Effect of superatmospheric oxygen packaging on sensorial quality, spoilage, and Listeria monocytogenes and Aeromonas caviae growth in fresh processed mixed salads

Atmospheres with O-2 levels higher than 70 kPa have recently been suggested as an innovation to modified atmosphere packaging (MAP) for fresh processed vegetables to maintain sensory quality and safety. In the present work, mixed vegetable salad collected from a commercial processing plant and stored with the MAP technique was studied. Two gas mixtures were actively generated by using an initial O-2 concentration of 95 kPa and combined with two plastic films. The low-barrier film permeability for O-2 was 1,629 mlO(2)/m(2) X 24 h X atm with 30 mum of thickness (Hyplast, Hoogstraten, Belgium) and the O-2 permeability of the hiah-barrier film was 2 mlO(2)/m(2) x 24h X atm. with 150 mum of thickness (Euralpack, Wommelgen, Belgium) at 23degreesC. As control, active conventional MAP with application of 3 to 5 kPa of O-2 and 6 to 8 kPa of CO2 was used. Packaged salads were stored up to 8 days at 4degreesC and at temperatures simulating chilled distribution chain conditions. Microbial safety and sensory quality, as well as the survival of inoculated Listeria monocytogenes and Aeromonas caviae, were monitored. The effect of superatmospheric O-2 On the growth of aerobic microflora was variable. Under superatmospheric conditions, lactic acid bacteria and members of Enterobacteriaceae were inhibited. Nevertheless, growth of yeast and A. caviae seem to be stimulated by superatmospheric O-2, whereas growth of psychrotrophic bacteria and L. monocytogenes was not affected. The overall visual appearance (mainly color) of the mixed vegetable salads was better maintained and the shelf life prolonged when packaged under O-2 concentrations greater than 50 kPa.