Investigation of glass transition behavior in a rice kernel drying process by mathematical modeling

Rice fissuring during the drying process may decrease the head rice yield after milling. To better understand the rice fissure formation, a 3D body fitted mathematical model was developed based on the glass transition hypothesis. The simulated temperature, moisture content, and glassy/rubbery state distribution inside the rice kernel were used to analyze the glass transition behavior of the kernel in the hot air drying process. It was found that the changes of the kernel temperature and moisture content caused the glass transition behavior. The rice temperature dominated the glass transition occurring in the initial heating and final cooling stage, while the moisture content played a more important role in the main drying stage. No rubbery to glassy state transition occurred when the drying temperature is lower than 35 °C; the rubbery to glassy state transition occurred gradually in both the drying and cooling stage in 35 ∼ 45 °C, while took place sharply and only in the cooling stage when the drying temperature is larger than 45 °C. The glass transition behaviors obtained in this work were related well with experimental observations about the rice fissuring rate.