Temporal shifts in phenolic composition and antioxidant responses of two Turkish grape cultivars (‘Kureyş’ and ‘Tahannebi’) during berry development

Phenolic compounds play a vital role in grape quality, antioxidant potential, and stress resilience; therefore, tracking their variation across developmental stages is essential for both viticultural practices and functional food production. The aim was to characterize variety-specific phenolic dynamics and antioxidant activity changes to guide optimized harvest timing and functional quality improvement. In this regard, present study evaluated the accumulation patterns of phenolic compounds and antioxidant activity across berry developmental stages from EL-27 (Eichhorn–Lorenz phenological scale) to EL-41 in two grape (Vitis vinifera L.) cultivars, ‘Kureyş’ and ‘Tahannebi’. A total of 17 phenolic compounds were quantified by high-performance liquid chromatography (HPLC-DAD), and total phenolic content (TPC) and antioxidant activity were determined by Folin–Ciocalteu, ABTS (2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid), and DPPH ((1,1-diphenyl-2-picrylhydrazyl) assays. Significant differences (p < 0.001) were observed between varieties, phenological stages, and their interactions for all analyzed compounds. In general, phenolic concentrations peaked during the early stages (EL-27: K1, T1) and declined progressively through EL-31 (K2, T2), EL-33 (K3, T3), EL-35 (K4, T4), EL-36 (K5, T5), EL-38 (K6, T6), and EL-41 (K7, T7). ‘Kureyş’ consistently exhibited higher levels of gallic acid, catechin, chlorogenic acid, and caftaric acid, with chlorogenic acid decreasing by 98.8% from EL-27 to EL-41. In contrast, ‘Tahannebi’ showed lower initial concentrations but retained specific compounds like ellagic acid and p-coumaric acid longer. Multivariate analyses revealed distinct metabolic clustering. PCA explained 85% of total variance, with early-stage samples characterized by enriched antioxidant profiles. Correlation analysis indicated strong associations among TPC, antioxidant capacity (ABTS, and DPPH) assays, suggesting coordinated biosynthetic regulation. Hierarchical clustering clearly distinguished early high-phenolic samples (e.g., K1, T2) from late-stage samples (K7, T7) with reduced biochemical activity. Overall, this study highlights genotype-dependent differences in phenolic composition and antioxidant capacity during grape ripening, offering integrated insights into their physiological basis and implications for harvest optimization, nutraceutical enhancement, and breeding for functional quality.