Dynamic monitoring of fissure development in rice kernels during drying and subsequent cooling using acoustic emission technology

Rice kernel fissuring during postharvest drying and subsequent cooling is a major cause of quality deterioration and its dynamic evolution from unvisitable microcrack to visible macrocracks to visible fissure is important for better understanding of rice fissuring. In this study, a new acoustic emission (AE) technique was tried to monitor the dynamic evolution process of the rice kernels. The AE detecting experiments were conducted on rice kernels during drying at 35, 40, and 45 °C and subsequent cooling at 20 °C. The glassy/rubbery transition behavior during drying was simulated and the relationship among glass state transition, AE events, and fissure development were analyzed based on these experimental and numerical results. It was found that the AE signals emitted by microcracking inside the rice kernels can be detected. A strong correspondence existed between AE activities and fissure growth during both drying and cooling. In drying process, the major AE clustering appeared approximately 3 min before the peaks of fissure growth rate. The ringing count was more sensitive during drying, whereas AE energy was more informative during cooling. AE technology provided dynamic information to study fissure initiation and propagation during rice drying/cooling. The study results indicated that AE has a promising potential to serve as an early-warning indicator for fissure development during both rice drying and subsequent cooling.