Effect of Precooling and Harvesting at Different Times on Respiration, Browning and Microbial Growth of Fresh-cut Iceberg Lettuce

This study was carried out to investigate the effects of precooling and harvesting at different times on respiration, browning and microbial growth of fresh-cut iceberg lettuce (Lactuca sativa L. cv. U-lake). Iceberg lettuce was harvested at dawn (06:00) and midday (12:00), cooled immediately to 4℃ by precooling, and then transported under refrigerated condition. Iceberg lettuce leaves were cut, washed, dried and packaged into plastic bags (80 ㎛ Ny/PE) and stored at 5℃ for 12 days. Results indicated that respiration rate increased after cutting in all treatments and was lower in precooling treated lettuce than non-treated one. However, no significant difference in O₂ and CO₂ composition was found among treatments during storage. Precooling treatment was effective in inhibiting discoloration for up to 12 days. Samples treated with precooling had lower total phenol content, and a similar tendency was also observed in the result of discoloration development by sensory test. Although precooling treatment having lower aerobic microbial count (5.3 log) than control (6 log) before processing, precooling did not affect microbial population of packaged samples during storage.