476 Handbook of herbs and spices
products, such as tooth-pastes, etc. There are other varieties of so-called peppermint
oil on the market that are residues from Menthol manufacture and are inferior even
to the oil imported from Japan. These are not suitable for use in pharmacy.
Felklova et al. (1982) examined the qualitative and quantitative aspects of different
cultural varieties of M. piperita volatile oils and found that the Ukrainian variety had
the highest content of oil. Ruiz del Castillo et al. (2004) found that the enantiomeric
composition of chiral terpenes in M. piperita is 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. The enantiomeric composition of
bioactive chiral terpenes in M. piperita can be used in authenticity studies.
The effects of mint type, planting density, and planting time on the composition
and yield of mint oils in Mentha piperita and other Mentha species in northern
Finland were studied by Galambosi et al. (1998). The content of menthol in peppermint
grown in Finland was low in comparison to international standards. The highest
menthol percentage was obtained with the highest plant density (spacing of 10 cm)
while the highest yield was achieved by planting in the early spring.
28.6.1 Pesticide residues
Pharmacopoeial grade peppermint leaf must be composed of the dried whole or cut
leaf with not more than 5% stem fragments greater than 1 mm in diameter and not
more than 10% leaves with brown spots caused by Puccinia menthae. The whole leaf
must contain not less than 1.2% (ml/g) and the cut leaf must contain not less than
0.9% volatile oil. Botanical identity must be confirmed by macroscopic and microscopic
examinations and organoleptic evaluation (Wichtl and Bisset, 1994). The ESCOP
peppermint leaf monograph requires that the material comply with the European
pharmacopoeia (ESCOP, 1997).
The residue levels of broad-spectrum, systemic fungicides propiconazole and
tebuconazole, used to control rust in peppermint were studied by Garland et al.
(1999). An analytical method, using gas chromatography combined with detection by
high-resolution mass spectrometry was developed to allow for the simultaneous
monitoring of both pesticides in peppermint leaves and oil. At harvest, 64 days after
the final application, propiconazole was detected at levels of 0.06 mg/kg and 0.09
mg/kg of dry weight, and tebuconazole was detected at 0.26 and 0.80 mg/kg dry
weight, in identical trials. The Lindane residue dynamics in peppermint was studied
by Beitz et al. (1971). In the crop sprayed with a 0.05% formulation in May, the
residue was reduced to below 0.1 ppm, similar to those in the untreated controls after
four months.
Golcz et al., (1975) observed that sprayings with Sinbar herbicide in an appropriate
dose and at fixed dates do not have any negative effect on the development of mint
and the concentration of essential oil in the crude drug. The residual terbacil (an
active ingredient of Sinbar) in Herba Menthae piperitae was 0.008 ppm during
harvesting, when Sinbar was applied before and after drying of mint. Later sprayings
increased the concentration of Terbacil in the crude drug (0.21–0.27 ppm). The
treatment of peppermint with Terbacil did not influence the essential oil content.
Similarly, the application of a herbicide formulation did not cause detectable changes
in relative representation of main and secondary components of the essential oil
(Vaverkova et al., 1997).