间歇升温对采后香蕉李贮藏中酶促褐变的影响

以香蕉李为试材，研究不同的间歇升温对低温贮藏的李果实酶促褐变的影响。结果表明，李果实在冷藏20d 时启动冷害，多酚含量和PPO 活性逐渐下降，冷害指数显著增大，果实正常后熟过程受阻。同时，低温胁迫诱导了SOD 活性的增加，而冷害又激发CAT 或POD 活性的上升，说明受冷害果实的保护酶系统在抵抗逆境胁迫方面具有一定的协同作用。随着贮藏时间的延长，MDA 含量逐渐上升，冷害和褐变程度加剧。而间歇升温提高了SOD、POD 和CAT 的活性，抑制了活性氧的积累，减弱了膜脂过氧化的程度，延缓了冷害的发生，特别是间歇升温到18℃抑制冷害的效果更好，促进果实逐渐后熟，延迟了果实的衰老进程。而间歇升温到10℃贮藏前期虽然对冷害症状有所缓解，但果实成熟老化速度较快，贮藏后期老化的果实不耐低温贮藏，导致冷害加剧，果实褐变现象严重。

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.