## 3 Results and Discussion
### SEM Imaging Analysis  
Figure 2 shows the microstructure of the spray-dried powders, as observed using SEM. The images in the first column (a) showed an overview of the spray-dried powders, and those in column (b) and (c) provided a detailed observation on a single particle and its cross section, respectively. The mean particle diameters of sample A1, A2, and A3 were calculated as 100.27 \(\pm\) 10.05, 84.13 \(\pm\) 8.42, and 78.04 \(\pm\) 9.67 \(\upmu\)m, respectively. For powders of RS1, RS2, and RS3, the particle mean diameter was 99.57 \(\pm\) 8.76, 81.15 \(\pm\) 8.34, and 71.37 \(\pm\) 6.52 \(\upmu\)m, respectively. Overall, a smaller particle size was observed for the mandarin powder that was made from the whole fruit juice. This could be associated with the presence of pectin in the mandarin peel, which could participate as the wall material during spray drying. The literature [35] showed that the addition of pectin in the wall materials resulted in producing spray-dried powders with a much lower mean diameter as compared to the use of maltodextrin as a wall material (3.2-5.5 \(\upmu\)m vs. 22.9-45.9 \(\upmu\)m), which could be responsible for the phenomenon that was observed in the current study. The spray dried particles that were produced in this study exhibited an intact surface without fissures (Figure 2, column a). This indicates that the wall material has provided an effective protection against the possible oxidation and degradation of bioactive compounds in the mandarin juices. The morphology of the mandarin juice powders was discrete, and it showed uniformity in particle size and shape, which was very different from the uneven and agglomerated morphology of spray-dried powders that were found in most of the previous studies [14; 22; 23]. The similar surface morphology of each microcapsule could ensure a uniform quality of the final product, and such desirable powder morphology was due to the advantages of the special nozzle that was designed for the MFJ spray dryer [18]. Particles from the whole fruits (column b, C and F) exhibited a relatively severer winkled surface with deeper indentations and bigger bulges, while spray-dried powders that were prepared from the peel-removed mandarin juices showed relative mild indentations (Figure 2, column b, A and D). [PERSON] et al. observed a similar morphology feature when studying Noni juice particles produced by MFJ spray drying, and they ascribed this phenomenon to the properties and different concentrations of wall materials that are used during spray drying [21]. However, in the current study, the morphology difference could not be related to the effect of wall materials or drying conditions, as these parameters were not considered. Figure 2: Scanning Electron Microscopy (SEM) micrograph of Afourer mandarin and Richard Special mandarin microcapsules. (**a**), 180\(\times\) magnification; (**b**), 1500\(\times\) magnification; (**c**), 1000\(\times\) magnification; (**A**), A1 microcapsules; (**B**), A2 microcapsules; (**C**), A3 microcapsules; (**D**), RS1 microcapsules; (**E**), RS2 microcapsules; and, (**F**), RS3 microcapsules. exactly the same for all of the samples. In this regard, a possible reason accounted for the morphology difference in these samples could be due to the variation of sugar and organic acid contents in different mandarin juices. The presence of sugars and acids could lessen the surface tension of particles during spray drying and, thus, yielding shallower and less rugged surface trough [36]. Generally, the interior surface was smoother than the exterior surface (column c and b). A solid inner was observed for all spray-dried particles, and some small vacuoles were present in the interior of the A1 and RS1 particles (A and D). The literature reported that two drying patterns could exist during spray drying of a particle, i.e., \"dry shell\" route and \"wet shell\" route [17]. These two routes largely decide the interior morphology of the final particles, determining whether a solid or a hollow inner structure would be formed.