Effect of packaging treatments and vacuum-cooling on quality of winter harvested iceberg lettuce

Heads of winter harvested iceberg lettuce (Lactuca sativa L. cv. Coolguard) individually packed or sealed in perforated (22 μm thickness) or unperforated (25, 30 or 40 μm thickness) polypropylene films were stored up to 2 weeks at 2°C (storage period) and then held for 2.5 days at 12°C (shelf-life period). Five packaging treatments together with passive or active modification of the atmosphere within the package were applied. Vacuum-cooling was superimposed on these five treatments. Weight loss, wilting, physiological disorders, bacterial decay and quality were monitored. In all treatments, both slight severity of pink rib and russet spotting occurred. Brown stain and heart leaf injury were only detected on heads in unperforated bags. Low oxygen was generally related to a high quality score. Passive MAP in 40 μm PP and active (initial 5% O₂ and 0% CO₂) MAP in 30 μm PP were the best treatments for overall visual quality. Vacuum-cooling reduced both pink rib and heart-leaf injury but the effect only showed up during shelf-life period.