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United States Department of Agriculture

Agricultural Research Service

Title: Determination of Protein in Ground Wheat Samples by Mid-Infrared Diffuse Reflectance Spectroscopy

Authors
item Reeves Iii, James
item Delwiche, Stephen

Submitted to: Journal of Applied Spectroscopy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 10, 1997
Publication Date: N/A

Interpretive Summary: Diffuse reflectance spectroscopy is a non-destructive method using light to determine the composition and quality of materials. Such spectroscopic determinations can be performed using various types of light (i.e, visible light or invisible forms such as infrared or radiant heat). Each form of light having particular advantages and disadvantages. Extensive work using gnear-infrared light has been carried out on agricultural products such as hays and wheat. While quite good for quantitatively determining the composition of such products, the near-infrared is not as good for understanding the basis for the compositional differences (qualitative analysis. The mid-infrared, on the other hand, while excellent for qualitative efforts, has, until recently, not been found useful for quantitative analysis. The objective of this study was to determine if the mid-infrared could be used in the same manner as near-infrared diffuse reflectance spectroscopy to quantitatively determine the protein content o ground wheat samples. One hundred and thirty hard red winter wheat samples were assayed for protein in the near-infrared and mid-infrared. Results based on mid-infrared spectra, while not quite as good as those using near- infrared spectra, were nevertheless quite good. These results demonstrate that it is possible to determine protein in ground wheat using mid-infrared spectra, with the added advantage of the ease of understanding found in the mid-infrared. Finally. future work needs to concentrate on factors which would optimize the mid-infrared for such determinations.

Technical Abstract: The objective of this study was to determine if mid-infrared diffuse reflectance spectroscopy could be used in the same manner as near-infrared diffuse reflectance spectroscopy to quantitatively determine the protein content of ground wheat samples. One hundred and thirty hard red winter wheat samples were assayed for protein by combustion and scanned in the near-infrared and mid-infrared. Samples (UDY ground) were scanned neat in the near-infrared from 1100 nm (9091 cm-1) to 2498 nm (4003 cm-1) on a scanning monochromator and in the mid-infrared from 4000 cm-1 (2500 nm) to 400 cm-1 (25,000 nm) on a Fourier transform spectrometer at 4 and 16 cm-1 resolutions. Protein content varied from a low of 8.98% to a high of 18.70% (average of 12.86% with a SD of 1.66%). Calibrations developed using PLS gave R2 and RMSD of 0.999 and 0.054 for the near-infrared and 0.997 and 0.085 for the mid-infrared (4 cm-1 resolution). Calibration results based on mid-infrared spectra, while not as good as those using near-infrared spectra, were nevertheless quite good. These results demonstrate that it is possible to develop satisfactory calibrations for protein in ground wheat using mid-infrared spectra without the need for sample dilution with KBr, with the added advantage of the ease of spectral interpretation found in the mid-infrared. Finally. future work needs to concentrate on factors which would optimize the mid-infrared for such determinations.

Last Modified: 12/18/2014
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