Insight into effects of isolated Eurotium cristatum from Pingwu Fuzhuan brick tea on the fermentation process and quality characteristics of Fuzhuan brick tea.

BACKGROUND: Pingwu Fuzhuan brick tea is a type of post-fermented tea manufactured from leaves of the tea plant, Camellia sinensis var. sinensis, the quality of which is influenced by numerous factors, especially microorganisms. Currently, there is little research on the effect of microorganisms on the fermentation and quality characteristics of Pingwu Fuzhuan brick tea. Investigation of the main fungus in this tea and its effect on the fermentation process and tea quality can provide insights into the manufacturing of 'western road' border-selling tea and could lay the foundation for the popularization of Pingwu Fuzhuan brick tea. RESULTS: The main 'golden flower fungus' in Pingwu Fuzhuan brick tea was isolated and identified as Eurotium cristatum (GenBank accession number: MF800948.1; strain PW-1). Compared with natural fermentation, PW-1 inoculated fermentation accelerated biotransformation of phenolic compounds, which provided tea samples with better taste and tea infusion color. The proportions of velvety and sweet-tasting amino acids increased after 16-day fermentation with PW-1. Alcohols were the most abundant volatiles, with 40.13% and 39.43% content in NF16d and IF16d tea samples, respectively. Orthogonal partial least-squares discriminant analysis (OPLS-DA) and hierarchical clustering analysis (HCA) further revealed that naturally fermented and PW-1 fermented teas were significantly different. CONCLUSION: Strain PW-1 plays an important role in the fermentation process of Fuzhuan brick tea. Considering fermentation efficiency and tea quality, fermentation inoculated with E. cristatum PW-1 can be applied in the manufacturing of 'western road' border-selling tea. © 2020 Society of Chemical Industry.

Amount of Eurotium sp. in Chinese Liupao tea and its relationship with tea quality.

OBJECTIVE: Eurotium sp. are the sexual states of the genus Aspergillus, and their ascospore is a spherical closed capsule with a golden colour. The growth of Eurotium sp. during tea production is a key step in achieving the unique quality of dark tea. This study aimed to evaluate the relationship between Eurotium sp. amount and Liupao tea quality. METHODS AND RESULTS: The amounts of Eurotium sp. in 26 differently aged Liupao tea samples from several factories were studied. Indicators related to the quality of Liupao tea were investigated. The amounts of Eurotium sp. were divided into 0, 105 and 106 levels, and quantitative real-time polymerase chain reaction (qPCR) was performed. Using ultrahigh-performance liquid chromatography and high-performance liquid chromatography, the amounts of emodin and physcion were determined to be closely related to the amount of Eurotium sp. Emodin was not found or occurred in minimal amounts in all raw Liupao tea samples. By contrast, physcion was found in Liupao tea at the 106 level of Eurotium sp. Liupao tea samples with varying levels of Eurotium sp. also exhibited evident differences in aroma and chromaticity. Result of the Pearson correlation test showed that the amount of Eurotium sp. plays a key role in creating the unique quality of Liupao tea. CONCLUSION: The amount of Eurotium sp. in dark tea detected via qPCR can be used as a quantitative quality indicator for evaluating dark tea. SIGNIFICANCE AND IMPACT OF THE STUDY: The present study provides an efficient method for identifying the different qualities of dark tea and addressing quality control issues in fermenting dark tea.