# Characterization of the Key Aroma Compounds of Shandong Matcha Using HS-SPME-GC/MS and SAFE-GC/MS
## 3 Results
### Differential Volatile Components in Three Grades of Shandong Matcha  
#### 3.4.1 The Common Volatile Components in the Three Grades of Matcha  
Based on the screening conditions of OPLS-DA, there were relatively few differential volatile components between M-G1 and M-G2, with only 57 differential compounds (10 up-regulated, 47 down-regulated), while a total of 380 (205 up-regulated, 175 down-regulated) differential volatile components between high-grade matcha (M-GS) and medium- and low-grade matcha (M-G1 and M-G2) were screened (Table S2). Among the up-regulated volatile components in M-GS, there were 48 terpenoids, of which alpha-pinene (herbal), 3-carene (citrus), alpha-ionone (loral), trans-beta-ionone (loral), alpha-cadinol (wo woody, herbal), beta-element (sweet) and (+)-alpha-pinene (herbal) \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Group**} & \multicolumn{2}{c}{**HS-SPME**} & \multicolumn{2}{c}{**SAFE**} \\ \cline{2-5}  & **R\({}^{2}\) (\%)** & **Q\({}^{2}\) (\%)** & **R\({}^{2}\) (\%)** & **Q\({}^{2}\) (\%)** \\ \hline T-GS\_vs\_T-G1 & 96.42 & 99.6 & 75 & 94.5 \\ T-GS\_vs\_T-G2 & 94.19 & 99.1 & 84.2 & 98.3 \\ T-G1\_vs\_T-G2 & 85.3 & 99.3 & 76 & 91.3 \\ M-GS\_vs\_M-G1 & 84.5 & 99.2 & 85.5 & 99.2 \\ M-GS\_vs\_M-G2 & 86.2 & 98.7 & 82.8 & 98.8 \\ M-G1\_vs\_M-G2 & 71.1 & 95.4 & 77.9 & 89.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The fitting parameters of OPLS-DA model. Figure 3: PCA score plot of Shandong matcha and tencha. (**a**) HS\(-\)SPME. (**b**) SAFE. were the main ones contributing to the formation of matcha's fresh and floral aroma. Thirty-six heterocyclic compounds with roasted aroma characteristics were screened out, such as (E)-2-(1-pentenyl)-furan (roasted), hydrocoumarin (tonka), 2H-pyran-2-one and 5,6-dihydro-6-pentyl-(coconnut, sweet),. Twenty-three esters with fruity aroma characteristics were screened out, such as bicyclo[2.2.1]heptan-2-ol, 1,7,7-trimethyl-, formate, endo-(green, earthy, herbal), n-propyl acetate (fruity), benzoic acid, 2-propenyl ester (fruity). Seventeen aldehydes and fourteen alcohols with green aroma characteristics were screened out, such as (E,E)-2,4-hexadienal (green), (E,E)-2,4-ocatadienal (green), 2-nonenal (fatty, green), hexanal (green), (E,E)-2,4-heptadien-1-ol (green), (Z)-2-penten-1-ol (green) and (E,Z)-3,6-nonadien-1-ol (green). Most of these substances exhibit characteristics similar to seaweed, fresh and roasted aromas. Among the up-regulated volatile components in M-G1 and M-G2, there were 40 kinds of heterocyclic compound; 2H-pyran-2-one, tetrahydro-6-nonyl-(waxy, fatty, cheesly), 2-ethyl-3,5-dimethyl-pyrazine (nutty, caramellic), 2,3-dimethyl-5-ethylpyrazine (burnt, roasted), coumarin (tonka, hay) were the main ones, with roasted, burnt and fatty aroma characteristics. Forty esters with fatty, grassy and green aroma characteristics were screened out, such as 3-hexen-1-ol, formate, (Z)-(green, fresh, grassy), 3-hexen-1-ol, acetate, (Z)-(green, fresh, grassy), butanoic acid, 3-hexenyl ester, (Z)-(green, metallic, buttertery), 4-decenoic acid, methyl ester, Z-(fruity, fishy, green) and cis-3-hexenyl cis-3-hexenoate (green, metallic). Twenty-five terpenids with fatty, green and herbal aroma characteristics were screened out, such as linalool (floral, woody, green), (-)-beta-bourbonene (herbal, woody, floral), (E)-beta-famesene (woody, citrus, herbal) and (E)-neroldold (floral, green, woody, waxy). Most of these volatile components present characteristic attributes of fatty, green and grassy aromas. Previous studies showed that \(\beta\)-damascone, \(\alpha\)-ionone, furan, 2-pentyl-, hexanal, 1-octen-3-ol, benzaldehyde, 2,4-dimethyl-,\(\alpha\)-cadinol, indole and coumarin are key aroma components of Japanese matcha [10; 27], and these components were all detected in this study (Figure 4). Figure 4: Venn diagram and important differential compounds of different grades of Shandong matcha (**group 1**). Venn diagram of differential compounds in Shandong matcha (**group 2**).