Aromatic Profiles and Enantiomeric Distributions of Chiral Volatile Compounds in Pu-Erh Tea

Pu-Erh tea, as a typical post-fermented tea, can be divided into raw Pu-Erh tea (RAPT) and ripened Pu-Erh tea (RIPT) according to the processing technology. It is famous for its unique aroma after aging. Although previous research on the aroma characteristics of Pu-Erh tea mostly focused on the aroma compounds, little research on chiral compounds in RAPT and RIPT has been performed. Therefore, the current work aims to explore the aroma characteristics of Pu-Erh tea from the perspective of enantiomers of chiral compounds. A total of 15 enantiomers were determined in this study, among which (R)-(-)-2,2,6-trimethylcyclohexanone, (R)-(-)-linalool, (S)-(+)-linalool, (R)-(+)-delta-octanolactone, (R)-(+)-gamma-nonanolactone, (2R,5R)-(+)-the-aspirone A, and (R)-(-)-dihydroactinidiolide were identified as enantiomeric compounds that play an important role in the aroma of RAPT and RIPT. Furthermore, (2S,5R)-trans-linalool oxide and (R)-(+)-alpha-terpineol were important contributors to the aroma profile of RAPT, while (S)-(+)-2-methylbutanal, (S)-(-)-limonene, S-(-)-alpha-terpineol, and (1R,2R)-(-)-methyl jasmonate contributed to the characteristic aroma of RIPT. The addition of these enantiomeric compounds brings the aroma closer to that of the original tea sample. In addition, the analysis of chiral enantiomers of linalool, limonene, theaspirone A, and gamma-nonanolactone can provide guidance for the quality and flavor control of Pu-Erh tea aroma.