A COMPARATIVE STUDY OF DIFFERENT TYPES OF COW'S MILK MARKETED IN TIARET REGION

Abstract

The first objective of the current research was to determine the influence of season and stage of lactation on the physico-chemical characteristics of imported crossbred dairy cows in Tiaret city (Algerian West High Lands). A total of 557 raw individual milk samples from fifty cows were collected and analyzed by ultrasonic milk analyzer “Lactoscan SP”, over four seasons and at various stages of lactation (early, mid, and late). The physicochemical investigated parameters include fat, protein, minerals, lactose, solids not fat, total solids, pH, conductivity, density and freezing point. The overall findings revealed a wide variation in milk chemical composition by season. Winter milk had higher levels of the main components of cow's milk (solids not fat: 96.4±0.04 g/l, protein: 35.3±0.01 g/l, minerals: 7.8±0.04 g/l, and lactose: 53±0.02 g/l). Moreover, the physical parameters also varied greatly depending on the season of the year. The highest conductivity 5.29±0.04 (μS cm-1) and density 1.0346±0.29 (kg/l) were registered during the summer. On the other hand, the physico-chemical features showed less variability depending on the stage of lactation. However, both fat and conductivity were significantly affected by this factor (p≤ 0.05). The second objective of this work was to compare the physicochemical properties of three different types of whole milk (raw, pasteurized, and UHT) commercialized in Tiaret city. A total of 290 milk samples were analyzed, including 140 raw mixed milk samples collected from the "SIDI KHALED" dairy and 90 random samples of processed whole milk (60 UHT milk and 30 pasteurized milk), obtained from various points of sale. The comparative analysis of the different kinds of milk revealed significant variations in almost all of the physico-chemical properties examined, with the exception of the density (p>0.05). Furthermore, raw milk contained more nutritional components (fat: 34.2±0.04 g/l, solids not fat: 86.8±0.03 g/l, protein: 32±0.02 g/l, minerals: 7±0.003g/l, lactose: 47.7±0.01 g/l and total solids 121.2±0.05 g/l) than pasteurized and sterilized milk, which could be a result of poor storage conditions and the heat treatment effect.