Infrared analysis of raw milk: PLS calibrations of casein, whey protein, true and crude protein content with native calibration samples

摘要

The simultaneous infrared spectrometric determination of protein fractions (crude protein, true protein, whey protein and casein) in milk requires calibrations on the basis of suitable calibration samples analysed using reference methods. 'Natural' PLS-calibrations were set up with 82 raw milk samples, statistically analysed and assessed with respect to relevant analytical performance criteria. The results show that the measurement uncertainties of 'natural' calibrations are about the same as known from calibrations based on designed or mixed calibration sets. The statistical analysis of the concentration residuals of whey protein and true protein (IR predictions minus reference values) showed no significant reduction of the measurement uncertainties by using a dedicated calibration for whey protein, i.e. whey protein contents can be calculated as differences between true protein and casein results without loss of accuracy. The implementation of independent calibrations for casein, crude protein, true protein, and whey protein can be reasonable if individual quality control and flexible maintenance of these calibrations are required.