Food Research Institute, University of Wisconsin-Madison, 1550 Linden Drive, Madison 53706.
Department of Statistics, University of Wisconsin-Madison, 1276 Medical Sciences Center, Madison 53706.
J Dairy Sci. 2021 Dec;104(12):12332-12341. doi: 10.3168/jds.2021-20350. Epub 2021 Sep 30.
Certain cheeses can be legally produced in the United States using raw milk, but they must be aged for at least 60 d to reduce pathogen risks. However, some varieties, even when aged for 60 d, have been shown to support growth of Listeria monocytogenes or survival of Shiga toxin-producing Escherichia coli (STEC). Thermization, as a subpasteurization heat treatment, has been proposed as a control to reduce the risk of pathogens in raw cheese milk while retaining some quality attributes in the cheese. However, the temperature and time combinations needed to enhance safety have not been well characterized. The objective of this research was to determine and validate decimal reduction values (D-values) for L. monocytogenes and STEC at thermization temperatures 65.6, 62.8, and 60.0°C; a D-value at 57.2°C was also determined for L. monocytogenes only. Nonhomogenized, pasteurized whole-milk samples (1 mL) were inoculated with 8-log cfu/mL L. monocytogenes or STEC (5- or 7-strain mixtures, respectively), vacuum-sealed in moisture-impermeable pouches, and heated via water bath submersion. Duplicate samples were removed at appropriate intervals and immediately cooled in an ice bath. Surviving bacteria were enumerated on modified Oxford or sorbitol MacConkey overlaid with tryptic soy agar to aid in the recovery of heat-injured cells. Duplicate trials were conducted, and survival data were used to calculate thermal inactivation rates. D-, D-, and D-values of 17.1 and 7.2, 33.8 and 16.9, and 146.6 and 60.0 s were found for L. monocytogenes and STEC, respectively, and a D-value of 909.1 s was determined for L. monocytogenes. Triplicate validation trials were conducted for each test temperature using 100 mL of milk inoculated with 3 to 4 log cfu/mL of each pathogen cocktail, A 3-log reduction of each pathogen was achieved faster in larger volumes than what was predicted by D-values (D-values were fail-safe). Data were additionally compared with published results from 21 scientific studies investigating L. monocytogenes and STEC in whole milk heated to thermization temperatures (55.0-71.7°C). These data can be used to give producers of artisanal raw-milk cheese flexibility in designing thermal processes to reduce L. monocytogenes and STEC populations to levels that are not infectious to consumers.
某些奶酪可以合法地使用生奶在美国生产，但它们必须经过至少 60 天的老化，以降低病原体风险。然而，一些品种，即使经过 60 天的老化，也被证明支持李斯特菌或产志贺毒素大肠杆菌（STEC）的生长。作为一种亚巴氏杀菌热处理，热杀菌被提议作为一种控制措施，以降低生奶酪牛奶中病原体的风险，同时保留奶酪中的一些质量属性。然而，增强安全性所需的温度和时间组合尚未得到很好的描述。本研究的目的是确定和验证李斯特菌和 STEC 在热杀菌温度 65.6、62.8 和 60.0°C 下的十进制减少值（D 值）；仅确定了李斯特菌在 57.2°C 下的 D 值。未均质的巴氏杀菌全脂奶样品（1 毫升）用 8 对数 cfu/ml 的李斯特菌或 STEC（分别为 5 或 7 株混合）接种，真空密封在不透水的小袋中，通过水浴浸泡加热。在适当的时间间隔取出重复样品，并立即在冰浴中冷却。在改良的牛津或山梨糖醇麦康凯琼脂上覆盖胰蛋白酶大豆琼脂，以帮助回收受热损伤的细胞，对存活的细菌进行计数。进行了两次重复试验，并使用生存数据计算了热失活动力学。李斯特菌和 STEC 的 D、D 和 D 值分别为 17.1 和 7.2、33.8 和 16.9，146.6 和 60.0 s，李斯特菌的 D 值为 909.1 s。使用 100 毫升牛奶接种每个病原体混合物 3 到 4 个对数 cfu/ml，对每个测试温度进行了 3 次验证试验，每种病原体的 3 个对数减少都比通过 D 值预测的速度更快（D 值是防故障的）。数据还与 21 项研究李斯特菌和 STEC 在加热至热杀菌温度（55.0-71.7°C）的全脂奶中的科学研究的公布结果进行了比较。这些数据可以为手工生产生奶奶酪的生产者提供灵活性，以设计热加工过程，将李斯特菌和 STEC 减少到对消费者没有传染性的水平。
