Study flags up 'viable alternative' to chlorine as spinach decontaminant
The authors, writing in the Journal of Food Science, said the novel treatment improves the shelf life of minimally processed fruits and vegetables and results in a high level of microorganism inactivation using lower doses than the conventional irradiation treatments.
The researchers note that the FDA recently approved irradiation treatment of leafy greens such as spinach up to 1 kGy. But the study's authors said that it is important to reduce the dose required to decontaminate the produce while maintaining its quality.
The decontamination of minimally processed fruits and vegetables from food-borne pathogens, continue the researchers, presents technical and economical challenges to the produce industry. And they argue that internalized microorganisms cannot be eliminated by current leafy veg decontaminaton procedures such as water-washing or 200-ppm chlorine treatments.
They explained that the objectives of their research thus were to assess the radiation sensitivities of Salmonella spp. and Listeria spp. inoculated in ready-to-eat baby spinach leaves under MAP and irradiated using a 1.35-MeV Van de Graff accelerator at room temperature and furthermore they wished to understand and optimize the synergistic effect of MAP and irradiation.
"By understanding the mechanism of radiolysis of ozone and its decomposition, it is possible to optimize its production to enhance irradiation effectiveness in eliminating pathogenic microorganisms while maintaining the overall quality of fresh and fresh-cut produce," explained the scientists.
The authors found that a treatment by e-beam irradiation of 0.7 kGy on baby spinach leaves under 100 per cent oxygen at room temperature would assure a 5-log reduction of either Salmonella spp. and Listeria spp. without detrimental effects on product quality.
The team reported that Irradiation of baby spinach under high concentrations of oxygen should retain its quality throughout storage and could be successfully applied to foods to control disease and deterioration caused by microorganisms.
They said that their findings indicated that "increased concentrations of oxygen in the packaging significantly increased the radiation sensitivity of the test organisms, ranging from 7 per cent up to 25 per cent reduction in D10-values."
The authors found that radiosensitization, in particular, could be affected by the production of ozone, which rises with increasing dose-rate and oxygen concentration, and reducing temperatures. And they said that their results showed that: "radiosensitization was demonstrated for both microorganisms with irradiation of either fresh or frozen (−5 °C) baby spinach."
The researchers concluded that once ozone has completely decomposed approximately 1.5 hours after irradiation, the headspace composition inside the bag throughout the shelf life of spinach will be mainly oxygen and this modified atmosphere should not affect product quality during storage period.
Source: Journal of Food Science
Published online ahead of print
Title: Radiosensitization of Salmonella spp. and Listeria spp. in Ready-to-Eat Baby Spinach Leaves
Authors: C Gomes, R G. Moreira, E. Castell-Perez
