Residue Chemistry and Predictive Microbiology Research Unit, Eastern Regional Research Center, Agricultural Research Service, The United States Department of Agriculture, 600 E. Mermaid Lane, Wyndmoor, PA 19038, United States.
Food Res Int. 2018 May;107:248-256. doi: 10.1016/j.foodres.2018.02.028. Epub 2018 Feb 14.
The objective of this study was to investigate the growth kinetics of Clostridium botulinum LNT01, a non-toxigenic mutant of C. botulinum 62A, in cooked ground beef. The spores of C. botulinum LNT01 were inoculated to ground beef and incubated anaerobically under different temperature conditions to observe growth and develop growth curves. A one-step kinetic analysis method was used to analyze the growth curves simultaneously to minimize the global residual error. The data analysis was performed using the USDA IPMP-Global Fit, with the Huang model as the primary model and the cardinal parameters model as the secondary model. The results of data analysis showed that the minimum, optimum, and maximum growth temperatures of this mutant are 11.5, 36.4, and 44.3 °C, and the estimated optimum specific growth rate is 0.633 ln CFU/g per h, or 0.275 log CFU/g per h. The maximum cell density is 7.84 log CFU/g. The models and kinetic parameters were validated using additional isothermal and dynamic growth curves. The resulting residual errors of validation followed a Laplace distribution, with about 60% of the residual errors within ±0.5 log CFU/g of experimental observations, suggesting that the models could predict the growth of C. botulinum LNT01 in ground beef with reasonable accuracy. Comparing with C. perfringens, C. botulinum LNT01 grows at much slower rates and with much longer lag times. Its growth kinetics is also very similar to C. sporogenes in ground beef. The results of computer simulation using kinetic models showed that, while prolific growth of C. perfringens may occur in ground beef during cooling, no growth of C. botulinum LNT01 or C. sporogenes would occur under the same cooling conditions. The models developed in this study may be used for prediction of the growth and risk assessments of proteolytic C. botulinum in cooked meats.
本研究旨在研究非产毒梭菌 62A 突变株 C. botulinum LNT01 在熟绞碎牛肉中的生长动力学。将 C. botulinum LNT01 的孢子接种到绞碎牛肉中，在不同温度条件下进行厌氧孵育，以观察生长并绘制生长曲线。采用一步动力学分析方法同时分析生长曲线，以最小化全局残差。使用 USDA IPMP-Global Fit 进行数据分析，以 Huang 模型作为主模型，以基数参数模型作为二级模型。数据分析结果表明，该突变体的最低、最适和最高生长温度分别为 11.5、36.4 和 44.3°C，估计的最适比生长速率为 0.633ln CFU/g·h，或 0.275log CFU/g·h。最大细胞密度为 7.84log CFU/g。使用额外的等温生长曲线和动态生长曲线对模型和动力学参数进行验证。验证的剩余误差遵循拉普拉斯分布，约 60%的剩余误差在实验观察值的±0.5log CFU/g 范围内，表明模型可以合理准确地预测 C. botulinum LNT01 在绞碎牛肉中的生长。与 C. perfringens 相比，C. botulinum LNT01 的生长速度较慢，延迟时间较长。它的生长动力学也与 C. sporogenes 在绞碎牛肉中非常相似。使用动力学模型进行的计算机模拟结果表明，虽然 C. perfringens 在冷却过程中可能在绞碎牛肉中大量生长，但在相同的冷却条件下，C. botulinum LNT01 或 C. sporogenes 不会生长。本研究中开发的模型可用于预测熟肉中蛋白水解性 C. botulinum 的生长和风险评估。
