Effects of mode of heat transfer on puffing quality of rice grain: A modeling and simulation analysis

Abstract

AbstractCereal grains can be puffed by heating in hot sand bed or domestic microwave oven. The purpose of this study was to explore and compare the reasons of transformational changes in preconditioned rice during its sand bed heating and microwave heating in domestic microwave oven. Mathematical modeling and simulation techniques were used to estimate the changes in microwave power absorption density and temperature of rice with the heating methods. Sand puffing, initiated from the tips of rice, progressed toward the central region of the rice following the change in temperature profile of rice and outcomes were completely puffed rice. The rice grains, placed in the different radial zones on the turntable of oven cavity, experienced nonuniform and inconsistent rate of microwave power absorption within the rice due to its placement and rotation, the oven factors, grain's shape, size, and dielectric properties. Microwave puffing, initiated from the central region of rice, progressed toward the tips of the rice. The slow rate of heating resulted in evaporative cooling of rice and most of the rice were unable to puff completely. However, the rate of microwave heating of rice was comparable with that of sand heating and about 92.0 ± 2.3% puffed was observed when rice was place in radial zone of 5.0 cm. Hence, the exact placement of rice in the oven cavity was required for achieving good puffing quality of rice.Practical applicationsThe present study helps to understand the reasons for uneven puffing of rice in domestic microwave oven. This understanding of puffing process in domestic microwave oven provides an opportunity to develop strategy for microwave puffing of rice or design a specific microwave puffing equipment suitable for achieving quantitative and qualitative puffing of rice.