Piccaglia et al. (1993) compared the oil compositions of the first and second cuttings over two seasons of the ‘Italo-Mitcham’ cultivar of peppermint grown in the experimental garden of the University of Bologna. The oils, which were produced by hydrodistillation, were obtained from first cutting (plants in full bloom) and second cutting in the autumn at maturity growth. The authors found that the first season’s biomass harvest (ca 54 metric tonnes/ha) was much greater than that of the second season (33 tonnes/ ha). The results of this study are summarized in T-1. Examination of these results revealed a compositional change in the second cutting oil versus the first cutting oil. It is believed that the photoperiodic effect of the short autumn days could be responsible for this biosynthetic change in the contents of menthone, menthofuran and menthyl acetate, particularly in the second season.
Culp et al. (1998) reported that the commercial samples of peppermint oil of U.S. origin that they examined by capillary GC coupled with online isotope ratio mas spectrometry contained the following constituents:
menthyl acetate (4.5–6.6%)
germacrene D (0.5–2.1%)
Maffei and Scannerini (2000) determined that when peppermint plants (cv ‘Italo-Mitcham’) were exposed to only UV-B light, the menthone, menthofuran and menthyl acetate content of oil produced from them increased, while the menthol content decreased. Furthermore, the authors found that exposure of the plants to UVA light stimulated the biosynthesis of some monoterpenes such as menthol.