Accordingramsly, the relationship ranging from pressure and you may temperature analysis through the heating is calculated

Accordingramsly, the relationship ranging from pressure and you may temperature analysis through the heating is calculated

We hypothesized that there would be a difference among aw conditions in glass transition temperature (Tg) for bacterial cells. Differential scanning calorimetry (DSC) is widely used as a method for measuring angelreturn Tg [29,38,39]. However, it is difficult to measure Tg of a composite using DSC because the thermogram shows intricate thermal responses . Therefore, here, thermal rheological analysis (TRA) was used to measure Tg. TRA, which measures Tg by attaching a temperature control device to a rheometer, is based on the principle of thermal mechanical analysis [28–30]. Previous studies used by TRA investigated the effect of water content on the Tg of cookies [29, 40], hazelnuts , and deep-fried food . To conduct the measurements, a sample is compressed at a temperature below Tg, and heated above Tg with compression. Then, the Tg of the sample can be determined as a force drop induced by the glass transition. This is a useful method to apply to amorphous powders. By determining Tg values, we could confirm the glass transition of bacterial cells. In addition, we sought to elucidate the influence of aw on bacterial survival and its relationship with Tg. Finally, we aimed to resolve the relationship between the state change of several Salmonella serotypes that is known to be present in low water activity foods due to glass transition and the changes in thermal resistance in a desiccation environment. The results obtained here will help to understand bacterial survival in a dry environment, which has not been clarified.

Bacterial strains and you may culturing

Salmonella enterica Typhimurium (RMID 1985009 throughout the Research Institute having Bacterial Infection from Osaka University; remote out-of patients inside the sporadic circumstances), S. enterica Chester, S. enterica Oranienburg (on the Aomori Prefectural Look Research away from Public Health; remote off dried squid potato chips of a break out inside 1999), S. enterica Stanley (RIMD 1981001 in the Browse Institute to have Bacterial Ailment away from Osaka University; separated regarding patients inside sporadic circumstances), and S. enterica Enteritidis (RIMD 1933001 from the Search Institute to own Microbial Sickness away from Osaka University; isolated of customers in sporadic instance) were chosen for this study.

These serovars had been managed from the -80°C into the tryptic soya broth (TSB, Merck, Darmstadt, Germany) with 10% glycerol. The fresh strains have been activated shortly after incubating from the 37°C having twenty-four h on the tryptic soya ager (TSA, Merck) plates. An isolated colony of every bacteria was then relocated to 5 mL regarding TSB in a great sterile centrifuge tubing, incubated during the 37°C to own 24 h, then an one hundred ?L aliquot away from cultured bacterium is actually added to help you 400 mL TSB and you may incubated in the 37°C to have forty eight h. The brand new cultured structure have been built-up because of the centrifugation (3,000 ? grams, ten min) while the pellets had been resuspended from inside the 5 mL out-of clear water. Bacterial-cell pellets was in fact obtained because of the pipetting off of the a lot of water and amassed to the a plastic material dish. The plates was frozen from the -80°C for twenty four h prior to drying out for twenty-four h using good frost more dry (FDU-2200, EYELA, Tokyo, Japan). Dried bacterial muscle were soil, listed in an environment-rigid container during the need cousin dampness (% RH), which was put using over loaded sodium aqueous choices (43% RH: potassium carbonate, 57% RH: sodium bromide, 75% RH: salt chloride, and 87% RH: potassium chloride), and kept on 4°C having 48 h. Water hobby and you can temperatures floating around-rigid container was indeed constantly checked using thermo recorder (TR-72wf, T and you can D, Nagano, Japan). Together with drinking water passion of one’s bacteria is actually confirmed by the an excellent liquids craft meter (Aqualab 4TE, Decagon Gizmos, Washington, USA).

Devotion from cup transition temperatures (Tg)

Thermal rheological analysis (TRA) was used to measure Tg by attaching a temperature control device to a rheometer (EZ-SX, SHIMADZU, Kyoto, Japan) (illustrated in Fig 1); the analysis is based on the principle of thermal mechanical analysis [28–30]. A dried bacterial cell sample (ca. 100 mg) was placed in the forming die (? = 3 mm) and compacted with a rheometer at ca. 10 MPa. Subsequently, the sample was compressed at ca. 5 MPa ca. for 1 to 3 min and then heated at a rate of approximately 3°C/min until the temperature reached 120°C. Pressure-time data were collected with software attached to the rheometer. In parallel, a thermocouple was attached to the bottom of the forming die and time-temperature data were collected every second using a data logger. Since pressure reduction begins at the point at which the bottom temperature of the sample reaches the mechanical Tg, the onset temperature of pressure reduction could be regarded as the Tg of the sample .

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