Influence of UV-C irradiation on some phytochemicals and antioxidant activities in ‘Sultana’ table grape skin

The effect of UV-C irradiation, either alone or in combination with other treatments, on the biosynthesis of secondary compounds in plants has been recently become a matter of interest. In this study, the influence of UV-C light on some phytochemical traits and activity of enzymes involved in phenolic metabolism in grape was investigated. At first, the berries of table grape cv. Sultana were subjected to UV-C irradiation in different doses of 0 (control), 0.8, 1.2, and 4.2 kJm-2, then they were kept at 15°C for 6 days. UV-C low doses induced total phenol in the berry skin. The lowest flavonoid content was observed in berries subjected to the highest dose of UV-C (4.2 kJm-2) on the first day, whereas those irradiated by the low dose of UV-C (0.8 kJm-2) had the most flavonoid content after 5 days (0.45 mg Rutin/g FW). Also, UV-C application improved antioxidant capacity of treated samples in comparison with control. It should be noted that UV-C irradiation had no effect on total tannin content of the berry skin. However, the effect of UV-C radiation on phenylalanine amonialyase (PAL) activity was remarkable during storage. The UV-C restricted the POD activity up to the middle of storage. However, in terms of polyphenol oxidase (PPO), this behavior was dosage-dependent. The results showed that UV-C application at the low doses is an appropriate way to increase phenolic content and antioxidant capacity of table grapes cv. Sultana during limited storage time.