Identification of factors affecting the deterioration rate of fresh-cut lettuce in modified atmosphere packaging

Authors: PENG, HUI - University Of California; Sthapit Kandel, Jinita; MICHELMORE, RICHARD - University Of California; Simko, Ivan

Submitted to: Food and Bioprocess Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/21/2020
Publication Date: 10/27/2020
Citation: Peng, H., Sthapit Kandel, J., Michelmore, R.W., Simko, I. 2020. Identification of factors affecting the deterioration rate of fresh-cut lettuce in modified atmosphere packaging. Food and Bioprocess Technology. 13:1997–2011. https://doi.org/10.1007/s11947-020-02538-2.
DOI: https://doi.org/10.1007/s11947-020-02538-2

Interpretive Summary: Lettuce is an important leafy vegetable produced in many countries around the world. Fresh-cut lettuce is a common component of bagged salads, which have become highly popular in the U.S. and other parts of the world. Fresh-cut lettuce stored in ambient packaging is subject to several problems such as wilting, pinking, and browning. Modified atmosphere packaging (MAP) using low oxygen and high nitrogen has been used to prevent these problems by increasing relative humidity in the MAP and reducing damaging oxidation of the cut lettuce. Fresh-cut lettuce in MAP is, however, still inclined to show discoloration, off-odor, tissue breakdown, water-logging, or turning to completely to liquid, which leads to substantial waste. This non-microbial deterioration is affected by internal, e.g., genetics and physiology, and external, e.g., processing and storage, factors. We comprehensively examined factors potentially associated with deterioration rate of fresh-cut lettuce in MAP, including plant physiological status, salad processing procedure, storage environment, and treatments with compounds known to affect plant physiological processes. This study provided further evidence of critical involvement of storage temperature and wounding on the rate of deterioration, and identified the effects of other factors on deterioration of fresh-cut lettuce in MAP, such as leaf maturity, product quantity, relative humidity, and treatment with ethanol, and hexanal. Comprehensive information on the influence of multiple deterioration-associated factors will allow us to precisely control and evaluate deterioration rate of fresh-cut lettuce, which is needed in order to identify and sequence gene(s) involved in the deterioration process, and to develop new strategies to prolong the shelf life of fresh-cut lettuce.

Technical Abstract: 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. 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). In contrast, leaf maturity of rapidly deteriorating cultivars was positively correlated with the shelf life, i.e., younger leaves deteriorated more rapidly than older leaves). 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 constant volume) usually had a slower deterioration rate than larger samples. Reduced humidity in MAP slowed the rate of deterioration, particularly for the rapidly deteriorating cultivars that were evaluated. 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 deterioration of high-quality fresh-cut salad.