Study On The Effects And Mechanism Of UV-C Treatment On Quality Regulation Of The Post-harvest Citrus Fruit

Short wave ultraviolet (UV-C) irradiation on harvested fruits and vegetables is a physical preservation method, which is in accordance with the trend of pursuit of consumers on safe and nutritious food. The citrus are rich in many kinds of biological active components such as flavonoids, limonoids and phenolic acids, and demonstrate very good antioxidant activity. Therefore, the improvement of quality and flavonoids antioxidants by ultraviolet irradiating on post-harvest fruits and vegetables has important meaning in the regulation of fruit and vegetable quality.The rotting incidence, main quality parameters and flavonoids and total phenol contents were analyzed in harvested Mandarin fruit after irradiated with different doses of UV-C and stored at 15℃. The result showed that treatments withl.5 and 3 kJ/m doses of UV-C delayed rotting infection by 6 and 12 days, and reduced rotting rate by 42.9% to 85.7% as compared to untreated fruits after 27 days of storage.1.5 and 3 kJ/m2 doses of UV-C irradiation reduced weight loss, increased SSC, SS/TA and vitamin C contents, and promoted synthesis and accumulation of flavonoids and total phenol, therefore maintained better quality and nutrition of Mandarin fruit.1.5 and 3 kJ/m2 doses of UV-C irradiation also improved the content of flavonoid and total phenol in fruit peel. These results demonstrated that UV-C treatment has the potential as a non-chemical tool for extending the shelf life of harvested Mandarin fruit.The rind pitting, chromatism index and the ultra-structural of peel were analyzed in harvested "honey" Mandarin fruit after irradiated with3 kJ/m2 doses of UV-C and stored at 15℃. The result showed that treatments with 3 kJ/m2 doses of UV-C reduced the rind pitting rate during the late period of storage, increased L value (P＜0.05), and decreased a value and a/b ratio, then therefore delay the senescence of Mandarin fruit. The epidermal cells of Mandarin fruit after irradiated with3 kJ/mz doses of UV-C still arranged regularly and densely. These results demonstrated that UV-C treatment helped in maintaining normal appearance and function of the epidermal cells of Mandarin fruit.The changes of antioxidant activity in harvested Mandarin fruit treated with 3 kJ/m2 doses of UV-C were analyzed. FRAP value, DPPH scavenging capacity and activity of PAL and POD in Mandarin fruit were analyzed. Gradient elution of RP-HPLC was used to analyze the content of phenolics. These results demonstrated that UV-C treatment showed high antioxidant activities by two antioxidant activity assays, increased PAL and POD activity, and improved the content of caffeic acid, p-Coumaric acid and Ferulic acid in the fruit.