TY - JOUR T1 - IImpacts of diurnal variation on essential oil properties and antioxidant activity of endemic Origanum dubium Boiss TT - Diurnal varyasyonun endemik Origanum dubium Boiss'in uçucu yağ özellikleri ve antioksidan aktivitesi üzerine etkileri AU - Maral, Hasan PY - 2025 DA - September Y2 - 2025 DO - 10.46309/biodicon.2025.1644458 JF - Biological Diversity and Conservation JO - BioDiCon PB - Ersin YÜCEL WT - DergiPark SN - 1308-5301 SP - 342 EP - 348 VL - 18 IS - 3 LA - en AB - Purpose: This study aimed to investigate the impact of diurnal variation on the essential oil (EO) yield, chemical composition, and antioxidant activity of Origanum dubium Boiss., an endemic and carvacrol-rich species naturally distributed in Türkiye.Method: The aerial parts of O. dubium were collected at five different harvest times during the flowering stage (06:00, 09:00, 12:00, 15:00, and 18:00) in Ermenek (Türkiye) in 2020. Essential oils were obtained by hydrodistillation using a Clevenger-type apparatus and analyzed by GC-FID/MS. Antioxidant activity was evaluated by the DPPH radical scavenging method.Findings: The EO content ranged between 6.4% (12:00) and 8.6% (18:00). Oxygenated monoterpenes (79.9–88.0%) were the dominant group, with carvacrol (72.0–83.4%) as the main compound. The highest carvacrol concentration was recorded at 09:00, whereas the lowest was at 12:00. Other major constituents were α-thujene (1.3–1.5%), γ-terpinene (1.9–6.3%), and p-cymene (4.0–5.4%). Antioxidant activity varied significantly depending on the harvest time, with radical scavenging activity ranging from 32.21% (06:00) to 63.90% (18:00).Conclusion: Diurnal variation significantly influences the EO yield, composition, and antioxidant activity of O. dubium. The results suggest that harvesting between 06:00–12:00 in the morning and 15:00–18:00 in the afternoon is optimal for obtaining higher oil yield, carvacrol content, and antioxidant potential. KW - essential oil KW - Origanum dubium KW - diurnal variation KW - carvacrol KW - anttioxidant activity KW - DPPH N2 - Amaç: Bu çalışmada, endemik ve karvakrolce zengin bir tür olan Origanum dubium Boiss.’un uçucu yağ (UY) verimi, kimyasal bileşimi ve antioksidan aktivitesi üzerine günlük değişimlerin etkisinin araştırılması amaçlanmıştır.Yöntem: O. dubium bitkisinin toprak üstü kısımları, 2020 yılında Türkiye’nin Ermenek (Karaman) ilçesinde, çiçeklenme döneminde beş farklı hasat zamanında (06:00, 09:00, 12:00, 15:00 ve 18:00) toplanmıştır. Uçucu yağlar, Clevenger tipi aparat ile su distilasyonu yöntemiyle elde edilmiş ve GC-FID/MS cihazında analiz edilmiştir. Antioksidan aktivite, DPPH serbest radikal süpürme yöntemiyle belirlenmiştir.Bulgular: UY oranı %6.4 (12:00) ile %8.6 (18:00) arasında değişmiştir. Oksijenli monoterpenler (%79.9–88.0) baskın grup olup, karvakrol (%72.0–83.4) ana bileşen olarak tespit edilmiştir. En yüksek karvakrol oranı 09:00’da, en düşük değer ise 12:00’da kaydedilmiştir. Diğer önemli bileşenler α-tujene (%1.3–1.5), γ-terpinen (%1.9–6.3) ve p-simen (%4.0–5.4) olmuştur. Antioksidan aktivite hasat zamanına göre önemli farklılık göstermiştir ve serbest radikal süpürme aktivitesi %32.21 (06:00) ile %63.90 (18:00) arasında değişmiştir.Sonuç: Günlük değişimlerin O. dubium’un UY verimi, bileşimi ve antioksidan aktivitesi üzerinde önemli etkileri olduğu belirlenmiştir. Sonuçlar, daha yüksek yağ verimi, karvakrol içeriği ve antioksidan potansiyel elde etmek için sabah 06:00–12:00 ile öğleden sonra 15:00–18:00 saatleri arasında hasadın uygun olduğunu göstermektedir. CR - [1] Sirin, E., & Ertuğrul, K. (2015). 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