Protein degradation in bovine milk caused by Streptococcus agalactiae
Protein degradation in bovine milk caused by Streptococcus agalactiae
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DOI：
10.1017/s0022029912000301
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发表时间：
2012-08-01
影响因子：
2.1
通讯作者：
Johansson, Monika
中科院分区：
文献类型：
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作者：
Akerstedt, Maria;Wredle, Ewa;Johansson, Monika
链球菌（Str.）无乳症是一种传染性乳腺炎细菌，通常与亚临床乳腺炎病例相关。不同的乳腺炎细菌以前已经从诊断的角度进行了评估，但缺乏关于它们对牛奶成分的影响的知识。当牛奶被加工成发酵产品如奶酪和酸奶时，蛋白质组成对于获得最佳产量和质地是重要的，因此具有很大的经济价值。本体外研究的目的是评价主要由天然无乳链球菌来源的外源性蛋白酶引起的蛋白降解。将样品在37 ℃下孵育，以模拟乳房中细菌引起的降解。还研究了由无乳链球菌的不同菌株引起的蛋白质降解。当无乳链球菌被添加到牛奶中时，观察到蛋白质降解发生，但细菌菌株之间存在差异。酪蛋白是牛奶中最重要的经济蛋白质，在接种无乳链球菌的牛奶中降解高达75%，而无菌超高温（UHT）牛奶用作对照牛奶。主要乳清蛋白，α-乳白蛋白和β-乳球蛋白，降解高达21%的无菌对照牛奶。这些结果表明，不同的乳房炎细菌，但也不同菌株的乳房炎细菌应从牛奶质量的角度进行评估，以了解他们的能力，降解牛奶中的经济上重要的蛋白质。
Streptococcus (Str.) agalactiae is a contagious mastitis bacterium, often associated with cases of subclinical mastitis. Different mastitis bacteria have been evaluated previously from a diagnostic point of view, but there is a lack of knowledge concerning their effect on milk composition. Protein composition is important in achieving optimal yield and texture when milk is processed to fermented products, such as cheese and yoghurt, and is thus of great economic value. The aim of this in vitro study was to evaluate protein degradation mainly caused by exogenous proteases originating from naturally occurring Str. agalactiae. The samples were incubated at 37 degrees C to imitate degradation caused by the bacteria in the udder. Protein degradation caused by different strains of Str. agalactiae was also investigated. Protein degradation was observed to occur when Str. agalactiae was added to milk, but there were variations between strains of the bacteria. Caseins, the most economically important proteins in milk, were degraded up to 75% in milk inoculated with Str. agalactiae in relation to sterile ultra-high temperature (UHT) milk, used as control milk. The major whey proteins, a-lactalbumin and beta-lactoglobulin, were degraded up to 21% in relation to the sterile control milk. These results suggest that different mastitis bacteria but also different strains of mastitis bacteria should be evaluated from a milk quality perspective to gain knowledge about their ability to degrade the economically important proteins in milk.