低水分食品中等温水分活度对肠炎沙门氏菌抗热性的影响研究

Pathogenic bacteria, such as Salmonella enterica, exhibits strong survivability and high heat resistance in low-moisture environment. They are able to survive in low-moisture foods for long time, re-grow and cause foodborne illnesses under suitable conditions. Water activity at elevated temperature (aw,T) is the real-time water activity of foods at pasteurization temperature (T). It is one of the key factors which regulates the resistance of pathogens against high temperature. and may play important role in understanding high heat resistance of bacteria in low-moisture environment. However, the mechanism of aw,T’s impact on heat resistance of Salmonella enterica in low-moisture foods was unknown. Through studying the role of aw,T on bacteria activity in food, the applicant has reported that reduced aw,T’s is exponentially able to enhance the heat resistance of Salmonella enterica in low-moisture environment (silica dioxide granules). Following this study, this project aims to: 1) uncover the effect of aw,T on the heat resistance of Salmonella enterica in different low-moisture foods, 2) determine the synergistic effect of aw,T and temperature on heat resistance of Salmonella enterica, 3) elucidate that how the factor aw,T regulates thermal inactivation kinetics of Salmonella enterica, and 4) reveal the mechanism on how Salmonella enterica is resistant against high temperature in low-moisture foods. This study will provide insights on understanding the mechanism of heat resistance of bacteria in low-moisture food. This study will also offer potential thermal pasteurization process to protect low-moisture foods from high temperature resistant pathogens.

致病菌，如肠炎沙门氏菌，在干燥环境下表现出强生存能力与高抗热性，能长时间存活于低水分食品中，并在适合的环境中生长繁殖、引起消费者食物中毒。等温水分活度（aw,T）是灭菌温度T下测定的实时水分活度，也是影响低水分环境中致病菌高抗热性的潜在因素，对明晰细菌抗热性增强规律具有重要价值。但其对低水分食品中肠炎沙门氏菌抗热性的影响机制尚未报道。通过控制等温水分活度与温度，申请人发现等温水分活度在低水份环境（二氧化硅颗粒）中以指数形式增强肠炎沙门氏菌的热抗性。本项目拟明确等温水分活度在不同低水分食品中对肠炎沙门氏菌抗热性的作用；分析等温水分活度和温度对肠炎沙门氏菌抗热性的协同作用；解析等温水分活度调节肠炎沙门氏菌抗热性动力学原理，以揭示低水分食品中致病菌高抗热性的机制，为设计低水分食品热杀菌工艺奠定重要理论基础。

低水分食品（常温水分活度低于0.85）属于食品加工制造中的一大类食品，通常缺乏有效的灭菌措施而成为病原微生物的载体，已经在国际范围内引发了多起食品安全事件。回答不同低水分食品/环境中细菌如何、为何表现高抗热性，建立可靠的致病菌抗热性预测模型至关重。负责人围绕等温水分活度这一关键因子，选择标准菌株肠炎沙门氏菌PT 30为目标菌，在模式低水分食品/环境——鸡蛋粉/滤纸——中量化了等温水分活度对目标菌抗热性指标（D与z值）的影响作用，揭示了低水分环境中微生物存活与抗热性变化的客观规律，并借助转录组学与蛋白组学初步阐述了微生物存活与抗热性指标的分子生物学机理。重要研究结果及关键数据如下所示：.1）对鸡蛋粉中蛋白质与脂肪含量影响肠炎沙门氏菌PT 30抗热性指标进行建模，证实了食品质构与组分（尤其是脂肪）对细菌抗热性有着不可忽视的作用；完成了不同鸡蛋粉中高温水分活度变化的测量与建模，发现鸡蛋粉的极细粒径对其高温水分活度有着强影响作用，首次揭示了低水分食品物理特性对其高温水分活度及灭菌效率的影响作用；2）完成了不同水分活度下滤纸中肠炎沙门氏菌PT 30的存活与抗热性实验，原创性地发现水分活度0.65条件下肠炎沙门氏菌PT 30存活率最低，这说明0.65是肠炎沙门氏菌在低水分环境中存活的关键节点，蛋白组数据也表明：这或与其胞内蛋白质YhbO表达显著下调有关；3）肠炎沙门氏菌的温度敏感性（z值）随着水分活度的降低而呈线性增强，这对低水分食品灭菌工艺设计有着重要指导作用；4）在水分活度0.84时，肠炎沙门氏菌的烯烃还原酶WP_000092932.1显著下调，该蛋白可能也是影响其存活与抗热性的重要因子。.本项目量化了致病菌在不同（等温）水分活度下的存活、抗热性指标与基因表达，建立了以肠炎沙门氏菌PT30为代表的细菌抗热性变化模型，鉴定到关键基因与蛋白质数个。为细菌热致死理论提供了丰富的表征数据与组学数据，为低水分食品中微生物安全风险及热巴氏杀菌工艺设计提供了重要数据支撑。

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