Catherine M. Cook*, Eleni Maloupa, Stella Kokkini and Thomas Lanaras

Abstract: The composition of the inflorescence (I), leaf (L) and stem (S) essential oils of wild Mentha pulegium plants from three populations (1-3) on the island of Zakynthos were examined. Pulegone (32.8 %, S1 to 75.8 %, I3) was the major constituent of all of the oils. The other main constituents were piperitenone (5.1 %, L3 to 35 %, I2), isomenthone (4.3 %, I2 to 28.6 %, L3) and piperitone (0.5 %, I3 to 5.2 %, L2). In total, C-3-oxygenated p-menthane compounds constituted from 73.0 % (S1) to 96.2 % (I2) of the oils. The piperitenone content of the inflorescence oils was up to 2.4 (Loc 3) times higher than that of the leaf oils. Correspondingly, the isomenthone content of the leaf oils was up to 4.2 (Loc 2) times higher than that of the inflorescence oils. The ratio of the isomenthone:piperitenone content of the oils (n=3) was markedly different for the inflorescence (mean 0.31 ±SD 0.21 ), leaf (mean 2.91 ± SD 2.37) and stem (mean 1.12 ± SD 0.68) oils. The essential oil yields (mL /100g DW) were for the inflorescences 3.1-5.0 %, leaves 3.1-4.0 %, stems <0.1-0.1% and whole plant (aerial parts) 2.4-3.9 % and are among the highest oil yields reported to date in Greece for M. pulegium.

Wild Mentha pulegium L. (syn. Pulegium vulgare Miller) plants, known also as European Pennyroyal, are found widely in all but the most northern parts of Europe extending from Ireland to W. and S. Ukraine and are very variable in habit, leafshape and pubescence (1). In Greece, plants grow abundantly both on the mainland and the islands (2,3). Traditionally, plants have been used as herbal teas and remedies. Pulegone is considered to be the major constituent of the commercial essential oil produced from M. pulegium plants (4). Pulegone is known for its abortificient, hepatotoxic and pulmonary toxic effects and is potentially lethal, and thus the use of pennyroyal oil in the pharmaceutical and food industry is regulated (4,5). In wild plants however, three chemotypes of M. pulegium have been described (6) with the following major oil constituents 1) pulegone 2) piperitenone and/or piperitone and 3) isomenthone and neoisomenthol. In 38 wild M. pulegium populations in Greece, the pulegone content ranged from <0.1–90.7 % of the oil while oils of low pulegone content contained other intermediates of the C-3-oxygenated p-menthane biosynthetic pathway from isopiperitenone to menthone and isomenthone and to piperitenone and piperitone, as the major constituents (2,3). Oils of different chemical compositions have also been reported for wild M. pulegium populations from Portugal (7) and Turkey (8,9). Literature concerning Pennyroyal oil compositions has been reviewed (6,10). A relationship between the essential oil composition and oil yield of wild populations of M. pulegium and the climatic zone from which the plants originated has been reported (3). In addition, variations in M. pulegium oil composition and content in different sections of the plant and in plants of different developmental stage have been reported with pulegone content ranging from 7–85.3 %, menthone from 2.7–32.3 % and neomenthol from 0.4–35.5 % (11). An earlier study (12) also reported changes in M. pulegium oil composition with plant developmental stage. A seasonal variation in the oil composition of M. pulegium leaves has also been reported with highest pulegone contents occurring in July (13). Based on the wide variations in reported M. pulegium oil compositions between wild populations, plants of different developmental stage and season, the oil composition of the inflorescences, leaves and stems of three wild populations of M. pulegium, collected from locations within the onshore limits of the National Marine Park of Zakynthos, are examined in this study.