Near infrared spectroscopy for biomonitoring: Cow milk composition measurement in a spectral region from 1,100 to 2,400 nanometers

The potential of near infrared spectroscopy (NIRS; 1,100 to 2,400 nm) to me asure fat, total protein, and lactose content of nonhomogenized milk during milking and the influence of individual characteristics of each cow's milk on the accuracy of determination were studied. Milk fractions were taken d uring milking, twice per month, for 6 mo. Samples were taken every 2nd and 4th wk at the morning and the evening milkings. Teatcups were removed at ea ch 3 L of milk yield as determined with a fractional sampling milk meter. A total of 260 milk samples were collected and analyzed with an NIRSystem 65 00 spectrophotometer with 1-mm sample thickness. Partial least squares (PLS ) regression was used to develop calibration models for the examined milk c omponents. The comparison with the reference method was based on standard e rror of cross validation (SECV). The obtained SECV varied from .107 to .138 % for fat content, from .092 to .125% for total protein, and from .066 to . 096% for lactose content, and the accuracy of the reference method (AOAC, 1 990, method No 972.16) was .05% for all measured milk components. The obtai ned models had lower SECV when an individual cow's spectral data were used for calibration. The reduction of SECV for each cow's individual calibratio n, when compared with SECV for the set of all samples, differed with the di fferent constituents. For fat content determination, the reduction reached 22.46%, for protein 26.40%, and for lactose 31.25%. This phenomena was inve stigated and explained by principle component analysis (PCA) and by compari ng loading of PLS factors that account for the most spectral variations for each cow and the measured milk components, respectively. The results of th is study indicated that NIPS (1,100 to 2,500 nm, 1-mm sample thickness) was satisfactory for nonhomogenized milk compositional analysis of milk fracti ons taken in the process of milking.