HEADSPACE SOLID-PHASE MICROEXTRACTION GAS CHROMATOGRAPHY-MASS SPECTROMETRY (HS SPME-GC-MS) DETERMINATION OF ODORANTS IN GREEN TEA

Green tea, the most widely consumed beverage in Asia, has recently become more widespread in the West where black tea is traditionally consumed. Green tea is made solely with the leaves of Camellia Sinensis that have undergone minimal oxidation under processing. The popularity of this tea is due to many factors. Although some evidence suggests that regular tea drinkers have a lower chance of developing heart disease and certain types of cancers, one of the most contributory factors is its flavor. The characteristic manufacturing process of green tea includes steaming during which the enzyme in tea leaves is inactivated and the green color of the leaves is maintained. Usually the flavor extract of green tea infusions are prepared by steam distillation under reduced pressure and the steam distillate is extracted (liquid-liquid extraction) and concentrated before the injection in a gas chromatography system. The most potent odorants are characterized by Aroma Extract Dilution Analysis (AEDA) and the flavor dilution (FD) determined [1]. In this study, a headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) analysis is proposed as a complementary and alternative method to steam distillation for the characterization of odorants in different kinds of Chinese and Japanese green teas. Recently, solid-phase microextraction (SPME) has gained acceptance in many fields as an accurate, rapid, sensitive and solvent-free sampling method [2,3]. Its application is reported by many researchers as a useful approach in sample preparation of volatile compounds from complex matrices. After the optimization of extracting conditions (fiber, temperature, time of extraction, stirring rate, etc.), a 65 m polydimethilsiloxane/divinylbenzene (PDMS/DVB) fiber was used to extract the volatile compounds from tea infusion and leaves. The extracted compounds were then desorbed and analyzed by GC-MS on a Phenomenex ZB-WAX capillary column (30 x 0.25 mm ID x 0.15 m film). Some of the main odorants were identified by comparing the mass spectra and the Kovats Index to those of pure standards, or to the library data (NIST). This method has been also applied to the comparison of the aroma contents of green tea before and after roasting treatment at two different temperatures (160 and 180 °C) for 20 minutes. Under these conditions, the volatile components profile changed and some potent odorants were formed at adequate levels for contributing to the Houjicha flavor [4]. To this purpose, an internal standard (menthol) was used to calculate the relative percentage of the considered compounds. HS-SPME combined with GC-MS can be considered a rapid approach by which we can characterize the aroma profile of green tea as a complementary tool to steam distillation and liquid-liquid extraction.