## 3 Results and Discussion
### GC-MS Analysis of _P. amboinicus_ essential oil Extract  
GC-MS analysis of _P. amboinicus_ essential oil extracted from leaves harvested at different time points was conducted to evaluate the influence of harvesting time on the chemical constituents present in the extracts. Twenty-five compounds were identified and categorized according to their phytochemical classes (Table 1 and Figure 6). Compositions of the essential oil constituents were found to be consistent at all time points and were dominated by carvacrol (47.00-60.00%), \(\gamma\)-terpinene (8.00-10.00%), caryophyllene (\(\sim\) 6.00%), p-cymene (4.90-6.50%), _trans_-\(\alpha\)-bergamotene (4.70-5.00%), and thymoquinone (3.30-5.65%). From the GC-MS data, it can be seen that the percentages of carvacrol and thymoquinone, the monoterepene compounds, were higher in the leaves extracted at 2 p.m. than at the other time points. Carvacrol and thymoquinone have been studied for many years for their functional properties and bioactivities, including antioxidant and oxidative stress effects [21; 22; 23]. Figure 5: Total phenolics and total flavonoids contents in _Plectranthus amboinicus_ leaf essential oil extracts (expressed as gallic acid equivalent (GAE) and catechin (CE) equivalent). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Peak** & **Compounds** & **RT a (min)** & **RI b ** & **Harvesting Time/Relative Content c (\%)** \\ \cline{3-6}  & & & & **8 a.m.** & **2 p.m.** & **8 p.m.** \\ \hline \multicolumn{6}{c}{_Monoterpene hydrocarbons_} \\
1 & \(\beta\)-Thujene & 8.21 & 926 & 0.25 & 0.21 & 0.39 \\
2 & \(\alpha\)-pinene & 8.39 & 932 & 0.10 & 0.10 & 0.12 \\
3 & \(\beta\)-Myrcene & 10.17 & 991 & 0.47 & 0.41 & 0.63 \\
4 & \(\alpha\)-Phellandrene & 10.55 & 1004 & 0.17 & 0.14 & 0.17 \\
5 & \(\alpha\)-Terpinene & 10.93 & 1016 & 1.25 & 1.02 & 1.40 \\
6 & p-Cymene & 11.19 & 1025 & 5.42 & 5.03 & 6.44 \\
7 & Limonene & 11.30 & 1028 & 0.26 & 0.23 & 0.38 \\
8 & \(\gamma\)-Terpinene & 12.26 & 1060 & 10.11 & 8.89 & 10.33 \\ \multicolumn{6}{c}{_Oxygenated monoterepenes_} \\
9 & \(\beta\)-Terpineol & 12.50 & 1067 & 0.69 & 0.77 & 1.03 \\
10 & Thymouinone & 17.90 & 1252 & 3.92 & 5.65 & 3.31 \\
11 & Thymol & 19.10 & 1296 & 0.51 & 0.49 & 0.27 \\
12 & Carvacrol & 19.45 & 1309 & 59.25 & 59.79 & 48.13 \\ \multicolumn{6}{c}{_Sesquiterpene hydrocarbons_} \\
13 & Caryophyllene & 22.43 & 1424 & 6.66 & 6.29 & 6.17 \\
14 & _Trans-\(\alpha\)-Bergamotene & 22.80 & 1439 & 4.94 & 4.79 & 4.84 \\
15 & Humulene & 23.28 & 1458 & 1.86 & 1.80 & 1.75 \\
16 & (E)-6-Farnesene & 24.01 & 1487 & 0.12 & 0.11 & 0.14 \\
17 & \(\beta\)-Bisabole & 24.58 & 1511 & 0.26 & 0.26 & 0.26 \\ \multicolumn{6}{c}{_Oxygenated sesquiterpenenes_} \\
18 & Caryophyllene oxide & 26.41 & 1590 & 0.96 & 1.08 & 1.11 \\ \multicolumn{6}{c}{_Alkane and alcohol_} \\
19 & 3-Methylcyclopentanol & 5.86 & 841 & 0.26 & 0.29 & 0.17 \\
20 & 4-Ethyl-octane & 9.07 & 954 & - & - & 0.37 \\
21 & 3-Ethyl-octane & 9.44 & 967 & - & - & 0.29 \\
22 & 3-methyl-nonane & 9.54 & 970 & - & - & 0.89 \\
23 & 1-Octen-3-ol & 9.86 & 980 & 0.54 & 0.63 & 0.51 \\
24 & 3,8-Dimethyl decane & 15.56 & 1171 & - & - & 0.55 \\
25 & 3-Methylpentadecane & 25.98 & 1571 & - & - & 0.35 \\ \hline \multicolumn{6}{c}{Chemical class} \\ \hline \hline  & Monoterpene hydrocarbons & & 18.03 & 16.03 & 19.86 \\  & Sesquiterpene hydrocarbons & & 64.37 & 66.70 & 52.74 \\  & Total monoterepnes & & 82.40 & 82.73 & 72.60 \\  & Sesquiterpene hydrocarbons & & 13.84 & 13.25 & 13.16 \\  & Oxygenated sesquiterpenenes & & 0.96 & 1.08 & 1.11 \\  & Total sesquiterpenes & & 14.80 & 14.33 & 14.27 \\  & Others & & 0.80 & 0.92 & 3.13 \\ \hline Total & & 98.00 & 97.98 & 90.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Compounds identified from _Plectranthus amboinicus_ leaf essential oil extract. The major constituents were constitutively present at relatively high percentages throughout the day, and they contributed to the unique, strongly aromatic oregano-like odor of the _P. ambionicus_ leaves.