Effect Of Ultrasonic Treatment On Physicochemical Properties Of Brown Rice And Its Mechanism

Brown rice is rich in nutrients, but not acceptable by most consumers because of the poor taste and longer time to be fully cooked. In the aim of maintain most nutrient component and reducing the optimum cooking time, the midimun grain brown rice M202 was used in this study to investigate the effect and mechanism of ultrasonic treatment on the optimun cooking time, the cooking properties, the texture and get better sensory quality. In addition, the Peleg's equition was used to model the water absorbtion characters of ultrasonic treated brown rice below 60℃, the mechanism of reducing the optimum cooking time of brown rice by ultrasonic was explained based on the water absorption equition. Moreover, the prossibility of using ultrasonic probe to reduce the optimun cooking time was also disscussed, the texture and sensory characters of treated brown rice was evaluated. The treating parameters for ultrasonic probe treatment were optimized based on fuzzy comprehensive evaluation. The main results are as follows:(1)Brown rice was ultrasonically treated in a tank at temperatures of 25℃, 40℃and 55℃for 30 min,respectively. The most of the chemical composition was remained in rice kernel, the optimal cooking time of treated brown rice were 37.3min, 35.3min and 33.3min after the treatments at 25℃, 40℃and 55℃, respectively, compared to the control of 39.6min. The texture and sensory properties of treated brown rice were improved.(2) Brown rice was treated by ultrasonic probe combined with different heating mode, the result showed that heating could reduce the output power of ultrasonic, led to unefection of optimum cooking time.Ultrasonic probe without heating could reduced the optimal cooking time of brown rice.(3) The major effect of ultrasonic is on the bran of brown rice, the rice starch properties changed a little during ultrasonic treatment, both of which acceletated the water absorption in cooking processing. Peleg's equation was used to model the water absorption chaaracters of brown rice below 60℃, and the water absorption character of brown rice above 60℃was also investigated. The results indicated that ultrasonic treatment significantly accelerated the water absorption properties of brown rice. Peleg's equation fit the measured moisture data below gelatinization temperature well, the coefficients of regressions r~2≥0.996 and there was no significant difference between the measured and predict moisture content (R<5%).(4) Optimize the treating condition of ultrasonic probe using fuzzy comprehensive evaluation. The best ultrasonic treating parameter was amplitude setting in 8.0, treating 1.25g brown rice at 40℃for 1.6min. The validation data showed that the moisture content of brown rice was 24.20±0.84%, solid loss was 9.85±0.69%,clour change was 8.89±2.47, panels acceptable value was 68.66±0.60(n=3).(5) The results proved that ultrasonic reduced the optimum cooking time successfully, enhanced the panels'acceptable of brown rice. The use of ultrasonic in brown rice cooking processing is a promising technology.