Original flavour compounds and the essential oil composition of marjoram ( Majorana hortensis moench)

The analysis of spice plant flavour compounds usually starts with the so‐called essential oil, which is obtained by steam‐distillation. Comparative investigations of marjoram flavour extracts, separated using different isolation techniques, showed the great influence of the isolation method on the composition of the resulting flavour extract. Experiments with triturations of leaf material under liquid nitrogen, extractions with supercritical carbon dioxide and direct injections of the oil of individual secretory cells demonstrated that cis ‐sabinene hydrate and its acetate represent the original flavour compounds in the intact leaf. The great number of monoterpenes described in marjoram essential oils therefore appear to be artefacts, arising from a multitude of rearrangement, hydration and deprotonation reactions from cis ‐sabinene hydrate acetate and from an activated precursor form, that possesses the sabinene hydrate skeleton. The nature of these artefact‐forming reactions was investigated by model experiments with synthetic sabinene hydrate and its acetate. The biosynthetic capacity of the marjoram plant with regard to the monoterpenes seems to be confined to the synthesis of the sabinene hydrate skeleton.