Deep bed rough rice air-drying assisted with airborne ultrasound set at 21 kHz frequency: A physicochemical investigation and optimization.

This study investigates the feasibility of achieving a modified rough rice air-drying with ultrasound intervention (US) set at 21 kHz frequency. The process was carried out using an ultrasound assisted convective dryer and analyzed in terms of drying time, energy consumption (EC), evaporation rate (ER), broken kernel (BK), water activity (a), vitamin B (niacin), and total phenolic content (TPC). The lab-scale dryer was set to transmit energy at power levels of 30, 60, 90, 120, and 150 W in the air temperatures of 35, 40, 45, 50, and 55 °C and velocities of 0.2, 0.5, 0.8, 1.1, and 1.4 m/s for a thickness of 20 cm. The results showed that in-range drying parameters played a major role in response analysis, suggesting that ultrasound efficiency during convective drying heavily depends on the power, air temperature, and velocity levels. Ultrasound assistance significantly increased bed evaporation rate up to 38.93%. Subsequently, it caused a reasonable reduction in total drying time, EC, and BK percentage up to 27.92%, 25.98%, and 34.22%, respectively in the case of 35 °C, v = 0.8 m/s, and P = 90 W. Remarkable advances were attained in the ultrasound assisted drying domain in grain quality via acceptable decrease in niacin and TPC losses within shorter drying time. There was a significant linear trend in BK, niacin, and TPC values across the bed thickness, which all was increased by the ultrasound application. The highest nutrient retention and physical quality preservation belonged to the top layer, which was influenced by the ultrasound radiation by the highest degree.