Identification of the Potent Odorants Contributing to the Characteristic Aroma of Darjeeling Black Tea Infusion

Abstract

The odorants contributing to the characteristic aroma of Darjeeling black tea infusion were investigated using aroma extract dilution analysis (AEDA) of the volatile fractions of eight black tea infusions, prepared by a combination of the adsorptive column method and the solvent-assisted flavor evaporation (SAFE) techniques. Principal component analysis (PCA) of the flavor dilution (FD) factors of all the detected odorants in the AEDA revealed that 3,7-dimethyl-1,5,7-octatrien-3-ol (floral: FD factor 4³), 2,3-diethyl-5-methylpyrazine (roasty: FD factor 4⁵) and an unknown compound (green, meaty: FD factor 4⁶) were characteristic odorants of the Darjeeling infusions. In order to identify the unknown compound, the simultaneous distillation extraction (SDE) extract of Darjeeling tea leaves was highly purified by a combination of silica-gel column chromatography and off-line two-dimensional gas chromatography-mass spectrometry (GC-MS). Comparison of the GC retention indices, mass spectrum and odor quality to the authentic compound indicated that the unknown odorant was 4-mercapto-4-methyl-2-pentanone (MMP), which is known as a potent odorant of muscat grapes. Furthermore, comparison of the potent odorants of the Darjeeling tea to those of muscat grapes suggested that the muscatel flavor of Darjeeling tea is formed by the combination of linalool, geraniol, β-damascenone and MMP. In addition, the relationship between the contents of the characteristic odorants in Darjeeling tea and its unusual growing environment or manufacturing process was discussed.