Effect of low oxygen modified- and controlled-atmospheres on quality attributes and microbial population dynamics in fresh-cut iceberg lettuce

Fresh-cut iceberg lettuce is usually packed in bioriented propylene bags under equilibrium modified atmosphere (E-MAP). Within 3 days of packaging, the concentration of oxygen is near zero. The anaerobic atmosphere prevents pinking and browning of cut edges but stimulates the development of lactic acid bacteria. These bacteria release lactic and acetic acids giving rise to sour off-smell and product deterioration. The effect of storage of fresh-cut iceberg lettuce at 7°C under controlled atmosphere (CA) condition with low, but not zero, oxygen content was investigated. During E-MAP storage the expected rise in lactic acid bacteria and associated sour off-smell was detected, whereas pinking and browning of cut edges was greatly delayed. Under CA condition with approximately 0.5 kPa oxygen the development of lactic acid bacteria was much less pronounced and sour off-smell was absent. The low oxygen CA condition could not, however, prevent pinking of cut edges. Application of packaging solutions that allow low concentrations of oxygen can potentially prolong the shelf life, but additional measures to prevent pinking should be taken.