Thermal resistance of Listeria monocytogenes and background microbiota in unsalted and 10% salted liquid egg yolk

Abstract

Listeria monocytogenes is a major foodborne pathogen that may contaminate liquid egg yolk (LEY). A background microbiota, purified and identified as Enterococcus faecium with a 99.0% probability, was found in pasteurized unsalted LEY. This study was conducted to investigate the thermal resistance of L. monocytogenes and the background microbiota in unsalted and 10% salted LEY at temperatures between 55 and 67.5 C.Both Weibull model and linear survival model were used to analyze the survival curves.Data analysis showed that the thermal resistance of E. faecium was not affected by the addition of 10% salt in LEY, and it was almost two orders in magnitude higher than that of L. monocytogenes in unsalted LEY. Adding 10% salt to LEY significantly elevated the thermal resistance of L. monocytogenes to the level of E. faecium. It can be concluded that the heating conditions used to inactivate L. monocytogenes or Salmonella Enteritidis would not be able to kill E. faecium if it is found in unsalted LEY, while similar heating conditions can be used to kill both L. monocytogenes and E. faecium in 10% salted LEY.The results of this study may be used to design adequate heating conditions to inactivate L. monocytogenes and E. faecium in LEY. Practical applicationsSalted liquid egg yolk (LEY) contaminated with L. monocytogenes may require higher temperature or longer time to process. This study determined the thermal processing conditions that may be required to inactivate L. monocytogenes. The results attained from this study may be useful to the food industry that uses 10% salted LEY in the products.