The Study On Effects Of Somatic Cell Count On The Properties Of Raw Milk And Colby Cheese

Somatic cell count (SCC) in cow milk had been recognized as one of the indexesof health situation of cow udder, and had been put into raw milk standard in more andmore country and dairy company. The properties of raw milk with different SCC werecompared and properties of Colby cheese and pasteurized milk made from these rawmilks were analyzed, aimed to provide data supports on the establishment of raw milkevaluation system.Dairy cows were separated into five groups following the test result of its SCC inmilk, in order to collect raw milk with different SCC as LL (<1×10~5cell/mL), L (1-4×10~5cell/mL), M (4-7×10~5cell/mL), LL (7-10×10~5cell/mL), LL (>1×106cell/mL).Firstly, the differences among five groups of raw milk with different SCC on maincomponents (Protein, Fat, Casein etc.) and properties, fat decomposition degree (lipaseactivity, free fatty acid content and its ratio in total fat), protein decomposition degree(water soluble nitrogen in total nitrogen, non-protein nitrogen in total nitrogen, andcasein profile) were compared, and effects of SCC on raw milk quality were studied;Then, Colby cheeses were made from these raw milks with different SCC, and theiryield, changes of protein and fat decomposition, casein profile etc., were tested;Secondly, five different groups of SCC of raw milk were confected with theapplication of microfiltration membrane separation technology, proteolysis andlipolysis changes of those pasteurized milk were analyzed during storage.The results show that:1. There was no difference in main components and properties for the raw milkgroups with SCC lower than4.0×10~5cells/mL; There was higher correlation betweenfree fatty acid content and lipase vitality (correlation coefficients is0.9609), fatdecomposition deteriorated following the growth of raw milk SCC, however, there wasno difference between two raw milk groups with SCC lower than4.0×10~5cells/mL;The protein decomposition degree (ratios of water soluble nitrogen and none-protein nitrogen to total nitrogen, WAN/TN, NPN/TN) strengthened along with the growth ofraw milk SCC, but no difference was detected between two groups of raw milk withSCC lower than4.0×10~5cells/mL.2. L and LL cheese yield was the highest, H and HH group was the lowest;Changes of WSN/TN and NPN/TN of five groups of cheese show the same tendencyduring ripening, and has a positive correlation (r=0.55,0.54) with the level of SCC;FFA content of H and HH group were significantly higher than that of L and LL groups(P<0.05), and the changes of FFA were positively correlated with SCC, namely, fatand protein hydrolysis speed of cheeses made from higher SCC raw milks were higherthan those made from lower SCC raw milk in the mature period.3. Pasteurized milk made from higher SCC raw milks show faster fat and proteinhydrolysis speed during storage at the same condition (0.5℃or4℃). Hydrolysisspeed of α-casein was slower than that of-casein and γ-casein.The above results indicated that,SCC had effects on the properties of raw milkand Colby cheeses in different degree,their pasteurized milk also showed differenceduring the storage.