## 3 Results and Discussion
### Effect of Spray drying on Complex Coacervate Microcapsules  
In order to evaluate the effect of spray drying on the stability, size distribution and potential loss of encapsulated peppermint oil, the complex coacervate microcapsules were spray dried and subsequently resuspended in water. Samples without the crosslink were destabilized during spray drying, and so were not included in further analyses. Figure 2 shows typical optical microscopy images before (Figure 2A) and after (Figure 2B) spray drying and resuspension, together with the corresponding differential number and volume size distributions (Figure 2C,D respectively). From optical microscopy and the differential number size distributions (Figure 2A-C), there is an apparent loss of the largest capsules during spray drying, resulting in a narrowing of the microcapsule size. While  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & & \multicolumn{3}{c}{**Mean Number Average Diameter**} & \multicolumn{3}{c}{**Microencapsulation Yield**} \\ \hline
**PolymerOil** & **[Crosslinker]** & **[Polymer]** & **Coacervates** & **After Spray Drying** & **SD Yield** & **CC (\%)** & **SD (\%)** \\
**(w:\(w\))** & **(wt\%)** & **(wt\%)** & **(\(\mu\)m)** & **(\(\mu\)m)** & **(\(\%\))** & **(\%)** & **CC (\%)** & **SD (\%)** \\ \hline
1:2 & 0 & 3 & \(7\pm 3\) & - & - & - & - \\
1:2 & 5 & 3 & \(7\pm 3\) & \(6\pm 3\) & 26 & \(100\) & \(17\pm 1\) \\
1:1 & 5 & 3 & \(7\pm 3\) & \(7\pm 3\) & 21 & \(100\) & \(19\pm 1\) \\
1:1 & 5 & 6 & \(7\pm 4\) & \(6\pm 4\) & 32 & \(100\) & \(27\pm 3\) \\
2:1 & 2.5 & 6 & \(7\pm 4\) & \(6\pm 3\) & 29 & \(100\) & \(54\pm 2\) \\
2:1 & 5 & 6 & \(5\pm 3\) & \(6\pm 3\) & 31 & \(100\) & \(47\pm 1\) \\
2:1 & 10 & 6 & \(22\pm 4\) & \(27\pm 4\) & 35 & \(100\) & \(31\pm 1\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Overview of system parameters, capsule size and microencapsulation yields (\(w\):\(w\)).  
Figure 1: Optical microscopy images of process steps during complex coacervation of peppermint essential oil: oil-in-water emulsion at pH \(>\) 5 (**A**), coacervation at pH = 4.2 (**B**), crosslinking at pH 9 (**C**) and crosslinked capsules (**D**). The scale bar corresponds to 50 \(\mu\)m.  
the optical microscopy images and the differential number distributions largely are in agreement regarding capsule size, differential volume size distributions (Figure 3D) are significantly shifted towards larger diameters. Thus, the number size distributions likely reflect single or primary capsules, whereas the differential volume size distribution reflects partial flocculation as the microcapsules flow in DI water. However, the effect of spray drying can also be seen from a narrowing of the differential volume size profile as well as a loss of an intermediate floc population after spray drying.  
Figure 3: Optical microscopy images of peppermint oil complex coacervate microcapsules with different Polymer:Oil ratios before (upper row) and after (bottom row) spray drying. Polymer:Oil = 1.2 (**A**,**D**), Polymer:Oil = 1.1 (**B**,**E**), Polymer:Oil = 2.1 (**C**,**F**). Crosslinker concentration = 5% (_w:w_) with respect to BSA for all capsules. The scale bar corresponds to 50 \(\upmu\)m.  
Figure 2: Optical microscopy images of peppermint oil complex coacervate microcapsules before (**A**) and after (**B**) spray drying, as well as their respective size distribution according to differential number (**C**) and differential volume (**D**). The scale bar corresponds to 50 \(\upmu\)m. Samples shown here: Polymer:Oil = 2:1 and crosslinker concentration = 5% (_w:w_) with respect to BSA.