Revealing the flavor profile of citrus Pu-erh tea through GC-MS-O and untargeted metabolomics

Chinese citrus Pu-erh tea is recognized for its unique flavor, which is composed of key aroma-active compounds and affected by taste-impact metabolites. In this study, the whole citrus Pu-erh tea (CP), its out-layer fruit (OF) container and inside tea (IT) powder, were analyzed by solvent-assisted flavor evaporation (SAFE) coupled with GC-MS-O and UHPLC-MS/MS. As the result, 47 important volatiles were identified, including 27 (IT), 30 (OF) and 27 (CP) volatiles that were screened out based on their OAV (odor activity value) and ACI (aroma character impact value), and further validated by aroma omission/recombination experiment. Combined with the sensory evaluation and PLSR model, the aroma profile of CP was characterized with the following ten flavor attributes: sweet (vanillin); floral (β-ionone); fruity (methyl anthranilate, methyl methanthranilate, citronellal); roasted (thymol); musty (p-cymene), woody (perillaldehyde); herbal (linalool, α-terpineol); phenolic (2,4-di-tert-butylphenol, p-cresol); minty (dihydrocarvone); and fatty (octanoic acid) volatiles. As for the non-volatile taste-impact chemicals, the most prominent metabolites were identified as flavonoids that mainly contributed to the taste of bitter (catechin, epicatechin, gallocatechin), astringency (leucopelargonidin) and sweet (neohesperidin). This novel finding has provided an insight and better understanding of the aroma profile of citrus Pu-erh tea and some guidance for flavor pairing and taste improvement.