Unlocking glass transition phenomenon in mitigating drying-induced kernel fissuring in rough rice: A review

Rough rice kernel fissuring during drying is a critical issue that can lead to breakage during milling, reducing head rice yield. This review discusses moisture-related fissuring in rough rice kernels, focusing on the effects of temperature, relative humidity, and initial moisture content. It also explains the fissuring mechanism in terms of compressive and tensile stresses within the kernel, and explores the relevance of the glass transition phenomenon to these thermomechanical behaviors. The review further outlines the principles of glass transition measurement methods, both in general and as explicitly applied to rice. A comprehensive discussion is presented on the thermophysical properties of rice in the glassy and rubbery states, including their transitions during drying as influenced by temperature and moisture content, and how these transitions relate to kernel fissuring and head rice yield. The roles of tempering temperature, above and below the glass transition temperature (Tg), tempering duration, adsorption (post-drying), and fluctuations in drying air conditions related to kernel fissuring are also discussed. The review further explores drying techniques that can mitigate fissuring in rough rice. Finally, the paper identifies potential directions for future research, including a deeper investigation into the interaction of internal and external factors influencing fissuring, as well as the application of integrated drying techniques and control systems to enhance the reliability of the drying process and the quality of the resulting rice.