Effect of Number of Freeze-Thaw Cycles on the Properties and Structure of Ultrasonically Modified Corn Starch Gel

We investigated the changes of gel characteristics and structure of ultrasonically treated corn starch during freeze-thaw cycles, with a view to providing theoretical guidance for improving the quality of quick-frozen starch-based foods. The effects of the number of freeze-thaw cycles on the dynamic rheological and textural properties of ultrasonically modified corn starch gels were analyzed and their structures were characterized by using a rheometer, a texture analyzer, a low-field nuclear magnetic resonance (NMR) spectrometer, a Fourier transform infrared (FTIR) spectrometer and an X-ray diffractometer (XRD). The results showed that compared with native corn starch, the water separation rate of ultrasonically modified corn starch gels significantly decreased by 5.19% (P < 0.05) at the 4th freeze-thaw cycle, indicating improved freeze-thaw stability; the storage modulus and loss modulus of ultrasonically modified corn starch gels decreased, and the gel strength was weaker; the hardness significantly decreased by 10.83% (P < 0.05), and the amylose content decreased 0.15%. Moreover, the iodine binding force was weakened, the transverse relaxation time distribution curve was shifted to the left, the short-range ordered structure was weakened, and the relative crystallinity was reduced. The gel properties and the structural characterization results indicate that ultrasonic treatment can inhibit water migration and double helix structure formation in the corn starch gel system during freeze-thaw cycles and consequently improve its freeze-thaw stability.