A comparison of non-selective with selective counts indicated that the proportion of injured cells (Eq.
(2), data not shown) was not significantly influenced by temperature (p = 0.228), aw (p = 0.371) or water mobility (p = 0.411). Storage time just significantly influenced the proportion of injured cells (p = 0.044), as longer storage times led to check details increasing proportions of injured cells. These results do not support a hypothesis that the mechanism of inactivation changed from membrane damage at lower temperatures (≤ 50 °C) to ribosomal degradation at higher temperatures (> 50 °C) as suggested by Aljarallah and Adams (2007). Heating cells to temperatures just above their maximum growth temperature causes damage to the cytoplasmic membrane, which in enteric bacteria can be detected by plating the cells on non-selective media and media containing bile salts. If cells are treated at sufficiently high temperatures, death results from ribosome degradation, and there will be a small or no difference in the ability of the survivors to grow on selective and non-selective media. Aljarallah and Adams (2007) observed these effects using Salmonella treated at 53 °C and
Alpelisib manufacturer 60 °C at water activities of 0.99 and 0.94. Results in the present study indicated that there were no significant differences in the proportion of injured cells among those exposed to different water activities and temperatures. However, one major difference in our study is that we investigated lower water activities
(< 0.6) over a wider temperature range (21 °C–80 °C). Salmonella survival data at 21 °C during 168 days (6 months) of storage (results not shown) showed that populations were maintained under these conditions, with log reduction values of 0.001, 0.003, 0.002, 0.003 and 0.005 log CFU/day at aw levels of 0.16 ± 0.01, 0.26 ± 0.002, 0.34 ± 0.009, 0.41 ± 0.01 and 0.53 ± 0.05, respectively. These data indicated a significantly better survival of Salmonella at lower aw levels (0.16 Non-specific serine/threonine protein kinase and 0.26) as compared to higher ones (0.34 to 0.53) (p < 0.001). Significant differences in survival were also observed between the two highest aw levels (0.41 and 0.53). However, no significant differences in survival were found between aw levels of 0.16 and 0.26 (p = 0.541), 0.34 and 0.41 (p = 0.730) or 0.34 and 0.53 (p = 0.074). No influence of water mobility at the same aw level was observed (p = 0.917). Because the survival rates were essentially linear at 21 °C, the Geeraerd-tail model, the Weibull model (with β ≠ 1 in Eq. (5)) and the biphasic-linear model were not suitable for describing the data. The Baranyi and the log-linear models were appropriate in describing the data for all conditions (ftest < Ftable) and showed similar statistical fit parameter values ( Table 2). Fig. 1 presents data on Salmonella survival at 36 °C during 168 days (6 months) of storage.
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