Looking at the spectra (Wheat / Flour / Starch)

This is another post, to exercise the visualization of the spectra, the NIR bands, mathematical treatments,…..etc.
Starch and gluten are major constituents in wheat, and therefore flour. Wheat starch is used as an excipient in the pharmaceutical industry; on the other hand, the gluten is the major protein of wheat (about 80% of total protein).
I do not have a spectrum of gluten, but for this exercise I have overplot spectra of wheat, flour and starch.
Red spectra is the spectra of "wheat starch" (range of 1100-2500 nm), blue of "wheat flour" (range of 400-2500 nm) and green spectrum "wheat" (range of 400-2500 nm).
Let's see, therefore, the spectral region common to the three: 1100-2500 nm.
If we do not apply any mathematical treatment, the particle size obviously gives these separations on the scale of intensity, which is not a good way to compare them.

Let´s apply a second derivative math treatment, where we can find some better conclusions.

One of the reasons of this exercise is to understand better the developments of calibrations for protein in wheat flour, developed by Osborne et al. where the absorption band at 2100 nm for the starch is used because is interfering with the protein band (gluten) at 2180 nm. Water is of course another major constituent and has an absorption band at 1940 nm, which interfere with the other wavelengths. Osborne et al. used as well, a neutral wavelength (1680 nm) in order to correct the effect of particle size in the sample.

With these four wavelengths (four filters in an instrument) an MLR calibration was developed.