EFFECTS OF PARTICLE-SIZE ON THE NEAR-INFRARED REFLECTANCE SPECTRA OF WHEAT AND RAPE SEED MEAL MIXTURES

Binary mixtures were jointly studied by near-infrared (near-IR) spectroscopy and image analysis. Fine and coarse fractions of wheat and rape seed meal were mixed in proportions varying from 0 to 100% as follows: fine wheat and fine rape seed meal (FF), coarse wheat and fine rape seed meal (CF), fine wheat and coarse rape seed meal (FC), and coarse wheat and coarse rape seed meal (CC). Principal component analysis (PCA) was applied to the near-IR spectra. Certain deviations were observed in the proportions described by principal component 2, which showed an underestimation of the coarse fractions. Images of the cell were recorded immediately after each near-IR measurement. The logarithm of the mean gray level [log(MGL)] was characteristic of the wheat fractions areas actually visible at the sample surface. The correlation coefficients of log(MGL) with principal component 2 were -0.998, -0.989, -0.997, and -0.991 for series FF, FC, CF, and CC. An interpretation of the principal components was proposed: principal component 1 described the scattering effect, component 2 described the proportions of the fractions at the sample surface, and component 3 contained certain information about the deeper particles.