Study on the drying characteristics of rice by microwave and hot air drying

Abstract

This study presents the experimental methods of microwave drying and hot air drying of rice to simultaneously improve the dry storage effect of rice, reduce the mouldy and spoilage of rice, and measure the moisture content, water activity and temperature changes. A thermal imaging camera was used to photograph the temperature distribution of rice at different times to study the changing law of rice drying characteristics and analyse the relationship between rice water activity and drying speed. Results show that the changes in the moisture content and water activity of rice are inversely proportional with time. A 400 W microwave drying has a more pronounced heating effect on rice than 850 W hot air drying. The efficiency of the first 20 min of rice drying is better than that of the last 20 min. The highest temperature of 40 • C was reached after microwave drying for 8 min, while nearly 40 • C was reached after hot air drying for 56 min. These results can be applied to further analyse the influence of different drying methods on rice water activity and guide the reduction of bacterial propagation in rice and the improvement of the quality of rice. This work provides a theoretical basis for choosing the optimal drying method. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Drying and intermittence processes on the polished and brown rice physicochemical and morphological quality by near-infrared spectroscopy, X-ray diffraction, and scanning electron microscopy

“…The intermittence period aims to provide a resting time for the grain mass so that water is displaced in the form of liquid and vapor from the interior of the grain to the surface, optimizing the transfer of thermal energy and mass when exposing the grain again to heated air in the drying chamber. However, some factors such as recirculating the product several times in the dryer until drying is completed and the high temperature reached by the grain mass throughout drying can impact the rice quality ( Ling & Sun, 2021 ).…”

Investigation of a Precise Control Scheme for Rice Quality

“…Grain drying is a complex and dynamic process involving mass and heat transfer. Currently, hot air drying is the predominant method used in industrial settings [5]. However, the moisture content of grains and various parameters of drying air (e.g., temperature, velocity, and relative humidity) are critical factors that can limit both efficiency and quality outcomes for operators [6].…”

Effects of soaking temperature and ultrasonic power on the cooking time and physical properties of brown rice

“…Pores formed on the surface of brown rice by cavitation were proved to promote the evaporation of water inside and reduce the drying time consequently (Guo et al, 2020). As a pretreatment method, parboiling was proven to reduce the hardness and decrease the acidity and bacterial counts of brown rice during preservation period (Huang et al, 2021; Ling & Sun, 2021). And research had also found that high‐temperature soaking could promote the gelatinization of starch without decline in quality (Saniso et al, 2020), meanwhile, high‐temperature soaking could minimize the level of breakage‐susceptible white bellies and fissured rice grains (Buggenhout et al, 2014).…”