Quality changes of hydroponically produced leaf lettuce (Lactuca sativa L., cv. Cheongchima) during postharvest storage

Leaf lettuce is much more popular than head lettuce in Korea, and is produced year-round using hydroponics. Maintaining the freshness of leaf lettuce during postharvest handling and storage is important, yet difficult because of the tender, thin and broad nature of leaf lettuce. Quality changes in leaf lettuce during postharvest storage at 20 degrees C and 4 degrees C were studied. The shelf-life of leaf lettuce to the limit of visual acceptance by the consumer was 4 days when the lettuce was stored in a polyethylene film-lined caton (PE film; 0.03 mm thick) in an environmental room set at 20 degrees C and 50% RH, and 10 days when it was stored in PE pouch at 4 degrees C in a refrigerator. At the end of shelf-life, the lettuce stored at 20 degrees C kept ca. 81% of the relative fresh weight (RFW), 82% of the water-soluble protein (WSP), 61% of the vitamin C (VC), and 54% of the chlorophylls (CHL), and the lettuce stored at 4 degrees C had ca. 87% of the RFW, 41% of the VC, and 64% of the CHL, as compared to initial levels at harvest. Considering the important role of fresh vegetables in supplying vitamin C, and much easier loss of vitamin C in the leaf lettuce kept at lower temperature, the shelf-life of leaf lettuce is recommended to be the period allowing for the preservation of 80% of the vitamin C. The shelf-life meeting this requirement was 3 days for both lettuce stored at 20 degrees C and 4 degrees C.