Teagasc Food Research Centre, Moorepark, Fermoy, Cork, Ireland; School of Microbiology, University College Cork, Cork, Ireland.
Teagasc Animal and Grassland Research and Innovation Centre, Moorepark, Fermoy, Cork, Ireland.
Int J Food Microbiol. 2017 Aug 16;255:1-6. doi: 10.1016/j.ijfoodmicro.2017.05.019. Epub 2017 May 22.
Low temperature is used to control the growth of bacteria in milk, both pre- and post-pasteurization. As the duration of refrigerated storage extends, psychrotrophs dominate the milk microbiota, that can produce heat stable lipases which negatively impact the organoleptic qualities of milk. Here we examine the influence that refrigeration temperature (2°C, 4°C and 6°C) and storage duration (96h) have on the microbiota composition (16S profiling) of raw bulk tank milk (BTM). To reflect a proposed change to current farming practices, raw milk was blended after each milking (8 milkings) and stored for five consecutive days in each temperature-specific tank. Here 16S rRNA-based microbiota compositional analysis was performed after milk was collected on day 1 and again after the final addition of milk at day 5. In addition to assessing the impact of the duration and temperature of storage, the influence of lactation stage, i.e. mid- versus late-lactation, on the microbiota of the blended BTM was also examined. Overall, both temperature and length of storage had surprisingly little influence on the raw milk microbiota, other than an increase in proportions of Gammaproteobacteria in the blended milk samples collected after pooling on day 5, and in samples stored at 6°C. However, lactation stage had a considerable influence on microbiota composition, with milk from mid-lactation containing higher proportions of Bacteroides, Faecalibacterium, Campylobacter and Rhodanobacter, and late-lactation milk containing higher proportions of Actinobacteria. Overall, the study demonstrates that current temperature and storage duration practises impact the microbiota of raw milk, but these impacts are modest relative to the more considerable differences between mid and late-lactation milk.
低温用于控制巴氏杀菌前后牛奶中细菌的生长。随着冷藏储存时间的延长，低温微生物在牛奶微生物群中占主导地位，它们会产生耐热脂肪酶，从而对牛奶的感官质量产生负面影响。在这里，我们研究了冷藏温度（2°C、4°C 和 6°C）和储存时间（96 小时）对生大桶奶（BTM）微生物群组成（16S 分析）的影响。为了反映当前养殖实践的拟议变化，生奶在每次挤奶后（8 次挤奶）进行混合，并在每个特定温度的罐中连续储存 5 天。在这里，在第 1 天收集牛奶后和第 5 天最后一次添加牛奶后，进行基于 16S rRNA 的微生物群组成分析。除了评估储存时间和温度的影响外，还研究了泌乳阶段（中期与晚期）对混合 BTM 微生物群的影响。总体而言，除了在第 5 天混合后收集的牛奶样本中γ变形菌的比例增加，以及在 6°C 下储存的样本外，温度和储存时间的长短对生奶微生物群的影响很小。然而，泌乳阶段对微生物群组成有相当大的影响，中期泌乳的牛奶中含有较高比例的拟杆菌属、粪杆菌属、弯曲杆菌属和罗达杆菌属，而晚期泌乳的牛奶中含有较高比例的放线菌属。总体而言，该研究表明，当前的温度和储存时间实践会影响生奶的微生物群，但与中期和晚期泌乳奶之间更显著的差异相比，这些影响是适度的。
