Effects of process severity on survival and growth of Escherichia coli and Listeria innocua on minimally processed vegetables

The effects of different slicing methods on subsequent growth and survival of Escherichia coli, Listeria innocua, and background microflora, during storage (8 °C) on modified atmosphere packaged vegetables (sliced carrots, sliced iceberg and butterhead lettuce) were evaluated. E. coli and L. innocua were used as models for E. coli O157:H7 and Listeria monocytogenes. Gas atmospheres within packages of minimally processed vegetables (MPV) were monitored to identify any effects of slicing treatments on oxygen and carbon dioxide levels. In general, the slicing method had no significant effect on initial inoculation levels. L. innocua grew better and E. coli survived better on vegetables sliced with blades that caused the most damage to cut surfaces. Slicing manually with a blunt knife or with machine blades gave consistently higher E. coli and L. innocua counts during storage than slicing manually with a razor blade. The effects of hand tearing were similar to slicing with a razor blade. The slicing method also affected the growth of the total background microflora; razor sliced vegetables tended to have lower counts than other treatments. Results also indicated that product respiration was affected by slicing method.