# Microencapsulation of Tomato
## 3 Results and Discussion
### Microparticles' Morphology  
The size of the particles obtained by atomization is an important parameter due to its great influence on appearance, rehydration capacity, solubility, fluidity, and dispensability [PERSON] et al. (2016). Furthermore, it is known that the diameter of the particles depends on various factors, such as the drying conditions, concentration, and viscosity of the encapsulated material and the wall material properties [PERSON] (1999). As examples, particle size distributions of particles dried at 155 \({}^{\circ}\)C are presented in Figure 1. They showed a diameter ranging from 0.69 to 26.51 \(\upmu\)m and from 0.58 to 21.67 \(\upmu\)m for the arabic gum and inulin particles, respectively, with about 45% of them having a diameter between 2.5 and 5 \(\upmu\)m and 90% lower than 10 \(\upmu\)m. It was not observed as a significant influence of temperature on particle size distribution for both inulin and arabic gum microcapsules. However, an increase in particle size was observed with the increase of the wall material concentration at the temperature of 155 \({}^{\circ}\)C. This behavior was clearer for arabic gum particles, as shown in Figure 1. The increased viscosity of the spray drying feed solution may explain this fact. According to [PERSON] and [PERSON] and [PERSON] (2016), the size of theliquid droplet during atomization varies directly with the viscosity of the liquid at the constant speed of the atomizer, resulting in larger particles. These results are in agreement with other spray drying powders, such as \(\beta\)-carotene in arabic gum [24] and blackberry juice in maltodextrin [24,25]. Particles collected from spray drying were in the category of skin-forming structures (microcapsules) (Figure 2). These structures are usually formed by fast heat transfer from drying air to feed droplets and water vapor transfer in the opposite direction. When the droplet water content reaches a critical value, the wall material forms a continuous network and a dry outer layer appears at the droplet surface. Afterwards, there is a decrease in the drying rate with the drying front progression that becomes dependent on the water diffusion rate through this layer. Drying is eventually finished when the microcapsule temperature becomes equal to that of the air. In addition, the results on Figure 2 show that the arabic gum particles presented a different morphology when compared to the inulin ones. The majority of the inulin particles had a smooth outer surface, whereas the arabic gum particles showed the formation of teeth or concavities. However, for the same wall material, there was no difference amongst the particles obtained with different spray drying conditions. Figure 1: Relative frequency (Bars) and cumulative frequency (Line) equivalent to the diameter of microcapsules: (**a**) 5% AG, 155 \({}^{\circ}\)C; (**b**) 35% AG, 155 \({}^{\circ}\)C; (**c**) 5% inulin, 155 \({}^{\circ}\)C; (**d**) 35% inulin, 155 \({}^{\circ}\)C.  
This difference in morphology between wall materials may be related to a greater skin rigidity of inulin capsules compared to that of arabic gum, allowing the particles to dry without shrinkage [26]. These results are in agreement with [PERSON] et al. [27] that used two wall materials for the microencapsulation of different wine fruit by spray drying and observed that the inulin particles had a smooth spherical shape, while the particles of the other wall material, hydroxypropyl-\(\beta\)-cyclodextrinrin, had a spherical shape with wrinkled surfaces. [PERSON] et al. [19] in analyzing microcapsules using lycopene as the core material and modified food starch as wall material, also found microcapsules with the rounded outer surface showing teeth formation. The authors reported that the appearance of the teeth formed on the surface was due to the rapid evaporation of the liquid droplets during the spray drying process. In Figure 2c,d, fragmented particles of inulin and arabic gum are depicted.