Preventing Salmonella from affecting raw eggs

Researchers from Flinders University have found a solution for preventing salmonellosis affecting eggs through surface contamination, by developing a decontamination method that removes contamination from the eggshell without impacting the egg’s usability. Salmonella is often linked to cases of foodborne gastroenteritis in Australia, with increasing case numbers linked to eggs, poultry meat, fresh produce, pork and dairy. A bacterium known as Salmonella enterica serovar Typhimurium (ST) can contaminate eggshells, thereby affecting many food products that use raw eggs (such as mayonnaise, mousse, eggnog and artisanal ice cream).

Using a method that employed commercial kitchen equipment for sous-vide cooking, researchers decontaminated eggs by placing them in a sous-vide cooker with the water heated to 57°C, with complete decontamination of ST achieved by treating eggs for nine minutes. Findings from the study were published in Foodborne Pathogens and Disease. Researchers used measurements and acceptability scores to find differences in quality or performance as ingredients in decontaminated eggs, then compared their scores to untreated eggs.

Researchers performed a second study to analyse the effectiveness of current Australian guidelines regarding the preparation of raw egg mayonnaise, which recommend that the product should be prepared and stored under 5°C and adjusted to a pH less than 4.6 or 4.2. Despite these guidelines, salmonellosis outbreaks continue to be recorded every year in Australia. Researchers discovered that the survival of ST in mayonnaise improved at 4°C, with lower temperatures protecting ST from the bactericidal effect of low pH.

“We found that the preparation of mayonnaise at pH 4.2 or less and incubating it at room temperature for at least 24 hours could reduce the incidence of salmonellosis. But there is a risk of storing mayonnaise at 37°C. If the pH is not correctly measured, the warmer temperatures will promote the growth of Salmonella. As such it is crucial to ensure the pH of the mayonnaise if at pH 4.2 or less,” said Thilini Keerthirathne, Flinders environmental health researcher.

The second study was published in the Pathogens journal, with both studies carried out to ultimately decrease the instances of foodborne salmonellosis outbreaks related to eggs and raw egg products in Australia. One of the most common sources of salmonellosis has been identified as raw eggs and egg products.

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