Overtone carbohydrates

Near-infrared (NIR) spectroscopy is also an excellent tool for examining plant tissue. As in the mid-infrared region, plants produce bands in the NIR region due to the presence of carbohydrates. The latter exhibit overlapped combination and overtone bands of the 0-H and C-H groups. Multivariate analysis of the near-infrared spectra of different plant species can be used to differentiate samples [54]. 

Commercial grains are commonly analysed by using NIR spectroscopy [12, 15]. The major constitnents of grains are water, protein, oil, fibre, minerals and carbohydrates and it is commercially important to quantitate the composition. The NIR spectra of snch materials are, thus, dominated by the overtones and combination bands of C-H, N-H, O-H and C=0 bonds. Figure 8.16 illustrates the NIR spectra (in reflection mode) of a number of common grains, i.e. sesame seeds, sunflower seeds, wheat, barley, grass and oats. 

Carbohydrates in general may have a free OH-stretch absorption near 6940 cm (1440 nm). This band has been reported in crystalline sucrose, for example, and has been assigned specifically to the C4 hydroxyl within a crystalline matrix. Trott et al. discuss four different OH first overtone bands in carbohydrates in different solvent systems, using a monomer (glucose) and its polymer (glycogen) as models. 

Fox, D.G., L.O. Tedeschi, T.P. Tylutki, J.B. Russell, M.E. Van Amburgh, L.E. Chase, A.N. Pell and T.R. Overton, 2004. The Cornell Net Carbohydrate and Protein System model for evaluating herd nutrition and nutrient excietioiL... 

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