## 2 Results and Discussion
### Peppermint's Volatile Organic Compound (VOC) Composition  
The chromatogram (Figure 3) shows the composition of the VOCs obtained from plants derived using various combinations of growth regulators. Overall, 53 VOCs were found, and 51 were identified (the mass spectra of unidentified VOCs are available in the Supplementary Materials). There were no significant differences in the composition of any them; however, the type of plant hormones used affected the percentage of particular compounds in the VOC composition (Table 2). The VOCs of peppermint could represent up to 300 compounds, with major components such as menthol (30-55%) and menthone (14-32%). The Polish Pharmacopoeia VIII [39] determines the content of other ingredients as follows: cineole (3.5-14%), menthyl acetate (2.8-10%), isomenthone (1.5-10%), menthoturan (1.0-9.0%), limonene (1.0-5.0%), pulegone (<4.0%), and carvone (<1.0%). The quantitative composition of VOCs depends on many factors, such as in vivo and in vitro growing conditions, the date of harvest, post-harvest treatments, plant chemotypes, and others [40]. It should be emphasized that the chemotype of plants is extremely important, as [PERSON] et al. (2016) [41] showed in their studies focused on plants of _Mentha_ species and their cultivars, where the range of possible differences in mint chemotypes was very wide. Some of them were characterized by higher amounts of limonene and 1,8-cineole (eucalypt), which corresponded to the results of this study (limonene + eucalypt7.4-36.12%), but a difference was found in other major constituents which are expected to occur along with limonene and 1.8-cineole, such as carvone. This difference, as well as the lack of most characteristic peppermint VOCs--menthone, menthol, and their derivatives [42]--may have been caused by the very early stage of plant development in the in vitro culture. Figure 4 presents a chromatogram illustrating a comparison of peppermint VOC compositions depending on the source of the plant. Blue represents VOCs obtained from peppermint derived directly from in vitro culture from a medium without regulators. The sample marked in pink was made using plants subjected to acclimatization (in vivo). The green color shows the result obtained for mint plants after acclimatization, when earlier plants were cultivated on 0.5 IBA. The third option was tested because IBA had a greater effect on individual chemical compounds produced in vitro (Table 2). There were no differences in the qualitative compositions. The [PERSON] team (2013) [1] conducted similar research to maximize the growth and production of Eos in micropropagated peppermint seedlings. The experiment showed that supplementation with BAP alone resulted in the highest values of root length, root dry matter, shoot length, and number of nodes, leaves, and branches. The addition of IBA or IBA and BAP caused an approximately 50% increase in fresh shoot mass. The production of secondary metabolites such as menthone, menthol, menthoturan, and pulegone was influenced only by the addition of BAP,which resulted in a 40% increase in the total yield of EO. It has been established that the use of growth regulators increases the production of oils and biomass in herbaceous species rich in commercially valuable terpen. In Figure 5, the overall influence of growth regulators on the quantities of particular groups of peppermint VOCs is illustrated. The strongest influence was observed for VOCs occurring in small and moderate quantities (Figure 5A,B). For VOCs occurring in high amounts (Figure 5C), the variability was lower and was related mainly to mentofluaranolactone, which, apart from limonene and 1.8-cineole, was the most abundant VOC in in-vitro-cultivated peppermints (24.69-67.27%). The literature review showed that this result was unique. Nevertheless, [PERSON] et al. (2002) [45] pointed out that \(p\)-methane lactones such as mentofluarolactone may have a significant impact on peppermint quality.