Diurnal Dynamics of Essential Oil Yield and Chemical Profile in Helichrysum italicum (Roth) G. Don: Identifying the Optimal Harvest Window

This study evaluated the effect of harvest time on the essential oil (EO) yield and chemical composition of Helichrysum italicum (Roth) G. Don subsp. italicum. The research was conducted in Afyonkarahisar during the 2023 growing season. Inflorescences were harvested at seven different times between 06:00 and 18:00 at 2-hour intervals. EOs were extracted via hydrodistillation and analyzed using GC/FID-MS. Results showed that EO yield varied between 0.30% (06:00) and 0.47% (14:00). The highest number of volatile compounds (36) was observed at 08:00. Major constituents exhibited distinct diurnal accumulation patterns. γ-curcumene reached its maximum level at 06:00 (23.60%). Neryl acetate peaked at 14:00 (23.59%), while α-pinene reached its highest concentration at 18:00 (28.97%). Additionally, 3-decen-2-one reached 16.73% at 12:00. Multivariate analyses revealed descriptive intraday shifts between sesquiterpene- and monoterpene-rich profiles. These findings provide a scientific basis for defining optimal harvest windows to meet specific industrial and pharmacological standards.