A universal hypoxic threshold and genotype-dependent metabolic decoupling determine postharvest shelf life of fresh-cut lettuce

Fresh-cut lettuce is one of the most commercially important and perishable products in the fresh-cut vegetable industry. Tissue deterioration following processing is driven by a complex interplay of genetic, physiological, and preharvest factors determining both respiration rate and membrane stability. Fifteen accessions of Lactuca sativa were evaluated across 15 independent experiments spanning production environments, leaf developmental stages, storage temperatures, and processing conditions. Nine respirometric parameters were assessed for their capacity to predict electrolyte leakage (electrical conductivity, EC), a measure of membrane deterioration. Across three analytical approaches (Pearson correlation, partial least squares, and random forest), Time Under Hypoxia (TUH) was the strongest predictor of EC, while CO₂ area was the most robust continuous metabolic predictor. A universal critical oxygen threshold of approximately 0.50% O₂ was identified as the anaerobic compensation point, below which both the Gas Stability Index (GSI) and EC diverged sharply from their baselines, independent of cultivar, leaf age, and production environment. Temperature sensitivity (Q 10 ) was similar for O₂ consumption (3.0) and EC (2.9), but EC was disproportionately sensitive to the 2–13 °C shift (Q 10 = 4.3 vs. 1.9), underscoring the importance of cold-chain maintenance. A meta-analysis revealed a borderline non-significant correlation between CO₂ area and EC across cultivars (r = 0.489, p = 0.062), with perfect concordance between the favorable qSL4 allele and low deterioration regardless of respiration rate. A 10-day jar assay predicted 37-day MAP performance with high accuracy (r = 0.764, p = 0.0004), validating it as a rapid platform for postharvest screening and breeding.