## 3 Results and Discussion
### Profiling of VOCs and Their Distribution
However, during the S2-2 (70 DAS) stage, eugenol, and linalool content increased, reaching 35.6% and 31.9%, respectively, making them the most abundant compounds (see Figure 6C). This composition of OPB consisted of reported paper [85]. Methyl eugenol was the dominant constituent of OBP, followed by eugenol. The strong correlation between these two phenylpropenes (\(r\) = 0.8458, \(p\) < 0.005) suggests the possibility of conversion from eugenol to methyl eugenol through the catalysis of the EOMT gene [86]. Both eugenol and methyl eugenol exhibited a very strong correlation with total VOCs content ( eugenol: \(r\) = 0.9451, \(p\) < 0.005; methyl eugenol: \(r\) = 0.9678, \(p\) < 0.005, respectively). Meanwhile, the other major compound, linalool, which is one of the terpene alcohols, showed a weak correlation with total VOCs (\(r\) = 0.2844, \(p\) < 0.005). Therefore, eugenol and methyl eugenol were revealed as the principal factors to determine total VOCs emission in OBP. The highest content of phenylpropene compounds was observed during the initial vegetative stage (S2-1). This finding is consistent with the results of [PERSON] et al. [87], who reported an increase in total VOC content during the juvenile stage (S2-1), followed by a rapid reduction during the pre-flowering and flowering stages in Ocimum species. In SO, 34 VOCs, including aldehydes (3), monoterpenes (17), sesquiterpenes (2), terpene alcohols (9), phenylpropenes (2), and fatty alcohol (1), were found, as described in Table 6. Several compound groups constituted a large portion (more than 10%) of the total VOCs. Monoterpenes (63.4-79.2%), sesquiterpenes (10.1-15.6%), and terpene alcohols (9.1-18.2%) were associated with the aroma of SO (Table 6 and Figure S3). Unlike AR and MO, where several components determine the total amount, the sum of some of the main compounds, such as (\(Z\))-thujone (28.4-43.1%), camphor (15.5-29.4%), and humulene (8.8-13.7%), accounted for approximately only half (Figure 6D). The total VOCs content varied across different growth stages, including S2-1 (60 DAS; 128.5 \(\pm\) 8.5 ng/mg), S1 (30 DAS; 94.5 \(\pm\) 7.5 ng/mg), S2-3 (80 DAS; 75.9 \(\pm\) 12.8 ng/mg), and S2-2 (70 DAS; 61.5 \(\pm\) 3.4 ng/mg) (Table 6). Interestingly, there were no remarkable major VOCs in SO. Without overwhelming compounds, diverse volatile compounds were evenly distributed, and relatively predominant volatile compounds (making up more than 8% of the total VOCs content) included two monoterpenes, (\(Z\))-thujone and (\(-\))-camphor, and one sesquiterpene, humulene. Among three high-ratio components, in correlation analysis, only (\(-\))-camphor showed a very strong correlation coefficient (\(r\) = 0.9638, \(p\) < 0.005), while others ((\(Z\))-thujone and humulene) exhibited comparatively lower correlation coefficients (\(r\) = 0.7560 and 0.7322, respectively). The aromatic properties of SO have been reported to be composed of thujone diastereomeric forms (\(\alpha\)-thujone and \(\beta\)-thujone), 1,8-cineol, camphene, humulene, \(\alpha\)-pinene, limonene, and borneol, among others, varying with the species. These compounds make SO a commonly used savory food flavoring in the form of dried leaves and essential oil [88,89]. Therefore, the worth of the S1 and S2-1 stages was evaluated to be higher due to higher total VOCs content. For the _Lamiaceae_ plants, VOCs are important quality indicators. However relatively little is known about the effect of growth stages on VOCs distribution. Some studies have provided evidence that some VOCs stimulate seed germination and seedling stages [90]. Thus, young stages show dramatic changes in VOCs emissions, and leaf ontogeny can greatly influence VOCs production [91]. This study indicated that variations of the VOCs emitted by _Lamiaceae_ species significantly depend on the growth stage. Although the main components and their proportions were all different, the total VOCs of four _Lamiaceae_ plants showed the highest content while passing from the S1 to S2 stage.