Effect of water activity on the mechanical glass transition and dynamical transition of bacteria
Effect of water activity on the mechanical glass transition and dynamical transition of bacteria
复制标题
水分活度对细菌机械玻璃化转变和动力学转变的影响
DOI：
10.1016/j.bpj.2022.09.001
复制
发表时间：
2022
影响因子：
3.4
通讯作者：
Kawai Kiyoshi
中科院分区：
文献类型：
--
作者：
Sogabe Tomochika;Nakagawa Hiroshi;Yamada Takeshi;Koseki Shigenobu;Kawai Kiyoshi
本研究的目的是澄清的玻璃化转变行为的细菌（坂崎克罗伊氏菌）作为一个功能的水活度（aw）。根据298 K的等温吸水曲线，测得坂崎栎的单层含水量为0.0724 g/g干物质，单层含水量为0.252 g/g干物质。在298 K下研究了机械弛豫。在大于0.529的较高范围内，机械松弛度随aw的增大而增大。从机械松弛程度的影响，机械awc（在298 K发生机械玻璃化转变）被确定为0.667。用非相干弹性中子散射研究了细菌中原子的均方位移。均方位移随温度的升高而逐渐增大，这取决于样品的尺寸。从线性拟合，两个或三个动态转变温度（低，中，和highTds）在每一个测定。低Td值（142-158 K）几乎与温度无关。除无水样品（261 K）外，在温度中间（214-234 K），温度的影响较小。高Td（252-322 K）随aw的减小而增大。由高Td的awc依赖性，确定了动态awc为0.675，与机械awc基本相当。最高的玻璃化转变温度（Tg）为Td，无水玻璃化转变温度（Tg）为409 K。此外，计算了细菌的分子弛豫时间（τ）作为faw的函数。从结果来看，细菌系统中的代谢进程需要低于约6 × 10−5s的τ。
The purpose of this study was to clarify the glass-transition behavior of bacteria (Cronobacter sakazakii) as a function of water activity (aw). From the water sorption isotherm (298 K) forC.sakazakii, monolayer water content and monolayerawwere determined to be 0.0724 g/g-dry matter and 0.252, respectively. Mechanical relaxation was investigated at 298 K. In a higherawrange of over 0.529, the degree of mechanical relaxation increased with an increase inaw. From the effect ofawon the degree of mechanical relaxation, the mechanicalawc(awat which mechanical glass transition occurs at 298 K) was determined to be 0.667. Mean-square displacement of atoms in the bacteria was investigated by incoherent elastic neutron scattering. The mean-square displacement increased gradually with an increase in temperature depending on theawof samples. From the linear fitting, two or three dynamical transition temperatures (low, middle, and highTds) were determined at eachaw. The low-Tdvalues (142–158 K) were almost independent fromaw. There was a minor effect ofawon the middleTd(214–234 K) except for the anhydrous sample (261 K). The highTd(252–322 K) largely increased with the decrease inaw. From theawdependence of the highTd, the dynamicalawcwas determined to be 0.675, which was almost equivalent to the mechanicalawc. The highTdwas assumed to be the glass-transition temperature (Tg), and anhydrousTgwas estimated to be 409 K. In addition, molecular relaxation time (τ) of the bacteria was calculated as a function ofaw. From the result, it is suggested that the progress of metabolism in the bacterial system requires a lowerτthan approximately 6 × 10−5s.