Head rice yield, pasting property and correlations of accelerated paddy rice aging properties by microwave heating conditions

Head rice yield (HRY) and eating qualities can be improved by accelerated newly harvest paddy rice aging. In this study, microwave heating of continuous microwave dryer was applied to heat the newly harvested paddy rice. The microwave power level (MWL), exposure times (ET), and heating rounds (HR) on accelerated rice aging properties such as head rice yield and pasting properties, water uptake, solid loss, texture of cooked rice and color changes were investigated. The newly harvested paddy rice without microwave treatment was used as a control sample. The results showed that three chosen factors were mainly affected the HRY and the hardness. One round and two rounds of microwave heating caused lower HRY; however, three rounds resulted in the sample with the noticeably improved HRY when compared to one round, two rounds, and newly harvested rice. The HRY had a positive correlation with the hardness (P ≤ 0.001) and the color intensity (P ≤ 0.05) but a negative correlation with the moisture content (P ≤ 0.001), water uptake (P ≤ 0.01), solid loss (P ≤ 0.05), and lightness (P ≤ 0.001). The stickiness and solid loss were diversely changed after microwave heating but insignificantly different by varied microwave heating conditions. The hardness and the stickiness of cooked rice did not have a significant correlation with microwave heating. The MWL and HR produced the changes in viscosity properties of flour of newly harvested rice especially in peak and final viscosity. The peak viscosity and the final viscosity were decreased while breakdown and setback viscosity were slightly increased with increased HR and MWL. These changes seem to demonstrate the aging characteristics. The effect of HR on aging properties was particularly noticeable in this study. Furthermore, the resulting higher order polynomial interaction among microwave heating conditions on respective aging properties suggests that microwave-accelerated rice aging is a complex process.