Improving rice Quality and Processing Efficiency - 09

 

 

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Project Leader and Principal  Investigators

Zhongli Pan, research engineer, USDA-ARS, Albany, CA

 

 

 

Previous research demonstrated that infrared radiation could be used to dry rice with high milling quality. In 2009 researchers turned their attention to observed differences in fissuring between M-202 and M-206 during drying. Broken or fissured rice can significantly reduce crop value, so a better understanding of these differences could help in the development of new drying methods and in breeding new fissure-resistant varieties.

Rice drying previously had been studied in bulk quantities, with little emphasis given to moisture changes occurring inside individual kernels. Moisture gradients occurring within rice kernels are believed to be the cause of fissuring and, thus, lower milling quality. The gradients may be influenced by humidity conditions in the field, through harvesting, and during drying and processing.

Differences in moisture absorption properties of rice varieties M-202 and M-206 were analyzed with magnetic resonance imaging (MRI) technology.

Moisture removal was observed to be greater in regions near the rice embryo or germ during the first two hours of drying, regardless of temperature. Drying rates of both varieties were similar. Higher drying rates may lead to higher moisture gradients and fissuring in either variety.

Absorption properties of rough rice, brown rice, white rice, and husks were also examined. Fractions of M-202 absorbed moisture faster than M-206, which may help explain the latter’s higher resistance to fissuring. This information was used to develop a mathematical model to predict moisture content in rice components at different relative humidity environments.

Scanning electron microscopy (SEM) was used to determine the distribution of carbohydrates, lipids, and proteins in M-206 rice kernels. Lipids and proteins were concentrated in germ and bran, while most of the carbohydrates were located n the endosperm. Researchers plan a similar examination of M-202 to compare with the M-206 observations to create a more thorough understanding of the factors affecting moisture absorption and fissure resistance.

During SEM imaging, researchers found that rice kernels contain a small gap between the husk and brown rice. X-ray imaging confirmed this observation. The gap also appeared bigger in dry kernels than in wet ones, and the gap appeared larger at the top and bottom of the kernel.

 

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