| Citrus contain high levels of antioxidant and hygienical components, and are rich sources of Vc, flavonoids and other antioxidants which can be ingested by people. Thus, it has been focus to open out and utilize the antioxidants of citrus. To open out and utilize the antioxidants in reason, it is necessary to know the change of their content during fruit maturation and senescence, and to seek appropriate storage technique. This study is to evaluate the change of enzyme and non-enzyme antioxidants in 'Cara cara' navel orange(Citrus sinensis cv. Cara cara), 'Newhall' navel orange(C. sinensis cv. Newhall), and 'Sanguine' orange(C. sinensis cv. Sanguine), and to estimate the effect of salicylic acid (SA) preharvest treatment on antioxidant quality of 'Cara cara' navel orange pulps during the storage. The main contents and results in the present study are as follows:(1) The changes of active oxygen species(AOS) contents and antioxidant enzymes activities during the orange fruit developmentThe contents of hydrogen peroxide, superoxide anion radical and malondialdehyde in the pulps and peels in three cultivars of sweet orange('Cara cara' navel orange, 'Newhall' navel orange, and 'Sanguine' orange) increased throughout fruit ripening. In the most of developing stage, the 'Newhall' navel orange contained the highest levels, whereas the 'Sanguine' orange had the lowest contents. The tendencies of changes in enzyme activities were resembled in the same tissue of the three cultivars of sweet orange. In the pulps, the highest activities of catalase(CAT), superoxide dismutase(SOD), guaiacol peroxidase(G-POD), ascorbate peroxidase(AsA-POD) and dehydroascorbate reductase (DHAR) were detected at the initial stage(June 15), and the lowest activities were found at harvest stage(December 15). In the peels, the activities of glutathione reductase(GR), G-POD and AsA-POD decreased along with fruit ripening, but the tendencies of changes in SOD and CAT activities were V-shaped curves and DHAR was double-peaked curve. In the most of developing stage, the highest activity of antioxidant enzymes was found in 'Cara cara' navel orange and the lowest level was present in 'Newhall' navel orange. In addition, the activities of all enzymes in peels were significant higher than pulps in the same cultivar.(2) The changes of antioxidant components during the orange fruit development and estimate in antioxidant capabilityIn pulps, the tendencies of change in the glutathione(GSH), total phenolics and flavonoids contents, together with ferric reducing/antioxidant power(FRAP) value, O2 (?) scavenging capacity and H2O2-scavenging capacity, were∧-shaped curves. There were significantly positive correlations between antioxidant capability(FRAP value, O2 (?) scavenging capacity and H2O2-scavenging capacity) and antioxidant component(GSH, total phenolics and flavonoids) contents. However, there was no significantly positive correlation between AsA contents and antioxidant capability(p＞0.05). In peels, the contents of AsA, GSH, total phenolics, flavonoids, FRAP, O2 (?) scavenging capacity and H2O2-scavenging capacity constantly descended during orange fruit development, and the max values of them were shown at the initial stage of fruit growth. The significantly positive correlations existed between all of antioxidant components and FRAP value, O2 (?) scavenging capacity or H2O2-scavenging capacity. The all antioxidant components contents and FRAP value in 'Cara cara' navel orange were higher than those in 'Newhall' navel orange. The contents of all antioxidant components in peels were significant higher than pulps in the same cultivar. Thus it can be seen, the young fruits which were discarded in fruit thinning and physiological drop and peels were good sources of natural antioxidants. Especially, 'Cara cara' navel orange may be an excellent variety to develop antioxidant and hygienical components.(3) The effect of SA-preharvest-treatment with different concentration on sugar and organic acid content in 'Cara cara' navel orange during harvest and storage periodSA-preharvest-treatment significantly increased contents of glucose and fructose at the fruit harvest stage and 1.0 mmol/L SA showing the best result compared with other concentrations. However, the effect of SA-preharvest-treatment on sucrose varied with different concentrations. For example, the content of sucrose increased by 3.55％when the concentration of SA was 0.25 mmol/L, and it decreased by 2.35％when the concentration of SA was 1.0 mmol/L. On the other hand, there was no effect on citric acid and malic acid when the concentration of SA was lower, but SA-preharvest-treatment with 1.0 mmol/L significantly increased malic acid content and 2.0 mmol/L SA makes against accumulating in citric acid. In comparison with control fruit, the content of total soluble solid and total soluble sugar in SA-preharvest-treatment fruit had no difference when the fruit harvested, but there was significant decrease in content of titratable acid and soluble protein and the decrease degree was considerably enhanced by increasing SA supply. During the fruit storage, the content of sucrose decreased and SA-preharvest-treatment could hold it back. At the end of storage, the fruit with 0.25 mmol/L SA treated had the highest sucrose content. However, the tendencies of glucose and fructose were double-peaked curves, and SA-preharvest-treatment significantly increased their contents, furthermore, the fruit with 2.0 mmol/L SA treated had the highest glucose and fructose contents. One the other hand, SA-preharvest-treatment could slower the decrease in citric acid and malic acid in the fruit during storage. To citric acid, the restraining effectiveness was considerably decreased by increasing SA supply, but the opposition was found on malic acid. (4) The effect of SA-preharvest-treatment with different concentration on antioxidant components content and capability in 'Cara cara' navel orange during harvest and storage periodSA-preharvest-treatment significantly increased antioxidant components(lycopene,β-carotene, AsA, GSH, total phenolics and flavonoids) content and antioxidant capability (FRAP value) at the fruit harvest stage and the increase degree was considerably enhanced by increasing SA supply. The contents of lycopene,β-carotene, AsA, GSH decreased with fruit storage, whereas total phenolics and flavonoids constantly increased. At the same time, SA-preharvest-treatment also significantly increased antioxidant components content during the fruit storage period and the best concentration of SA was 2.0 mmol/L. The antioxidant capability enhanced at first and then decreased, and at the 45 d of storage, it reached the peak which was 1.41～1.80 times than that in harvest stage. At the end of storage (105 d), the FRAP value in fruit with 1.0 or 2.0 mmol/L SA was significant higher than that in control fruit, reached 1.28 and 1.23 times, respectively.(5) The reciprocity effect of SA-preharvest-treatment and storage temperatures on antioxidant character in 'Cara cara' navel orange during harvest and storage period'Cara cara' navel orange which was potted in greenhouse was sprayed by 2.0 mmol/L SA at preharvest, storing at low temperature(6℃) and room temperature(20℃). The effect of SA and storage temperature on antioxidant components and capability was tested. The results showed: SA-preharvest-treatment significantly increased activities of SOD, GR, DHAR and contents of AsA, lycopene,β-carotene, total phenolics and flavonoids in fruit at harvest stage. At the same time, it also significantly increased antioxidant capability. However, there was no remarkable effect of SA on activities of AsA-POD and CAT, as well as contents of DHAsA, GSH and GSSG. SA-preharvest-treatment and low temperature significantly increased the contents of antioxidant components(AsA, GSH, lycopene,β-carotene, total phenolics and flavonoids) and FRAP value in the fruit during storage. It was suggested that SA-preharvest-treatment combining with lower storage temperature could maintain the higher nutrition and health protection value. On the other hand, SA-preharvest-treatment also significantly increased activities of antioxidant enzymes in fruit during storage, whereas there was some restraint effect at lower storage temperature. During the whole storage, storage temperature and SA had no interaction on CAT, AsA-POD, DHAsA and GSSG. However, they had significant interaction on other components at some storage stage.
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