Puffing Characteristics of Parboiled Milled Rice in a Domestic Convective-Microwave Oven and Process Optimization

Microwavable products are gaining worldwide acceptance as convenience foods, where hygiene can be maintained when processed in small quantities at the domestic level. One such ready to eat products are puffed or popped starchy grains like corn, rice, sorghum, etc. Owing to its high starch content, rice has high expandability, and the puffed rice produce thence has better digestibility. Considering these aspects, an attempt was made to produce puffed rice in a domestic convective-microwave oven. Puffing characteristics were studied for Gurjari variety of rice at 14 % (wb) moisture content for different preheating temperatures of the glass base plate (180, 200, and 220 A degrees C), microwave power level (300, 600, and 900 W), and residence time (10-100 s), from which the range of residence time was selected for the optimization study. It was found that the puffing of rice was better at higher power level and preheating temperature of the base plate, and puffing started only after certain residence time. Further study was carried out to optimize the process parameters by using response surface methodology, for a Box-Behnken design at three levels for four parameters, i.e., moisture content (12, 14, and 16 % wb), preheating temperature of the base plate (180, 200, and 220 A degrees C), microwave power level (300, 600, and 900 W), and residence time (50, 60, and 70 s). The optimized conditions were found to be 14 % (wb), 220 A degrees C, 900 W, and 60 s. The second-order polynomial model was validated by conducting three trials at the optimized point and found to be agreeing with the predicted values.