## 3 Results and Discussion
### In Vitro Release Characteristic of Eugenol  
A release study of eugenol from the spray-dried powder was carried out to determine the effect of chitosan concentration on the eugenol released from microcapsules at a predetermined time. The results showed that F1-chi 0.0% powder had the lowest cumulative percentage of eugenol release (41.35%) among other F1 spray-dried powders at the end of the observation time (Figure 3A). However, among the samples containing chitosan, F1-chi 0.33% powder showed the lowest eugenol cumulative release (57.22%) as compared with F1-chi 0.067% (69.78%) and F1-chi 0.2% (59.22%). Chitosan concentration seemed to have the effect of inhibiting the release of eugenol in F1 encapsulation formulations. The difference in eugenol concentration affected its interaction with the WPMD conjugates and chitosan, which was thought to influence the release profile of eugenol from F2 microcapsules. The spray-dried powder of F2-chi 0.0% (40.16%) had a greater percentage of eugenol cumulative release than the F2 powder containing chitosan at the end of the observation time (Figure 3B). The F2-chi 0.067% (34.68%), 0.6% (35.55%), and 1.0% (32.89%) had adjacent release graphs; however, the F2-chi 0.33% appeared to have the lowest cumulative release percentage at 48 h. Thus, it can be concluded that the presence of chitosan retarded the release of eugenol from microcapsules. The percentage of eugenol release increased for 6 h and began to slow down after that until 48 h (Figure 3A,B). The retardation of eugenol release was probably related to the diffusion of active compounds contained in the particles [24]. Furthermore, [PERSON] et al. [46] explained that drug release through a diffusion mechanism began with penetration of the medium into the particle system, which caused the particles to swell, and then the drug was released from the swollen matrix. The mechanism and eugenol release kinetic model of the spray-dried powders were also studied. The calculation to determine the mechanism and release kinetics used the Korsmeyer-Peppas equation (Equation (5)). The results of the calculation of the release kinetics showed that the values of the diffusion exponential (n) of all samples were less than 0.43 (Table 5). This indicates that the release mechanism in the eugenol microcapsules followed Fickian release (case I transport). Release of eugenol occurred through a diffusion process. [PERSON] and [PERSON] [47] explained the criteria of the n value as follows: n \(\leq\) 0.43 indicates Fickian release, n = 0.85 indicates case II transport, and 0.43 \(<\) n \(<\) 0.85 indicates non-Fickian release (an anomalous behavior). The results also revealed the diffusion constant value (k) and Pearson coefficient (\(R^{2}\)). The k value indicates the kinetics of the release. The greater the value of k, the faster the release of an active compound from microcapsules [48]. Figure 3: Release profile of eugenol from F1 (**A**) and F2 (**B**) spray-dried powders. Regarding some of the phenomena encountered in this experiment, the F1 formula samples had a cumulative release percentage greater than the formula F2 samples. The result was supported by the k value of the samples. The k value of F1 samples was higher than that of the F2 samples, indicating that the release of eugenol from F1 samples was faster than that from the F2 samples. The F1-chi 0.0% had the lowest cumulative release percentage and k value among other F1 microcapsules, while F2-chi 0.0% had the highest cumulative release percentage among other F2 microcapsules. According to [PERSON] and [PERSON] [24], the amount and release rate of a component were influenced by the pH of the media. However, the media used in this release trial had the same pH (7.4) for all samples. The differences between each sample were the combination of eugenol concentration and chitosan concentration. The eugenol spray-dried powders were obtained from eugenol emulsions with different emulsion pH values.