Characterisation of key odourants in Japanese green tea using gas chromatography-olfactometry and gas chromatography-mass spectrometry

Japanese green tea is becoming increasingly popular worldwide due to its pleasant aroma. The volatiles of four types of Japanese green tea (Sencha, Matcha, Gyokuro, and Hojicha) were extracted separately by headspace solid-phase microextraction (HS-SPME) and solvent-assisted flavour evaporation (SAFE), and then analysed using gas chromatography-mass spectrometry (GC-MS). The aroma-active compounds in each type of green tea were identified by aroma extract dilution analysis (AEDA) of its SAFE extract. The odourants exhibiting the highest flavour dilution (FD) factor of 27 in Sencha were indole and methional. For Matcha, nonanal had the highest FD factor of 243. The odourant in Gyokuro with the highest FD factor of 27 was indole. For Hojicha, the odour-active compounds exhibiting high FD factor of 729 and 243 were 2,3-diethylpyrazine and 2,3-diethyl-5-methylpyrazine, respectively. Sensory evaluation was then done on the SAFE extract to understand the overall aroma profile of each type of green tea. Based on sensory evaluation results, steamed green teas (Sencha, Matcha, and Gyokuro) had leafier and higher floral notes while roasted green tea (Hojicha) showed higher roasty and woody notes. Finally, principal component analysis (PCA) of data obtained from GC-MS analysis demonstrated marked separation of these four types of Japanese green tea.