Changes in Biochemical and Bioactive Compounds in Two Red Grape Cultivars during Ripening and Cold Storage

The market value of grapes (Vitis vinifera L.) is affected by their quality and harvesting time. Veraison and stage of ripening are the most important factors determining table grape quality. Therefore, the present research was performed to determine the effects of various ripening stages on the combination and postharvest quality of two red grape cultivars. Based on color change, fruits were harvested at the veraison stage, two weeks after the veraison stage, and at the full ripening stage. Fruits harvested at the fully ripe stage were stored for 7, 14, and 21 days (at 1 °C with 85–90% relative humidity). The greatest soluble solids content (SSC) (16.1%) and SSC/TA ratio were observed in ‘Khoshnav’, while the greatest titratable acidity (TA) (0.45%) and pH (3.60) were observed in ‘Rashah’. The results of the present study showed that regardless of the storage period, fruits harvested at time V (veraison time) and two weeks after veraison (2WAV) had significantly higher firmness and vitamin C content. ‘Khoshnav’ had the lowest weight loss (2.05%), and ‘Khoshnav’ and ‘Rashah’ had the greatest firmness (5.95 N) and vitamin C content (89.48 mg 100 g−1 FW). The greatest anthocyanin content was observed on day 7 of storage in ‘Rashah’. Total phenol (TP) and total flavonoid (TF) contents and antioxidant capacity (AC) increased significantly until harvest and decreased thereafter during cold storage. ‘Rashah’ showed the greatest AC, TP, and TF values. Based on the findings of this study, the ‘Rashah’ grape cultivar is shown to be rich in vitamin C, anthocyanins, flavonoids, phenolics, and antioxidants. It holds potential for utilization in both processing and breeding programs as a functional food ingredient.