Purification and Gas Chromatography-Combustion-Isotope Ratio Mass Spectrometry of Aroma Compounds from Green Tea Products and Comparison to Bulk Analysis

A method for carbon isotope ratio (delta C-13) analysis was developed for compound-specific isotope analysis of tea volatiles, and the values were compared with the delta C-13 value from bulk isotope analyses. The delta C-13 value of 2-phenylethanol liberated via enzymatic hydrolysis of the 2-phenylethyl beta-primeveroside standard was examined first. Isotope fractionations for 2-phenylethyl beta-primeveroside from preparative high-performance liquid chromatography (HPLC) were also analyzed. The enzymatic treatment and the preparative HPLC process did not cause carbon isotope fractionations, substantiating the strategies available for delta C-13 analysis of volatile compounds. On the basis of the gas chromatography combustion isotope ratio mass spectrometry data from 2-phenylethanol, it was possible to derive the conditions for enzyme treatment and preparative HPLC of the glycoconjugates of 2-phenylethanol, (Z)-3-hexenol, and benzyl alcohol isolated from green tea leaves. Larger variations in delta C-13 were found for individual volatile compounds compared with bulk analytical data from the leaves, indicating the potential to utilize this strategy in assigning the geographical origin of green tea.