Bücher Carola, Burtscher Johanna, Zitz Ulrike, Domig Konrad J
Austrian Competence Centre for Feed and Food Quality, Safety and Innovation (FFoQSI), Technopark 1D, 3430 Tulln, Austria.
Institute of Food Science, Department of Food Science and Technology, University of Natural Resources and Life Sciences, Vienna, Muthgasse 18, 1190 Vienna, Austria.
Foods. 2024 Jun 18;13(12):1921. doi: 10.3390/foods13121921.
Even low levels of dairy propionic acid bacteria (dPAB) can cause cheese defects, resulting in severe economic losses for the producers of selected raw milk cheeses. Therefore, routine quality control of raw cheese milk for dPAB contamination is essential if propionic acid fermentation is undesired. Although knowledge of dPAB contamination of raw milk is important to understand cheese spoilage, long-term dPAB screening data are outdated, and studies taking into account different farm management parameters and their potential influence on dPAB levels are scarce. This study aims to provide insight into the dPAB levels of raw milk over time, to identify farm management factors that potentially influence dPAB levels, and to compare a cultural yeast extract lactate agar (YELA) and lithium glycerol agar (LGA) and a culture-independent method (qPCR) for dPAB quantification with respect to their applicability in routine quality control for the dairy industry. For this purpose, bulk tank milk from 25 dairy farms was screened for dPAB contamination over a one-year period. We were able to identify significant differences in the dPAB contamination levels in raw milk depending on selected farm-specific factors and observed relationships between the different types of milking systems and dPAB contamination levels in raw milk. When dPAB were quantified by cultivation on YELA, strong overgrowth of commensal microbiota impeded counting. Therefore, we conclude that quantification on LGA or by qPCR is preferable. Both methods, colony counting on LGA as well as quantification of dPAB using qPCR, have advantages for the application in (routine) quality control of raw milk, one being low-tech and inexpensive, the other being fast and highly specific, but the detection of (low level) dPAB contamination in raw milk remains a challenge.
即使是低水平的乳制品丙酸杆菌（dPAB）也会导致奶酪出现缺陷，给特定原料乳奶酪的生产商造成严重经济损失。因此，如果不希望发生丙酸发酵，对生奶酪乳进行dPAB污染的常规质量控制至关重要。尽管了解原料乳中的dPAB污染对于理解奶酪变质很重要，但长期的dPAB筛查数据已过时，且考虑不同农场管理参数及其对dPAB水平潜在影响的研究很少。本研究旨在深入了解原料乳中dPAB水平随时间的变化情况，确定可能影响dPAB水平的农场管理因素，并比较用于dPAB定量的两种培养方法，即酵母提取物乳酸琼脂（YELA）和甘油锂琼脂（LGA），以及一种非培养方法（qPCR）在乳制品行业常规质量控制中的适用性。为此，在一年时间内对25个奶牛场的贮奶罐奶进行了dPAB污染筛查。我们能够确定，根据选定的农场特定因素，原料乳中dPAB污染水平存在显著差异，并观察到不同类型挤奶系统与原料乳中dPAB污染水平之间的关系。当通过在YELA上培养对dPAB进行定量时，共生微生物群的过度生长阻碍了计数。因此，我们得出结论，在LGA上进行定量或通过qPCR进行定量更为可取。这两种方法，即在LGA上进行菌落计数以及使用qPCR对dPAB进行定量，在原料乳（常规）质量控制中应用都有优势，一种是技术含量低且成本低，另一种是快速且特异性高，但检测原料乳中（低水平）dPAB污染仍然是一项挑战。
