The relative proportions of chemical classes (hydrocarbons, oxides, alcohols, ketones, esters) in the essential oil of rosemary (Rosmarinus officinalis L., Lamicaeae) and in the volatile fraction of the infusion extracts were examined and showed remarkable differences. The volatile compounds of the infusion were isolated by two different methods, hydrodistillation and solid phase extraction (SPE). The main constituents of the volatile fraction of the infusion were (hydrodistillation/SPE): 1,8-cineole (42.4%/44.7%), camphor (31.4%/31.8%), α-terpineol (8.6%/8.1%) and borneol (8.3%/7.8%). The qualitative and quantitative composition of the volatile compounds of the infusion was compared to the essential oil isolated by hydrodistillation directly from the leaves. The major constituents of the essential oil of the leaves were 1,8-cineole (41.6%), camphor (17.0%), α-pinene (9.9%), α-terpineol (4.9%) and borneol (4.8%). Comparison of the total essential oil yield quantified by hydrodistillation of the infusion (0.36% v/w) with the essential oil yield of the leaves (1.84% v/w) revealed that only 19.6% of the initial oil could be extracted by infusion.
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