Automated analysis of 4-mercapto-4-methyl-2-pentanone in Japanese green tea (Sen-cha) by headspace Solid-Phase Microextraction and Gas Chromatography with mass spectrometric determination

Abstract

The objective of this study was to establish a new approach that could be used to characterize trace levels of 4-mercapto-4-methyl-2-pentanone (MMP) in Japanese green tea (Sen-cha). MMP included in the headspace of the powdered tea leaf was extracted using a Solid-Phase Microextraction (SPME) fiber, and subsequently, the determination of MMP in Sen-cha was achieved by Gas Chromatography-Mass Spectrometry (GC-MS) with Selected Ion Monitoring (SIM). To efficiently extract MMP from Sen-cha, the effect of the fiber composition, extraction temperature and time, sample amount, solvent and moisture present in the matrix were investigated, and then the optimum extraction conditions were selected. The calibration curve, which was obtained by the standard addition method, for MMP ranging from 0 to 2.0 ppb showed good linearity, and the difference in the matrix was only slightly affected by this analytical procedure. Therefore, this simple and rapid analytical method proved effective in determining trace levels of MMP in various Sen-cha products by the standard addition method using the same slope of the calibration curve. In addition, based on application of this new analytical technique for the characterization of MMP in Sen-cha, the total flavor intensities of Sen-cha were determined to have a close relationship to the amount of MMP, and its amounts were assumed to be dependent on the steaming conditions of the fresh tea leaves during Sen-cha production.