Non-targeted LC-MS metabolomics reveal shifts from wound-induced enzymatic browning to lignification during extended storage of fresh-cut lettuce in modified atmosphere packaging

Modified Atmosphere Packaging (MAP) is a conventional method used to prolong the shelf-life of fresh-cut vegetables, including lettuce. However, MAP-stored lettuce remains perishable, and its deterioration mechanism is not fully understood. Here, we utilized non-targeted LC-MS metabolomics to evaluate the effects of cutting and extended storage time on metabolite profiles of lettuce stored in MAP. Additionally, hyperspectral imaging was used to measure perceptual changes. Our findings reveal a bipartite response to wounding. In early storage, enzymatic browning was the main response to wounding, evidenced by accumulation of caffeic acid derivatives and flavonoids, substrates for polyphenol oxidases. As storage progressed, enzymatic browning was inhibited, and a shift towards lignification became apparent, evidenced by accumulation of monolignol derivatives. These findings offer new insights into the deterioration mechanism of fresh-cut lettuce occurring in MAP.