FISSURE FORMATION CHARACTERIZATION IN RICE KERNELS USING VIDEO MICROSCOPY

摘要

The dynamic behavior of fissure initiation and propagation in a rice kernel during therndrying process was studied using a video microscopy system. Three rice varieties grownrnin the U.S. (vars. Bengal, Cypress and Drew) were collected using a plot combinernharvester and studied for characterization of fissure formation. The objectives were tornvisually understand fissure initiation, and development in a rice kernel, during therndrying process and to validate a new hypothesis relating glass transition and fissurernformation in rice drying. The hypothesis explains the formation of fissure due to stressesrnproduced by sufficient moisture gradients as the kernel starch undergoes state transitionrnfrom a rubbery to glassy state, which can occur during drying and tempering. Samplesrnof brown rice kernels from medium- and long-grain varieties were exposed to a range ofrndrying air conditions that according to this hypothesis would create fissures. A videornmicroscopy system was used capture the photo image of the rice kernel underrninvestigation and any fissures that formed when the kernel of rice was exposed to arnvariety of controlled air temperature conditions. Fissures originated from the internalrnareas of the kernel and happened after drying when the kernel was cooled orrnequilibrated to an ambient condition. Fissure formation was found affected by therndrying air temperature and the variety of the rice. The mode of fissure formation, spatialrnorientation with in the kernel major axis, timing and magnitude are discussed.