Near-infrared spectroscopy for dairy management: Measurement of unhomogenized milk composition

The potential of near-infrared spectroscopy to measure fat, total protein, and lactose contents of unhomogenized milk was studied for use in dairy man agement, as a new tool for on-line milk analysis in the process of milking. Influence of the spectral region, sample thickness, and spectral data trea tment on the accuracy of determination was investigated. Transmittance spectra of 258 milk samples, collected at different stages of the milking process, were obtained with a spectrophotometer (NIRSystems 65 00; FOSS-NIRSystems, Silver Spring, MD) in the wavelength range from 400 to 2500 nm with sample thicknesses of 1 mm, 4 mm, and 10 mm. The spectral region and sample thickness were found to be significant facto rs for milk fat and total protein determination but not the lactose determi nation. The best accuracy was obtained with the 1100 to 2400 nm region, 1-m m sample thickness, and the first derivative data transformation. For the s pectral region from 700 to 1100 nm, close accuracy was obtained for fat wit h a 10-mm sample and for total protein with a 1-mm sample thickness. The sa mple thickness did not change significantly the accuracy of lactose determi nation. Different treatments of spectral data did not improve the calibrati ons for fat and protein. For the region from 700 to 1100 nm, where inexpensive on-line sensors could be used, the highest positive coefficients for fat were at 930, 968, 990, 1026, 1076, and 1092 nm; for lactose were at 734, 750, 786, 812, 908, 974, 982, and 1064 nm; and for total protein were at 776, 880, 902, 952, and 103 4 nm.