The visual quality of minimally processed lettuces stored in air or controlled atmosphere with emphasis on romaine and iceberg types

Five different types of lettuce (iceberg, romaine, butter, green leaf, and red leaf) were prepared as salad pieces and stored for 16 days at 5 degrees C in air or in a controlled atmosphere (CA) (3% O-2 + 10% CO2). Samples were evaluated for overall visual quality, surface and edge browning, and russet spotting. After 8 days, differences in overall visual quality between air and CA-stored samples were observed; after 12 days, air-stored samples were below the limit of salability, whereas visual quality was maintained in CA-stored pieces from all lettuce types except butter lettuce. Transferring lettuce to air for 12 h at 15 degrees C accentuated the differences between storage atmospheres. An analysis of the various components of overall visual quality showed that surface and edge browning were the defects which most contributed to a decrease in quality. Among the lettuce types studied, the CA benefit for overall visual quality was highest for iceberg lettuce, and some differences between cultivars were observed. There was no CA benefit for butter lettuce, but CA induced surface discoloration and tissue softening. Pre-processing storage of lettuce heads at 5 degrees C for 7 and 14 days negatively affected overall visual quality and leaf edge browning of the prepared salad pieces; this intact head storage effect was more evident on romaine than iceberg pieces.