# NMR Analysis of Pulegone in Food Products
## 2 Results and Discussion
### Quantification of Pulegone in Essential Oils  
No pulegone was detected in spearmint; therefore, no standard addition of pulegone to spearmint oil was performed. In this study, a total of 15 peppermint oils, 4 corn mint oils, 1 penmyroyal oil, 2 mura oils, 2 buchu oils, 1 water mint oil, 1 oil produced from a lesser calamint, 1 bergamot mint oil, and 1 balm mint bush oil were examined. The pulegone concentrations in the peppermint oils ranged from 4.05 to 18.8 mg/kg (see Appendix A, Table A1). This results in a pulegone content in the oil of 0.4% to 1.9%. No pulegone was detected in 1 peppermint oil. In the literature, a pulegone content of 1.2% and 12.3% were found in peppermint oil [2,9]. In this study, the pulegone content of the peppermint oil samples was around the lowest reported value. The different pulegone contents in the respective mint species can be explained by the different cultivation conditions and environmental influences. In the case of peppermint and corn mint, the higher the temperature, the more pulegone could be detected. In addition, the salt content during plant cultivation influences the pulegone content. A high salt concentration is conducive to a high pulegone concentration. In contrast, drought has a negative effect on the concentration of pulegone [29]. The pulegone content of corn mint oil in our sample ranges from 0.31% to 1.47%, while the literature pulegone content of corn mint oil ranges from 0.85% and 2.27% [8,10]. The pulegone content in corn mint samples 1 and 3 was below 0.85%. The lower pulegone content can be explained by various environmental factors during cultivation. In penmyroyal oil, the pulegone content ranges from 61.3% to 77.9% [1]. With a pulegone content of 63.1% \(\pm\) 4.6%, the penmyroyal oil investigated in this study was within this range. According to the literature, mura oil contains 30.8% to 83.3% pulegone in the oil [5]. The 2 mura oils investigated in this study had pulegone contents of 28.9% and 55.9%, which are in line with the literature values. The pulegone content of buchu oil is 3.0% \(\pm\) 0.2%. The literature indicates that the pulegone content in buchu oil ranges from 2.4% to 8.4% [6]. The pulegone content determined in this study was in accordance with the findings of previous studies. In the literature, a pulegone content of 0.45% has been reported in the oil of water mint [8]. The water mint content determined in this study was more than twice as high (1.32%). It is plausible that the two water mints were cultivated under different conditions. The oil of the lesser calamint was found to contain 27.1% \(\pm\) 0.9%. The literature indicates that the pulegone content in the essential oil of lesser calamint ranges from 2.4% to 64.4% [12]. The pulegone content determined in this study was in accordance with the literature value. The essential oils of bergamot mint, balm mint bush, horse mint, and spearmint were found to be devoid of pulegone. No evidence of pulegone was found in the literature on bergamot mint either [30]. The same is true of balm mint bush. In contrast, pulegone has been detected in horse mint (0.17-69.49%) and spearmint (0.30-29.59%) [3,11,31]. A section of the spectrum of spearmint oil is shown in Figure 6. The spearmint oil was spiked with pure pulegone for verification. The dt at \(\delta_{\mathrm{H}}\) = 2.74 ppm is overlaid by a multiplet. The multiplet belongs to (+)-carvone. In addition, the remaining signals cannot be clearly assigned to the pulegone. An additional attempt was made to achieve a more effective separation of the signals from pulegone and carvone by employing a different \begin{table}
\begin{tabular}{c c c} \hline
**Matrix** & **LOD [mg/kg]** & **LOQ [mg/kg]** \\ \hline Peppermint & 59.9 & 214 \\ Pennsylvania & 134 & 491 \\ Spearmint & 371 & 1363 \\ Pastille & 14.5 & 51.5 \\ Dragee & 7.15 & 26.2 \\ \hline \end{tabular}
\end{table} 
Table 2: Comparison of the limits of detection and quantification of pulegone in peppermint, penmyroyal, spearmint, pastilles, and dragee.