Ultrasound has been rapidly applied successfully in diverse food technological aspects including improvement of functional properties of food ingredients such as starch. This work was carried out to compare the influence of two types of sonication, bath and probe, on several physicochemical and microstructural properties of wheat starch. Two sonication probes (200 and 400 W) and a sonication bath (690 W) were applied to treat wheat starch suspensions at 15 and 30 min. Sonication time in 400 W probe was intermittent while for the other treatments, it was continuous. Swelling capacity (SC), solubility (SB), turbidity (TB), and oil absorption (OA) parameters were investigated for native (control) and sonicated wheat starch. Moreover, scanning electron microscopy (SEM) was performed to determine the influence of sonication treatments on the morphology of wheat starch granules. The highest level of SB and OA, as well as the lowest SC, was obtained for starch samples treated with 200 W sonication probe, while no significant difference (p < 0.05) was observed between two sonication times (15 and 30 min). The SEM images showed significant and nonuniform impact of ultrasound on the structure of starch granules in which some granules remained almost smooth, but some showed high irregular surfaces or even in some cases structure collapse. The highest disintegration of granules was obtained in probe 200 W treatments.
Keywords: microstructure; physicochemical properties; ultrasound; wheat starch.