Natural variability of the enantiomeric composition of bioactive chiral terpenes in Mentha piperita

The variability of the enantiomeric distribution of biologically active chiral terpenes in Mentha piperita plants from different geographical origins was evaluated by solid phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS). The optimisation of some parameters (i.e. exposure temperature, extraction time and type of fibre) affecting SPME-extraction enabled relative standard deviations ranging from 4 to 13% to be achieved. The use of two different chiral stationary phases allowed to separate the identified chiral terpenes into their corresponding enantiomers as well as to verify the enantiomeric excesses of those compounds which were enantiomerically resolved on both phases. For all chiral terpenes, the enantiomeric composition varied within a very narrow range all over the samples. Consequently, it may be stated that the enantiomeric composition of chiral terpenes in Mentha piperita appears to be independent of the geographical origin of the plant and, thus, any alteration in the characteristic value may be related to an adulteration or inadequate sample handling. These results support the usefulness of the enantiomeric composition of bioactive chiral terpenes in Mentha piperita in authenticity studies.