Characterization of the key compounds responsible for the fermented soybean-like cup aroma of raw Pu-erh tea using instrumental and sensory methods

Cup aroma refers to the volatiles emitted from an empty cup after tea infusion. In this study, gas chromatography–olfactometry (GC–O) and the odor activity value (OAV) approach were employed to investigate the composition of fermented soybean-like cup aroma from raw Pu-erh tea. Further, the aroma recombination and omission tests were performed, and the results demonstrated that 2-methylbutyric acid, acetic acid, 4-methyl-3-penten-2-one, ethyl isobutyrate, nonanoic acid, and phenylacetic acid exhibited relatively high aroma intensities (AI) and OAVs among the 12 odor-active compounds that were detected in the fermented soybean-like cup aroma. The aroma recombination, which was performed employing the 12 odorants with AI ≥1 successfully mimicked the overall aroma profile of the fermented soybean-like cup aroma. The omission test revealed that 2-methylbutyric acid contributed significantly to the fermented soybean-like cup aroma. And the enantiomeric ratio (ER) of the (S)- to (R)-forms of 2-methylbutyric acid was 67:33.