| The characters of PPO in'Dahongpao'pomegranate fruit peel were studied. The physiological and biochemical characteristics of peel of fruits treated with 1-MCP and DPA were determined during storage in order to elucidate the mechanism of peel browning. At the same time, the relation between antioxidants and peel browning was analyzed. The results were as followed:1. The optimum temperature and pH for PPO activity was 40℃and 7.0, respectively. Citric acid could significantly inhibit the activities of PPO, ascorbic acid was also effective, but sodium sulfite andβ-cyclodextrin were less effective. Tannin had the biggest affinity with PPO among three substrates tested and was possibly the natural substate of PPO. Citric acid and heating treatment before storage may reduce PPO activities directly or decreases the pH value, and be a useful way to control pomegranate peel browning.2. The effects of 1-MCP on physiological and biochemical characteristics of pomegranate fruits in storage were studied. Browning index of fruit treated with 1-MCP decreased obviously. 0.5μl/L 1-MCP gave the browning decrease of 35% after 7 weeks storage. The 1-MCP lowered ethylene production, PPO activity, but had not significantly effects on total phenols and free phenols content; delayed the decomposition of anthocyanins in peel, and decreased malondialdehyde (MDA) level. The effect of Diphenylamine (DPA) was also compared with 1-MCP; DPA has lower effects on controlling pomegranate peel browning. Above all, 0.25μl/L- 1.0μl/L 1-MCP delayed the senescence of Dahongpao pomegranate and inhibited the peel browning to some extent. It was considered that the senescence of non-climatic fruits (at least pomegranate) was related to ethylene which is one of the signal molecules of senescence.3. The relation between peel browning and antioxidants in pomegranate fruit peel was analyzed. The result showed that the content of water soluble antioxidants was not but the content of lipid soluble antioxidants was correlative to peel browning. The lipid soluble antioxidants may play an important role in preventing peel browning.4. Radical scavenging activities of water soluble extracts from leave, fruit peel, seeds and juice of pomegranate were measured by the 1, 1-diphenyl-2- picrylhydrazyl (DPPH) and 2, 2'-Azinobis 3- Ethyl -benzothiazoline -6- Sulphonate (ABTS) methods. In the both methods, compared to seeds and juice, both leaf and peel exhibited very strong antioxidant activities and high polyphenol contents. The polyphenol contents were clearly correlative to antioxidative activities. Therefore, the peel and leaves of pomegranate showed the potential market value, especially the peel. The antioxidative capacities between pomegranate juice and apple juice, orange juice were also compared. The pomegranate juice as a healthful drink is obviously higher than the apple juice and the orange juice to two kinds of free radicals elimination strength, and apple juice showed the lowest both DPPH and ABTS radical scavenging activities. Compared with leave and peel, seeds of pomegranate had the lowest antioxidant activity. |
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