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 mu m thickness) or unperfo rated (25, 30 or 40 mu m thickness) polypropylene films were stored up to 2 weeks at 2 degrees C (storage period) and then held for 2.5 days at 12 deg rees 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, wilt ing, physiological disorders, bacterial decay and quality were monitored. I n all treatments, both slight severity of pink rib and russet spotting occu rred. Brown stain and heart leaf injury were only detected on heads in unpe rforated bags. Low oxygen was generally related to a high quality score. Pa ssive MAP in 40 mu m PP and active (initial 5% O-2 and 0% CO2) MAP in 30 mu m PP were the best treatments for overall visual quality. Vacuum-cooling r educed both pink rib and heart-leaf injury but the effect only showed up du ring shelf-life period. (C) 2000 Canadian Institute of Food Science and Tec hnology. Published by Elsevier Science Ltd. All rights reserved.