Differences in Non-Anthocyanin Phenolics and Antioxidant Capacity of 27 Red Grapevine Varieties Grown in Northern Portugal

Climate change imposes significant challenges on vitiviniculture, increasing the need to identify more resilient grapevine varieties. While red grape varieties are known for their high anthocyanin content, other phenolic compounds should also be considered when assessing adaptability to biotic and abiotic stresses. For this, the phenolic composition and antioxidant capacity of 27 red <i>Vitis vinifera</i> L. varieties grown in Portugal were studied across two years. Under warmer and drier conditions, most varieties exhibited higher total phenolic content (TPC) and antioxidant activity, with 'Donzelinho Tinto' and 'Zinfandel' displaying the most pronounced increases. These varieties also had the highest increases in phenolic acids and flavan-3-ols, highlighting how environmental stress modulates secondary metabolites. Varieties such as 'Aragonez', 'Trincadeira', 'Touriga Franca', and 'Tinta Francisca', demonstrated stable profiles, indicating a robust response to climatic fluctuation. Correlation analysis revealed strong associations between TPC and antioxidant capacity, highlighting the importance of phenolics in mitigating oxidative stress. By identifying varieties with enhanced phenolic and antioxidant plasticity, the diversity observed in this work offers valuable insights for future varietal selection aimed at mitigating climate change-induced challenges. Overall, this work reinforces the potential of varietal selection to promote sustainable viticulture in regions increasingly impacted by climatic variability.