Understanding the physicochemical properties, multi-scale structure, and in vitro digestibility of sweet potato starch noodles supplemented with fucoidan

This study aimed to explore the effects of fucoidan on the physicochemical properties, multi-scale structure, and in vitro digestibility of sweet potato starch noodles (SPSNs). The underlying interaction mechanisms between SPS and fucoidan were also investigated. Results showed that fucoidan decreased the rehydration time (18.75-15.25 min), rehydration ratio (365.38-341.09%), and expansion ratio (165.75-137.70%) of SPSNs, whereas the broken rate (0-10%) and cooking loss (0.11-0.18%) increased. In addition, the hardness, chewiness, springiness, and gumminess of SPSNs were improved with the addition of 100-200 g/kg fucoidan. Moreover, Fourier transform infrared spectroscopy and X-ray diffraction analyses revealed that fucoidan elevated the ratio of 1047 to 1022 cm -1 (1.79-2.92) and 995 to 1022 cm -1 (3.41-5.52), and the crystallinity (4.41-6.58%) of SPSNs. Scanning electron microscope demonstrated that SPSNs with fucoidan exhibited a porous structure with larger pore size and greater pore density. These structural alterations led to an increase in slowly digestible starch (SDS) (14.65-28.87%) and SDS+RS (68.58-81.32%), and a decrease in rapidly digestible starch (31.28-18.68%), without affecting the resistant starch (RS) content. The enthalpy, peak temperature, pasting temperature, final viscosity, and setback of SPSNs increased upon fucoidan addition, whereas the peak viscosity, trough viscosity, and breakdown decreased. In addition, principal component analysis and Pearson correlation analysis confirmed that the cooking properties and in vitro digestibility were significantly correlated with the starch structure. Molecular dynamics simulations further revealed that fucoidan bound to sweet potato starch via hydrogen bonding and electrostatic interactions. This study provides new insights into the potential of fucoidan as a functional ingredient for developing low-glycemic starch-based foods.