Identification of Factors Affecting the Deterioration Rate of Fresh-Cut Lettuce in Modified Atmosphere Packaging

Fresh-cut lettuce, stored in modified atmosphere packaging (MAP), is a frequent component of bagged salads. However, even in MAP, fresh-cut lettuce is highly perishable due to non-microbial deterioration manifested by tissue liquefaction. The present study investigated the effects of plant physiology, lettuce processing, storage conditions, and exogenous stimuli on the deterioration of fresh-cut lettuce stored in MAP. Tests were performed on genotypes with a known rate of deterioration after processing. Leaf maturity of slowly deteriorating cultivars was generally negatively correlated with the shelf life, i.e., younger leaves deteriorated more slowly than older leaves. Leaf maturity of rapidly deteriorating cultivars was positively correlated with the shelf life, i.e., younger leaves deteriorated more rapidly than older leaves. The deterioration rate increased with temperature. Larger salad pieces deteriorated slower than smaller pieces and pieces that had additional wounding. Packaged samples of smaller size (less tissue per MAP bag with a constant volume) usually had a slower deterioration rate than larger samples. Reduced humidity in MAP slowed the rate of deterioration, particularly for rapidly deteriorating cultivars. Ethanol and hexanal accelerated the deterioration process of all cultivars in a dose-dependent manner. Sanitization of lettuce with chlorine, or treatments with abscisic acid, methyl jasmonate, salicylic acid, melatonin, or calcium lactate, had no obvious effect on the deterioration rate at the tested concentrations. This work provides insights into factors that need to be optimized to slow the rate of physiological deterioration of fresh-cut salad and identifies the most suitable conditions to reveal genotypic differences among lettuces.