface hydrophobicity (302.30 ± 15.78). Molecular docking and molecular dynamics simulations showed that the main binding ways might be hydrogen bonds, van der Waals forces, and hydrophobic interactions. GE-KA and GE-FIS showed an exothermic interactions, whereas GE-LUT exhibited a pronounced entropy-driven binding mode.