Effects of Microbial Action and Moist-Heat Action on the Nonvolatile Components of Pu-Erh Tea, as Revealed by Metabolomics

Abstract

Microbial action and moist-heat action are crucial factors that influence the piling fermentation (PF) of Pu-erh tea. However, their effects on the quality of Pu-erh tea remain unclear. In this study, the effects of spontaneous PF (SPPF) and sterile PF (STPF) on the chemical profile of Pu-erh tea were investigated for the first time, and sun-dried green tea was used as a raw material to determine the factors contributing to the unique quality of Pu-erh tea. The results indicated that the SPPF-processed samples had a stale and mellow taste, whereas the STPF-processed samples had a sweet and mellow taste. Through metabolomics-based analysis, 21 potential markers of microbial action (including kaempferol, quercetin, and dulcitol) and 10 potential markers of moist-heat action (including ellagic acid, β-glucogallin, and ascorbic acid) were screened among 186 differential metabolites. Correlation analysis with taste revealed that metabolites upregulated by moist-heat and microbial action were the main factors contributing to the staler mellow taste of the SPPF-processed samples and the sweeter mellow taste of the STPF-processed samples. Kaempferol, quercetin, d-glucuronic acid, and dulcitol were the main active substances formed under microbial action. This study provides new knowledge regarding the quality formation mechanism of Pu-erh tea.

The carbohydrate metabolism and expression of carbohydrate-active enzyme genes in Aspergillus luchuensis fermentation of tea leaves

“…To summarize, the fermentation of A. luchuensis led to an increase in the levels of soluble sugar, total lignin, total hemicellulose, and monosaccharide, whereas it reduced the amounts of polysaccharide and cell wall cellulose. Previous studies have also reported an increase in the levels of arabinose (Gong et al, 2010), glucose (Wang et al, 2022), mannitol (Zhang et al, 2023), xylitol, sorbitol (Shao et al, 2022), and dulcitol (Li et al, 2022), which is consistent with the findings presented here.…”

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

“…Sample preparation: The raw material of SDGT was provided and processed by Menghai Tea Factory, consistent with the samples used in our previous study ( Li, Zhang, et al, 2022 ; Li et al, 2023 ) ( Fig. 1 a).…”

“…1 Analyze the flowchart. (a) Schematic diagram of sample preparation ( Li, Wu, et al, 2022 ; Li, Zhang, et al, 2022 ), (b) Demonstration of tea samples, (c) Comparative descriptive aroma profiles of different tea infusions, (d) Key aroma components in different samples. Note: SDGT, sun-dried green tea; SPPF, spontaneous piling fermentation; and STPF, sterile piling fermentation.…”

“…Ripened Pu-erh tea is a unique post-fermented tea that is prepared from sun-dried green tea (SDGT) leaves using modern piling fermentation (PF) techniques ( Cao et al, 2018 ; Wang et al, 2022 ; Wang et al, 2022 ; Li et al, 2022 ; Zhang, Zhang, Zhou, Ling, & Wan, 2013 ). The core of Pu-erh tea processing is PF, which is essential for developing the distinct qualities of ripened and raw Pu-erh tea ( Li et al, 2023 ; Mo, Zhu, & Chen, 2008 ; Zhao et al, 2015 ).…”

“…During PF, SDGT leaves undergo significant alterations caused by microbial and moist-heat action ( Li et al, 2023 ; Akacha & Gargouri, 2015 ; Xie et al, 2020 ). In our previous study, we processed the same raw materials into sterile piling fermented (STPF) samples and spontaneous piling fermented (SPPF) samples and used omics-based analysis to detect nonvolatile components in tea leaves ( Li, Zhang, et al, 2022 ; Li et al, 2023 ). Metabolomic analysis revealed 21 key metabolites were influenced by microorganisms.…”