Effects of oxygen-depleted atmospheres on survival and growth of Listeria monocytogenes on fresh-cut Iceberg lettuce stored at mild abuse commercial temperatures

摘要

The effects of oxygen-depleted atmospheres, 0.25% O_2 +12% CO_2 (balance N_2) and 2% O_2 + 6% CO_2 (balance N_2), on growth of Listeria monocytogenes on fresh-cut Iceberg lettuce were determined. The study was carried out at mild abuse temperatures using controlled atmosphere chambers. During storage at a constant temperature of 7 ℃, growth was enhanced at the lower oxygen level of 0.25% O_2 by Day 10. Over 17 days of storage at temperatures designed to mimic mild abuse commercial conditions, there were again significantly higher counts under 0.25% O_2 from Day 10 onwards. These were 0.9 and 0.7 log cycles higher on Days 14 and 17, respectively. When a model lettuce agar medium was used to eliminate possible interactions with competing flora the direct effects of the atmosphere enhancing the growth of L monocytogenes was also observed. It is concluded that use of very O_2-depleted atmospheres for control of enzymatic browning of fresh-cut Iceberg lettuce may introduce a potential hazard under some commercial conditions. There is a need for greater vigilance and possibly additional measures to ensure consumer safety.