Dual-frequency ultrasound effect on structure and properties of sweet potato starch

Effects on the structure and properties of sweet potato starch under single frequency ultrasound of 25, 80 kHz and dual‐frequency ultrasound of 25 and 80 kHz were investigated at the same treating conditions else. Dents and pores were found by SEM at the surface of starch with both ultrasounds. Starch–iodine complex analysis showed above ultrasounds destroyed amylopectin and starch chains. FT‐IR indicated that with ultrasonic treatments, the functional groups of starch were not destroyed, but its crystal structure was damaged. As a result, its crystalline index decreased. Brabender curves showed that the peak viscosity of starch with dual‐frequency ultrasound was 14.09% lower than that of the native starch. In addition, the solubility and transmittance of starch increased by ultrasound, and the solubility went up as ultrasonication time was increased. It reached the maximum when the starch was treated for 60 min by dual‐frequency ultrasound, which increased by 2.69% compared to that of native starch. The starch being treated by dual‐frequency ultrasound for 30 min showed maximum transmittance, increasing it by 5.1% compared to the native starch; however, continuously increasing ultrasonic treatment resulted in a decrease of transmittance. Therefore, compared to single frequency ultrasound, dual‐frequency ultrasonic treatment caused more obvious changes to the structure and properties.