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Effect of Ultrasonic Treatment of Brown Rice at Different Temperatures on Cooking Properties and Quality

¹College of Food Science and Engineering, Northwest Agriculture and Forestry University, Yangling, Shaanxi, 712100, China. ²Department of Biological and Agricultural Engineering, University of California, Davis, One Shields Avenue, Davis, CA 95616. ³Processed Foods Research Unit, USDA-ARS-WRRC, 800 Buchanan St., Albany, CA 94710. ⁴Corresponding author. Fax: 510-559-5851. E-mail: zhongli.pan@ars.usda.gov

This research studied developing quick cooking brown rice by investigating the effect of ultrasonic treatment at different temperatures on cooking time and quality. The medium grain brown rice was ultrasonically treated in water at temperatures of 25, 40, and 55°C for 30 min and then dried by air at 25°C to its initial moisture content (11.0 ± 0.6%, wb) before cooking. The microstructure of rice kernel surface, chemical composition, and optimal cooking time of treated brown rice were determined. The pasting and thermal properties and chemical structure of flour and starch from treated brown rice were also examined. The results showed that the optimal cooking times were 37, 35, and 33 min after treatment at 25, 40, and 55°C, respectively, compared to the control of 39.6 min. The ultrasonic treatment resulted in a loss in natural morphology of rice bran, allowing water to be absorbed by a rice kernel easily, particularly at high-temperature treatment. Even through rice flour still maintained an A-pattern in the pasting properties, the crystallinity significantly increased after treatment at 55°C. Ultrasonic treatment increased the peak, hold, and final viscosities and decreased the onset temperature (T_o) and peak temperature (T_p), significantly. Thus, ultrasonic treatment could be used for reducing cooking time of brown rice.