Comparative Chemical Composition and Antioxidant Properties of the Essential Oils of three Sideritis libanotica Subspecies.

The phytochemical composition of the essential oils of three Sideritis libanotica subspecies, namely S. libanotica ssp. libanotica, S. libanotica ssp. linearis and S. libanotica ssp. michroclamys, all collected in Lebanon, was analyzed by GC and GC-MS. The diterpene sideridiol was recognized as the main constituent of both S. libanotica ssp. libanotica (50.8%) and S. libanotica ssp. michroclamys (18.4%) oils, while hexadecanoic acid (10.5%) prevailed in S. libanotica ssp. linearis. The antioxidant activity of the oils was studied in two cell free systems by DPPH radical scavenging and ferric ion reduction (FRAP) assays; only S. libanotica ssp. linearis showed a moderate activity when assayed by the FRAP test (0.6 ± 0.01 mmol TE/mL).