Inactivation of Salmonella enterica serovar enteritidis in shell eggs by sequential application of heat and ozone

Aims:  To assess the contribution of ozone to lethality of Salmonella enterica serovar Enteritidis in experimentally inoculated whole shell eggs that are sequentially treated with heat and gaseous ozone in pilot-scale equipment.
Methods and Results:  Whole shell eggs were inoculated with small populations of Salmonella Enteritidis (8·5 × 10⁴–2·4 × 10⁵ CFU per egg) near the egg vitelline membrane. Eggs were subjected to immersion heating (57°C for 21 min), ozone treatment (vacuum at 67·5 kPa, followed by ozonation at a maximum concentration of approx. 140 g ozone m⁻³ and 184–198 kPa for 40 min) or a combination of both treatments. Survivors were detected after an enrichment process or enumerated using modified most probable number technique. Ozone, heat and combination treatments inactivated 0·11, 3·1 and 4·2 log Salmonella Enteritidis per egg, respectively.
Conclusions:  Sequential application of heat and gaseous ozone was significantly more effective than either heat or ozone alone. The demonstrated synergy between these treatment steps should produce safer shell eggs than the heat treatment alone.
Significance and Impact of the Study:  Shell eggs are the most common vehicle for human infection by Salmonella Enteritidis. Many cases of egg-related salmonellosis are reported annually despite efforts to reduce contamination, including thermal pasteurization of shell eggs and egg products. Treatment with ozone-based combination should produce shell eggs safer than those treated with heat alone.     

Ecophysiological attributes of Salmonella typhimurium in liquid culture and within a gelatin gel with or without the addition of oregano essential oil

The growth of Salmonella typhimurium in liquid culture and in a gel matrix system at two pH values (5.0 and 7.0) with (0.03% w/v) or without oregano essential oil was studied. It was shown that the type of growth media (liquid or gel) influenced significantly both the type of end-product formation and growth of bacteria as well as the inhibitory efficacy of the essential oil. The oil inhibited S. typhimurium more strongly in the liquid medium than in the gelatin matrix. In particular, the addition of essential oil in gelatin matrix delayed the initiation of growth and caused a slight suppression of the maximum population level, while in liquid culture, growth was prevented completely in identical conditions. Structure also was found to affect the rate of consumption of glucose and the rate of production of end products. Formic and acetic acids were produced in both systems, while an unidentified peak was formed only in broth samples.