The Reactive Oxygen Species Metabolic Mechanism Of Oleocellosis Induced By Orange Oil And Mechanical Injury In Postharvest Citrus Fruits

Citrus fruits were choosen as experimental materials. In sense organ evaluation, citrus fruits were treated with different concentrations orange oil and then stored at different temperature after 100% orange oil treatment. Besides, citrus fruits were also treated with mechanical damage and stored at different temperature after 300 r/min mechanical damage treatment. During induced time, citrus fruits were treated with 100%orange oil for 72 h, but 300r/min mechanical damage for 48 h, as non-treated fruits for comparison. During storage period, citrus fruits were treated oil and mechanical damage, but stored for 8 d. The treated and control fruit were individually packaged with plastic bags, and finally stored at 5℃and 85%-90%relative humidity (RH). In order to well understand the mechanisms of oleocellosis induced by orange oil and mechanical damage in citrus fruits, the text was measured MDA and H2O2 content, superoxide reductase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6) activity, peroxidase (POD, EC 1.11.1.7) activity, ascorbate peroxidase (APX, EC 1.11.1.11) activity, glutathione reductase (GR, EC 1.6.4.2) activity and polyphenoloxi-dase (PPO; EC 1.14.18.1) activity. Otherwise, the contents of Total phenols, flavonoid, ASA and GSH were measured; chlorophyll, carotenoid and anthocyanin content were also discussed. Moreover, DPA was used to control the oleocellosis in citrus peel. The main conclusions of this paper were as followed:(1) Oleocellosis in citrus peel showed a gradual increase as the concentrations of citrus oil increased. The most serious oleocellosis in citrus peel could arise from 100%citrus oil treatment. In addition, mechanical vibration stress also could induce oleocellosis in citrus peel. Mechanical vibration stress with 500r/min revealed the most obvious effect on oleocellosis formation. Moreover, citrus fruit treated with orange oil or mechanical vibration stress was also used to explore the effect of storage temperature on oleocellosis in their peels. As a result, citrus stored at 20℃or 0℃had the severest changes in oleocellosis. However, citrus had the slightest change in oleocellosis during 5℃storage.(2) In this experiment, our goal was to evaluate how oleocellosis induction and reactive oxygen species (ROS) metabolism in harvested navel oranges (Citrus sinensis L. Osbeck) may be affected by oil application and mechanical damage. Citrus were induced by orange oil, mechanical damage in this experiment. The results indicated that H2O2 content was enhanced by oil and mechanical damage treatment, superoxide reductase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11) or glutathione reductase (GR, EC 1.6.4.2) activities increased before 36 hours, but peroxidase (POD, EC 1.11.1.7) activity and ASA, GSH content decreased after oil and mechanical damage treatment. The results showed that POD activity and ASA, GSH may play an important part in clearing H2O2 to protect cell from damaged in the first stage. However, the activities of SOD, POD, CAT and GR decreased after 36 hours. Meanwhile, there was an increase in ASA, GSH contents and APX activity. The result showed that the activities of POD and CAT may be two of the main key enzymes in protecting cell from damaged in the later stage. Moreover, our study showed that chlorophyll content was enhanced by oil and mechanical injury treatments, but carotenoid content was stable. Total phenols content was inhibited and polyphenoloxi-dase (PPO; EC 1.14.18.1) activity was improved after 36 hours. The result showed that little phenols in intercellular space may cause intracellular phenols oxidation degraded. Thus, the colour of treated fruits had kept orange-yellow during induced time.(3) The result showed that fruits treated with oil and mechanical damage had a sudden increase in malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents which were much higher than control. Before 4 days storage, oil application and mechanical damage treatments effectively enhanced the activities of catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11), glutathione reductase (GR, EC 1.6.4.2), but decreased the activities of superoxide reductase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7) which might be the key enzymes in clearing reactive oxygen at the first stage. However, fruits with oil and mechanical damage treatments had an increase in SOD activity, but had lower CAT, POD, APX, GR activities than control after 4 days storage, which contributed to high H2O2 level. During storage, Navel orange peel had a notable change in chlorophyll content, which led to pale-green appeared in citrus peel during 2-4 day. Besides, there was a sharp increase in total phenols, flavonoid content and polyphenoloxi-dase (PPO; EC 1.14.18.1) activity, which might partly connect with browning in navel orange peel.(4) DPA treatment could effectively control oleocellosis of citrus peel, especially 7mM DPA treatment. Besides, DPA with Ca treatment had more effective than DPA treatment on oleocellosis of citrus. The results showed that DPA could control oleocellosis by decreasing membrane lipid per-oxidantion and increasing catalase (CAT, EC 1.11.1.6), peroxidase (POD, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.11), glutathione reductase (GR, EC 1.6.4.2) activities. Moreover, DPA could inhibit total phenols and chlorophyll content and PPO activity to decrease browning.