Effect of freezing‐assisted treatment on the formation of stable VII‐type complex of fried sweet potato starch and its mechanism

To comprehensively understand the effect of freezing-assisted treatment on the physicochemical properties of the fried sweet potato starch, the structural changes at granular and crystalline level were investigated. The results suggested that the freezing temperature exerted a significant effect on the interactions between sweet potato starch (SPS) and fried oil. With decreasing the freezing-assisted temperature, the gelatinization enthalpy of the fried frozen SPS remarkably increased by 1.5-4.9 J·g-1 and the transition temperatures of the second peak were elevated from 132.5°C to 136.5-141.1°C compared to that of native SPS, which suggested that more stable VII -type starch-lipid complexes were formed during frying. This finding was consistent with the results of the X-ray diffractometer that the intensity of the diffraction peak at 20.1° for V-type complex increased sharply as the temperature decreased from 20°C to -80°C, and the corresponding relative crystallinity and R1047/1022 values were increased from 16.5% and 0.35 to 26.4% and 0.45, respectively. The scanning electron microscopy revealed that the lower freezing-assisted temperature before frying promoted a membrane-like material covered on surfaces. The results showed that decreasing the freezing temperature promoted the formation of stable VII -type complex during frying. PRACTICAL APPLICATION: The purpose of this study was to comprehensively understand the effect of freezing-assisted treatment on the physicochemical properties of the fried sweet potato starch. These results provided useful information and effective method for producing fried starch-based foods with low digestibility.