NCHU Institute of Food

Roasted stem tea has a characteristic flavour, which is obtained by roasting tea stems, by-product of green tea production. The difference between roasted stem and leaf tea derived from the same tea plants were investigated using GC–MS. Pyrazine compounds exhibited a roasted odour and high flavour dilution (FD) factors, as determined via aroma extract dilution analysis (AEDA). Roasted stem tea was richer in these pyrazines than roasted leaf tea. Geraniol and linalool exhibited high FD factors and a floral odour, and roasted stem tea was richer in these compounds than roasted leaf tea. Introduction Although tea stems are considered as worthless in commercial tea production, roasted stem tea has a characteristic flavour that attracts many people. The volatile compounds from roasted tea have been studied and are reported to contain pyrazine, pyrrole and furan compounds and organic acids . Recently, GC-olfactometry (GC-O) with AEDA was utilised to clarify the odorants in tea and many potent odorants were identified. however, the flavour characteristics of roasted stem tea have not yet been reported. The purpose of this study was to understand the characteristic odorants in roasted stem tea. Pyrazine compounds that contribute to the roasted odour are produced from amino acids in the heating process. Free amino acids and catechins are major taste components in tea. Because these compounds are important for the production of odorants and the quality of tea. Material and Methods 1. Materials 2. Sample preparation 3. Stir bar sorption extraction 4. Thermal desorption 5. Gas chromatography-mass spectrometry and gas chromatography-olfactometry 6. Identification of odorants 7. Aroma extract dilution analysis 8. Analyses of free amino acids and catechins 9. Statistical analysis