Albenzio Marzia, Caroprese Mariangela, Santillo Antonella, Marino Rosaria, Muscio Antonio, Sevi Agostino
Dipartimento PRIME, Università di Foggia, Via Napoli, 25, 71100 Foggia, Italy.
J Dairy Res. 2005 Feb;72(1):86-92. doi: 10.1017/s0022029904000676.
A total of 120 milk samples were collected from Comisana ewes throughout lactation. The ewes were ranked into two somatic cell count (SCC) categories: normal milk (N Milk) with SCC lower than 5.00x 10(5)/ml and high somatic cell milk (HSC Milk) with SCC higher than 1.00 x 10(6)/ml. Milk samples were analysed in triplicate for pH, fat and protein contents, renneting parameters, and plasmin and plasminogen activities. The peptide profile due to total proteolytic activity (endogenous and exogenous enzymes) on alpha- and beta-CNs were determined using urea-PAGE on sodium caseinate (pH 8.0 and pH 5.0) incubated at 37 degrees C for 4 d after sampling. The peptide profile due to non-plasmin enzyme activities at pH 5.0 was also determined using urea-PAGE. Plasmin activity was higher in the HSC milk than in the N milk throughout the study period. A decrease in plasmin activity was observed in the N milk during mid-lactation, which was probably related to decrease in pH, and in the HSC milk during late lactation, which may be ascribed to an enhanced influx of plasmin inhibitors from the blood stream. Proteolytic patterns in Comisana ewe milk were mainly affected by plasmin activity that increased with the SCC in milk. Also non-plasmin proteolytic activity was strongly enhanced by elevated SCC and resulted in a higher degradation of alpha-casein than of beta-casein. In general, plasmin activity did not increase with the advancement of lactation and exhibited a different trend in HSC and N milk, suggesting that physiological factors did not play a key role in regulating the plasminogen-plasmin system in ewes' milk. Plasmin activity, detected with the colorimetric assay was consistent with proteolytic activity on sodium caseinate shown in urea-PAGE electrophoregram.
在整个泌乳期，从科米萨纳母羊中总共采集了120份乳样。这些母羊被分为两个体细胞计数（SCC）类别：体细胞计数低于5.00×10⁵/ml的正常乳（N乳）和体细胞计数高于1.00×10⁶/ml的高体细胞数乳（HSC乳）。对乳样进行了三次重复分析，以测定pH值、脂肪和蛋白质含量、凝乳参数以及纤溶酶和纤溶酶原活性。在取样后于37℃孵育4天的酪蛋白酸钠（pH 8.0和pH 5.0）上，使用尿素聚丙烯酰胺凝胶电泳（urea-PAGE）测定了α-和β-酪蛋白上由总蛋白水解活性（内源性和外源性酶）产生的肽谱。还使用尿素聚丙烯酰胺凝胶电泳测定了pH 5.0时非纤溶酶酶活性产生的肽谱。在整个研究期间，HSC乳中的纤溶酶活性高于N乳。在泌乳中期，N乳中观察到纤溶酶活性下降，这可能与pH值降低有关；在泌乳后期，HSC乳中纤溶酶活性下降，这可能归因于来自血流的纤溶酶抑制剂流入增加。科米萨纳母羊乳中的蛋白水解模式主要受纤溶酶活性影响，纤溶酶活性随乳中SCC的增加而升高。SCC升高也强烈增强了非纤溶酶蛋白水解活性，导致α-酪蛋白的降解高于β-酪蛋白。一般来说，纤溶酶活性不会随着泌乳进程而增加，并且在HSC乳和N乳中表现出不同的趋势，这表明生理因素在调节母羊乳中的纤溶酶原-纤溶酶系统中不起关键作用。用比色法检测到的纤溶酶活性与尿素聚丙烯酰胺凝胶电泳图谱中显示的酪蛋白酸钠上的蛋白水解活性一致。
