## 2 Results and Discussion
### Antioxidant Activity and Total Phenolic Content Analysis  
Analysis of antioxidant activity showed that the highest antioxidant activity was observed for VMD 6 W/g samples 2,2\({}^{\prime}\)-Azinobis (3-ethylbenzothazoline-6-sulfonic acid (ABTS), 11.00 uM Trolox/100 g dw; ferric reducing antioxidant power (FRAP), 15.99 uM Trolox/100 g dw). The lowest antioxidant activity was obtained with VMD 12 W/g with an ABTS value of 6.62 uM Trolox/100 g dw, whereas the lowest FRAP value of 8.26 uM Trolox/100 g dw was shown by CD 40 \({}^{\circ}\)C samples (Table 2). Active compounds of thermally dried herbs were assumed to have undergone thermal degradation and oxidative degradation in the case of CD and CPD-VMFD, thereby leading to the lower antioxidant activities observed. The results clearly indicate that a suitable application of hot-air temperature and microwave power, during CD and VMD, have the potential in yielding high antioxidant activities. A low microwave power of 6 W/g (VMD) and a higher temperature of 60 \({}^{\circ}\)C in CD were beneficial in yielding high antioxidant activities. The intensity of drying treatment also affected antioxidant activity. The increase in temperature of CD, from 40 to 60 \({}^{\circ}\)C, shortened the drying length within 360 to 180 min. At 50 and 60 \({}^{\circ}\)C, the degradation of heat-sensitive compounds was considerably lower compared to CD at 40 \({}^{\circ}\)C, which was confirmed by relatively high antioxidant activity. These results indicate that the increase in temperature during CD is effective in accelerating the drying process, thereby shortening sample's exposure to elevated drying temperature in a highly oxygenated condition. With increased microwave power of VMD, from 6 to 12 W/g, antioxidant activity decreased. The increase in microwave power from 6 to 12 W/g decreased the drying time from 28 to 21 min, which; however, did not contribute to the preservation of antioxidant activity in the same way as observed in the case of CD. Evidently, the reduction in drying  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Drying Method**} & \multicolumn{2}{c}{**Antioxidant Activity (uM Trolox/100 g dw)**} & \multirow{2}{*}{**Total Phenolic Content**} \\ \cline{2-3} \cline{3-4}  & **ABTS** & **FRAP** & **(mg/100 g dw)** \\ \hline Fresh & 14.34 \(\pm\) 0.93  & 18.25 \(\pm\) 0.54  & 1484.64 \(\pm\) 30.68  \\ CD 40 \({}^{\circ}\)C & 7.60 \(\pm\) 0.46  & 8.26 \(\pm\) 0.54  & 1609.73 \(\pm\) 69.24  \\ CD 50 \({}^{\circ}\)C & 10.25 \(\pm\) 0.77  & 14.18 \(\pm\) 1.69  & 1762.20 \(\pm\) 31.38  \\ CD 60 \({}^{\circ}\)C & 10.54 \(\pm\) 1.22  & 14.17 \(\pm\) 0.91  & 1828.92 \(\pm\) 110.18  \\ VMD 6 W/g & 11.00 \(\pm\) 0.19 [FOOTtime did not compensate for the degradation of the antioxidant compounds resulting from the greater amount of heat generated inside the material by increased microwave radiation. The lengthy CD process can be shortened with microwave heating, as seen in CPD-VMFD. Results of FRAP assay showed that CPD-VMFD produced samples of higher or not significantly different antioxidant activity from samples dried exclusively with CD or VMD. The higher antioxidant activity of CPD-VMFD samples compared to CD at 40 \({}^{\circ}\)C (for FRAP assay) can be explained by the shortened drying time of the former. The presence of high moisture, oxygen, and heat during the lengthy drying process of CD 40 \({}^{\circ}\)C may have facilitated the degradation of antioxidant compounds by enzymes [23]. As for the higher antioxidant activity of CPD-VMFD samples compared with VMD at 9 and 12 W/g, the oxygen exposure during CPD-VMFD did not cause a large reduction in antioxidant activity. Several previous studies have indicated that phenolic content and antioxidant activity increase after heat treatment of peppermint leaves, _Artemisia annua_ leaves [24], and culinary herbs, namely basil, rosmary, oregano, sage, thyme, and marjoram [25]. [PERSON] et al.