Previous studies on the influence of food matrix fat content on thermal inactivation kinetics of food pathogens have shown contradictory results due to the combined influence of fat content and other factors such as composition. Therefore, thermal inactivation of Listeria monocytogenes at 59, 64, and 69°C was systematically investigated in emulsion and gelled emulsion food model systems with various fat content (1, 5, 10, and 20%), such that the effect of fat content was isolated. Thermal conductivity and rheological properties of the model systems were quantified, as well as the effect of these properties on the thermal load of the model systems. Thermal conductivity was complexly related to fat content, the nature of the food matrix (i.e., viscous or gelled), and temperature. For the emulsions, the consistency index K increased with increasing fat content, while the flow behavior index n followed the opposite trend. For the gelled emulsions, the storage modulus G' was always larger than the loss modulus G″ (i.e., measure of elastic and viscous properties, respectively). The phase angle δ [i.e., arctan (G″/G')] was proportional with fat content, but this relation became more complex at higher temperatures. The thermal load of the model systems was not largely affected by food matrix fat content. Thermal inactivation of L. monocytogenes was investigated by means of the maximum specific inactivation rate k max, log reductions, and sublethal injury (SI). Both for emulsions and gelled emulsions, k max decreased with increasing fat content below approximately 60°C, while a more complex behavior was observed at higher temperatures. In the emulsions, log reductions were considerably lower (i.e., 2-3 log) at 1% fat than in systems with higher fat content. In the gelled emulsions, log reductions generally decreased with increasing fat content. SI decreased with increasing fat content, both in emulsions and gelled emulsions. In conclusion, the inactivation rate (i.e., k max) of L. monocytogenes was affected by a complex relation between food matrix fat content, thermal conductivity, rheological properties, and inactivation temperature. Due to the small scale of the model systems, differences in k max did not directly affect the final log reductions in a similar fashion.

中文翻译：

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食品基质脂肪含量对单核细胞增生李斯特氏菌热灭活的复杂影响：乳液和凝胶乳液模型系统的案例研究。

以往关于食品基质脂肪含量对食品病原体热灭活动力学影响的研究由于脂肪含量与成分等其他因素的综合影响而显示出相互矛盾的结果。因此，在具有不同脂肪含量（1、5、10和20%）的乳液和胶凝乳液食品模型系统中系统地研究了单增李斯特菌在59、64和69°C下的热灭活，从而了解脂肪含量的影响被孤立了。量化了模型系统的导热率和流变特性，以及这些特性对模型系统热负荷的影响。导热率与脂肪含量、食品基质的性质（即粘性或胶凝）和温度复杂相关。对于乳液，稠度指数 K 随着脂肪含量的增加而增加，而流动行为指数 n 则呈现相反的趋势。对于凝胶乳液，储能模量G'总是大于损耗模量G''（即，分别测量弹性和粘性性能）。相位角δ[即反正切(G″/G')]与脂肪含量成正比，但这种关系在较高温度下变得更加复杂。模型系统的热负荷很大程度上不受食物基质脂肪含量的影响。通过最大特异性灭活率 k max、对数减少和亚致死损伤 (SI) 来研究单核细胞增生李斯特菌的热灭活。对于乳液和凝胶乳液，在低于约 60°C 时，k max 随着脂肪含量的增加而降低，而在较高温度下观察到更复杂的行为。在乳液中，脂肪含量为 1% 时，对数减少量明显低于脂肪含量较高的系统（即 2-3 个对数）。在凝胶乳液中，对数减少通常随着脂肪含量的增加而减少。在乳液和凝胶乳液中，SI 随着脂肪含量的增加而降低。总之，单增李斯特菌的灭活率（即 k max）受到食品基质脂肪含量、热导率、流变特性和灭活温度之间复杂关系的影响。由于模型系统规模较小，k max 的差异不会以类似的方式直接影响最终的对数减少。