## 2 Results and Discussion
### Characterization of Microcapsules
#### 2.3.2 Characteristics over Time  
The characteristics of the microcapsules were investigated over time. After collecting microcapsules generated at a constant flow rate in a dish containing an outer oil phase,  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Liquid Properties**} & **Theral** & **Measured Sensor Intensity** \\  & & **Stimulation** & **(Mean \(\pm\) SD)** \\ \hline
1 & Microcapsule & With & 7.1 \(\pm\) 0.2 * \\
2 & Microcapsule & Without & 6.7 \(\pm\) 0.4 \\
3 & Simply stirred solution & With & 9.3 \(\pm\) 0.1 \\
4 & Simply stirred solution & Without & 8.8 \(\pm\) 0.2 \\ \hline \hline \end{tabular}
\end{table}
Table 5: The intensities of the sample vapors were measured using an odor sensor. * Significantly different from No. 2 (\(p\) = 0.04, Student’s \(t\)-test).  
microscopic images (phase-contrast observation) were acquired over time. Two types of outer oil phases were used: mineral oil with and without surfactants. Specifically, the mineral oil with surfactant was the same 1 wt% SY-Glyster/mineral oil solution as the outer oil phase (the PVA used in this study is water-soluble; therefore, it was not used as a surfactant for the oil phase). To maximize the coagulation inhibition effect, the surfactant concentration was set to almost the maximum solubility in the mineral oil. When surfactant-containing mineral oil was used as the outer oil phase poured into the dish, the microcapsules gradually turned black over time (Figure 6). This change was caused by the surfactant in the outer oil phase acting on the water in the shell to form reverse micelles (a phenomenon called spontaneous emulsification), which then covered the microcapsules [22]. These reverse micelles may affect the release of odor from the microcapsules. Coalescence was significant when mineral oil without a surfactant was used as the outer oil phase and poured into the dish. The microcapsules (immediately after formation) were collected from a dish containing the outer oil phase. To reduce coalescence by increasing the shell fluidity, they were subsequently cooled at 4 \({}^{\circ}\)C (below the gelling point of the agarose gel used) for 17 h. The samples were then observed under a microscope (Figure 7). The microcapsules did not exhibit black discoloration. This indicates that reverse micelles formed by surfactants hardly formed around the microcapsules. In this study, mineral oil containing surfactants was used as the outer oil phase during microcapsule formation; therefore, surfactants were also added to the mineral oil in the dish. However, the surfactants were diluted with mineral oil in the dish. This may have had little effect on the formation of reverse micelles. In addition, it has been reported that reverse micelles change in size depending on the temperature [23]. The interfacial phenomenon related to this characteristic of the reverse micelles may have been involved in the suppression of reverse micelle formation. In this study, the microcapsules were stable for several days. However, further investigations are required to fully evaluate their long-term storage potential.  
Figure 6: \(Cont.\)