Physicochemical properties, structure and in vitro digestibility on complex of starch with lotus (Nelumbo nucifera Gaertn.) leaf flavonoids

Lotus leaf flavonoids (LLF) are a group of bioactive natural substances. In this study, the structure, thermal properties, rheology behaviors and in vitro digestibility of cooked LLF-starch complex were investigated. Differential scanning calorimetry (DSC) analysis showed the shift in gelatinization peak to a higher temperature and the decrease in gelatinization enthalpies in the complexes significantly. The short-term retrogradation was retarded either. The flow behaviors of starch pastes changed with adding LLF. Scanning electron microscope (SEM) images showed a less compact structure in LLF-starch complex and laser confocal scanning microscope (CLSM) images detected that LLF mostly distributed around starch granules, which further prove the binding between LLF and starch. Moreover, fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) elucidated LLF probably interacted with starch by non-covalent bond especially hydrogen bond. In addition, LLF-starch complex exhibited inhibitory effect on starch digestion compared to pregelatinized starch, and the reasonable content of LLF-starch complex was (0.7 g/100 g). Thus, LLF-starch complex can be potentially used as a functional additive for high resistant starch (RS) and low glycemic index (GI) diets.