Effect of Gelatinization and Retrogradation Cycle Treatments on the Structure and Physicochemical Properties of Sweet Potato Starch

The effects of different repeated gelatinization and retrogradation(RGR) treatments at temperatures of 75, 95, and 121 ℃ on the structural and physicochemical properties of sweet potato starch were investigated. Scanning electron microscopy(SEM), X-ray diffraction(XRD), differential scanning calorimetry(DSC), and rapid visco analysis(RVA) were used to evaluate the changes in the structural, crystalline, thermal, and pasting properties of sweet potato starch. The swelling power, solubility, and in vitro digestibility were also determined. The starch granule morphology was damaged or disappeared and irregular lumps formed after RGR treatment at 75, 95, or 121 ℃. For the RGR cycle treatment at 75 ℃, the intensities of the crystal absorption peak and heat absorption peak of sweet potato starch were reduced, while its gelatinization enthalpy decreased. The gelatinization temperature increased and the gelatinization temperature range became smaller. After RGR cycle treatments at 95 and 121 ℃, the X-ray diffraction patterns of sweet potato starch were converted from A-type to B-type and the heat absorption peak disappeared completely. In addition, with the increasing RGR cycles at different temperatures, the solubility of sweet potato starch increased first and then decreased, resulting in a decrease of starch viscosity characteristic value, a weakening retrogradation trend, and an increase of the slowly digestible starch(SDS) content. The highest SDS content(29.25%) of sweet potato starch was found in one RGR cycle treatment(RGR-1) at 121 ℃.