## 2 Results and Discussion
### Color Analysis  
Color values of fresh and dried _P. nodiflora_ leaves are shown in Table 6. Parameters investigated include lightness (\(L^{*}\)), 0 (black) to 100 (white); greenness or redness (\(a^{*}\)), \(-60\) (green) to 60 (red); \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Compound**} & \multicolumn{2}{c}{**Retention Time (min)**} & **Fresh** & **CD 50 \({}^{\circ}\)C** & **CPD–VMFD** \\ \cline{2-5}  & **Exp.** & **Lit.** & **Concentration (mg 100 g\({}^{-1}\)db)** \\ \hline \(\beta\)-Sitosterol & 28.99 & 28.98 & 529.67 & 268.88 & 280.99 \\ Stigmasterol & 28.06 & 28.15 & 323.47 & 173.34 & 191.72 \\ Campesterol & 27.58 & 27.58 & 205.81 & 100.24 & 99.65 \\ Betulin & 31.16 & 31.17 & 30.68 & 37.30 & 39.17 \\ Desmosterol & 26.64 & 26.63 & 76.89 & 35.59 & 37.94 \\ Cycloartenol & 30.00 & 30.05 & 28.15 & 24.15 & 22.43 \\ Lanosterol & 26.89 & 26.88 & 40.58 & 19.88 & 20.31 \\ \(\alpha\)-tocopherol & 25.97 & 25.95 & 2.14 & 9.30 & 18.86 \\ \hline Total & - & - & 1237.39 & 668.66 & 711.07 \\ \hline \hline \end{tabular} Exp.—experimental; Lit.—Retention time according to [PERSON] [42]; CD—convective drying; CPD—convective pre-drying VMFD—vacuum microwave finish drying.  
\end{table} 
Table 4: Phytosterols profile of _P. nodiflora_ dried using different drying methods. and blueness or yellowness (_b*_), \(-60\) (blue) to \(60\) (yellow). Color changes in herbs subjected to drying are usually due to the loss of green pigments and carotenoids or enzymatic browning [48]. However, the shaping of the color profile of the dried product depends not only on the time and drying conditions but also on the amount of residual water, which can be estimated by the water activity values. Fresh leaves recorded the highest \(L^{*}\) value, whereas VMD at 12 W/g resulted in the darkest colored leaves with lowest \(L^{*}\) value, but these values were not significantly different from those of VMD 6 and 9 W/g and CD 40 \({}^{\circ}\)C. These conditions promote PPO activity, which results in browning characteristics of dried products [49; 50]. An increase in microwave power, from 6 to 12 W/g, associated with increased maximal temperature of dried material from 52 to 57 \({}^{\circ}\)C, decreased the \(L^{*}\) value from 45.62 to 43.94. At higher microwave powers, increased amounts of absorbed energy used to vaporize water were observed, which may have been sufficiently large to increase the sample temperatures further during the falling rate period, thereby producing darker leaves [38]. This finding was evidenced in a previous study, in which burnt spots were observed on mint leaves after VMD [38]. The loss in green color was assumed to be related to the loss of chlorophyll [48], as indicated by an increase in \(a^{*}\) values (Table 6) which is thought to be associated with decreased \(\mathrm{a_{w}}\) (Table 7). This relationship was confirmed for CD and VMD samples because the decrease in \(\mathrm{a_{w}}\) from 0.2252 to 0.1081 and from 0.2780 to 0.2353 resulted in increased \(a^{*}\) values from \(-6.35\) to \(-5.21\) and from \(-5.96\) to \(-5.86\), respectively. The lowest values of \(a^{*}\) were \(-6.35\) and \(-7.02\), which were found for CD 40 \({}^{\circ}\)C and CPD-VMFD samples, respectively. In the case of CD 40 \({}^{\circ}\)C, the processing temperature was the lowest, whereas combined drying CPD-VMFD underwent at a relatively short time and moderate conditions in terms of temperature and microwave power, thereby leading to lower extents of chlorophyll degradation.