Microbiological Properties of Hard-Cooked Eggs in a Citric Acid-Based Preservative Solution

Hard-cooked and peeled eggs were placed in .5, .75 or 1.0% citric acid solutions (with .2% sodium benzoate) and held at 4°C for 30 d (experiment 1), or in .75% acid and held at 4°C for 21 d (experiment 2) to allow equilibration. Following equilibration, the solutions were sampled for pH and total plate counts and then inoculated with either 10 or 10,000 cells each of Salmonella typhimurium , Yersinia enterocolitica , Escherichia coli and Staphylococcus aureus . The eggs were stored for an additional 10 d at 4°C (experiment 1) or for 10 and 24 d at either 1.2, 7.2 or 12.8°C (experiment 2) before sampling for pH, aerobic plate count, total Enterobacteriaceae and each of the individual inoculated test organisms. No growth was detected in the solutions following the 30- and 21-d equilibration periods. The .75% citric acid solution was adequate in reducing the bacterial population and retarding growth of the inoculated organisms. Storage temperature appeared to have little influence on growth of inoculated organisms. Results indicate that the microbiological quality of hard-cooked eggs stored in citric acid based solutions was more dependent on acid concentration than on temperature in resisting bacterial growth following potential recontamination.