## 3 Discussion  
As the processed ginseng products such as WG, TG, RG, and BG have been widely used in the herbal markets, it is critical to perform quality control on these products. For this, in this study, we applied the metabolomics approach to profile various metabolites and to statistically analyze the metabolic datasets for characterizing the four processed ginseng products. First, the previously constructed method based on UPLC-QTOF/MS with an in-house library was used to profile various metabolites including ginensoides. UPLC provided a fast and high-resolution separation of compounds, and QTOF/MS was effective for detecting various metabolites including ginensosides, due to its function in the mass scan of whole ions. Second, multivariate analyses such as PCA and OPLS-DA were effectively used to distinguish and characterize the four processed ginseng products. In a PCA score plot, each point indicates an individual sample. Samples having similar metabolic compositions were scattered close to each other, whereas those having different metabolites were divided. The samples of WG, TG, RG, and BG were well differentiated, and this means that each product has a distinct metabolic composition. WG, TG, RG, and BG were also scattered in order from the right side to the left side. In the processing of _P. ginseng_, the degree of heat treatment to produce the four ginseng products differs (WG < TG < RG < BG). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**No. **} & **RT** & \multirow{2}{*}{**Ginsensosides**} & **White Ginseng** & **Tae-Geuk** & **Red** & **Black** \\  & **(min)** & & & & **Ginseng** & **Ginseng** & **Ginseng** \\ \hline  
alonyl ginensoside Rc (M-Rc) & 1.1 \(\pm\) 0.2 & 0.10 \(\pm\) 0.03 & 0.04 \(\pm\) 0.02 & Not detected \\
21 & 16.31 & Ginsenoside Rb2 (R2b) & 0.8 \(\pm\) 0.1 & 1.2 \(\pm\) 0.1 & 2.0 \(\pm\) 0.2 & 1.2 \(\pm\) 0.1 \\
22 & 16.7 & Ginsenoside Rb3 (R3b) & 0.19 \(\pm\) 0.05 & Not detected & 0.45 \(\pm\) 0.03 & 0.28 \(\pm\) 0.09 \\
23 & 16.92 & Malonyl ginensoside Rb2 (M-Rb2) & 1.2 \(\pm\) 0.2 & 0.03 \(\pm\) 0.01 & 0.014 \(\pm\) 0.002 & Not detected \\
24 & 18.39 & Ginsenoside Rd (Rd) & 0.041 \(\pm\) 0.005 & 0.01 \(\pm\) 0.004 & 0.5 \(\pm\) 0.1 & 0.6 \(\pm\) 0.1 \\
25 & 23.43 & Ginsenoside Rg4 (Rg4) & Not detected & Not detected & 0.11 \(\pm\) 0.03 & 0.46 \(\pm\) 0.05 \\
26 & 23.54 & Compound O (CC) & 0.07 \(\pm\) 0.03 & Not detected & 0.06 \(\pm\) 0.03 & 0.14 \(\pm\) 0.05 \\
27 & 23.92 & Ginsenoside R3 (R3k) & Not detected & 0.04 \(\pm\) 0.01 & 0.23 \(\pm\) 0.04 & 0.69 \(\pm\) 0.07 \\
28 & 24.3 & Ginsenoside F4 (F4) & Not detected & 0.40 \(\pm\) 0.03 & 2.5 \(\pm\) 0.3 & 9.0 \(\pm\) 1.1 \\
29 & 24.69 & Ginsenoside Rb4 (Rh4) & Not detected & 0.48 \(\pm\) 0.07 & 3.4 \(\pm\) 0.4 & 8.9 \(\pm\) 0.7 \\
30 & 25.26 & Ginsenoside F2 (F2) & 0.002 \(\pm\) 0.0001 & Not detected & 0.004 \(\pm\) 0.002 & 0.016 \(\pm\) 0.004 \\
31 & 26.03 & Ginsenoside Rg3 (R3) & 0.002 \(\pm\) 0.001 & 0.044 \(\pm\) 0.004 & 0.30 \(\pm\) 0.02 & 1.10 \(\pm\) 0.07 \\
32 & 26.4 & Ginsenoside Mc (Mc) & Not detected & Not detected & 0.01 \(\pm\) 0.002 & 0.08 \(\pm\) 0.02 \\
33 & 26.56 & Compound Y (CY) & Not detected & Not detected & 0.09 \(\pm\) 0.02 \\
34 & 27.38 & Compound K (CK) & Not detected & Not detected & 0.004 \(\pm\) 0.002 \\
35 & 27.45 & Ginsenoside R1 (R1) & Not detected & 1.60 \(\pm\) 0.04 & 4.4 \(\pm\) 0.3 & 14.6 \(\pm\) 1.1 \\Hence, the metabolic alteration of four ginseng products might be related to the degree of heat treatment. Furthermore, in the PCA loading plot, several ginsengides were mainly identified as critical variables to differentiate the four ginseng products. This indicated that the ginseng contents were mainly affected by the processing methods, including hydration and heat treatment. Next, in the OPLS-DA and S-plot, the different compositions of metabolites were distinguished between the two selected samples. In the S-plot, the points of the metabolites that greatly contributed to the variance between two groups, were plotted the farther along the x-axis and y-axis.