Pu-erh tea unique aroma: Volatile components, evaluation methods and metabolic mechanism of key odor-active compounds

Pu-erh tea aroma is the comprehensive result of various volatile compounds (VCs). More than 1000 VCs were reported in Pu-erh tea. Pu-erh tea aroma was widely studied using sensory evaluation, instrumental analysis, odor activity value (OAV), aroma recombination, and omission test. The activities of microorganism is the key to the formation of Pu-erh tea aroma. The main purpose of this review is to elaborate on the volatile components contributing to the unique aroma, methods used for VCs extraction and evaluation, and metabolic mechanism of key odor-active compounds of Pu-erh tea. The reported VCs, odor-active compounds, and their extraction methods were summarized. Sensory evaluation, extraction methods, and analytical methods were elaborated concerning aroma analysis. The possible metabolic pathways of key odor-active compounds and related microorganisms were combed. The composition of VCs varies greatly with different extraction methods. Combining multiple extraction methods will be an effective strategy to fully extract the VCs of Pu-erh tea. Sensory evaluation provides a fast and intuitive strategy to determine the aroma profile or aroma attributes. GC–O–MS combines with OAV, aroma recombination, and omission test can not only realize quantitative and qualitative detection but also realize the screening of key aroma compounds. E-nose combined with multivariate statistical provides an easier strategy for distinguishing Pu-erh tea aroma. Most VCs are formed by the activities of microorganisms, but their exact metabolic mechanisms are still unclear, which needs further exploration.