The aroma compounds contributing to the characteristic flavour of ripe Pu-erh tea and their molecular mechanisms of interaction with olfactory receptors

Abstract

In order to study the dynamic evolution of the aroma profile of tea leaves from sun-dried green tea processing and fermentation into MPT (ripe Pu-erh tea Fermented by Monascus purpureus) at different pile turning stages, the changes in volatile compounds (VOCs) content and aroma profiles of tea samples were determined using headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS), sensory evaluation, multivariate analysis. Orthogonal Partial Least Squares Discriminant Analysis (OPLS-DA) combined with Odor Activity Value (OAV) screened 24 key VOCs, with the greatest change in OAV of 1,2,3-trimethoxybenzene. The sixth pile turning stages the most important stage to form the unique flavour of MPT. The metabolic transformations of key VOCs were systematically summarised and a dynamic flavour wheel of aroma was established. Additionally, molecular docking was employed to analyze the interaction regions, binding energies, and forces between key VOCs (1,2,3,4-tetramethoxybenzene, 1,2,3-trimethoxybenzene, 1,2,4-trimethoxybenzene, and 1,2-dimethoxybenzene) and six olfactory receptors (ORs) (OR1A1, OR1G1, OR2W1, OR5M3, OR7D4, and OR8D1). The average binding energies of these compounds across five receptors were −4.71, −5.06, −5.26, and −5.00 kcal/mol, respectively. These findings reveal the mechanism of aroma formation during the piling stage of MPT, contributing to the quality control and targeted processing of RIPT (Ripe Pu-erh tea).