SALMONELLA is a key cause of foodborne gastroenteritis in Australia and case numbers are increasing, with most outbreaks linked to eggs, poultry meat, pork, dairy and fresh produce.
Flinders University researchers have found a simple solution for preventing salmonellosis affecting eggs through surface contamination, giving crucial assistance to Australia’s vast food services industry. Raw eggs are used in many food products such as mayonnaise, mousse, eggnog and artisanal ice cream.
However, a problem is associated with eggshells being contaminated with the bacterium salmonella enterica serovar typhimurium. The Flinders research team aimed to develop a decontamination method for removing ST from the eggshell without impacting usability. Using equipment commonly found in commercial kitchens, the researchers decontaminated eggs by placing them in a sous vide cooker with water heated to 57C.
Complete decontamination of ST was achieved by treating eggs for nine minutes. The results of the first study to look at decontamination of ST on the eggshell were recently published in the journal ‘Foodborne Pathogens and Disease’. The decontaminated eggs were found, by chefs using measurements and acceptability scores, to have no significant difference in their quality or performance as an ingredient when compared with nontreated eggs.
You can go online to find a preview of ‘A Successful Technique for the Surface Decontamination of Salmonella enterica Serovar Typhimurium Externally Contaminated Whole Shell Eggs Using Common Commercial Kitchen Equipment’ (November 2019), a paper by Thilini Keerthirathne, Kirstin Ross, Howard Fallowfield and Harriet Whiley.
A second study by the Flinders environmental health research team examined the effectiveness of current Australian guidelines recommending raw egg mayonnaise should be prepared and stored under 5C and adjusted to a pH less than 4.6 or 4.2. Despite these guidelines, a significant number of salmonellosis outbreaks continue to be recorded every year in Australia.
The researchers found the survival of salmonella typhimurium in mayonnaise is significantly improved at 4C and lower temperatures protected ST from the bactericidal effect of low pH. Flinders environmental health researcher Thilini Keerthirathne said, “We found 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 storing mayonnaise at 37C. “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 is at pH 4.2 or less.” This study, ‘The Combined Effect of pH and Temperature on the Survival of Salmonella enterica Serovar Typhimurium and Implications for the Preparation of Raw Egg Mayonnaise’ (November 2019) by TP Keerthirathne, K Ross, H Fallowfield and H Whiley, has been published in ‘Pathogens’ journal.
PhD candidate Ms Keerthirathne said the results of the two studies will help decrease the current levels of foodborne salmonellosis outbreaks related to eggs and raw egg products in Australia. It is estimated 4.1 million cases of foodborne illness are recorded annually nationwide, including 30,000 hospitalisations and 100 fatalities.
Salmonellosis is one of the most prevalent causes of foodborne illness in the country, increasing from 40.9 per 100,000 population in 2005 to 71.5 per 100,000 population in 2015. A common source of salmonellosis has been identified as raw eggs and egg products.
Background
Salmonella entericais is transmitted via food, the environment, water, people and animals, and often causes gastroenteritis in humans.
Common foods associated with salmonellosis in outbreak investigations and source attribution studies include eggs, poultry meat, pork, beef, dairy products, nuts and fresh produce.
More than 70 percent of salmonellosis in Australia is estimated to be transmitted through contaminated food. Worldwide salmonella infections, excluding those caused by S. typhi and S. paratyphi, were estimated to cause 93.8 million cases of gastroenteritis per year, 80.3 million of which are considered foodborne.