Rauh Valentin M, Johansen Lene B, Ipsen Richard, Paulsson Marie, Larsen Lotte B, Hammershøj Marianne
Arla Foods Strategic Innovation Centre , Rørdrumvej 2, DK-8220 Brabrand, Denmark.
J Agric Food Chem. 2014 Jul 16;62(28):6852-60. doi: 10.1021/jf502088u. Epub 2014 Jul 7.
Plasmin, the major indigenous protease in milk, is linked to quality defects in dairy products. The specificity of plasmin on caseins has previously been studied using purified caseins and in the indigenous peptide profile of milk. We investigated the specificity and proteolytic pathway of plasmin in directly heated UHT milk (>150 °C for <0.2 s) during 14 weeks of storage at 20 °C in relation to age gelation and bitter peptides. Sixty-six peptides from αS- and β-caseins could be attributed to plasmin activity during the storage period, of which 23 were potentially bitter. Plasmin exhibited the highest affinity for the hydrophilic regions in the caseins that most probably were exposed to the serum phase and the least affinity for hydrophobic or phosphorylated regions. The proteolytic pattern observed suggests that plasmin destabilizes the casein micelle by hydrolyzing casein-casein and casein-calcium phosphate interaction sites, which may subsequently cause age gelation in UHT milk.
纤溶酶是牛奶中的主要内源蛋白酶，与乳制品的质量缺陷有关。此前已使用纯化的酪蛋白和牛奶的内源肽谱研究了纤溶酶对酪蛋白的特异性。我们研究了在20℃下储存14周期间，直接加热的超高温瞬时灭菌牛奶（>150℃，<0.2秒）中纤溶酶的特异性和蛋白水解途径，这与老化凝胶化和苦味肽有关。在储存期间，来自αS-酪蛋白和β-酪蛋白的66种肽可归因于纤溶酶的活性，其中23种可能具有苦味。纤溶酶对酪蛋白中最有可能暴露于血清相的亲水区具有最高亲和力，而对疏水或磷酸化区域的亲和力最低。观察到的蛋白水解模式表明，纤溶酶通过水解酪蛋白-酪蛋白和酪蛋白-磷酸钙相互作用位点来破坏酪蛋白胶束的稳定性，这可能随后导致超高温瞬时灭菌牛奶的老化凝胶化。
