Effect of Ultrasound on Physicochemical Properties of Wheat Starch

Application of ultrasound process is growing in food industry for different purposes including homogenization، extraction، blanching and removal of microorganisms، etc. On the other hand، starch is a natural polymer which exists in many foods or added into the food as an additive. Therefore، determination of the effects of ultrasound on starch characteristics can be useful in interpretation of the properties of starch-containing products. The main aim of this study was to determine the physicochemical changes of wheat starch treated by ultrasound waves. Therefore، an ultrasound probe device was used which ran at 20 kHz، 100 W and 22°C. Starch suspension in distilled water (30% w/w) was prepared and treated with ultrasound for 5، 10، 15 and 20 min. The results showed that increases in processing duration led to increases in water solubility of starch، water absorption and gel clarity (as determined by spectrophotometry). Starch intrinsic viscosity as measured using an Ostwald U-tube showed lower intrinsic viscosity with increases in ultrasound time. Gel strength of the samples as determined using a texture analyzer was reduced by longer processing time. The scanning electron microscopy revealed that increasing the duration time of the ultrasound treatment could produce some cracks and spots on the surface of the granules. In total، it was concluded that the ultrasound treatment resulted in some changes from the starch granular scale to molecular levels. Some of the starch molecules were degraded upon ultrasound processing. Such changes may be observed for the starch-containing foods treated with ultrasound and they are enhanced with increases in ultrasound time intervals.