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Influence of Storage Conditions on the Growth of Pseudomonas Species in Refrigerated Raw Milk

机译：冷藏条件对生乳中假单胞菌种类生长的影响

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The refrigerated storage of raw milk throughout the dairy chain prior to heat treatment creates selective conditions for growth of psychrotolerant bacteria. These bacteria, mainly belonging to the genus Pseudomonas , are capable of producing thermoresistant extracellular proteases and lipases, which can cause spoilage and structural defects in pasteurized and ultra-high-temperature-treated milk (products). To map the influence of refrigerated storage on the growth of these pseudomonads, milk samples were taken after the first milking turn and incubated laboratory scale at temperatures simulating optimal and suboptimal preprocessing storage conditions. The outgrowth of Pseudomonas members was monitored over time by means of cultivation-independent denaturing gradient gel electrophoresis (DGGE). Isolates were identified by a polyphasic approach. These incubations revealed that outgrowth of Pseudomonas members occurred from the beginning of the dairy chain (farm tank) under both optimal and suboptimal storage conditions. An even greater risk for outgrowth, as indicated by a vast increase of about 2 log CFU per ml raw milk, existed downstream in the chain, especially when raw milk was stored under suboptimal conditions. This difference in Pseudomonas outgrowth between optimal and suboptimal storage was already statistically significant within the farm tank. The predominant taxa were identified as Pseudomonas gessardii , Pseudomonas gessardii -like, Pseudomonas fluorescens -like, Pseudomonas lundensis , Pseudomonas fragi , and Pseudomonas fragi -like. Those taxa show an important spoilage potential as determined on elective media for proteolysis and lipolysis.
机译：在热处理之前，整个乳制品链中的生乳都经过冷藏，为产生抗精神病菌的细菌创造了选择性条件。这些细菌，主要属​​于假单胞菌属，能够产生耐热的细胞外蛋白酶和脂肪酶，这些酶和蛋白酶会导致巴氏灭菌和超高温处理的牛奶（产品）变质和结构缺陷。为了绘制冷藏存储对这些假单胞菌生长的影响，在第一次挤奶之后采集牛奶样品，并在模拟最佳和次最佳预处理存储条件的温度下孵育实验室规模。通过不依赖培养的变性梯度凝胶电泳（DGGE）随时间监测假单胞菌成员的生长。分离物通过多相方法鉴定。这些温育揭示了假单胞菌成员的生长是在最佳和次佳的存储条件下从乳制品链（农场储罐）的开始发生的。链中的下游存在更大的增长风险，这表现为每毫升原料乳大约增加2 log CFU，特别是当原料乳在次优条件下存储时。最佳和次最佳存储之间的假单胞菌生长差异在养殖场内已经具有统计学意义。鉴定出的主要分类群为假单胞菌，类假单胞菌，荧光假单胞菌，隆德假单胞菌，脆弱假单胞菌和脆弱假单胞菌。那些分类单元显示出重要的变质潜力，这是在选择性介质上确定的用于蛋白水解和脂解的。

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