Survival and development of Staphylococcus in egg products

Abstract

In this work, Staphylococcus has been employed to simulate a contamination of different egg foodstuffs. Liquid (egg white, egg yolk and whole egg) and also solid (Spanish potato omelette) products have been employed as model foods. The effect of different parameters, i.e. oxygen availability, cooking temperature and storage temperature, on microorganism survival and development has been evaluated. In addition, the structure of solid foods has been analysed by means of rheological measurements. Results showed that Staphylococcus behaviour in liquid media was strongly influenced by the oxygen concentration, which is determinant for the specific growth rates (μ). In solid foods, the increase of cooking temperature to 100ºC reduced the microbial viability by one order of magnitude with respect to the raw foodstuff. Additionally, it was observed that the structure of the omelette, which depended on the cooking temperature, was a key parameter regarding the μ values. Therefore, to avoid the risk of food poisoning by Staphylococcus proliferation, in the case of egg products cooked only for few minutes, the cooking temperature should be higher than 100ºC and *Manuscript Click here to view linked References 2 the subsequent storage should be at refrigeration temperatures that increase the lag phase and decrease the growth rate.

Coupling effects of structure, oxygen availability and temperature on microbial growth in a pastry filling

“…These results are not in accordance with those found by Ananou et. al (2018) who reported that when S. aureus was incubated in liquid yolk at refrigerated temperatures the concentration of viable bacteria remained constant during 96 h. Similarly, and also in liquid yolk, Sanchez et al (2019) found that the concentration of S. warneri was approximately the same during 72 h at 11°C. This can be explained mainly by the different composition of the media, since the model pastry filling contained a high concentration of sugar that favoured microorganism growth.…”

“…The model food was prepared by mixing 100 g of sugar, 250 g of margarine and the preinoculum pellet resuspended in 20 g of raw egg yolk. The preinoculum was prepared from a refrigerated stock of Petri dishes as described in Sanchez et al (2019). Sterile 12 mL syringe-bodies (1:5 cm in diameter and 7:6 cm in length; HSW Norm-Ject) were packed with approximately 10 g of this inoculated medium, reaching inside 4 cm in height.…”

“…Sterile 12 mL syringe-bodies (1:5 cm in diameter and 7:6 cm in length; HSW Norm-Ject) were packed with approximately 10 g of this inoculated medium, reaching inside 4 cm in height. Then, the syringes were closed by placing a cotton wool plug on the top and an aluminium foil sealed with Teflon at the syringe tip (Noriega et al, 2010a;Sanchez et al, 2019). The initial concentration of microorganism was approximately 1 10 7 CFU g 1 .…”

“…Although S. warneri can survive in presence or absence of oxygen, the environmental oxygen level determines the metabolism of this facultative bacterium (Wallace et al, 2016;Sanchez et al, 2019). The presence of diffusional limitations plays an important role in solid systems, so oxygen is the main factor to limit microbial growth in solid food.…”

Rheological characterisation of yolk‐based gels and Staphylococcus growth

“…Due to its lower associated risk, S. warneri , an opportunistic pathogenic species of staphylococcus that has been isolated from eggs, has been employed as a surrogate for S. aureus (Neira et al ., 2019). Specifically, Staphylococcus warneri (CECT 236) acquired from the Spanish Collection of Type Cultures was employed as a model bacterium (Sanchez et al ., 2019).…”