Ballou L U, Pasquini M, Bremel R D, Everson T, Sommer D
Department of Dairy Science, University of Wisconsin, Madison 53706, USA.
J Dairy Sci. 1995 Oct;78(10):2186-95. doi: 10.3168/jds.S0022-0302(95)76846-1.
A longitudinal study was carried out on samples of bulk tank milk collected from 200 farms for 12 mo to evaluate SCC, plasmin and plasminogen activities, psychrotrophic bacteria count, and protein quality in milk and to examine the proteolytic effects of plasmin on milk proteins. Herds were selected randomly from client lists of two dairies to create four groups based on milk SCC of the month before the study; herds were reassigned monthly to one of four groups based on SCC for that month. Overall means were 3.73% fat, 3.13% protein by infrared analysis, 3.16% protein by Kjeldahl analysis, 2.42% casein percentage, 4.65% lactose, 5.43 cells/ml of log SCC, 1.13 U of plasmin, 45.6 U of plasminogen, and log 2.86 cfu/ml of psychrotrophic bacteria. The ANOVA showed a significant effect of month on all factors except SCC, which was fixed by the experimental design. Plasmin and plasminogen activities were high from December to May. Plasmin activities and psychrotroph counts were significantly higher for the high SCC group. Casein percentage and number were significantly higher for the low SCC group.
对从200个农场采集的散装罐奶样本进行了为期12个月的纵向研究，以评估牛奶中的体细胞计数（SCC）、纤溶酶和纤溶酶原活性、嗜冷菌计数以及蛋白质质量，并研究纤溶酶对乳蛋白的蛋白水解作用。从两个奶牛场的客户名单中随机选择牛群，根据研究前一个月的牛奶SCC将其分为四组；每月根据当月的SCC将牛群重新分配到四组中的一组。通过红外分析，脂肪平均含量为3.73%，蛋白质平均含量为3.13%；通过凯氏定氮法分析，蛋白质平均含量为3.16%，酪蛋白百分比为2.42%，乳糖为4.65%，SCC对数为5.43×10⁵个细胞/ml，纤溶酶为1.13 U，纤溶酶原为45.6 U，嗜冷菌对数为2.86 cfu/ml。方差分析表明，除SCC外，月份对所有因素均有显著影响，SCC由实验设计固定。12月至5月期间，纤溶酶和纤溶酶原活性较高。高SCC组的纤溶酶活性和嗜冷菌计数显著更高。低SCC组的酪蛋白百分比和数量显著更高。
