Table 1_Aroma metabolism during the low-temperature storage of Hami melons: volatile odor-active compounds, precursors, and enzyme activity.docx

To explore the regulatory effect of low-temperature storage on the aroma quality of Hami melons, this study examined the dynamic changes in their aroma precursors, enzyme activities, gene expression profiles, and odor-active compounds content following storage at 3 °C. The low-temperature group exhibited significantly lower levels of primary odor-active compounds—including esters, alcohols, and aldehydes—than the ambient-temperature group, with the greatest disparity observed on day 6 (1211.33 μg/kg). Odour activity value analysis revealed that (E)-2-nonene (609.49), β-ionone (434.00), and ethyl 3-methylbutyrate (184.82) contributed most significantly to the aroma of Hami melons. Notably, low-temperature storage markedly reduced the activity of ACSL, BCAT, ADH, AAT, and CCD7 while also downregulating the genes encoding these enzymes, including CmADH, CmBCAT, and CmACSL. Among these enzymes, CCD7 exhibited the greatest difference in activity between the low- and ambient-temperature groups at 18 d of storage (81.04 U/L). Concurrently, low temperature was found to markedly inhibit the degradation of fatty acids, amino acids, and β-carotene in Hami melons. Linoleic acid and palmitic acid reached peak concentrations at 18 and 12 d of storage (519.16 mg/kg and 537.70 mg/kg, respectively), while the levels of amino acids and carotenoids remained generally lower than those of fatty acids (0–20 mmol/kg). Correlation analysis demonstrated significant associations between the activities of enzymes such as HPL, ADH, and BCAT and the levels of both aroma precursors and final odor-active compounds. This study provides a theoretical basis for optimising post-harvest storage methods and maintaining flavour quality in Hami melons.