# Encapsulation of Fennel Essential Oil in Calcium Alginate Microbeads via Electrostatic Extrusion
## 3 Results and Discussion
### Sphericity and Shrinkage of the Microbeads  
The size and sphericity (a value between 0 and 1, indicating how closely the shape of the bead resembles a sphere) of microbeads have a vital role in polymer application. It was shown that the alginate microbead's resistance to compressive pressures and shear increases as its size decreases and that the sphericity of a microsphere is in direct correlation with its mechanochemical stability [28]. In the present study, the microsphere size varied from 2.56 to 3.67 mm (mean diameter) for wet and from 1.18 to 2.75 mm for dry microbeads, respectively. The mean diameter of the wet beads differed from the diameter of the nozzle (1000 \(\upmu\)m), which was expected since the diameter of the beads was usually double the diameter of the used nozzle due to the dominance of surface tension force over the gravitational force during the droplet formation [29]. Since the size and sphericity of the microcapsules can be influenced by various parameters, this study examined the influence of alginate and whey content, as well as drying type, on the sphericity and shrinkage of the microbeads, and their effect is presented in Table 3.  
As can be observed, alginate content had no significant influence on the sphericity of wet microbeads, and all of the concentrations resulted in a spherical shape of microbeads (SF \(\leq\) 0.05) [12]. On the other hand, adding whey protein significantly influenced the sphericity of the wet microbeads, and it can be observed that at both 1 and 2% alginate, increased whey content improved the sphericity of the microbeads, indicating their higher mechanochemical stability. This could possibly be a result of denatured whey protein clusters forming cross-linkages with Ca\({}^{2+}\) ions [30], making the matrix tighter and, thus, allowing for the formation of a more spherical shape. Drying resulted in reduced size and roundness of the microbeads as none of the dry beads had a sphericity factor lower than 0.05, which was also observed by other authors [12; 31; 32]. The drying type had no significant effect, while higher sphericity of the microbeads was observed with a higher content of alginate. Only at 2% alginate, the addition of whey protein resulted in better sphericity, possibly due to its emulsifying properties [33], which reduced material contraction that would have occurred as a result of higher viscosity of higher alginate content. The effect was also likely more pronounced at a higher content of alginate due to more binding sites available for interaction with whey protein. The shrinkage of the microbeads was significantly influenced by alginate content and drying type, while the content of whey protein only had a significant effect when 0.75% was combined with 1% alginate. As the content of alginate increased, a higher shrinkage factor was observed, possibly due to high water loss from the hydrogel network, as a higher content of alginate allowed for a higher water uptake capacity during hydrogel formation [34]. Adding 0.75% whey protein to 1% alginate increased shrinkage of the microbeads, likely due to steric hindrance, which might have occurred between the bulky protein molecules and the alginate chains, therefore disrupting the formation of a well-defined gel structure and resulting in increased shrinkage. Adding a higher concentration of whey protein resulted in the same shrinkage factor as adding no whey protein at 1% alginate, which could have been a result of more opportunities for cross-linking between whey protein molecules and alginate chains, which compensated for the steric hindrance. In addition, whey protein has surface-active properties [35] and can form a film around particles, which may enhance the cohesion between alginate particles during bead formation, resulting in stronger microbeads that are less prone to shrinkage during drying [9].