Dual-frequency ultrasonic effect on the structure and properties of starch with different size

Single (40 kHz) and dual (40 kHz + 80 kHz) frequency sonication were applied to potato (large granule size) and millet starch (small granule size) at different temperature (25 degrees C and 60 degrees C). Starch with large granule size was more sensitive to ultrasound, as reflected by the reduction in peak viscosity, enthalpy, relative crystallinity and degree of order. Ultrasound caused the rough surface, crack and partial collapse on potato starch, however it did not change millet starch significantly. Particle size measurements indicated that the reduction in potato starch particle size was greater than millet starch. The peak viscosity of potato starch decreased by a maximum of 10.7%, whereas the peak viscosity of millet starch decreased by only a maximum of 3.9%. X-ray diffraction showed that the relative crystallinity of potato was reduced by up to 12.3%, however, this change of millet starch was 1.68%. The swelling power of both starches was increased at 25 degrees C and decreased at 60 degrees C. Additionally, dual-frequency ultrasound was more effective to modification than single-frequency, irrespective of the granule size of starch. In conclusion, the damage of large granule starch caused by ultrasound was more serious than that of small granule starch and the dual frequency and high temperature will promote the process.