Harvest month and time of day impact the content, chemical composition, and antioxidant activity of the essential oil of Tetradenia riparia (Hochst.) Codd

Harvest month and time of day may alter the content, composition, and bioactivity of essential oils in medicinal plants. In this study, we aimed to identify the optimal harvest month and time of day that enhance the content, chemical composition, and antioxidant activity of essential oil obtained from Tetradenia riparia . Different harvest months (May, June, and July) and diurnal times (08:00, 11:00, 14:00, and 17:00 h) were evaluated in 2021 and 2022. Antioxidant activity was assessed using the DPPH, FRAP, and ABTS •+ assays. Essential oil content differed among the examined harvest months and times. In 2021, the highest contents were recorded in May (0.52% at 08:00 h and 0.51% at 11:00 h). In 2022, the highest contents were found in May and June, reaching 0.61% and 0.65% at 17:00 h. Chemical composition was impacted by both harvest month and time. In 2021, fenchone (13.52%) and α-cadinol (12.80%) predominated in June and July at 08:00 and 14:00 h, respectively. In 2022, caryophyllene oxide (18.54%) and 14-hydroxyhumulene (28.50%) predominated in May and July, respectively, at 17:00 h, whereas fenchone (25.10%) predominated in July at 08:00 h. The highest antioxidant activity was recorded at 14:00 h in May 2022 in the ABTS assay (1,052.73 µg TE mg⁻¹ EO). In conclusion, harvest month and time determine essential oil content, composition, and antioxidant activity in T. riparia . May and June harvests favored higher essential oil content, whereas afternoon harvests increased antioxidant potential and profiles rich in terpenes. These data support commercial harvest scheduling for industrial applications.