Effect of main taste compounds on the release of methoxyphenolic compounds in Pu-erh tea

Exploring microbial and moist-heat effects on Pu-erh tea volatiles and understanding the methoxybenzene formation mechanism using molecular sensory science

Piling fermentation (PF) is crucial for Pu-erh tea aroma, yet its microbial and moist-heat impact on aroma quality is poorly understood. Solid-phase microextraction, solvent-assisted flavor evaporation, and gas chromatography-mass spectrometry were used to detected and analyses the samples of sun-green green tea, sterile PF and spontaneous PF. Microbiological action promotes the formation of stale aromas. Moist-heat action promotes the formation of plum-fragrance and sweet aroma. 20 microbial markers and 28 moist-heat markers were screened from 184 volatile components. Combining odor activity values and gas chromatography-olfactometry, 22 aroma-active compounds were screened (1,2,3-trimethoxybenzene, linalool, 1,2,4-trimethoxybenzene …), and analyzed during PF processing. Aroma omission and addition experiments verified its importance. Gallic acid addition experiments successfully verified that microorganisms are the main contributors to the synthesis of methoxybenzenes. Finally, Blastobotrys, Rasamsonia, and Thermomyces showed positive correlation with the synthesis of 1-ethyl-4-methoxybenzene, 1,2,4-trimethoxybenzene, 1,2,3-trimethoxybenzene, and 1,2-dimethoxybenzene. The formation mechanism of Pu-erh tea's aroma was clarified. Exploring microbial and moist-heat effects on Pu-erh tea volatiles and understanding the methoxybenzene formation mechanism using molecular sensory science.

Mellow and Thick Taste of Pu−Erh Ripe Tea Based on Chemical Properties by Sensory−Directed Flavor Analysis

The mellow and thick taste is a unique characteristic of pu−erh ripe tea infusion, and it is closely related to the chemical composition of pu−erh ripe tea, which is less studied. This paper clarifies and compares the chemical composition of pu−erh ripe tea to that of the raw materials of sun−dried green tea, and uses membrane separation technology to separate pu−erh ripe tea into the rejection liquid and the filtration liquid. The results show that microorganisms transformed most physicochemical components, except caffeine, during the pile fermentation. It was found that total tea polyphenols, soluble proteins, total soluble sugars, theabrownin, and galloylated catechins became enriched in the rejection liquid, and the rejection liquid showed a more obvious mellow and thick characteristic. Taste interactions between crude protein, crude polysaccharide, and theabrownin were determined. They illustrated that the mellow and thick taste of pu−erh ripe tea with the addition of theabrownin increased from 4.45 to 5.13. It is of great significance to explore the chemical basis of the mellow and thick taste in pu−erh tea for guiding the pu−erh tea production process and for improving the quality of pu−erh tea.

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)-(+)-δ-octanolactone, (R)-(+)-γ-nonanolactone, (2R,5R)-(+)-theaspirone 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)-(+)-α-terpineol were important contributors to the aroma profile of RAPT, while (S)-(+)-2-methylbutanal, (S)-(-)-limonene, S-(-)-α-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 γ-nonanolactone can provide guidance for the quality and flavor control of Pu-Erh tea aroma.