Integrating Sensory Evaluation and Metabolomics to Reveal the Metabolic Basis of Taste and Flesh Color in Melon (Cucumis melo L.)

Background: The sensory quality of melon (Cucumis melo L.) is determined by the complex interplay of metabolites within the fruit. However, the underlying metabolic mechanisms based on consumer sensory experience remain underexplored. Methods: Sensory evaluation was conducted on twelve melon cultivars, recording flesh color and quantitatively scoring acidity, sweetness, firmness, and aroma intensity. Based on the sensory results, eight cultivars were selected to establish two contrasting groups: sweet-type vs. acidic-type and orange-fleshed vs. green-fleshed. Untargeted metabolomics (UPLC-QTOF-MS) was then performed to analyze the samples, and differential metabolites were screened using OPLS-DA combined with univariate analysis. Results: Pathway enrichment analysis revealed that the key distinction between sweet and acidic taste profiles was associated with the specific accumulation of citric acid within the tricarboxylic acid (TCA) cycle in the acidic-type group. Regarding flesh color, the orange-fleshed group was enriched with carotenoid derivatives like β-citraurinene and the oxidized tocopherol product α-tocopherolquinone, whereas the green-fleshed group mainly accumulated phytol, a chlorophyll degradation product, along with more abundant terpenoids. Conclusions: By integrating sensory phenotyping with metabolomic analysis, this study identified key differential metabolites and candidate pathways associated with taste and color in melon, providing metabolic insights and data resources for quality evaluation and regulation.