Mid infrared attenuated total reflection spectroscopy as a rapid tool to assess the quality of Sicilo-Sarde ewe’s milk during the lactation period after replacing soybean meal with scotch bean in the feed ration

This study investigates the potential of attenuated total reflection spectroscopy in the mid infrared (MIR) for monitoring changes in the quality of ewe’s milk as a function of lactation period and feeding systems. Twelve 5-year-old lactating Sicilo-Sarde ewes (third lambing) were kept in environmentally controlled sheepfolds and were divided into two homogenous weight matched groups (n = 6). Ewes were fed ad libitum with two iso-energetic diets (20% barley, 3% vitamin and mineral premix, and 77% soybean meal or scotch bean). Physico–chemical analyses and MIR (3000–900 cm−1) were performed on milk samples after 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 weeks of lactation period. The inclusion of scotch bean in the diet resulted in a significant decrease (P ⩽ 0.05) of fat content (7.85 g 100 g−1 vs. 6.75 g 100 g−1) and a significant increase (P ⩽ 0.05) of lactose level (3.49 g 100 g−1 vs. 3.61 g 100 g−1). The principal component analysis (PCA) applied to the 1700–1500 cm−1 spectral region showed only some discrimination between milk samples according to diet compositions. The best results were obtained in the 3000–2800 cm−1 and 1500–900 cm−1 spectral regions since a good discrimination between milk from ewes fed soybean meal from those fed scotch bean meal was observed. It can be concluded that these spectral regions could be considered as fingerprint, regions allowing a good identification of milk according to diet composition. However, the MIR failed to discriminate milk samples according to the lactation period for the two feeding systems.