# Characterization of the Key Aroma Compounds of Shandong Matcha Using HS-SPME-GC/MS and SAFE-GC/MS
## 4 Discussion  
It is generally believed that matcha has a unique green aroma with some sweet and roasted odors. [PERSON] et al. gave some descriptors of the aroma profile to describe green tea and matcha, such as floral, hay, leafy, roasted, seaweed-like, sweet and woody [10]. [PERSON] et al. suggested that sweet, green, metallic and floral notes are essential for the aroma of Japanese matcha, and some odorants influence the characteristic aroma of each grade [27]. Most potential flavor-contributing compounds reported in matcha previously by [PERSON] et al., [PERSON] et al. and [PERSON] et al. were present in Shandong matcha [10; 27; 39]. Based on the aroma attributes of potential flavor-contributing compounds, the differences for sensory evaluations in matcha aroma could be explained. In this experiment, high-grade Shandong matcha had a light sweet and roasted aroma (seaweed-like aroma). Hexanal, 1-octen-3-ol and 2-pentyl-furan have been proven to contribute to the formation of seafood aroma [40], among which hexanal is a common aroma component in Pu'er tea [41]. \(\alpha\)-ionone, \(\beta\)-damascone and \(\beta\)-ionone are typical carotenoid degradation products, and the unique shading technology of tencha was found to enhance carotenoids, which may increase the content of derived aromatic precursors [10]. \(\alpha\)-cadinol is the main component of essential oil of fresh fruits [42]. In the aroma of tea, the alcoholic aroma substances contribute to floral and fruity aroma or fragrance. As one of the important glycoside hydrolases in tea, \(\beta\)-glucosidase mainly hydrolyzes and releases alcoholic aroma. Its activity can be enhanced by shading and fertilization so as to improve the aroma of tea, thus contributing to the formation of the flower and fruity note of matcha. 3-Hexen-1-ol, (Z)- can be obtained either  
Figure 5: Differential compounds of Shandong matcha made from different grades of tencha. (a) Number of up-regulated differential compounds. (b) Number of down-regulated differential compounds. by lipid degradation or by hydrolysis of its glycoside precursors during the withering stage [43]. It had a high concentration in green tea, and its content was proportional to the grade. Medium- and low-grade matcha showed a slightly grassy, harsh and high-fried note. Coumarin was reported to be a characteristic compound that affects the sweet quality of Chinese green tea and Japanese green tea [44]. Indole is the characteristic aroma component of Oolong tea [45]. (E)-linal oxide (pyranoid) is a glycoside derivative in green tea [43], and methyl salicate has been reported to be a key aroma component in black tea [8]. The above different aroma components are the key to determining the aroma quality of different grades of Shandong matcha, and this is consistent with the findings of [PERSON] et al. [27]. Heterocyclic compounds were the most differential compounds in different grades of matcha and were the main products of the Maillard reaction, and the most important intermediate product of this reaction was glycosamines. The formation of glycosamine compounds was significantly related to amino acids and reducing sugars in tea [46]. The high proportion of heterocyclic compounds in total volatile components of Shandong matcha may be due to the geographical advantages of Shandong province, and the fresh leaves were treated with shade, so the content of amino acids in fresh leaves was high, which was conducive to the formation of glycoamine compounds. [PERSON] et al. pointed out that stone-milled matcha was higher in roasted notes, containing a higher number of pyrazines [39]. Therefore, the stone grinding process in this study is another reason for the higher heterocyclic compounds in Shandong matcha. In addition, due to the different concentration ratios of some common components in different tea samples of different grades and the interaction between various aroma components, high grade matcha had a roasted note, while medium- and low-grade matcha had a high-fired note.