Effect Of Different Abiotic Factors On Postharvest Quality And Reactive Oxygen Species Metabolism Of 'okubao' Peach Fruit

This dissertation is to evaluate the effects of abiotic factors, including physical factors (storage temperature, fruit stem) and chemical factors (1-methylcyclopropene, calcium), on postharvest quality and reactive oxygen species (ROS) metabolism of'Okubao'peach fruits. The conclusions were obtained as follows:(1) Ripening of peach fruits was delayed when stored at 8°C, 5°C and 1°C , and the accumulation of H₂O₂ and lipoxygenase (LOX) activity, membrane lipid peroxidation as well as the increase of superoxide scavenging activity were significantly reduced. However, peach fruits easily developed chilling injury at 5°C compared to 1°C, and storage at 1°C could delay the the increase of superoxide anion (O₂^-) as well as the decline of superoxide dismutase (SOD) and LOX activity alone with superoxide scavenging activity.(2) The stem of peach fruit could significantly retard the decrease rate of membrane integrity during the periods stored at 5°C as well as after 3 days of post-storage ripening at 20°C, which might contribute to the reduction of membrane lipid peroxidation, the inhibition of the decline of ascorbate peroxidase (APX) activity and peroxidase (POD) activity, as well as the accumulation of H₂O₂ . However, the influence was dependent on fruit position and storage time.(3) The delay of peach ripening by 1-methylcyclopropene (1-MCP) was dependent on fruit maturity, and more efficiency was observed in fruit with lower maturity. 1-MCP significantly retarded fruit softenging, delayed the decline of membrane integrity and superoxide dismutase (SOD) activity as well as the increase of juice extraction rate in peach fruits with lower maturity. In addition, it could be observed that 1-MCP significantly delayed the accululation of malondialdehyde (MDA) content, total antioxidant activity, superoxide scavenging activity, DPPH radical-scavenging activity as well as the decline of catalase (CAT) and ascorbate peroxidase (APX) activity,alone with the increase of peroxidase (POD) activity in fruits with lower maturity, at early stage of storage at 20°C.(4) 1-MCP retarded the decrease of fruit firmness and the increase of juice extraction rate as well as the loss of membrane integrity, alleviated membrane lipid peroxidation during at both 20°C and 8°C. 1-MCP treatment inhibited the decrease of total antioxidant activity, DPPH radical-scavenging activity, total phenol and total flavonoid concentration of peach fruits stored at 20°C, but the influence of on 1-MCP antioxidant activities of peach fruits was dependent on storage time at 8°C. (5) 1-MCP retarded the decrease lipoxygenase (LOX) activity, SOD activity and antioxidant ability, alleviated the loss of membrane integrity and accumulation of H₂O₂ whereas improved the glutathione (GSH) content of peach fruit during early periods of storage at 0°C. In contrast, 1-MCP delayed the declined of antiociant ability and fruit softening, but accelerated the accumulation of H₂O₂, the loss of membrane integrity, and the decline of APX activity during the shelf-life period of later stage of storage at 0°C.(6) At 0°C, calcium treatment delayed fruit softening and of juice extraction rate raising, allevated the damage of membrane integrity, inhibited the decrease of CAT, APX and POD activity, but improved the glutathione (GSH) content, superoxide scavenging activity and DPPH radical-scavenging activity. In contrast, 1-MCP significantly elevated the decrease degree of fruit firmness and membrane integrity and increase degree of juice extraction rate, but reduced the decrease degree of CAT, APX and POD activity as well as the increase of H₂O₂ content, MDA content and lipoxygenase (LOX) activity during shelf-life after low temperature storage.(7) Correlation analysis for physical factors showed significant positive relativity between membrane lipid peroxidation and antioxidant activities, whereas significant negative relativity between membrane lipid peroxidation and antioxidant activities by correlation analysis for the effects of 1-MCP on peach fruits.