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United States Department of Agriculture

Agricultural Research Service

Title: Spectral Imaging Techniques for Grain

item Himmelsbach, David

Submitted to: United States Japan Natural Resources Protein Panel
Publication Type: Proceedings
Publication Acceptance Date: December 1, 2002
Publication Date: December 31, 2002

Interpretive Summary: Spectral imaging techniques were used to show the location of water and organic chemical constituents in wheat grains. Magnetic resonance images were best for revealing the distribution of water in whole grains and differentiated dormant from non-dormant types. Infrared and Raman based imaging techniques were most useful for locating organic chemical components such as starch, cellulose, aromatics and lipids in sections of grains. These three techniques complement each other and together provide unparalleled detailed information essential to the determination of genetic functionality and environmental effects with regard to grains.

Technical Abstract: Three spectral imaging techniques were employed for the purpose of assessing the quality of cereal grains. Each of these techniques provided unique, yet complementary, information. Nuclear magnetic resonance (NMR), also called magnetic resonance imaging (MRI), was used to detect mobile components such as water and oil in intact or excised parts grains. Two- and three-dimensional images were obtained that reveal the relative concentration of these components in anatomically distinct regions of the grain. NMR imaging is particularly useful in detecting the degree of water absorption in grains that differ genetically and/or have different environmental histories. It was successfully employed to detect the difference in water absorption in the embryo of dormant and non-dormant grains. The degree to which water penetrates into the bran layer was also observed. The optical imaging methods of mid-infrared (MIR) and Raman are more invasive than the NMR technique in that they require cryotoming either thin (6-8 um) or thick (40-80 um) sections, respectively. However, they provide better access to the location of the various chemical components of grains. MIR imaging was used to selectively reveal the location of lipids, protein, starch and cellulose in and near the aleurone region; plus lipids and aromatics in the pigment strand of wheat grains. Raman imaging was found to be less sensitive for the detection of all components, except aromatics, in these types of tissues. Raman was relatively more sensitive than MIR to presence of aromatics. Thus it was useful for detecting aromatics (structural phenolics or pigments) in the bran wheat grains. Raman imaging is the least sensitive to water and thus is the most immune to its interference. The possibility exists for sequentially performing all three of the techniques on the same sample.

Last Modified: 4/17/2014
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