Wang Xiang, Devlieghere Frank, Geeraerd Annemie, Uyttendaele Mieke
Laboratory of Food Microbiology and Food Preservation, Department of Food Safety and Food Quality, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium.
KU Leuven Department of Biosystems (BIOSYST), MeBioS, Faculty of Bioscience Engineering, Leuven, Belgium.
Int J Food Microbiol. 2017 Feb 21;243:70-77. doi: 10.1016/j.ijfoodmicro.2016.12.008. Epub 2016 Dec 14.
The objective of the present study was to compare the thermal inactivation and sublethal injury kinetics of Salmonella enterica and Listeria monocytogenes in broth (suspended cells) and on solid surface (agar-seeded cells). A 3-strain cocktail of S. enterica or L. monocytogenes inoculated in broth or on agar was subjected to heating in a water bath at various set temperatures (55.0, 57.5 and 60.0°C for S. enterica and 60.0, 62.5 and 65°C for L. monocytogenes). The occurrence of sublethally injured cells was determined by comparing enumerations on nonselective (TSAYE) and selective (XLD or ALOA) media. Results showed that the inactivation curves obtained from selective media were log-linear, and significant shoulders (p<0.05) were observed on some of the inactivation curves from TSAYE media. The D-values derived from the total population were higher than those from the uninjured cells. Generally, cells on agar surface exhibited higher heat resistance than those in broth. For S. enterica, cell injury increased with the exposure time, no difference was observed when treated at temperatures from 55.0 to 60.0°C, while for L. monocytogenes, cell injury increased significantly with heating time and treatment temperature (from 60.0 to 65°C). Moreover, the degree of sublethal injury affected by thermal treatment in broth or on agar surface depended upon the target microorganism. Higher proportions of injured S. enterica cells were observed for treatment in broth than on agar surface, while the opposite was found for L. monocytogenes. The provided information may be used to assess the efficacy of thermal treatment processes on surfaces for inactivation of S. enterica and L. monocytogenes, and it provides insight into the sublethally injured survival state of S. enterica and L. monocytogenes treated in liquid or on solid food.
本研究的目的是比较肠炎沙门氏菌和单核细胞增生李斯特菌在肉汤（悬浮细胞）和固体表面（琼脂接种细胞）中的热灭活及亚致死损伤动力学。将肠炎沙门氏菌或单核细胞增生李斯特菌的三菌株混合物接种于肉汤或琼脂上，在不同设定温度（肠炎沙门氏菌为55.0、57.5和60.0°C，单核细胞增生李斯特菌为60.0、62.5和65°C）的水浴中加热。通过比较在非选择性（TSAYE）和选择性（XLD或ALOA）培养基上的计数来确定亚致死损伤细胞的发生率。结果表明，从选择性培养基获得的灭活曲线呈对数线性，而在一些来自TSAYE培养基的灭活曲线上观察到明显的肩部（p<0.05）。从总菌数得出的D值高于未损伤细胞的D值。一般来说，琼脂表面的细胞比肉汤中的细胞表现出更高的耐热性。对于肠炎沙门氏菌，细胞损伤随暴露时间增加，在55.0至60.0°C的温度下处理时未观察到差异，而对于单核细胞增生李斯特菌，细胞损伤随加热时间和处理温度（从60.0至65°C）显著增加。此外，肉汤或琼脂表面热处理对亚致死损伤程度的影响取决于目标微生物。在肉汤中处理时观察到的肠炎沙门氏菌损伤细胞比例高于琼脂表面，而单核细胞增生李斯特菌则相反。所提供的信息可用于评估表面热处理对肠炎沙门氏菌和单核细胞增生李斯特菌灭活的效果，并深入了解在液体或固体食物中处理的肠炎沙门氏菌和单核细胞增生李斯特菌的亚致死损伤存活状态。
