Investigation on the pitting of potato starch granules during high frequency ultrasound treatment

In this paper, the pitting of potato starch granules in aqueous suspensions (1%) by high-frequency high-power ultrasound (850 kHz at a power of 0.2 W, 2 W or 3.7 W; and also 500 kHz and 1 MHz at a power of 2 W) is reported. The number of pits per starch granules was found to be independent of the amylose content of starches, and the surface properties of starch granules as modified through SDS and ethanol washing. At 850 kHz, the maximum number of pits per starch granule, for both normal and waxy starches, did not exceed 11. However, a close inspection of fractionated starch granules based on their sizes showed that there is an optimum granule size for which a maximum pit number is obtained. For example, starch granules with diameter size range of ∼15 to ∼30 μm had a maximum pit number (between 10 and 20 pits per granule) when sonicated (2 W, 850 kHz and 30 min); while sonication of small (<10 μm) and very large (>45 μm) granules resulted in a smaller number of pits per granule (∼5). Further, the maximum number of pits per granules is also found to be proportional to the ultrasound frequency, with values of approximately 7, 10 and 11 at 0.50, 0.85, and 1 MHz, respectively. FTIR measurements did not show any breakup of starch molecules.