Food Safety and Intervention Technologies Research Unit, Eastern Regional Research Center, Agricultural Research Service, US Department of Agriculture, 600 E Mermaid Lane, Wyndmoor, PA 19038, USA.
Food Microbiol. 2011 Aug;28(5):1095-100. doi: 10.1016/j.fm.2011.01.001. Epub 2011 Jan 9.
Listeria monocytogenes (Lm) continues to pose a food safety hazard in ready-to-eat (RTE) meats due to potential cross-contamination. Chlorine is commonly used to sanitize processing equipment and utensils. However, Lm may survive the treatment and then contaminate food products. The objective of this study was to characterize the behavior of chlorine-exposed Lm on RTE ham during refrigerated storage. A two strain cocktail of Lm serotype 4b was pre-treated with chlorine (0, 25, and 50 ppm) for one hour, and then inoculated onto the surface of RTE ham to obtain an inoculum of about 3.0 log CFU/g. The inoculated ham samples were stored at 4, 8, and 16 °C, and Lm was enumerated periodically during the storage. The growth characteristics (lag time and growth rate) of Lm were estimated using the DMFit software. The results indicated that Lm growth was suppressed by the chlorine treatment. At 4 °C, the lag time of Lm with no (0 ppm) chlorine exposure (4.2 days) was shorter than those exposed to 25 ppm (5.4 days) and 50 ppm (6.8 days). The lag time decreased with the increase of temperature, e.g., at 25 ppm, the lag times were 5.2, 3.8 and 2.6 days for 4, 8 and 16 °C, respectively, and increased with the increase of chlorine concentration, e.g., at 16 °C, the lag times were 1.2, 2.6 and 4.0 days for 0, 25 and 50 ppm, respectively. However, growth rate increased with the increase of temperature and decreased with the increase of chlorine concentration. The lag time and growth rate as a function of chlorine concentration and temperature can be described using a modified Ratkowsky model and a modified Zwietering model, respectively. The results showed that the growth of Lm on RTE ham was delayed by pre-exposure to chlorine (at ≤ 50 ppm). The predictive models developed will contribute to microbial risk assessments of RTE meats.
李斯特菌（Lm）由于潜在的交叉污染，继续对即食（RTE）肉类构成食品安全危害。氯通常用于消毒加工设备和器具。然而，Lm 可能在处理后存活下来，然后污染食品。本研究的目的是描述冷藏储存过程中暴露于氯的 RTE 火腿上 Lm 的行为。将李斯特菌血清型 4b 的两株混合菌预先用氯（0、25 和 50 ppm）处理 1 小时，然后接种到 RTE 火腿表面，以获得约 3.0 log CFU/g 的接种物。将接种的火腿样品在 4、8 和 16°C 下储存，并在储存过程中定期对 Lm 进行计数。使用 DMFit 软件估计 Lm 的生长特性（滞后时间和生长速率）。结果表明，氯处理抑制了 Lm 的生长。在 4°C 下，未暴露于氯（0 ppm）的 Lm 的滞后时间（4.2 天）短于暴露于 25 ppm（5.4 天）和 50 ppm（6.8 天）的滞后时间。滞后时间随温度的升高而降低，例如，在 25 ppm 时，滞后时间分别为 4、8 和 16°C 时的 5.2、3.8 和 2.6 天，并且随着氯浓度的增加而增加，例如，在 16°C 时，滞后时间分别为 0、25 和 50 ppm 时的 1.2、2.6 和 4.0 天。然而，生长速率随温度的升高而增加，随氯浓度的升高而降低。滞后时间和生长速率随氯浓度和温度的函数关系可以分别用修正的 Ratkowsky 模型和修正的 Zwietering 模型来描述。结果表明，Lm 在 RTE 火腿上的生长因预先暴露于氯（≤50 ppm）而延迟。所开发的预测模型将有助于对 RTE 肉类的微生物风险评估。
