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Two-Dimensional Vibration Spectroscopy of Rice Quality and Cooking

¹USDA-Agricultural Research Service, Richard B. Russell Agricultural Research Center, P.O. Box 5677, Athens, GA 30604-567. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable. ²Corresponding author. E-mail: wbarton@qaru.ars.usda.gov ³USDA-Agricultural Research Service, Rice Research Unit, Route 7, Box 999, Beaumont, TX 77713 ⁴USDA-Agricultural Research Service, Southern Regional Research Center P. O. Box 19887, New Orleans, LA 70179

Rice samples were taken from a study of rice milling properties that affect quality. The spectra of milled and cooked samples were taken in the near-infrared, mid-infrared, and Raman region. These spectra, two regions at a time, were regressed by a two-dimensional technique to develop contour maps that indicated the correlation of two spectral regions. These relationships demonstrate that it is possible to recognize the hydration effects caused by gelatinization (cooked samples vs. milled rice). Three water (O-H stretch) spectral bands (960, 1445, 1,930 nm) in the near-infrared (NIR) show marked differences between milled and cooked rice. The difference spectra indicated that there were additional phenomena occurring besides the addition of water. These differences are apparent in both C-O-H and N-H bands, which indicate that water is interacting with both starch and protein. The two-dimensional technique developed in this laboratory was used to get a better interpretation of what occurs during cooking. The Raman spectrum, which is relatively insensitive to water (O-H stretch), revealed only changes in protein that could be associated with denaturization.