Phenolics and Antioxidant Capacity of Basil (Ocimum basilicum L.) Genotypes Across Locations and Developmental Stages

Basil ( Ocimum basilicum L.) is a globally consumed edible herb whose phenolic fraction — dominated by rosmarinic acid and chicoric acid — is of direct relevance to dietary antioxidant intake and functional food formulation. Twelve basil genotypes were grown in a two-year field experiment at three ecologically contrasting Turkish locations: Bursa, Eskişehir, and Tokat. Agronomic performance, individual phenolic profiles (nine compounds by high-performance liquid chromatography–time-of-flight mass spectrometry, HPLC-TOF), total phenolic content (TPC; Folin–Ciocalteu), and antioxidant capacity by three assays — 2,2′-azinobis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH), and ferric reducing antioxidant power (FRAP) — were determined at all three locations. Developmental stage effects on phenolic composition were additionally characterised at the Bursa site. Genotype and location each exerted highly significant (p < 0.01) effects on all traits. Tokat consistently produced the highest rosmarinic acid (up to 131.8 mg 100 g⁻¹ dry weight [DW]; 91% above the Bursa site mean), TPC (up to 17.8 mg gallic acid equivalent [GAE] g⁻¹ DW), and antioxidant capacity (ABTS mean 90% above Bursa) across both years. At Bursa, vegetative-stage harvest maximised rosmarinic acid, while TPC peaked at full flowering. Genotype R-23 led for rosmarinic and chicoric acid across all locations; Y-7 achieved the highest TPC at Tokat; R-4 combined strong phenolic quality with competitive fresh herb yield. These outcomes provide an evidence-based framework for optimising basil as a high-antioxidant dietary ingredient.