Purpose: We conducted challenge studies to verify pickled egg processing parameters.
Methods: Hard-boiled eggs were acidified in ambient temperature brine at 60/40 egg/brine ratio. Four brine treatments were studied in triplicate: 5% acetic acid (AA) and 2.5% AA, with and without 0.05% sodium benzoate. Samples were stored at 7ºC until pH at the yolk center ≤ 4.6; subsequently, samples were held at ambient temperature. Egg pH was measured at 24-48 hour intervals until equilibrium pH was reached (4.0 and 4.4). Eggs and lids were challenged with separate pathogen cocktails (6 strains/serovars): Salmonella enterica, Escherichia coli O157:H7, Listeria monocytogenes, and Staphylococcus aureus.
Results: It took 5 and 9 days respectively for the pH to fall below 4.6 for 5% and 2.5% AA-brined eggs. Sodium benzoate did not affect acidification rate (P ≥ 0.05). No difference in pathogen die-off was observed between brines with and without preservative. E. coli O157:H7, Salmonella and L. monocytogenes were undetectable by enrichment (< 1 CFU/g), with eggs in 5% AA brine at 72 hours; S. aureus was undetectable after 7 days. In 2.5% brine, Salmonella was undetectable after 10 days; no pathogens were detectable by 14 days. No pathogens were detectable on lids within 72 hours for 5% AA brines. Only S. aureuswas detectable on lids after 72 hours in 2.5% AA brine and died off rapidly at ambient temperature.
Significance: Although pathogens studied on eggs begin die-off under refrigeration, heat treatment (ambient temperature storage) was required to reach undetectable levels; minimal inversion was adequate treatment for lids. Pickled eggs should be held under refrigeration for the length of time needed to acidify them to ≤ 4.6, and then held at ambient temperatures to ensure pathogen inactivation.