Influence of the initial cell number on the growth fitness of Salmonella in raw and pasteurized liquid whole egg

Salmonella growth and survival in egg and egg products has been widely studied. Nevertheless, there are still some aspects that are still not fully known. Therefore, the objective of this work was to study the influence of the initial cell number on the growth fitness of Salmonella in raw and pasteurized liquid whole egg.

Growth curves of Salmonella Enteritidis in raw and pasteurized liquid whole egg and starting from different initial numbers were obtained and fitted to the Baranyi and Roberts model. Results obtained revealed that in raw egg lower initial numbers led to longer lag phases (l) and lower maximum specific growth rates (m_max). However, the application of thermal treatments of increasing intensity to the liquid egg -before inoculation with Salmonella cells- led to a progressive reduction of this effect. Supplementation assays with lysozyme and ovotransferrin revealed that these proteins would not be the responsible for the decreased growth fitness of Salmonella cells when inoculated in raw egg at low concentrations. By contrast, addition of iron (0.20 g/l) to raw egg increased the growth fitness of Salmonella cells inoculated at a low an initial but not a high one. Thus, under these conditions the growth fitness of Salmonella was similar regardless of the initial dose and thermal history of the whole liquid egg, indicating the major role of Fe bioavailability on the phenomenon observed.