Antioxidative activity associated with chilling injury tolerance of muskmelon (Cucumis melo L.) rind

‘Galia’ melon (Cucumis melo L. var. reticulatus) is a climacteric fruit with a short storage life. To prevent over-ripening, fruits are stored at 4–6 °C, which also results in chilling injury (CI) that appears as numerous brown spots on the surface of the fruit. It has been suggested that exposure of ‘Galia’ fruits to high growth temperatures in the field renders them sensitive to low storage temperatures. Activity profile of the antioxidative enzymes catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX) and glutathione reductase (GR) was monitored in the rind of ‘Galia’ fruits during low-temperature storage, to associate each enzyme's activity with CI incidence. Experiments were performed with low-temperature-sensitive and tolerant varieties, 5080S and 1537T respectively, and included a pre-storage treatment of hot-water wash of 5080S fruits.Results suggested that SOD and POD activities play a general role in the rind's response to low temperatures and are not directly related to CI tolerance. APX activity showed varying levels and its association with development/prevention of CI symptoms remains unclear. However, activity profiles of GR and CAT suggested a role for these enzymes in CI tolerance of ‘Galia’ melon rind. Reduced activity of CAT in the rind of 5080S fruits was associated with CI development while unchanged or induced activity was monitored when no symptoms were observed. Likewise, lack of CI symptoms in the rind of 5080S fruits was associated with a significant induction of GR activity. Pre-storage hot-wash treatment resulted in induced CAT activity, which may contribute to the cold tolerance of the rind and prevention of CI development. However, GR activity was reduced following the heat treatment, which may explain the susceptibility of the fruit to CI following growth at high field temperatures.The present work emphasizes the need to develop ‘Galia’ melon varieties with an efficient antioxidative system to prevent the development of CI symptoms while preserving the high-quality taste and aroma characteristic of these fruits. Increasing the activities of CAT and GR could be the prime target in such breeding programs.

Research highlights
► ‘Galia’ melons are climacteric fruits, well known for their excellent organoleptic characteristics of aroma and taste.
► Due to short storage life and to prevent over-ripening, fruits are stored at 4–6 °C—a condition that results in chilling injury (CI) that appears as numerous brown spots on the surface of the fruit and reduce its marketability.
► The present work monitored for 3 years the activity profile of 5 antioxidative enzymes in the rind of CI sensitive and tolerant melon varieties during cold storage
► Results suggested a role for glutathione reductase and catalase in preventing CI development.