A critical review of key odorants in green tea: Identification and biochemical formation pathway

Green tea, which is non-fermented, has the longest production history in China and the rest of the world. Due to the unique processing techniques, green tea has the lowest concentration of volatile compounds, and the aroma quality of green tea is endowed with pure, pleasant and long-lasting characteristics. Not all of the volatile compounds detected in green tea contribute to the aroma profile, the key odorants that do contribute can be identified by odor activity values (OAVs) and/or flavor dilution (FD) factors. The aim of this review is to summarize the key odorants that have been identified in green tea and discuss the biochemical pathways involved in their formation. Key findings and conclusions: The extraction and identification methods have great effects on the measured composition and concentration of tea volatile compounds. It is therefore important to develop an appropriate combination of analytical-instrumental method to comprehensively improve our understanding of tea volatile compound profiles. The representative key odorants in green tea that have been identified to date are ketones (β-ionone, 3-methylnonane-2,4-dione, (Z)-1,5-octadien-3-one, and coumarin), alcohols (linalool and geraniol), aldehydes (hexanal, nonanal, decanal, octanal, phenyl acetaldehyde, (E,E)-2,4-nonadienal, and vanillin), heterooxygenates (4-hydroxy-2,5-dimethyl-3(2H)-furanone), nitrogenous compounds (indole), sulfide compounds (dimethyl sulfide), and phenols (2-methoxyphenol). Most of the key odorants are formed during green tea processing, but the biochemical pathways involved in their formation still need further study.