# Characterization of the Key Aroma Compounds of Shandong Matcha Using HS-SPME-GC/MS and SAFE-GC/MS
## 4 Discussion
It is worth mentioning that our previous electronic nose research found that sulfur compounds have an important impact on the aroma of matcha, but the proportion of sulfur compounds was minimal in this study, indicating that sulfide was vital to the aroma of Shandong matcha. Compared with medium- and low-grade matcha, high-grade matcha contained more sulfur compounds. The threshold of sulfur compounds was relatively low and contributed significantly to flavor [47]. 1-p-menthene-8-thiol is often reported in the literature as one of the most powerful flavor compounds found naturally, with a threshold below \(1\times 10^{-4}\) in water [48]. In addition, previous studies reported that dimethyl sulfide was the key aroma compound in Japanese matcha [27], which presented the aroma of seaweed in green tea; it was also a key aroma compound in green tea [49; 50]. However, dimethyl sulfide was not detected in this study, which may be a result of its unstable chemical properties and easy oxidation. [PERSON] et al. suggested that low molecular weight sulfur-containing compounds such as ethyl mercaptan and dimethyl sulfide were not present in Hojicha as they would have evaporated during the roasting step [10]. Consumers in the Shandong tea area prefer tea products with strong aroma, and the baking temperature and degree of baking are higher than those of Japanese matcha, so no dimethyl sulfide was detected in Shandong matcha. The above results strongly suggest that the aroma of Shandong matcha at different grades may be composed of some common components, and the concentration ratio of common components and the unique components of individual grades make the aroma different. Therefore, it is necessary to further study the odor activity value and aroma recombination test to more accurately evaluate the contribution of each aroma component to the aroma of Shandong matcha. The grinding process is an important processing link in the production process of matcha and plays an important role in the formation of the quality of matcha. Numerous studies have shown that changes in the grinding process may lead to changes in the chemical composition of matcha, especially in the concentration of non-volatile components [33; 39; 51]. It has also been demonstrated that there are differences in aroma components between different milling processes (cyclone, bead and stone millings), and stone-milled matcha was perceived to be higher in roasted notes, containing a higher number of pyrazines [39]. [PERSON] et al. also confirmed that there are differences in aroma components between green tea powder, green tea and green tea extracts [52]. Amongthe aroma components added after high-grade tencha is made into matcha, there were 53 kinds of aroma components that were different from high-grade matcha and middle and low-grade matcha. This demonstrated that the grinding process can fully strengthen the advantages of tencha materials and give the aroma characteristics of high-grade matcha, such as seaweed-like, fresh and roasted notes. After the medium and low-grade tencha is made into matcha, the added aroma components mainly present fatty, fruity and woody aromas, making the medium- and low-grade matcha gradually accompanied by grassy and fatty aromas. Similar observations were made by [PERSON] et al. for extracted non-volatile composition [39]. This might be due to an increase in exposed surface area, which encouraged greater extraction of these compounds upon brewing. Our previous research showed that grinding had a significant effect on the non-volatile components of tea powder [33]. This study further studied the effect of grinding on the volatiles of matcha and found that grinding could increase the concentration of matcha aroma components, enhance the unique aroma characteristics of matcha and play a positive role in the formation of matcha quality.