Effect of tempering drying on the physicochemical properties of paddy rice

To clarify the quantitative relationship between tempering drying parameters and the physicochemical properties of paddy rice, and to optimize the paddy rice drying process, a quadratic regression orthogonal rotational combination test was applied in this study. The initial tempering moisture content of paddy rice, tempering temperature, and tempering duration were the test factors, and the amylose starch content, alkali spreading value, and gel consistency were the test indicators. It was shown that under the conditions of the initial tempering moisture content of paddy rice of 20.5%, the tempering temperature of 43°C, and the tempering duration of 3.39 hr, the amylose starch content, alkali spreading value, and gel consistency were 17.83%, 7.08 grade and 86.4 mm, respectively. The average error between the actual value and the optimized theoretical value was 4.06%, indicating that the regression model was accurate and the physicochemical properties of rice were improved under the optimal process conditions. Then, the visual prediction model for the physicochemical properties of rice was established based on BP (Back Propagation) and GA‐BP (Genetic Algorithm‐BP) neural networks, respectively, and was compared with the regression model established by Design‐Expert software. The results showed that the root mean square error, mean absolute error, and mean absolute percentage error of GA‐BP were lower. Practical applications Drying is a significant primary process performed during the grain post‐harvest period, and it has a significant impact on the qualities of appearance, nutrition, and consumption. Traditional hot air drying has many problems such as low drying efficiency and high crack percentage, while tempering drying can alleviate those by reducing the gradient difference between the inside and outside of the grain, and this has become a hot spot for paddy rice drying research. To meet the current market demand for grain quality, most researchers have discussed the effects of tempering temperature and duration on the milling and nutrition qualities of rice. However, research on the initial tempering moisture content of paddy rice, tempering way, and its effect on the physicochemical properties of rice has rarely been reported. Therefore, it is important to study the influence of tempering drying process parameters on the physicochemical properties of paddy rice.