# Characterization of the Key Aroma Compounds of Shandong Matcha Using HS-SPME-GC/MS and SAFE-GC/MS
## 1 Introduction  
Matcha is a finely powdered green tea product made from the fresh leaves of tea plants cultivated in the shade, dried by steam (or hot air) and processed by grinding. Matcha has almost all the nutrition and health function of green tea, and its powder properties expand the range of applications [1, 2]. In recent years, with the change of matcha consumption from drinking to eating, the application of matcha has expanded to food [3], health products [4, 5], cosmetics [6, 7] and other industries, which has promoted a strong demand for matcha in China. Due to its fresh color, unique aroma and distinctive taste that is slightly bitter and sweet, matcha has quickly become a must-have for food lovers, especially among young people. With the increasing demand for matcha, some tea-producing areas in China that are rich in green tea have begun to gradually develop and produce matcha. The aroma and taste characteristics vary among the different tea-producing areas, so understanding these characteristics is important as they affect consumer preference. The Shandong tea area is the northernmost tea area in China, and its latitude (34\({}^{\circ}\)22.9\({}^{\prime}\)-38\({}^{\circ}\)24.01\({}^{\prime}\) north) is similar to that of Shizuoka, Japan. More chlorophyll and theanine, which are very suitable for the production of matcha, are accumulated in the tea leaves. Shandong matcha has the quality characteristics of soft, fine and uniform powder; bright green soup color; obvious seaweed aroma and strong, fresh and brisk taste. The aroma profiles vary among the different tea categories, and even the same category of tea can have different aroma characteristics. The composition of tea volatiles is complex, and many compounds exist in trace levels. HS-SPME, SAFE, SBSE, SDE and other technology are commonly used to extract volatiles and concentrate them to detectable levels [8; 9; 10]. Gas chromatography-mass spectrometry-olfactometry (GC-MS-O), two-dimensional gas chromatography-mass spectrometry (GC \(\times\) GC-MS) and odor activity value (OAV) have been used to elucidate the volatile components by separating, detecting and identifying them [11; 12; 13; 14; 15]. Using the above aroma extraction and identification techniques, researchers have identified the key aroma compounds in Laoshan green teas, Chinese high altitude and northernmost black tea, white tea and pu'er tea [16; 17; 18; 19; 20]. Some key odorants responsible for the chestnut-like aroma, clean aroma, orchid-like aroma and cooked corn-like aroma quality of green teas have been also identified [21; 22; 23; 24; 25]. There are also some research reports on the aroma of matcha, mainly involving Japanese matcha and Turkish tea powder. The effects of tea clones, shading and shooting period on volatile components in Turkish green tea powder were comparatively studied, and the potent odorants in Japanese matcha were reported using gas chromatography-olfactometry (GC-O) [26; 27], while [PERSON] et al. compared and characterized the volatiles of different Japanese green teas (sencha, matcha and hojicha) [10]. Ultrafine grinding is a commonly used material processing technology in food processing. While changing the physical properties of food materials, it also affects the sensory quality of products, such as taste and aroma. This technology has recently been widely used in the processing of food materials such as buckwheat flour, coix seed flour and rice flour [28; 29; 30]. Superfine powders could provide improved physicochemical properties, for example, higher antioxidant activity and total phenolic content, better thermal properties and solubility, superior taste and functional characteristics [29; 31; 32]. Although matcha is made from milled tencha leaves, its aroma characteristics are different from those of tencha. Our previous research showed that superfine grinding was beneficial to reducing bitterness and preserving briskness of green tea powders.