## 3 Results  
### Antioxidant Activity  
The optimization of antioxidant activity on ABTS-radical scavenging activity and phenolic content were studied using the simplex-centroid mixture design with three different _Melastoma_ extract components (\(x_{1}\): _M. malabathricum_, \(x_{2}\): _M. hirta_, \(x_{3}\): _M. decemfidum_). The proportions of the mixtures used are presented in Table 2 The experiments (1, 6, and 7) represent the pure components, the binary mixtures (2, 9, and 10), the tertiary mixtures (3, 4, and 11), and the center point (5, 8, and 12). The oxidant-ABTS radical cation is generated by persulphate oxidation of 2,2-azinobis (3-ethylbenzothiazoline-6-sulfonic acid). In this work, the radical-scavenging activity of each designed mixture was tested by measuring the decrease in its absorbance value at 734 nm, while the phenolic content of the mixtures of _Melastoma_ leaf extracts was measured based on the amount of phenolic compounds in dry weight gallic acid. The results show that the antioxidant activity from ABTS radical activity obtained from 100% _M. decemfidum_ gave the highest antioxidant activity at 93.11% and phenolic content at 29.25 mg/GAE. From this study, there is no significant difference between _M. hirta_ (92.96%) and _M. malabathricum_ (92.94%) in terms of ABTS radical activity. However, there were differences in the phenolic content of _M. hirta_ and _M. malabathricum_ which were 25.25 and 22.25 mg/GAE, respectively. Furthermore, it can also be seen that the percentage inhibition in ABTS radical assays of all _Melastoma_ samples increased in each experimental mixture compared to its actual pure component. For instance, the binary mixture of _M. malabathricum_ and _M. decemfidum_ increased up to approximately 2%, yielding the highest antioxidant activity of ABTS (94.89%). It also showed that the combination of _M. hirta_ and _M. decemfidum_ increased the inhibition activities of the ABTS radical (94.57%) as compared to the pure components. Tertiary proportions (experiments 3, 4, and 11) represented the percentage inhibition of ABTS radical scavenging activities significantly increased compared to its pure components and binary combination. Moreover, the center point (experiments 5, 8, and 12), which corresponds to the equal proportions, also showed that percentage inhibition of ABTS and phenolic content increased. Recently, a similar study from [PERSON] et al. [18] revealed that the antioxidant potential measured in the mixtures of essential oils (EOs), basil, marjoram, and rosmary gave higher results than the pure samples. The antioxidant activity of the _Melastoma_ leaf extract used in this study correlates with previous literature. For example, the decoction from the leaves of _M. decemfidum_ has been known to exhibit the phenol 2,4-bis (1,1-dimethylethyl) compound, which belongs to one of the important polyphenol  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & & \multicolumn{3}{c}{**ABTS (2, 2-azinobis} & & & \\  & & & & (ethylbenzothiazoline-6-sulfonic acid)) & & & & \\ \cline{3-10}
**Experiment. ** & & & & & & & & **Measured** & **Approx. ** & \\
**No 1** & **M.** & _malabathricum_ & **M.** & _decemfidum_ & **M.** & **Measured** & **Approx. ** & & **Phenolic** & **Phenolic** & **Pechnic** \\  & **(x\({}_{1}\))** & **(x\({}_{2}\))** & **(x\({}_{3}\))** & **(x\({}_{1}\))** & **(x\({}_{5}\))** & **(x\({}_{6}\))** & **(x\({}_{7}\))** & **(x\({}_{8}\))** & **Content** & **Residues** \\ \hline
1 & 0.00 & 1.00 & 0.00 & 92.96 & 92.99 & 0.03 & 25.25 & 25.39 & 0.14 \\
2 & 0.50 & 0.50 & 0.00 & 93.71 & 93.72 & 0.01 & 24.75 & 24.73 & \(-\)0.02 \\
3 & 0.17 & 0.67 & 0.17 & 93.83 & 93.84 & 0  
antioxidant constituents, exhibiting antifungal effects [19]. Phenolic compounds or polyphenols can be characterized as antioxidants, attractants (flavonoids and carotenoids), structural polymers (ligrin), and defense response chemicals (tannins and phytoalexins) [20]. Meanwhile, major antioxidant compounds were also found in both _M. malabathricum_ and _M. hirta_.