Growing Site and Cultivar Effects on Fruit Quality, Phenology and Antioxidant Capacity of Sweet Cherry (Prunus avium L.) Cultivars in Eskişehir, Türkiye

This study compared four sweet cherry cultivars—Regina, Sweetheart, Kordia and 0900 Ziraat—at two sites of contrasting altitude in Eskişehir province, Türkiye: Eskişehir (792 m) and Sarıcakaya (220 m). Across two growing seasons (2016–2017; n = 64), phenological stages were recorded and fruit were assessed for eighteen pomological traits and three phytochemical measures—total phenolic content (TPC), total flavonoid content (TFC) and DPPH radical scavenging activity. Location affected almost every pomological trait measured: fruit from the cooler Eskişehir site were heavier and more intensely red, whereas fruit from the warmer Sarıcakaya site had higher soluble solids content and acidity, and reached bud break and bloom roughly 13 days earlier. TPC, TFC and DPPH activity were all higher at Eskişehir than at Sarıcakaya (TPC: 1071.0 vs. 823.3 mg GAE kg−1 FW; TFC: 344.3 vs. 234.6 mg CE kg−1 FW; DPPH: 45.5% vs. 22.5% inhibition; p < 0.001). Kordia stood out with the highest antioxidant activity and was also among the cultivars richest in phenolics and flavonoids. TPC and TFC were strongly correlated (r = 0.93), and both tracked with skin redness and lower titratable acidity. Overall, growing location, rather than cultivar, was the strongest factor behind the pomological, phenological and phytochemical differences observed over the two study years.