Phenolics from sea buckthorn (Hippophae rhamnoides L.) modulate starch digestibility through physicochemical modifications brought about by starch – Phenolic molecular interactions

The phenolics from sea buckthorn (SP) exert various physiological functions. This study examined the interactions of SP on the digestive and physicochemical properties of rice (RS) and wheat starch (WS), as well as the stability of starch-phenolics during digestion. The predominant phenolics from SP were syringic acid (22.14%), gallic acid (15.23%), and catechin (11.45%). The addition of SP manipulated the rheology of starch pastes and affected the rearrangement and multi-scale structures of starch gels. Fourier transform infrared spectroscopy and X-ray diffraction revealed that SP interacted with starch mainly through non-covalent hydrogen bonds, leading to a loose starch gel structure. The content of rapidly digestible starch of RS and WS decreased by 5.66% and 7.75%; the predicted glycaemic index of RS (91.65) and WS (89.34) decreased to 81.81 and 80.84, respectively, when the addition level of SP reached 15%, due to the inhibition activity of SP against digestive enzymes, as well as the molecular reorganisation of starch. After the in vitro digestion, the bioaccessibility of SP in starch gels increased by a magnitude of 2.58-fold (RS) and 2.98-fold (WS). These results provide evidence of using SP as functional formulations in controlling gel-like foods structure behaviours and modulating the glycaemic response of starchy foods.