|Rice Utilization and
Project Leader and Principal InvestigatorsWalace H. Yokoyama USDA Western Regional Research Center, Albany, CA
|Research that will lead to new rice products for domestic and
foreign markets is the work of scientists at the USDA!s Western Regional Research Center
in Albany. Last year's work focused primarily on the textural properties of rice.
Desirable rice texture may be the single most important characteristic of the milled rice kernel. Knowledge of rice texture and accurate analytical methods will improve efficiencies in breeding new varieties for new markets. With that in mind these researchers have combined forces with the Food Science Department at UC Davis to develop more accurate instrumental and human sensory methods to understand the starch characteristics of rice as they relate to textural and functional properties.
Viscosity profiles are commonly used to evaluate the pasting properties of rice flours. Commonly available instruments require large quantities, so researchers developed a "micromethod" of developing viscosity profiles with a commercially available controlled stress rheometer. Since this technique requires only very small amounts of rice for testing, researchers say it will improve the efficiency of selecting for desired cooking characteristics.
Since rice is usually eaten as a cooked intact grain, evaluation usually requires human sensory analysis. Near infrared-based tasting machines have been used in Japan for several years, but recent evaluations indicate that they do not correlate well with human sensory panels. Albany researchers continue work on standard cooking tests, human sensory methods and an instrumental techniques to evaluate the textural characteristics of whole grains. The advantages of the instrumental method is that it requires a small sample size, less time and greater objectivity than human sensory evaluation. However, researchers say that more analysis and correlation with a larger sensory panel are required to develop the method rigorously.
Researchers also investigated the size, shape and mass of starch in different rice varieties and related these differences to cooking and textural properties. Until recently, information about the structure of starch has been limited by its partial solubility and extremely large size. These problems have been overcome by the innovative use of multiple-angle laser light detectors in combination with gel permeation chromatography to develop a clearer picture of molecular size and shape of starch fractions. Food scientists determined, for instance, that the starch in waxy rice like Calmochi is three to four times larger than the starch in long grains.
One of the most important indicators of rice texture is amylose content, which can vary widely among released California varieties. However, conventional laboratory methods using enzyme digestion and anion exchange chromatography may not be suitable for analysis of these complex "long-branch chain" molecules. Researchers are developing improved analytical methods to measure these complex components of starch.