# Characterization of the Key Aroma Compounds of Shandong Matcha Using HS-SPME-GC/MS and SAFE-GC/MS
## 3 Results
### Effect of Grinding Process on Volatile Components of Matcha Arroma  
To investigate the connection between the formation of matcha aroma and its grinding process, the volatile components of three grades of matcha before and after grinding were compared. After tencha is processed into matcha, except for a few volatile components, most of the volatile components tend to increase. When T-GS was processed into M-GS, 97 volatile components in M-GS were up-regulated. When T-G1 and T-G2 were processed into M-G1 and M-G2, 112 and 113 volatile components were up-regulated, respectively (Table S3).  
The up-regulated aroma substances in M-GS were 33 heterocyclic compounds, 14 terpenids, 13 esters and 10 alcohols in order of number of components. Heterocyclic compounds had 2-pentyl-furan (fruity, green), 1-(2-pyridyl)-ethanoneone (popcorn), 1-(2-furanyl)-1-pentanone (sweet, caramellic), etc. Terpenoids had terpinolene (herbal, fresh), safranal (herbal, fresh, metallic), beta-elemen (herbal, waxy, fresh), etc. Esters had 3-mercapto-3-methylbutyl formate (ester) (sulfurons), benzoic acid, 1-methylethyl ester (floral, sweet, fruity), benzoic acid, 2-propenyl ester (fruity), etc. Alcohols had (Z)-3-hexen-1-ol (fresh, green, grassy), (E,Z)-3,6-nonadien-1-ol (green) and so on. Fifty-three of these substances were differentially volatile components with higher content in the high-grade matcha screened as outlined in Section 3.4 (Table S4).The up-regulated aroma substances in M-G1 and M-G2 mainly include 16 alcohols, 14 terpenids and 13 alcohols, such as butanoic acid, 3-methylbutyl ester (fruity), hexanoic acid, pentyl ester cyclohexene (fruity), safranal  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**No.** & **Compounds** & **Odor Quality 1 ** & **Concentration 2 ** & **OAVs 3 ** \\ \hline
1 & 3-Methyl-2-butene-1-thiol & sulfurons & 0.0002 [36] & 0.46 \(\pm\) 0.1 ** & 2 & 2316.38 \\
2 & Phenol, 3-ethyl- & musty & 0.05 [36] & 3.51 \(\pm\) 0.83 ** & 70.26 \\
3 & 2-Tiophenethanethiol & fishy & 0.01 [36] & 0.19 \(\pm\) 0.04 ** & 19.13 \\
4 & (E,E)-2,4-Undecadienal & green & 0.02 [36] & 0.28 \(\pm\) 0.07 ** & 14.23 \\
5 & 2,6-Nonadienal, (E,Z)- & green & 0.02 [36] & 0.22 \(\pm\) 0.03 ** & 11.05 \\
6 & 2,4-Nonadienal, (E,E)- & fatty & 0.06 [36] & 0.55 \(\pm\) 0.1 ** & 9.24 \\
7 & (Z,Z)-3,6-Nonadienal & fatty, cucumber & 0.05 [36] & 0.43 \(\pm\) 0.05 ** & 8.68 \\
8 & 2-Decanal, (Z)- & fatty & 0.4 [37] & 0.75 \(\pm\) 0.12 ** & 1.87 \\
9 & 2-Nonanal, (E)- & fatty & 0.19 [38] & 0.29 \(\pm\) 0.03 ** & 1.54 \\
10 & Phenol, 2-methyl-5-(1-methylylethyl)- & spicy & 0.1 [36] & 0.11 \(\pm\) 0.01 ** & 1.07 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Specific aroma components with OAV > 1 in M-GS.  
(herbal, fresh, metallic), isopinocarveol (woody), 1-decanol (fatty) and (E)-2-decen-1-ol (fatty). The compounds with aromas mainly present fatty, fruits and woody notes.  
The Venn diagram showed that 24 volatile components were increased in all three grades of matcha, and these components could contribute to the different aroma characteristics of tencha from matcha (Figure 5). These volatile components mainly included four alcohols, three aromatic hydrocarbons, three esters, five heterocyclic compounds and three terpenoids, such as (2,2-dimethoxyylethyl)-benzene (green), cis-7-decen-1-al (citrus), safranal (herbal) and fenchyl acetate (balsamic).  
Matcha is a powder made by grinding tencha in a stone mill. The unique manufacturing process forms the unique aroma characteristics of matcha. The comparison of the aroma components of matcha before and after grinding showed that most of the aroma components increased, which is why the aroma concentration of matcha is stronger than that of tencha in the sensory evaluation of matcha. Considering the changes in the content of characteristic aroma components and the sensory evaluation scores of aroma characteristics, the grinding process has a very positive effect on the formation of matcha aroma.