Intermittent Warming Effects on Enzymatic Browning of Plum Fruits during Postharvest Cold Storage

Fresh plum fruits were subjected to prestorage treatment by intermittent warming and the effect of intermittent warming on enzymatic browning of plum fruits was examined during postharvest cold storage (at 0 ℃). Results showed that after 20 d of storage, chilling injury in plum fruits started to appear, the content of polyphenol and the activity of polyphenol oxidase (PPO) were decreased gradually, the index of chilling injury was increased significantly, and the normal fruit postripening was blocked. Meanwhile, the activity of superoxide dismutase (SOD) was induced by low temperature, and the activities of peroxidase (POD) and catalase (CAT) were stimulated by chilling injury. These results demonstrate the synergistic effect of antioxidant enzyme system against environmental stress. With prolonged storage time, the content of malondialdehyde (MDA) was increased gradually and chilling injury and browning were aggravated. Intermittent warming led to increased activities of SOD, POD and CAT, inhibited accumulation of reactive oxygen species and reduced level of lipid peroxidation and thereby delayed the occurrence of chilling injury. An intermittent warming to 18 ℃ significantly inhibited chilling injury and promoted fruit postripening, thereby delaying fruit aging. Despite alleviated chilling injury during the early storage, plum fruits subjected to intermittent warming to 10 ℃ exhibited accelerated postripening and aging and poor resistance to low temperature during the late storage so that chilling injury was aggravated and severe browning was observed.