Delaying Deterioration of Romaine Lettuce by Vacuum Cooling and Modified Atmosphere Produced in Polyethylene Packages1

Abstract

Abstract Yellowing and decay of leaves were reduced when romaine lettuce (Lactuca sativa L. cv. Hazera Yellow) was prepackaged in closed polyethylene (PE) bags in which O2 concentration was reduced by flushing with N2. Similar, but less effective results were obtained when the lettuce was prepackaged in closed PE bags (not flushed with N2 gas), or when open bags were placed in PE-lined cartons, as well as when lettuce was vacuum precooled after packaging in open bags. Vacuum precooling of PE-lined cartons of lettuce did not further delay deterioration, since the process of vacuum cooling eliminated the modified atmosphere previously produced in PE liners. The efficacy of PE-lined cartons and that of closed PE bags in delaying deterioration of lettuce was related to reduction of O2 and accumulation of CO2 in the ambient atmosphere in the package. Concentrations of CO2 in PE-lined cartons, which reached 8 to 12% at the end of holding at 18 to 20°C following storage at 1°C, had no adverse effect on romaine lettuce. However, about 64% of the heads of ‘Great Lakes’ lettuce packed in similar packages during cold storage showed CO2 damage, even when CO2 was not higher than about 3%.