Aroma metabolism during the low-temperature storage of Hami melons: volatile odor-active compounds, precursors, and enzyme activity

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.