Effects of regulated deficit irrigation at different times on organic acids, phenolics and antioxidant capacity of Cabernet Sauvignon grapes

• RDI at different growth stages reduced the contents of tartaric acid and malic acid in grape berries. • During the berry expansion stage, the 40 % RDI treatment significantly increased the total flavonoid content in grape berries. • During the veraison stage, the 40 % RDI treatment significantly increased the total anthocyanin content in grape berries. • During the veraison stage, the 40 % RDI treatment significantly enhanced the ferric reducing antioxidant power (FRAP) and the 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging capacity of grape skins. • The DPPH radical scavenging rate was significantly positively correlated ( p < 0.05) with the contents of total phenols, total tannins, and total flavonoids. Regulated deficit irrigation (RDI) is an effective strategy for improving grape quality while conserving water resources, particularly in arid regions. In this study, the effects of regulated deficit irrigation (RDI) at different growth stages on the organic acids, phenolic compounds, and antioxidant capacity of ripening berries of Cabernet Sauvignon grapes from the Ningxia region of China were evaluated over two consecutive years (2023 and 2024). The study compared 100 % full irrigation with RDI treatments at 80 %, 60 %, and 40 % during the berry expansion stage, and at 80 %, 60 %, and 40 % during the veraison stage. The findings of the study demonstrated that RDI treatments administered at varying stages of grape development resulted in a reduction in the levels of tartaric and malic acid in the fruit. The 40 % RDI treatment resulted in a significant increase in the total flavonoid content of grapes during the expansion period, meanwhile the 60 % RDI treatment led to a substantial increase in the total tannin content during the expansion period. Furthermore, the 40 % RDI treatment caused a notable increase in the total anthocyanin content of grapes during the veraison period. The 40 % RDI treatment at the veraison stage significantly enhanced the FRAP iron-reducing antioxidant capacity and DPPH scavenging rate of grape skins. In addition, a significant ( p < 0.05) positive correlation was observed between the DPPH radical scavenging rate and total phenols, total tannins, and total flavonoids. Furthermore, substantial variations in the content of catechins, chlorogenic acid, and gallic acid were identified between the 40 % RDI treatment at veraison and CK. In conclusion, the implementation of appropriate irrigation strategies at different stages of the grape's reproductive life increased the phenolic content and antioxidant capacity of wine grapes while conserving water, but showed a decrease in the organic acids of the grape berries.