Interpretation of Spectral Analyses. The FT-NIR original spectra of the pure and adulterated onion powder and the SNV-preprocessed spectra (Figure 1) reveal differencesin the absorption intensities between 1920 and 1980 nm (marked) and can easily be identified. The absorption bands in this region correspond to the O−H stretch and O−H band combination and the H−O−H deformation combination, which represent the starch content.21 Starch is a semicrystalline polymer composed of two polysaccharides, amylose and amylopectin. Amylose is a mostly linear chain consisting of
up to 3000 glucose molecules interconnected primarily by α-1,4-glycoside linkages.13 The spectral fluctuations from 1400 to 1600 nm correspond to the first overtone of the hydroxyl
group. The precise position of these bands is very sensitive to hydrogen bonding in the starch molecule.