Comparison between MIR and NIR spectroscopic techniques for the determination of fat and protein contents in milk

To compare mid-infrared (MIR) and near-infrared (NIR) spectroscopies for the determination of the fat and protein contents in milk, the same sample sets with varying concentrations of fat and protein were measured in the MIR range of 3200-700 cm^-1 and NIR range of 9000-4000 cm^-1. The spectral features in the two regions were analyzed. The MIR spectra of milk were characteristic due to the MIR inherent molecular specificity, whereas the NIR spectra were relatively characterless due to the NIR low selectivity. Partial least squares (PLS) regression models for fat and protein were developed by using both MIR and NIR spectra. MIR data with no pretreatment gave better results than NIR data. The square correlation coefficient (R²) and the root mean square error of prediction (RMSEP) were 0.98 and 0.10 g/dL for fat and 0.97 and 0.11 g/dL for protein. With NIR techniques, satisfactory results were not obtained with raw data. However, NIR data after pretreatment gave similarly good results to the ones using MIR method. This paper indicates that either of the MIR and NIR spectral methods is reliable for the determination of the fat and protein contents.