## 3 Results and Discussion
### Microstructural Features of the Spray-Dried Microcapsules  
The structural features of spray-dried microcapsules are affected by the combined influence of the composition and physico-chemical properties of the CIWE and its constituents, by the atomization conditions and by the drying conditions [45; 57; 58; 59]. CIWEs were spray-dried at the same conditions, thus allowing investigating the effects of compositional aspects on the microstructure of the microcapsules. The moisture content of the spray-dried microcapsules ranged from 0.83 to 1.58%. Spherical microcapsules, ranging in diameter from about 8 to about 50 \(\upmu\)m, were obtained with all of the investigated CIWEs (Figure 2). The dry microcapsules exhibited smooth outer surfaces with a limited extent of surface indentation (Figure 2A,B). Structural features of the outer topography of the investigated microcapsules were similar to those that were reported for spray-dried microcapsules prepared with blends of whey proteins and lactose [45] and superior to those reported for spray-dried microcapsules consisting of SPI and lactose [37]. A close examination of the outer surface of the microcapsules revealed the presence of round \"dimples\", with a diameter smaller than 0.2 \(\upmu\)m, that were evenly distributed all over the outer surfaces (Figure 2D). These \"dimples\" have been reported to represent the \"footprints\" of core droplets that were swept off the outer surface of the drying droplets, immediately after the atomization stage, and prior to the solidification of the outer surface and the formation of \"crust\" [31; 35; 40; 43; 45; 59]. In all cases, studying the inner structure of the microcapsules revealed that the core was embedded in the wall matrix in the form of protein-coated oil droplets that were evenly distributed throughout the wall matrix (Figure 2C,D). The thickness of wall matrix \"layers\" that separated core domains was inversely proportional to the core content in the microcapsules (Figure 2C,D). Results indicated the presence of a dense layer adsorbed at the O/W interfaces (Figure 2C,D). As previously reported [31; 35; 40], this layer consists of the surface active constituents of the WS, WHPI in the present case, that have become adsorbed at the O/W interface during the homogenization process. In general, the structural features of the microcapsules were similar to the microstructural features of spray-dried microcapsules with wall systems consisting of blends of whey proteins, WHPI, or SPI and carbohydrates [30; 31; 35; 40; 44], and consisted of structural elements and features that are desired in oil-containing spray-dried microcapsules [30; 31; 40; 59]. Results of the structural analysis did not reveal cracks, pores, or channels connecting core domains with the outer surfaces of the microcapsules. These results suggested that the wall matrices physically isolated the core domains from the external environment [30; 31; 40; 59].  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**WHPI/Lactose (\%/\%, \(w\)/\(\mathit{tv}\))** & \multicolumn{3}{c}{**Surface Excess (mg/m\({}^{2}\))**} \\ \cline{2-3}  & **75:25 1**  & **50:50** & **25:75** \\ \hline
2.5/17.5 & 2.741 \({}^{\text{a,A}}\) & 2.402 \({}^{\text{b,A}}\) & 1.597 \({}^{\text{c,A}}\) \\
5.0/15.0 & 3.513 \({}^{\text{a,B}}\) & 3.32 \({}^{\text{b,B}}\) & 3.047 \({}^{\text{c,B}}\) \\
7.5/12.5 & 4.628 \({}^{\text{a,C}}\) & 4.468 \({}^{\text{b,C}}\) & 4.198 \({}^{\text{c,C}}\) \\
10.0/10.0 & 5.316 \({}^{\text{a,D}}\) & 4.453 \({}^{\text{b,C}}\) & 4.089 \({}^{\text{c,C}}\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: The effect of wall composition and wall-to-core ratio on Surface Excess (\(\Gamma\)) of the investigated CIWEs.