Characteristic volatiles of Fu brick tea formed primarily by extracellular enzymes during Aspergillus cristatus fermentation.

Fu brick tea (FBT) has unique "fungal flower" aroma traits, but its source of crucial aroma compounds is still controversial. Aspergillus cristatus is the dominant fungus that participated in the fermentation of FBT. In this study, volatiles of Aspergillus cristatus and corresponding fermented FBT were examined using GC × GC-Q-TOFMS. A total of 59 volatiles were shared by three strains of Aspergillus cristatus isolated from representative FBT. Among them, 1-octen-3-ol and 3-octanone were the most abundant. A total of 133 volatiles were screened as typical FBT volatiles from three FBTs fermented by the corresponding fungi. Aspergillus cristatus and FBT had only 29 coexisting volatiles, indicating that the volatiles of Aspergillus cristatus could not directly contribute to the aroma of FBT. The results of no significant correlation between volatile content in FBT and volatile content in Aspergillus cristatus suggested that intracellular metabolism of Aspergillus cristatus was not a direct driver of FBT aroma formation. Metabolic pathway analysis and proteomic analysis showed that the aroma in FBT was mainly formed by the enzymatic reaction of extracellular enzymes from Aspergillus cristatus. This study enriched our understanding of Aspergillus cristatus in the aroma formation process of FBT.

Effects of pile-fermentation on the aroma quality of dark tea from a single large-leaf tea variety by GC × GC-QTOFMS and electronic nose.

Aroma is one of the significant quality factors of dark tea (DT). However, for a single large-leaf tea variety, there are few studies analyzing the effect of pile-fermentation on the aroma quality of DT. The GC × GC-QTOFMS, electronic nose (E-nose) and GC-olfactometry (GC-O) techniques were employed to analysis the difference of tea products before and after pile-fermentation. A total of 149 volatile metabolites (VMs) were identified, with 92 VMs exhibiting differential characteristics. Among these, 31 VMs with OAV > 1.0 were found to be correlated with E-nose results (|r| > 0.8). Additionally, GC-O analysis validated seven major differential metabolites. Notably, naphthalene, 2-methylnaphthalene, and dibenzofuran were found to enhance the woody aroma, while (Z)-4-heptenal, 2-nonenal and 1-hexanol were associated with an increase in mushroom, fatty and sweet odors, respectively. Moreover, 1-octen-3-ol was linked to reducing pungent fishy smell. These findings could provide a certain theoretical basis for understanding the influence of pile-fermentation on the aroma quality of dark tea.

The protective effects of yellow tea extract against loperamide-induced constipation in mice.

Yellow tea, a rare type tea from China, has a rich breadth of functional ingredients and benefits the gastrointestinal tract. However, it is not clear whether the yellow tea extract can alleviate constipation. Therefore, we used loperamide-induced constipation in mice to evaluate the effects of yellow tea extract. Fifty Kunming mice were randomly divided into five groups: normal, model, low-dose yellow tea extract, low-dose yellow tea extract prevention group, and high-dose yellow tea extract prevention group. Mice were administered yellow tea extract for 5 weeks followed by loperamide-induced constipation for the final 2 weeks. The results showed that yellow tea extract alleviated constipation symptoms by improving the fecal water content, defecation weight, and gastrointestinal transit rate. Yellow tea extract intervention also protected colon tissue, regulated serum neurotransmitters, and decreased the vasoactive intestinal peptide level. Furthermore, qRT-PCR indicated that yellow tea extract regulated genes associated with the constipation state, raised 5-HT3 and 5-HT4 and reduced AQP3 and AQP4 mRNA expression. Moreover, we found that yellow tea extract changed the gut microbiota composition. Community diversity and richness were increased and principal co-ordinate analysis demonstrated that the yellow tea extract prophylaxis groups differed from the model group. Difference analysis indicated that yellow tea extract increased Roseburia, Lachnospiraceae_UCG-006, and Bifidobacterium and decreased norank_f_Clostridiales_vadinBB60_group, unclassified_o_Bacteroidales, and Bacteroides, which are correlated with constipation. Based on these results, we believe that regular yellow tea consumption can effectively alleviate constipation.

Dynamic changes in the metabolite profile and taste characteristics of Fu brick tea during the manufacturing process.

Fu brick tea is a typical post-fermentation tea known for its special flavor and health benefits. Liquid chromatography-mass spectrometry, and sensory evaluation with multivariate analysis were used to characterize the dynamic changes in metabolite profile and taste characteristics. Seventy-one compounds were identified as critical metabolites, catechins, flavonoids, phenolic acids, terpenoids and others. During the manufacturing process, these compounds exhibited sharp fluctuations in content, the intensities of astringency, bitterness, and sourness of the tea materials reduced greatly, but the mellow intensity increased sharply. Several catechins and phenolic acids were positively related to the 'astringent', 'bitter', and 'sour' tastes attributes. The fungal genera, Aspergillus, Candida, unclassified_o_Hypocreales, unclassified_o_Saccharomycetales and Wallemia and the bacterial genus, Klebsiella, were identified as core functional microorganisms linked to the metabolic variations during the process. Overall, these findings provided a more comprehensive understanding of the formation of the sensory characteristics in Fu brick tea during the manufacturing process.