## 2 Results and Discussion
### Peppermint's Volatile Organic Compound (VOC) Composition
In particular, the MS-2 sample showed an interesting pattern in which the mentofluranolactone share was significantly increased, while the limonene and eucalypt mixture share was decreased. In the face of other moderate changes in this sample, it would be possible to obtain products which are less herbaceous and balsamic, with a stronger minty aroma. Such an outcome might be a key point for peppermint cultivation strategies, and could be applied in cosmetics and pharmaceutical industries. In light of this study, it might be possible to use in vitro cultures supplemented with 0.5 mg: dm\({}^{-3}\) 2 iP + 0.1 mg: dm\({}^{-3}\) IAA (MS-2) at a larger scale to obtain plants with an intense, clear, and fresh minty aroma; however, more tests, especially olfactometric and sensory ones, should be performed to confirm this. Additionally, further approaches to obtain other peppermint chemotypes with increased concentrations of compounds such as carvone, mentone, or menthol for pharmaceutical use should be considered. The production of aromatic plant OACs may depend not only on genetic factors and plant development, but also on environmental factors. All of these can affect biochemical and physiological processes, which could modify the quantity and quality of VOCs. Currently, PGRs or plant hormones are used to affect EO production and chemical composition. [PERSON] et al. (2010) ([PERSON] et al., 2010) have studied the effect of PGRs and VOC production on many plants of aromatic use-herbaceous (peppermint, spearmint, sage, thyme etc. ), shrubby (lavender, rose), and arborescent (spruce). Our experiment showed that the use of cytokines has an impact on the increase of peppermint EO production and the factor related to it, namely increased enzyme activity. Considering that the content of peppermint VOCs depends on the regulator, the potential for modifying the volume of secondary metabolites produced is obvious. Plants treated with appropriate hormones can produce several times more volatile compounds. The experience of [PERSON] and [PERSON] (2008) ([PERSON] and [PERSON], 2008) ([PERSON] and [PERSON], 2000) drew attention to the possibility of using growth regulators for commercial purposes. It is possible to modify not only the amount of chemical compounds contained, but also to eliminate undesirable substances, which was proven by the experiment of [PERSON] et al. (2012) ([PERSON] et al., 2012). [PERSON] and [PERSON] (2000) ([PERSON] and [PERSON], 2000) also conducted an experiment to test the influence of CO\({}_{2}\) on VOC composition in mint (_Mentha_ L. spp.) and thyme (_Thymus vulgaris_ L.). Although several terpenes occurred in the mint cultures in vitro, only two monoterpenes were conspicuous: limonene and piperitone oxide. An increase in the CO\({}_{2}\) levels did not appreciably increase limonene levels when shoots were grown on MS without sucrose. In contrast, limonene levels increased dramatically when shoots were cultured under 10,000 and 30,000 \(\upmu\)mol-mol\({}^{-1}\) CO\({}_{2}\) levels on MS containing 3% sucrose. Piperitone oxide levels increased to their highest levels at 3000 \(\upmu\)mol-mol\({}^{-1}\) CO\({}_{2}\) for mint cultures grown on MS with and without sucrose. However, piperitone oxide levels were markedly higher in cultures grown on MS with sucrose under ultra-high CO\({}_{2}\) levels (i.e., \(\geq\)3000 \(\upmu\)mol-mol\({}^{-1}\) CO\({}_{2}\)) than in cultures grown on MS without sucrose. As much as 0.85 mg piperitone oxide/g fresh weight of plant occurred in mint cultures grown on MS with sucrose under the 3000 \(\upmu\)mol-mol\({}^{-1}\) CO\({}_{2}\) level. This was a 14-fold increase over the level found in cultures on MS with sucrose under ambient air. It should be noted that while the 3000 \(\upmu\)mol-mol\({}^{-1}\) CO\({}_{2}\) level resulted in the highest growth and morphogenesis responses from mint plantlets in soil, it did not appreciably improve the levels of secondary metabolites.