低水分食品中冻干细菌的水分吸附特性。
Water sorption characteristics of freeze-dried bacteria in low-moisture foods.
机构信息
Department of Biological Systems Engineering, Washington State University, P.O. Box 646120, Pullman, WA 99164-6120, USA; Center for Nanotechnology and Nanotoxicology, Harvard T.H. Chan School of Public Health, Harvard University, Boston, MA 02115, USA.
Department of Biological Systems Engineering, Washington State University, P.O. Box 646120, Pullman, WA 99164-6120, USA.
出版信息
Int J Food Microbiol. 2022 Feb 2;362:109494. doi: 10.1016/j.ijfoodmicro.2021.109494. Epub 2021 Nov 25.
Water sorption isotherms of bacteria reflect the water activity with the change of moisture content of bacteria at a specific temperature. The temperature-dependency of water activity change can help to understand the thermal resistance of bacteria during a thermal process. Thermal resistance of bacteria in low-moisture foods may differ significantly depending on the physiological characteristics of microorganisms, including cell structure, existence of biofilms, and growth state. Previous studies demonstrated that the incremental change of a in bacterial cells during thermal treatments resulted in changes in their thermotolerance. In this study, a pathogen associated with low-moisture foods outbreaks, Salmonella Enteritidis PT30 (in planktonic and biofilm forms), and its validated surrogate, Enterococcus faecium, were lyophilized and their water sorption isotherms (WSI) at 20, 40, and 60 °C were determined by using a vapor sorption analyzer and simulated by the Guggenheim, Anderson and De Boer model (GAB). The published thermal death times at 80 °C (D-values) of these bacteria in low-moisture environments were related with their WSI-derived a changes. The results showed that planktonic E. faecium and biofilms of Salmonella, exhibiting higher thermal resistance compared to the planktonic cultures of Salmonella, had a smaller increase in a when thermally treated from 20 to 60 °C in sealed test cells. The computational modeling also showed that when temperature increased from 20 to 60 °C, with an increase in relative humidity from 10% to 60%, freeze-dried planktonic E. faecium and Salmonella cells would equilibrate to their surrounding environments in 0.15 s and 0.25 s, respectively, suggesting a rapid equilibration of bacterial cells to their microenvironment. However, control of bacteria with different cell structure and growth state would require further attentions on process design adjustment because of their different water sorption characteristics.
细菌的水分吸附等温线反映了在特定温度下细菌水分含量随水分活度的变化。水分活度变化的温度依赖性有助于理解细菌在热过程中的热抗性。在低水分食品中，细菌的热抗性可能因微生物的生理特性（包括细胞结构、生物膜的存在和生长状态）而有很大差异。先前的研究表明，细菌细胞在热处理过程中水分活度的增量变化导致其耐热性发生变化。在这项研究中，与低水分食品爆发相关的病原体，肠炎沙门氏菌 PT30（浮游和生物膜形式）及其经过验证的替代品粪肠球菌，被冻干，并使用蒸汽吸附分析仪确定它们在 20、40 和 60°C 的水分吸附等温线（WSI），并用 Guggenheim、Anderson 和 De Boer 模型（GAB）进行模拟。这些细菌在低水分环境中的 80°C 下的公布热致死时间（D 值）与它们的 WSI 衍生的 a 值变化相关。结果表明，与浮游培养的沙门氏菌相比，表现出更高热抗性的粪肠球菌浮游生物和沙门氏菌生物膜，在密封测试细胞中从 20°C 热处理到 60°C 时，a 值的增加较小。计算模型还表明，当温度从 20°C 升高到 60°C 时，相对湿度从 10%增加到 60%，冻干的浮游粪肠球菌和沙门氏菌细胞将分别在 0.15s 和 0.25s 内达到其周围环境的平衡，表明细菌细胞迅速与微环境达到平衡。然而，由于不同的细胞结构和生长状态，控制细菌需要进一步注意过程设计调整，因为它们具有不同的水分吸附特性。
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