## 3 Results and Discussion
### Antioxidant Activities of Coffee Bean Estimation  
Due to the complexity of bioactive compounds profiles in plants, mixed analytical procedures are generally used to estimate the antioxidant capacity of samples [34]. In this study, the antioxidant capacity of coffee beans was estimated using the result analyzed from the six antioxidant activity assays, as shown in Table 1. Overall, all assay results were correlated with the phenolic content assays and were consistent with previous studies, as fermented coffee beans exhibit higher antioxidant activity than unfermented coffee beans [35]. DPPH and ABTS assays are commonly used to determine the antioxidant capacity in samples based on their free radical scavenging capacity by transferring the hydrogen atom [36]. Both the fermented and unfermented coffee beans show a higher result for these two assays in the free phenolic compounds extracts than the bound phenolic compounds. Also, fermented coffee beans are shown to have a higher value in both assays compared with unfermented coffee beans. The increased DPPH and ABTS results after fermentation indicate that fermentation in coffee beans has the potential to generate some metabolites that improve the radical scavenging activity, i.e., the antioxidant capacity of the beans, which then suggests a health-promoting processing [37]. The highest value in the DPPH assay was observed in the fermented Geisha coffee beans, measuring 116.79 mg TE/g, which was 25.45 mg TE/g higher than the fermented Bourbon, which had a value of 91.34 mg TE/g. On the other hand, the unfermented Geisha, with a value of 32.81 mg TE/g, exhibited a significantly lower antioxidant activity compared to the fermented Geisha. A similar trend can be observed in both the Geisha and Bourbon coffee beans in the ABTS assay, with the highest value achieved in the fermented Geisha sample at 285.45 mg TE/g compared to 144.41 mg TE/g in the unfermented Geisha. RPA and FRAP assays were both based on the reducing powder of antioxidants by transferring one electron to turn Fe\({}^{3+}\) into an Fe\({}^{2+}\) ion [38]. The reducing capacity of fermented Bourbon coffee beans is the highest among the other groups of coffee beans, measuring 52.95 mg TE/g, and it is significantly higher than the value of the unfermented Bourbon group, which has a value of 34.16 mg TE/g. For FRAP, the highest value is also shown in the fermented Geisha coffee bean as 110.06 mg TE/g, which has a significant difference compared to the unfermented Geisha at 62.39 mg TE/g. Furthermore, the reducing capacity of fermented Bourbon coffee beans is also significantly higher than that of the unfermented Bourbon coffee beans, with values of 86.83 mg TE/g and 30.99 mg TE/g, respectively. The 'OH-RSA assay has a different mechanism compared to the previous four assays, which is based on the Fenton and Haber-Weiss reaction, producing Fe\({}^{3+}\) and hydroxyl radicals from Fe\({}^{2+}\) by reacting with hydrogen peroxide [39]. Similarly, both groups of fermented coffee beans have a higher value than the unfermented coffee beans (Fermented Geisha: 255.08 mg TE/g; Fermented Bourbon: 279.66 mg TE/g; Unfermented Geisha: 230.51 mg TE/g; Unfermented Bourbon: 196.61 mg TE/g). In FICA assays, the mechanism of testing the antioxidant potential of compounds is achieved by chelating ferrous ions to form the ferrous and ferrozine complexes [13]. The results showed a slight increase in both groups of fermented coffee beans compared with unfermented coffee beans as 0.79 mg EE/g, 0.68 mg EE/g, 0.77 mg EE/g, and 0.63 mg EE/g (fermented Geisha, unfermented Geisha, fermented Bourbon, and unfermented Bourbon, respectively). Generally, the results of these six antioxidant assays align with previous studies, suggesting that the antioxidant activity of coffee beans increases after the fermentation process, primarily due to the release of bound phenolics from the beans [28; 35].