Application of high pressure processing for prevention of greenish-gray yolks and improvement of safety and shelf-life of hard-cooked peeled eggs

Hard-cooked peeled eggs (HCEs) are value-added ready-to-use egg products susceptible to microbial re-contamination during post-processing stages. A post-processing terminal step using high hydrostatic pressure (HHP 500, 550, 600 MPa for 5 min at 25 °C) was applied to ensure maximum safety of HCEs and the effects of processing were evaluated and compared with a commercial thermal post-processing intervention using steam heating. A significant discoloration in the form of greenish-gray yolks was observed in HCEs after steam heat post-processing due to overcooking. Color values of the HCE yolk (L*, a*, b*) after HHP post-processing were not significantly different (P > 0.05) from non-post-processed HCEs. Non-thermal and thermal post-processing interventions each kept the growth of microbial contaminants at < 10⁴ CFU/g throughout 45 days of refrigerated storage. Microbial counts in non-post-processed HCEs exceeded this safety limit within 3 d. Sensory analysis showed significantly higher preference scores for the quality attributes of HCEs post-processed with HHP than with steam heating. Inactivation curves of Salmonella Enteritidis inoculated onto HCE surfaces after all HHP levels were well-fitted to the biphasic mathematical model. HHP post-package pasteurization at 550 MPa for 5 min showed potential as a terminal non-thermal kill step for commercial production of HCEs. Industrial relevance A non-thermal post-processing intervention using HHP can be considered as a terminal kill step during commercial production of HCEs to ensure maximum microbiological safety and to extend the shelf life of HCEs without formation of unappetizing greenish-gray yolks. The biphasic mathematical model can be used to predict growth and survival of Salmonella Enteritidis in HCEs and to conduct a risk analysis of this type of food products.