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) spectr oscopy 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 (PC A) was applied to the near-IR spectra. Certain deviations were observe d in the proportions described by principal component 2, which showed an underestimation of the coarse fractions. Images of the cell were re corded immediately after each near-IR measurement. The logarithm of th e mean gray level [log(MGL)] was characteristic of the wheat fractions areas actually visible at the sample surface. The correlation coeffic ients of log(MGL) with principal component 2 were -0.998, -0.989, -0.9 97, and -0.991 for series FF, FC, CF, and CC. An interpretation of the principal components was proposed: principal component 1 described th e scattering effect, component 2 described the proportions of the frac tions at the sample surface, and component 3 contained certain informa tion about the deeper particles.