The spontaneous and selective interactions between flavonoids and lotus seed starch in natural conditions: multi-scale structural changes, rheological and retrogradation properties before and after gelatinization.

Native lotus seed starch granules were mixed with structurally distinct flavonoids under ambient conditions. The interaction forces and the resulting starch properties were investigated. Flavonoid adsorption reduced the short-range helical order in the molecular chains, crystallite size (b-axis of the orthorhombic unit cell), the overall crystallinity, and the proportion of bound water, altering the surface charge of starch granules. The viscoelastic network of gelatinized starch paste was weak. In contrast, most flavonoids increased the starch gelatinization enthalpy (ΔHgel), water mobility, molecular chain flexibility, and granule size, and improved the color attributes. These effects are attributable to specific starch-flavonoid interactions, including hydrogen bonding and van der Waals forces. High levels of flavonoid adsorption weaken the network structure of starch paste. Depending on the flavonoid, this adsorption either inhibited or enhanced starch retrogradation, with hydrophobicity being the key factor. This study provides atomic-level insights into the influence of flavonoids on the helical arrangement and unit cell structure of native starch crystallites, which is crucial for the effective control of starch rheology and retrogradation.