The antioxidant activity of grapes after different drying treatments

Abstract

The antioxidative capacity of fruits varies depending on the drying process applied. This study compared the antioxidant and radical scavenging capacities of some selected grape varieties after different drying treatment applications. Freeze and conventional hot air drying at 60, 80, and 100 °C were applied to white and black grapes from Türkiye. The total phenolic content, total anthocyanin content, and antioxidant capacities of selected samples were determined using spectrophotometric tests. Values of black grape samples increased mainly with freeze drying and 100 °C convective drying treatments for all spectrophotometric analyses (p < 0.05). On the other hand, fresh state and 100 °C convective dried white grapes exhibited the highest spectrophotometric results. Regarding spectrophotometric tests, white grapes produced by drying procedures at different temperatures did not display statistically meaningful variations, whereas the simultaneous evaluation of antioxidant activity tests and modified CUPRAC test of hydrogen peroxide scavenging carried out on dried black grapes gave comparable results. The HPLC evaluation of the differences in phenolic profiles of raisins after drying is investigated in the scope of this work and results from spectrophotometric assays were compared. Phenolic acids, flavanols, and several anthocyanins were detected using HPLC analysis. Anthocyanins were not detected in black grapes after conventional drying as expected. Oven drying enhanced the accumulation of some flavonols in white grapes.