The composition and quality of cow milk from high-capacity milk processing plants in Izmir and their changes according to season and region

The objective of this study is to examine the composition and quality of cow milk from high-capacity milk processing plants in Izmir and their changes according to season and region. The study was carried out in 4 districts of İzmir that are on the top of the list regarding their milk production and number of milk processing plants. Milk samples were collected once a month from the transport tankers of the highest capacity milk processing plant in each district for 11 months. During the sample collection, the routes of each transport tank that picked up milk, the number of farms that have milk in tank, sample collection dates and times, temperature and pH values of milk were recorded. Then the milk samples were brought to the Milk Analysis Laboratory of the Animal Science Department of the Faculty of Agriculture of Ege University. In here somatic cell count (SCC) were determined using Somacount150 device and dry matter, fat, protein, lactose, solids-non-fat and freezing point were detected with Bentley150 device in 911 milk samples. In addition, total bacteria count (TBC) in the 44 samples from milk storage tanksof processing plants were determined by Standard Plate Count method. The data were analyzed in a model that included factors such as district, month, number of farms that have milk in tank, and SCC class, as well as calculating descriptive statistics. Descriptive statistics related to the traits determined in the milk samples were obtained as follows. Average dry matter content is 12.00% (min. 10.70%, max 13.35%), fat content is 3.54% (min. 2.24%, max. 5.25%), total protein content is 3.22% (min. 2.88%, max. 3.63%), lactose content is 4.64% (min. 4.13%, max. 4.94%), solids-non-fat is 8.46% (min. 7.86%, max. 9.03%), SCC is 568 000 cells/mL (min. 75 000, max. 2 300 000 cells/mL), TBC is 8 340 000 cfu/mL (min. 120 000, max. 57 300 000 cfu/mL), pH is 6.74 (min. 6.06, max. 7.00), and freezing point is -0.536 °C (min.-0.628 °C, max.-0.492 °C). The composition and quality of the milk varied greatly according to the season. The proportion of milk components increased during the winter months and decreased markedly in the summer months. Significant differences were found between the districts in composition and quality of milk. Especially milk quality is worse than the others in the districts where usually non-cooled milk is picked up. It has been found that the composition and quality of the milk vary also according to the number of farms that have milk in tank. The proportion of milk components were similar in the samples collected from the transport tanks which include milk from the farms between 1 and 10, whereas the proportions were found lower in the samples collected from the transport tanks which include milk from farms between 11 and 175. A similar trend was observed for milk quality measures. As the SCC in milk increased, the fat and dry matter percentage increased and the protein percentage slightly increased. On the other hand, the percentage of lactose and solids-non-fat decreased as the SCC increased. pH has been found low when SCC is too high. Freezing point was not affected by SCC level. Within the scope of the study, some recommendations have been introduced as follows: The relevant legislation should be implemented as required. Bulk tank milk SCC and TBC should be effectively monitored by an independent organization. Since heat stress affects the composition and quality of milk negatively, necessary precautions should be taken in summer months to minimize the effect of heat stress on dairy cows.