Effect of post-harvest UV-C radiation application on resveratrol and tannin concentrations in table grapes

Table grapes (Vitis vinifera L.) are among the most consumed fruits due to their antioxidant power, which is based on their high concentration of compounds such as tannins and resveratrol. However, the application of post-harvest treatments is necessary to increase the shelf life of this fruit, as well as to improve its organoleptic and nutritional properties. The objective of this work was to determine the effect of UV-C radiation on the resveratrol and tannin content of different table grape cultivars during the storage period. For this purpose, table grape fruits of the Red Globe and Muscatel varieties were subjected to different doses of UV-C radiation (0.3, 0.6, and 1.2 kJ/m²) and subsequently stored for 24 h. To evaluate the effect of UV-C radiation on the two grape varieties, the Bate--Smith reaction was used to determine the tannin content, while the resveratrol concentration was quantified by HPLC after extraction (80:20 v/v), maintained at 60ºC for 30 min. The effect that UV-C radiation had on the organoleptic and nutritional quality of table grapes was highly dependent on the variety. When UV-C radiation was applied at doses of 0.3 and 0.6 kJ/m², the ripening process of the berries was slowed down, increasing the shelf life of these fruits. For the Red Globe variety, the 0.3 kJ/m² dose was the most effective in terms of tannin and resveratrol content, increasing from 92.50 to 122.83 mg/kg and from 11.94 to 30.34 mg/kg, respectively. Regarding the Muscatel variety, the most effective dose was 1.2 kJ/m², even with a reduced shelf life, with an increase of 257.5% in tannins and 238.2% in resveratrol compared to the control (0 kJ/m²). It was concluded that further studies on radiation doses, times, and storage conditions are necessary to establish scalable results.