## 3 Results and Discussion
### Particle Size after Spray Drying and during In Vitro Digestion  
The particle sizes of the coacervated microcapsules after spray drying for WPI-SA and WPI-CMC systems resuspended in 2.5 pH buffer were \(21.67\pm 0.18\) um and \(23.20\pm 0.66\) um for equivalent sphere diameters (D4,3), respectively. On the other hand, the Sauter mean diameter (D3,2) for the same microcapsules prepared with the WPI-SA system was \(14.08\pm 0.13\) um and for the WPI-CMC system was \(15.28\pm 0.12\) um. Particle size and particle size distribution were determined at the beginning and end of the digestion process both for the gastric and intestinal phase. As shown in Table 1, a small increase in the Sauter mean diameter (D3,2) was observed for both coacervation systems at the end of the gastric phase; nevertheless, this increase was significantly different (\(p<0.05\)). Because the coacervate is stable at gastric pH, the small increase in particle size can be attributed to the particle expansion because of the polysaccharide hydration in contact with the gastric digestion solution [21; 22; 23]. Figure 4 shows the particle size distribution for both coacervation systems at gastric pH (2.5 pH). It can be seen that in both cases, after 120 min in the gastric phase there was a change in the distribution towards particles of greater size and an increase in their frequency. This was possibly caused by the fact that coacervates tend to group together because of the absence of repulsion charges on the surface [24], in addition to the aforementioned polysaccharide hydration. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Time** & **WPI-SA** & **WPI–CMC** \\ \cline{2-4}
**Gastric phase** & \(\begin{array}{c}\text{D}_{3,2}\\ (0\text{ min})\end{array}\) & \(15.21\) μm \(\pm\) 0.554\({}^{\text{D}}\) & \(18.74\) μm \(\pm\) 0.436\({}^{\text{C}}\) \\  & \(\begin{array}{c}\text{D}_{3,2}\\ (120\text{ min})\end{array}\) & \(20.75\) μm \(\pm\) 0.566\({}^{\text{B}}\) & \(22.47\) μm \(\pm\) 0.535\({}^{\text{A}}\) \\ \hline \multirow{2}{*}{**Intestinal phase**} & **Time** & **WPI–SA** & **WPI–CMC** \\ \cline{2-4}  & \(\begin{array}{c}\text{D}_{3,2}\\ (0\text{ min})\end{array}\) & \(12.85\) μm \(\pm\) 0.281\({}^{\text{B}}\) & \(13.35\) μm \(\pm\) 0.125\({}^{\text{A}}\) \\  & \(\begin{array}{c}\text{D}_{3,2}\\ (120\text{ min})\end{array}\) & \(2.82\) μm \(\pm\) 0.107\({}^{\text{D}}\) & \(4.24\) μm \(\pm\) 0.325\({}^{\text{C}}\) \\ \hline \hline \end{tabular}  
Means with different letters differ significantly (\(p<0.05\)).  
\end{table} 
Table 1: Particle size for whey protein isolate with sodium alginate (WPI-SA) and whey protein isolate with sodium carboxymethylcellulose (WPI-CMC) systems at the beginning (0 min) and end (120 min) of gastric and intestinal digestion (pH 2.5). Figure 4: _Cont._With regards to the action of pepsin present on the capsules in the gastric digestion solution, results suggest no action of the enzyme in the gastric phase. The coacervation pH was 2.5; therefore, the particle was stable at the gastric pH, and whey protein remained protected by the polysaccharide. Based on the capsule design, the microcapsules were expected to remain stable in the acidic conditions of the stomach and to disintegrate at the intestinal pH (7.0 pH). As is shown in Table 1, the particle size during intestinal digestion showed a considerable reduction in terms of Sauter mean diameter (D3,2). This was because complex coacervation is a reversible process, dissociating the complex coacervate when conditions (especially pH and temperature) are unfavorable [10,25]. At the same time, as the coacervate disintegrates, the protein layer was exposed to hydrolysis by trypsin and \(\alpha\)-chymotrypsin present in pancreatin of the SIF. When this protein layer was hydrolyzed, the particle size was reduced to the point of releasing the W/O first emulsion [23]. Considering the particle size and distribution of the microcapsules during the intestinal digestion, Figure 5a,b show a significant reduction in the particle size distribution.