Effect of pH, Water Activity, and Common Salt on the Growth/No Growth Boundary and Growth Kinetic Parameters of Shewanella putrefaciens
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Abstract:
Isolates of the spoilage organism Shewanella putrefaciens from farmed Pseudosciaena crocea stored in aerobic conditions were studied. The growth of S. putrefaciens was regulated by pH, water activity (Aw), sodium chloride (salt), and temperature, and the effect of regulatory factors on the growth kinetic parameters was analyzed. This study can aid in effectively inhibiting spoilage and bacterial growth to extend the shelf life of products. S. putrefaciens was inoculated in tryptic soy broth (TSB), and real-time optical density (OD) data were measured in different environmental conditions to determine the growth/no growth boundary. The OD data were fitted to a modified Gompertz equation in the growth range, and the goodness of fit of the model and the effect of regulatory factors on kinetic parameters were studied. The experimental results showed that at 15 ℃, S. putrefaciens could not grow at pH ≤ 5.0, Aw ≤ 0.930, or salt ≥ 7%. At 25 ℃, S. putrefaciens could not grow at pH ≤ 5.0, Aw ≤ 0.920, or salt ≥ 12%. At 37 ℃, S. putrefaciens could not grow. The goodness of fit of the growth model for S. putrefaciens showed that pH, Aw, and salt had a considerable effect on the maximum specific growth rate and lag phase of S. putrefaciens. The R2, bias, and accuracy values of the model were all near 1, and root mean square error (RMSE) was close to 0, indicating that the model is a good fit for the growth of S. putrefaciens in different conditions.
