Effect of ultrasonic pre-soaking conditions on the quality of parboiled japonica rice

To investigate the effect of ultrasonic pre-soaking process on the quality of parboiled japonica rice, japonica rice was used as the raw material, with traditional soaking (soaking at 65 ℃ for 4 hours) set as the control group. Different ultrasonic powers (100, 200, 300, 400, 500 W) and durations (10, 15, 20, 25, 30 min) were applied for pre-soaking rice, followed by soaking at 65 ℃ for 1 hour. The parboiled japonica rice was then prepared via steaming, drying, hulling, and milling. By analyzing the appearance, processing, physicochemical properties, and cooking quality indicators of parboiled japonica rice, a comprehensive evaluation model was established combined with principal component analysis to screen the optimal soaking process parameters for parboiled japonica rice production. The results showed that ultrasonic treatment significantly shortened the soaking time, increased the gelatinization degree, and reduced the white kernel rate, but darkened the grain color. Additionally, it improved the cooking and textural properties of parboiled japonica rice, enhancing the palatability of cooked rice. Comprehensive evaluation indicated that the optimal soaking process was 20 minutes of ultrasonic treatment at 300 W, followed by soaking at 65 ℃ for 1 hour. Under this condition, the milling yield of parboiled japonica rice reached its highest level (78.15%), with an L^* value of appoximately 69.94 and a white core rate of about 4.00%. For the cooked rice, the optimal steaming time, hardness, viscosity, elasticity, and chewiness were approximately 20.50 min, 2 096.48 g, 38.79 g·s, 0.75, and 861.51 g, respectively. Therefore, the optimal soaking process for parboiled japonica rice is ultrasonic treatment at 300 W for 20 minutes, followed by soaking at 65 ℃ for 1 hour.