Effect of initial oxygen concentration and film oxygen transmission rate on the quality of fresh-cut romaine lettuce

Modified atmosphere packaging (MAP) is widely used to maintain the quality of fresh-cut produce by matching the oxygen transmission rate (OTR) of the packaging film to the respiration rate of the packaged product. The effect of the interaction between film OTR and the initial headspace O-2 on quality of fresh-cut vegetables has not previously been reported. Romaine lettuce leaves were sliced, washed, dried and packaged with film OTRs of 8.0 and 16.6 pmol s(-1) m(-2) Pa-1, and with initial headspace O-2 of 0, 1, 2.5, 10 and 21 kPa. Packages were hermetically sealed and stored at 5 degrees C for up to 14 days. For samples packaged in 16.6 OTR film, increasing the initial headspace O-2 concentration delayed O-2 depletion within the packages, hastened the onset and increased the intensity of discoloration, and inhibited the development of CO2 injury, acetaldehyde and ethanol accumulation, off-odors and electrolyte leakage. With 8.0 OTR-packaged lettuce pieces, 51 kPa initial headspace O-2 treatments induced an essentially anaerobic environment within the packages and increased acetaldehyde and ethanol accumulation and off-odor development. Increasing the initial O-2 concentration above 1 kPa in 8.0 OTR packages transiently increased O-2 concentrations and reduced fermentative volatile production, off-odors, electrolyte leakage and CO2 injury. Regardless of initial headspace O-2 concentration, all 16.6 OTR-packaged samples had severe discoloration after 14 days of storage. Quality was better maintained in 8.0 OTR-packaged lettuce pieces as the initial headspace 02 concentration was increased. A 21 kPa initial 02 treatment of 8.0 OTR-packaged lettuce maintained good quality throughout storage and had the best overall quality score. (c) 2005 Society of Chemical Industry.