May low-temperature gas plasma be considered an innovative technique to decontaminate table eggs?

Contamination of table eggs by pathogens, mainly Salmonella enterica which is recognised as one of the main sources of food-borne outbreaks in Europe, represents a safety problem widely diffused all over the world, especially considering that no decontamination practice (e.g. cleaning or washing) is allowed in most European countries. The use of gas-plasma offers an original alternative to traditional decontamination techniques due to the intrinsic characteristics of this technology, i.e non-toxicity, atmospheric pressure and temperature, which results in minimal degradation of nutrients and change in food quality traits. The potentials of non-thermal gas-plasma treatments for the superficial decontamination of table eggs have been assessed in this work which has been supported by the EC-funded project RESCAPE (FOOD-CT-2006-036018) whose overall objective is to propose means to reduce the risk factors from eggs. The resistive barrier discharge prototype used to generate cold-plasma showed a good decontamination power towards both natural microflora and all the pathogens deliberately inoculated onto the surface of table eggs, i.e. Salmonella Enteritidis, Listeria monocytogenes, Escherichia coli and Bacillus cereus. The maximum cell load reductions ranged between 1.5 and 4 Log CFU/eggshell depending on the microbial species, time of exposure to the gasplasma and the relative humidity (RH) during the treatments. In particular, the most sensitive species were Listeria monocytogenes and Escherichia coli, while no cell reduction was observed for Bacillus cereus at the lowest RH value. However, the increase of the RH value during the gas-plasma treatments significantly improved the efficacy of the technology towards all the microorganisms resulting also in 1 Log CFU/eggshell inactivation for both spores and vegetative cells of Bacillus cereus. No recovery of the survivors was evidenced during a 30-days storage and cell counts detected in all treated samples resulted to be lower than the controls during the whole storage period. Moreover, the strongest gas-plasma treatment did not affect the main egg quality traits, i.e weight loss, egg shell breaking strength and stiffness, albumen pH and turbidity and yolk index.