## 2 Results and Discussion
### Specific Energy Consumption  
The profiles of specific energy consumption shown in Figure 2a,b represent the amount of energy required to remove moisture from fresh leaves per 1 g of fresh weight and 1 g of water, respectively. Evidently, the shape of the curves suggests that drastic increments of specific energy consumptions are noted at the last stages of the drying process, irrespective of drying methods used. This result indicates that a considerable amount of energy is required to remove the same amount of water compared with the initial drying stages at a specific drying parameter. This behaviour is common in plant products with osmotic cellular structure that functions to limit the loss of moisture from plant tissues [18].  
Figure 2c presents the final specific energy consumptions of CD, VMD and CPD-VMFD. VMD achieved the lowest energy consumptions compared with CD methods, particularly at a high microwave wattage. However, practicality wise, the installation of a large-scale microwave vacuum dryer is costly. Combined drying, involving CD followed by VMFD, is highly recommended for industrial processes considering cost-effectiveness. Therefore, CPD-VMFD is deemed as a compromise between CD and VMD methods in terms of energy consumption requirement. In this study, CPD-VMFD achieved lower final specific energy consumption (55.13 kJ/g fresh weight and 83.60 kJ/g water) than CD at 50 \({}^{\circ}\)C (82.06 kJ/g fresh weight and 113.15 kJ/g water) and slightly higher final specific energy consumption than VMD. CPD-VMFD achieved reduction in the final energy consumptions by 32.82% (kJ/g fresh weight) and 26.12% (kJ/g water) in comparison with CD at 50 \({}^{\circ}\)C.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Drying Method**} & **Final Moisture Content** & **Water Activity \(a_{w}\)** \\  & **(kg water/ kg dw)** & **Water Activity \(a_{w}\)** \\ \hline FD & 0.0575 \(\pm\) 0.001 & 0.2836 \(\pm\) 0.000 b \\ CD (40 \({}^{\circ}\)C) & 0.0372 \(\pm\) 0.000 & 0.2258 \(\pm\) 0.010 c \\ CD (50 \({}^{\circ}\)C) & 0.0336 \(\pm\) 0.001 & 0.1558 \(\pm\) 0.004 f \\ CD (60 \({}^{\circ}\)C) & 0.0289 \(\pm\) 0.001 & 0.1291 \(\pm\) 0.004 g \\ VMD (6 W/g) & 0.0372 \(\pm\) 0.003 & 0.1905 \(\pm\) 0.002 d \\ VMD (9 W/g) & 0.0347 \(\pm\) 0.002 & 0.1697 \(\pm\) 0.005 e,f \\ VMD (12 W/g) & 0.0423 \(\pm\) 0.002 & 0.2200 \(\pm\) 0.003 c \\ CPD-VMFD & 0.0343 \(\pm\) 0.002 & 0.1726 \(\pm\) 0.004 e \\ \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 1: Final moisture content and water activity of dried _C. alata_ dehydrated using different methods.  
Figure 2: **(a)** Specific energy consumption of _C. alata_ leaves per gram of fresh weight dried using CD, VMD and CPD-VMFD. **(b)** Specific energy consumption of _C. alata_ leaves per gram of water removed using CD, VMD and CPD-VMFD. **(c)** Final specific energy consumptions of CD, VMD and CPD-VMFD of _C. alata_ leaves.