Peppermint 475
at 0.002% and 0.0008% for HSV-1 and HSV-2, respectively. Peppermint oil exhibited
high levels of virucidal activity against HSV-1 and HSV-2 in viral suspension tests.
At noncytotoxic concentrations of the oil, plaque formation was significantly reduced
by 82% and 92% for HSV-1 and HSV-2, respectively.
The deterrent and toxicity effects of mint, M. virdis. and M. piperita on mite
(Tetranychus urticae Koch) were studied under laboratory conditions. Leaf discs
treated with increasing concentrations of both materials showed a reduction in the
total numbers of eggs laid (Momen et al., 2001). The fumigant toxicity of 28 essential
oils extracted from various spice and herb plants and some of their major constituents
were assessed for adult coleopterans, major stored products insects. The compound
1,8-cineole and the essential oils anise and peppermint were active against T. castaneum
(Shaaya et al., 1991).
28.6 Quality issues..................................................................................
The flavouring properties of the oil are due largely to both the ester and alcoholic
constituents, while the medicinal value is attributed to the latter only. The most
important determination to be made in the examination of peppermint oil, is that of
the total amount of menthol, but the menthone value is also frequently required.
European pharmacopeial grade peppermint oil is the volatile oil distilled with
steam from the fresh aerial parts of the flowering plant. Its relative density must be
between 0.900 and 0.916, refractive index between 1.457 and 1.467, optical rotation
between –10∞ and –30∞, among other quantitative standards. Identity must be confirmed
by thin-layer chromatography (TLC), organoleptic evaluation, and quantitative analysis
of internal composition by gas chromatography. It must contain 1.0–5.0% limonene,
3.5–14.0% cineole, 14.0–32.0% menthone, 1.0–9.0% menthofuran, 1.5–10.0%
isomenthone, 2.8–10.0% menthylacetate, 30.0–55.0% menthol, maximum 4.0%
pulegone, and maximum 1.0% carvone (Ph.Eur.3, 1997). French pharmacopeial grade
peppermint oil must contain not less than 44% menthol, from 4.5–10% esters calculated
as menthyl acetate, and from 15–32% carbonyl compounds calculated as menthone.
TLC is used for identification, quantification of compounds, and verification of the
absence of visible bands corresponding to carvone, pulegone, and isomenthone
(Bruneton, 1995).
The English oil contains 60–70% of menthol, the Japanese oil containing 85%,
and the American only about 50%. The odour and taste afford a good indication of
the quality of the oil, and by this means it is quite possible to distinguish between
English, American and Japanese oils. Menthol is obtained from various species of
Mentha and is imported into England, chiefly from Japan. The oils from which it is
chiefly obtained are those from M. arvensis var. piperascens in Japan, M. arvensis
var. glabrata in China, and M. piperita in America. Japan and China produce large
quantities of Mentha oil, which is greatly inferior to those distilled from M. piperita,
but have the advantage of containing a large proportion of menthol, of which they are
the commercial source. The cheapest variety of peppermint oil available in commerce
is partially dementholized oil imported from Japan, containing only 50% of menthol.
Adulteration of American peppermint oil with dementholized Japanese oil, known as
Menthene, which is usually cheaper than American oil, is frequently practised. The
Japanese oil, termed by the Americans corn-mint oil and not recognized by the
United States Pharmacopoeia, is at best only a substitute in confectionery and other