## 2 Results and Discussion
### Antioxidant Activity and Total Phenolic Content (TPC) Analysis
The results showed that CD at 40 \({}^{\circ}\)C could preserve phenolic compounds better than freeze drying (FD), contrary to the understanding that FD, a low-temperature dehydration method, could preserve high amounts of phenolic compounds. However, a previous report has suggested that FD treatment may not have deactivated degradative enzymes completely because of the low-temperature dehydration process. This could lead to the reactivation of degradative enzymes when freeze-dried samples are exposed to moisture in the air [23]. This is supported by the result obtained by [PERSON] et al. [24], which investigated the thermal inactivation kinetics of polyphenol oxidase (PPO) of chicory leaves. It was found that the residual activities of PPO at the end of hot air drying was considerably lower than that of FD, which indicates that hot air drying was more effective in the inactivation of PPO compared to FD, inhibiting enzymatic oxidative reactions to an extent. It was suggested that enzymatic oxidative reaction is more likely to occur during FD as the formation of ice crystals in the tissue matrix of the raw material will lead to cell rupture, subsequently exposing phenolic species to oxidative conditions. However, most studies have shown that FD is able to preserve phenolic compounds better than hot air drying, in the case of oregano leaves [25], strawberry [21] and citrus fruits [26]. Therefore, the influence of a particular drying method on the preservation of phenolic compounds is difficult to predict and is dependent on the specific compounds and the particular plant material involved. Overall, the antioxidant activity values failed to correlate well with TPC values. Thus, antioxidants other than phenolic compounds could have contributed to the total antioxidant activity (terpene compounds) contained in volatiles, phytosterols and fatty acid constituents in _C. alata_. For example, terpen contained in _C. alata_ (such as citronellol, linalool and fenchone; Figure 3) are amongst the identified terpen that could contribute to the total antioxidant activity. This result is based on the fact that terpen have been reported to be potential antioxidant compounds because of their capability to interact with free radicals. The antioxidant potential of terpen is suggested to be similar to flavonoids, and their antioxidant effect depends on the structural characteristics such as the presence of hydroxyl groups, multiple bonds, conjugated systems and phenolic structure [27]. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Drying Method**} & **Antioxidant Activity (\(\mu\)M Trolox/100 g dw)** & **Total Phenolic Content** \\ \cline{2-4}  & **ABTS** & **FRAP** & **(mg/100 g dw)** \\ \hline Fresh & 65.53 \(\pm\) 4.97 a & 30.69 \(\pm\) 6.91 a & 9368.59 \(\pm\) 1460.98 a \\ FD & 11.49 \(\pm\) 0.25 b,c & 5.34 \(\pm\) 0.17 b & 2883.05 \(\pm\) 146.45 b \\ VMD 6 W/g & 9.04 \(\pm\) 1.19 b,c & 3.28 \(\pm\) 0.08 b & 1982.44 \(\pm\) 53.17 b \\ VMD 9 W/g & 11.29 \(\pm\) 1.03 b,c & 4.70 \(\pm\) 0.25 b & 2379.87 \(\pm\) 216.92 b \\ VMD 12 W/g & 9.15 \(\pm\) 1.70 b,c & 5.39 \(\pm\) 0.38 b & 2414.91 \(\pm\) 82.86 b \\ CPD-VMFD & 11.19 \(\pm\) 0.33 b,c & 5.01 \(\pm\) 0.18 b & 2413.36 \(\pm\) 277.94 b \\ CD at 40 \({}^{\circ}\)C & 13.54 \(\pm\) 0.02 c & 5.55 \(\pm\) 0.24 b & 2965.12 \(\pm\) 54.97 b \\ CD at 50 \({}^{\circ}\)C & 8.65 \(\pm\) 0.27 b,c & 3.88 \(\pm\) 0.58 b & 2342.75 \(\pm\) 74.18 b \\ CD at 60 \({}^{\circ}\)C & 7.43 \(\pm\) 0.63 b & 2.58 \(\pm\) 0.09 b & 1821.54 \(\pm\) 41.18 b \\ \hline \hline \end{tabular} FD—freeze drying; CD—convective drying, VMD—vacuum microwave drying, CPD—convective pre-drying, VMFD—vacuum microwave finish drying. Values with the same letter in the same column are not significantly different (\(p<0.05\)) according to [PERSON]’s test.  
\end{table} 
Table 3: Antioxidant activity and TPC of _C. alata_, influenced by various drying methods and conditions.