Atmosphere modification extends the postharvest shelflife of fresh- cut leafy Asian brassicas

Abstract

Many leafy Asian brassicas are common constituents of fresh-cut pre-packaged salads. Brassicas in use include pak choy, tatsoi, mizuna and mibuna, choy sum and Chinese mustard. At retail temperatures (eg. 10oC) however, postharvest shelf-life of these vegetables can be severely curtailed by leaf yellowing. Atmosphere modification of oxygen and carbon dioxide was found to retard leaf yellowing of all brassicas tested. Both oxygen and carbon dioxide alone and in combination were found to have considerable impact on shelf-life. Carbon dioxide (2-15%) in combination with oxygen (1-4%) generally increased shelf-life of vegetables. A 2% O2 + 5% CO2 atmosphere increased shelf-life of Chinese mustard, pak choy, choy sum, tatsoi and mizuna by 153, 112, 105, 86 and 40%, respectively. Mibuna, which was the least tolerant to carbon dioxide, achieved a 70% increase in shelf-life by 2% O2 alone. Generally, injury occurred for all brassicas at 25% CO2. Although 0.5% O2 was usually conducive to extending shelf-life, leaves appeared more susceptible to carbon dioxide injury, with injury common when in conjunction with 10-15% CO2. Vegetables tended to fall into three groups based on response to atmosphere. Pak choy, tatsoi and choy sum all responded well to carbon dioxide up to 15%, mizuna and mibuna responded poorly to carbon dioxide above 5%, and Chinese mustard responded best to carbon dioxide when in combination with low oxygen. These groupings tended to follow taxonomic relationships. It is suggested that a combination of intermediate oxygen and carbon dioxide concentrations (eg. 2% O2 + 5% CO2) would be more suitable for modified atmosphere packaging, where fluctuations in the cold-chain can cause package atmosphere to vary away from the ideal. With the exception of mibuna, all vegetables responded well to this atmosphere, which would allow easy mixing of Asian brassicas with each other, as well as with pre-cut lettuce, which has a similar atmosphere optimum.