Increase of Caryophyllene Oxide in Ageing Lemon Balm Leaves (Melissa officinalis L.) - A Consequence of Lipid Peroxidation?

Oxidative processes, especially lipid peroxidation (LPO), are assumed to increase during ageing. In an attempt to provide experimental evidence for this assumption lemon balm plants (Melissa officinalis L.) of different age and location were analyzed for oxidatively caused changes in the etheric oil composition. The investigation revealed that the caryophyl­ lene oxide (CarO) content of lemon balm plants a main constituent depends on two factors: age and habitat. The content of CarO increased with age continuously up to a factor of 3. Poor nutritive conditions, as growth on unfertilized soil, also caused an increase in CarO content. Addition of Fe2+/ascorbate enhancing oxidative processes promoted the formation of CarO. Hydroperoxides of unsaturated fatty acids (LOOHs) in the lipid extract of lemon balm leaves were converted to corresponding hydroxy acids (LOHs) by sodium borohydride re­ duction. These were hydrogenated and subjected to GC/MS analysis after derivatisation. A surplus of 9-hydroxy-octadecanoic acid over the 13 isomer indicated at least in part enzymatic lipid peroxidation. Polarographie determination of the oxygen consumption revealed a gen­ erally low but in ageing plants increased lipoxygenase activity. This indicates a contribution of lipid peroxidation in the epoxidation process of caryophyllene.