Effect of harvest time on total phenolic and flavonoid contents and antioxidant capacities of two grape varieties from Trebinje vineyard area

The aim of this study was to analyse the effects of harvest timing on the total phenolic and flavonoid contents, in addition to the total antioxidant capacity in the berries of ‘ilavka’ and ‘Vranac’ varieties grown in the Trebinje vineyard area. Grape samples for both varieties were collected at three distinct points during their ripening. The chosen harvest dates were set 10 days apart, and the optimal date for grape harvesting was determined by assessing the sugar content and titratable acidity present in the grapes. Total phenolics, total flavonoids and total antioxidant activity of grape samples were determined by the Folin-Ciocalteu method, aluminium chloride method, and ferric reducing antioxidant power assay, respectively. The total phenolic and flavonoid contents, along with the total antioxidant capacity in the ‘Vranac’ grape, increased from the first to the second harvest date, but a decline was noted at the third harvest. ‘ilavka’ grape exhibited an increase in total phenolic and flavonoid contents, as well as total antioxidant capacity from the first to the second harvest date, with no decrease recorded by the third harvest. As expected, the red grape variety ‘Vranac’ contained higher levels of phenolics and flavonoids than the light-skinned grape variety ‘ilavka’.