Department of Biological Systems Engineering, Washington State University, Pullman, WA, USA.
Escuela de Ingeniería y Ciencias, Tecnologico de Monterrey, Monterrey, Nuevo León, Mexico.
Food Microbiol. 2018 Sep;74:92-99. doi: 10.1016/j.fm.2018.03.001. Epub 2018 Mar 3.
This study investigated the influence of temperature-dependent water activity (a) on thermal resistances of Enterococcus faecium NRRL B-2354 (E. faecium) and Salmonella Enteritidis PT 30 (S. Enteritidis) in wheat flour. The a for wheat flour samples at 20, 40, and 60 °C was determined by a vapor sorption analyzer and at 75, 80 and 85 °C using custom-built thermal cells with high temperature humidity sensors. Full-factorial isothermal inactivation studies of both strains in sealed aluminum-test-cells included three temperatures (75, 80, and 85 °C) and three a levels (0.30, 0.45 and 0.60 within ±0.02 range, prior to the thermal treatments). Isotherm results of wheat flour demonstrate a significant increase (P < 0.05) of a as temperature rises (e.g. a = 0.45 ± 0.02 became a = 0.71 ± 0.02 in a closed system). Inactivation kinetics of both microorganisms fitted a log-linear model, the yielded D-values varied from 2.7 ± 0.2 min (D of S. Enteritidis at a 0.60 ± 0.02) to 65.8 ± 2.5 min (D of E. faecium at a 0.30 ± 0.02). The z of E. faecium and S. Enteritidis decreased from 16.4 and 16.9 °C, respectively, to 10.2 °C with increased moisture content (dry basis) from 10 to 14%. Under all tested conditions, E. faecium exhibited equal or higher (1.0-3.1 times) D- and z-values than those of Salmonella. Overall, E. faecium should be a conservative surrogate for Salmonella in thermal processing of wheat flour for control of Salmonella over a moisture content of 10-14% and treatment temperatures between 75 and 85 °C.
本研究探讨了温度依赖性水活度（a）对小麦粉中屎肠球菌 NRRL B-2354（E. faecium）和肠炎沙门氏菌 PT 30（S. Enteritidis）耐热性的影响。使用蒸汽吸附分析仪在 20、40 和 60°C 下以及使用带有高温湿度传感器的定制热室在 75、80 和 85°C 下测定小麦粉样品的 a 值。在密封的铝测试小室中对两种菌株进行全因子等温失活动力学研究，包括三个温度（75、80 和 85°C）和三个 a 水平（0.30、0.45 和 0.60，在热处理之前）。小麦粉的等温结果表明，随着温度升高，a 值显著增加（P<0.05）（例如，在封闭系统中，a=0.45±0.02 变为 a=0.71±0.02）。两种微生物的失活动力学均符合对数线性模型，得到的 D 值从 2.7±0.2 min（S. Enteritidis 在 a=0.60±0.02 时的 D 值）变化到 65.8±2.5 min（E. faecium 在 a=0.30±0.02 时的 D 值）。E. faecium 和 S. Enteritidis 的 z 值分别从 16.4°C 和 16.9°C 降低到 10.2°C，随着水分含量（干基）从 10%增加到 14%。在所有测试条件下，E. faecium 的 D 值和 z 值均高于（1.0-3.1 倍）或等于肠炎沙门氏菌。总体而言，在 10-14%水分含量和 75-85°C 处理温度范围内，E. faecium 应是控制小麦粉中沙门氏菌的保守替代物。
