Application of near infrared spectroscopy to determine the basic chemical and physical parameters of sheep milk

Proteins, lactose, total solids, solids-non-fat and titratable acidity were analyzed from sheep milk without any previous sample treatment. The spectra were measured in the transflectance mode (0.1 mm path-length) in near infrared region 10 000 – 4 000 per cm, with an average of 100 scans. A set of 33 samples was used to calibrate the instrument by partial least squares regression method (PLS) and checked later with cross validation on the same set of samples. The following statistical results were obtained: correlation coefficient (R) of 0.966 and standard error of calibration (SEC) 0.328 for proteins, R = 0.999 and SEC = 0.027 for lactose, R = 0.968 and SEC = 0.684 for total solids, R = 0.951 and SEC = 0.237 for solids-non-fat, R = 0.949 and 0.312 for titratable acidity, respectively. All the parameters of calibration set as obtained by FT-NIR spectroscopy were compared with those obtained by the reference methods, linear regression and paired t-test and no significant results were obtained at statistical level P less than 0.05. The results of the study showed that FT-NIR spectroscopy is a suitable method for analysis of basic chemical and physical parameters of sheep milk.