Reduction of active oxygen metabolism and mitigation of chilling injury in Hami melon fruit as influenced by postharvest hot water treatment

Abstract: In the present study, we examined the effect of heat-treatment on chilling injury and active oxygen metabolism in Hami melon. Hami melon "Xizhoumi 25" was used in this experiment. The fruits were immersed fully in hot water of 55℃ or normal water at (22±2)℃ for 3 min, and then stored at (3-5)℃ for 35 d. Quality and physiological changes in fruits were measured during the storage period. The results showed that the contents of H2O2 and O2- in heat-treated fruits were higher than the control fruits within the first 14 d, which indicated that a prompt increase in H2O2 and O2- was induced after the treatment, and the accumulation achieved the maximum on the 14th day (P<0.05), but the treatment reduced the H2O2 and O2- accumulations at the middle and later period of storage (from the 14th to the 35th) (P<0.05). The active oxygen signal played a key role in cold resistance of fruit. Through improving the activities of peroxidase (POD) (P<0.05) and superoxide dismutase (SOD) (P<0.05), a higher scavenging capacity of reactive oxygen free radical was maintained, and the increase of cell membrane relative permeability except for the 21st day (P<0.05) and malondialdehyde (MDA) (P<0.05) from the 21st to the 35th day were inhibited effectively. So the heat-treatment reduced the chilling injury, prevented the loss of total soluble solids and ascorbic acid contents, and it could better maintain the quality of Hami melon. But the activities of POD and SOD of control fruits were lower than the heat-treatment fruits during the cold storage, and H2O2 and O2- content increased obviously at the middle and later periods of the storage, which led to the accumulation of reactive oxygen species, promoted the membrane lipid peroxide, and ruined the regionalization of the cell membrane; the cell membrane permeability and plasmalemma peroxide produced the MDA accumulation in great quantities, and eventually the serious chilling injury occurred on the 35th day. The control fruits showed the serious water loss shrinking and the weightlessness rate was 6.61% after moved to room temperature; the chilling injury rate of control fruits was 27% higher than that of the heat-treatment. Therefore, this method is effective to reduce the chilling injury of postharvest fruit storage and has a certain popularization value and application prospect. These results suggest that heat-treatment may induce active oxygen signal molecule, improve the active oxygen scavenging enzyme activities, delay membrane lipid peroxidation process, and thereby prevent the development of chilling injury in Hami melon fruit. The results provide a theoretical reference for Hami melon postharvest storage.