Influence of Packaging Treatments on the Keeping Quality of ‘Salinas’ Lettuce

Heads of lettuce (Lactuca sativaL., cv. ‘Salinas’) were individually wrapped or sealed in nonoriented perforated (22 μm thickness) or unperforated (25 or 50 μm thickness) new polypropylene (PP) films, and stored for 2 weeks at 2 °C plus 2·5 d at 12 °C. Vacuum cooling and/or active modification of the atmosphere within the package by flushing a gas mixture were applied. Quality of lettuce by scoring wilting, physiological disorders, bacterial decay and overall visual quality was determined. In naked heads stored in air and in lettuce wrapped in perforated PP, russet spotting and pink rib, the main disorders of lettuce during postharvest, developed. However, in all treatments with sealed PP bags, these disorders practically did not appear. Heart leaf injury and brown stain developed on lettuce sealed in PP bags, particularly after transfer to higher temperature. Pink rib and heart leaf injury mainly appeared in vacuum cooled lettuce. The reason for this susceptibility, that has not been previously reported, is unknown and additional research is needed to identify the factors involved. Low O2was related with high quality score. The best results were obtained in vacuum cooled lettuce packed in PP bags with initial 21·6 g/L O2and 0 g/L CO2atmosphere.