## 3 Results
### GC-MS Analysis
#### 3.2.3 Volatile Flavor Compound Analysis  
The concentrations of the 41 identified flavors in PPO are shown in Table 2. Encapsulation had a significant effect on the decrease in concentration of the compounds resulting from degradation and evaporation (\(p<0.05\)). The most abundant compound in PPO at day 0 was linalool, followed by D-limonene, sabinene, \(\beta\)-myrcene, and linalyl acetate. These findings are consistent with previous reports [3; 37]. After 15 days, the concentrations of these aroma components decreased, which may be attributed to the high volatility of these compounds or their susceptibility to degradation, oxidation, and isomerization [38].  
The odor activity value (OAV) of a flavor indicates its contribution to the overall flavor and is related to its concentration and odor detection threshold [39]. Of the 41 identified compounds, there were 17 with OAVs \(\geq\) 1 (Table 3), comprising 4 aldehydes, 1 alcohol, 8 olefins, 3 esters, and 1 ketone (Figure 4a). Of these, four were established as key flavors, with OAVs \(>\) 100, namely, linalool, \(\beta\)-myrcene, sabinene, and D-limonene. Heat map analysis showed that the OAVs of these compounds changed significantly during air exposure for 15 days (Figure 4b). These compounds are also significant flavors in other essential oils and exhibit distinct flavor characteristics. Linalool is abundant in lavender [40], sweet orange [7], cinnamon [5], and other essential oils. It exhibits a fresh floral and woody aroma [41]. Olefin substances primarily possess a refreshing grassy scent and pungent taste [41]. \(\beta\)-Myrcene, a common food flavoring agent and food additive, can be found in the essential oils of various plants, such as hops, hemp, lemongrass, verbena, and laurel [6]. D-Limonene is present in most citrus fruit essential oils and has a citrus scent [42]. The essential oil of Lepechinia betonicifolia has a high content of sabinene (27.98%), which contributes notably to the aromatic profiles associated with \"citrus\" and \"minty\" scents [36]. In PPO, the compounds linalool and \(\beta\)-myrcene contribute to the spicy, woody, and green aroma. The citrus scent is derived from D-limonene. \(\alpha\)-Pinene, sabinene, and \(\gamma\)-terpinene provide a pine wood flavor to PPO [43]. Combinations of these compounds may exhibit additive, synergistic, or antagonistic interactions that influence the perception of PPO's aroma.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Number**} & \multirow{2}{*}{**Name**} & \multirow{2}{*}{**CAS**} & \multicolumn{2}{c}{**Threshold**} & \multicolumn{4}{c}{**Day 5**} & \multicolumn{4}{c}{**Day 6**} & \multicolumn{4}{c}{**Day 10**} & \multicolumn{4}{c}{**Day 15**} \\  &  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Number**} & \multirow{2}{*}{**Name**} & \multirow{2}{*}{**CAS**} & \multicolumn{2}{c}{**Threshold**} & \multicolumn{8}{c}{**OAV**} & \multicolumn{8}{c}{**Day 10**} & \multicolumn{8}{c}{**Day 15**} \\ \cline{3-14}  & & & **Value** & & **Day  
The variations in OAV of the four key flavors were determined during the 15-day air-exposure period (Figure 4b). There was a significant decrease in the OAVs of all four compounds during air exposure. On day 10, the OAV of linalool in SS exceeded PPO. Within 15 days, the loss rate of linalool in POMs was half that of PPO (Figure 4e). There was no significant difference in the loss rate of \(\beta\)-myrcene between SS and SG (Figure 4e), but the loss rates of sabinene and D-limonene in SG were lower than that of SS (Figure 4d,f). In short, at day 15, OAV values of the microcapsule samples were significantly higher than PPO values. Encapsulation appeared to result in a considerably reduced evaporation of the main flavor, thereby functioning as a flavor retention formulation of PPO. SG had the best flavor retention effect.