Changes in phenolic compounds, enzymatic and non‐enzymatic antioxidant properties in “Thompson Seedless” grape after UV‐C irradiation

Abstract

In this study, the influence of postharvest UV-C irradiation on phenolic compounds, enzymatic and non-enzymatic antioxidants was assessed in table grape “Thompson Seedless” during short storage. The berries were exposed to UV-C at doses of 0, 0.8, 1.2, and 4.2 kJ/m2 and then stored at 15°C for 6 d to simulate retail condition. The result showed that UV-C treatment increased total phenolic content of the skin at the harvest time and its level remain unchanged during storage. Total flavonoid content of treated berries, however, dramatically increased. The increasing impact of UV-C on antioxidant activity of treated berries was evident; however, it varies in different assays performed. In contrast with PPO controlled under the lower doses of radiation, activity of PAL and POD were induced after irradiation. Similar to total phenolics, individual ones including catechin, quercetin, and rutin were largely affected by UV-C irradiation (especially at the doses of 0.8 and 1.2 kJ/m2), except epicatechin. These results indicated that mild doses of UV-C irradiation augmented the antioxidant capacity of table grapes, given a correlation between polyphenol content and these characteristics. Furthermore, along with the increased antioxidant enzymes, UV-C treatment could enhance berry tolerance to biotic and abiotic stress, which seems to need further research. Novelty impact statement Total phenols, flavonoids, and antioxidant potential of table grapes increased after UV-C irradiation. Although PAL and POD activity was increased under UV-C irradiation, lower doses of UV-C restricted the PPO activity. Contrary to epicatechin and resveratrol, UV-C irradiation induced catechin, quercetin, and rutin.