One-pass Drying of Rough Rice with an Industrial Microwave- Quality and Energy Use Consideration

Abstract. The use of industrial microwave at 915 MHz may have the potential to achieve one pass rough rice drying. However, it is vital to determine the optimal processing parameters for continuous flow drying operations that maximize drying throughput and minimize milled rice quality reduction. Therefore, the objective for this study was to quantify the effect of microwave (MW) energy applied per unit mass of rough rice on moisture, and milled rice quality reduction for a continuous one pass MW drying operation of rough rice. Freshly-harvested, medium-grain rough rice with moisture content of 25% wet basis were used for this study. A portion of the sample was used as control and the remaining were dried in a pilot scale 915 MHz MW for up to 8 minutes drying duration. The rough rice were heated at specific energies of 450, 600 and 750 kJ/kg at various rice bed thicknesses of 0.01, 0.03, and 0.05 m. The result showed that moisture removed varied between 6% and 15% point as specific energy increased (p <0.05). Also, increase in bed thickness with increase in specific energy from 450 to 600 kJ/kg resulted in reduction in milling yield from 73% to 62%. HRY reduced from as 66% to 37% as specific energy increased from 450 to 750 kJ/kg; there were marginal reduction in measured rice fat (0.50%– 0.34%) and protein (6.13% – 5.60%) contents. In conclusion, drying of medium-grain rough rice using a continuous flow, one pass MW heating at a specific at heating rate of 450 kJ/kg and bed thickness of 0.01 m appeared to be most promising treatment of all the studied conditions.