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.

Characterization of the key odor-active compounds in different aroma types of Fu brick tea using HS-SPME/GC-MSO combined with sensory-directed flavor analysis.

Fu brick tea (FBT) is popular for its unique 'fungal flower' aroma, however, its key odor-active compounds are essentially unknown. In this study, the odor-active compounds of "stale-fungal" aroma (CJX), "fresh-fungal" aroma (QJX), and "fermentation-fungal" aroma (FJX) types FBT were extracted and examined by headspace solid phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) and gas chromatographyolfactometry (GC-O). A total of 43 volatile and 38 odor-active compounds were identified by these methods. Among them, the content of dihydroactindiolide (4596-13189 µg/L), (E)-linalool oxide (2863-6627 µg/L), and benzyl alcohol (4992-6859 µg/L) were highest. Aroma recombination experiments further verified that these odor-active compounds could be simulated the overall aroma profile of FBT successfully. Furthermore, omission experiments confirmed that 15, 20, and 15 key odor-active compounds in CJX, QJX, and FJX FBT, respectively. This study will provide a theoretical basis for comprehensively understanding the formation of characteristic aromas in FBT.

Multiplex PCR Identification of Aspergillus cristatus and Aspergillus chevalieri in Liupao Tea Based on Orphan Genes.

"Golden flower" fungi in dark tea are beneficial to human health. The rapid identification method of "golden flower" fungi can verify the quality of dark tea products and ensure food safety. In this study, 6 strains were isolated from Liupao tea. They were respectively identified as A. cristatus, A. chevalieri, and A. pseudoglaucus. A. pseudoglaucus was reported as Liupao tea "golden flower" fungus for the first time. It was found that the ITS and BenA sequences of A. cristatus and A. chevalieri were highly conserved. It is difficult to clearly distinguish these closely related species by ITS sequencing. To rapidly identify species, multiplex PCR species-specific primers were designed based on orphan genes screened by comparative genomics analysis. Multiplex PCR results showed that orphan genes were specific and effective for the identification of A. cristatus and A. chevalieri isolated from Liupao tea and Fu brick tea. We confirmed that orphan genes can be used for identification of closely related Aspergillus species. Validation showed that the method is convenient, rapid, robust, sequencing-free, and economical. This promising method will be greatly beneficial to the dark tea processing industry and consumers.

Study on the key volatile compounds and aroma quality of jasmine tea with different scenting technology.

The aroma quality of jasmine tea refers to the strength and freshness of jasmine fragrance and its coordination with tea aroma, which is regulated by various volatile compounds. In this study, seventy volatile compounds of jasmine tea scented by different scenting technology were analyzed qualitatively and quantitatively by gas chromatography-mass spectrometry (GC-MS). And seven compounds were identified as the key volatile compounds by weighted gene co-expression network analysis (WGCNA), orthogonal partial least squares discriminant analysis (OPLS-DA) and odor activity value (OAV). According to the equation describing seven key volatile compounds and quality of jasmine tea, the optimal scenting technology was obtained, that is, the amount of flowers (AF) was 65-78%, scenting time (ST) was 15-17 h, and scenting temperature (SW) was 35-40 °C. This study lays a foundation for the study of aroma characteristics of jasmine tea, and guides enterprises to improve jasmine tea processing technology.

Coadministration of epigallocatechin-3-gallate (EGCG) and caffeine in low dose ameliorates obesity and nonalcoholic fatty liver disease in obese rats.

Epigallocatechin-3-gallate (EGCG) and caffeine in tea exert anti-obesity effects and induces nonalcoholic fatty liver disease (NAFLD) amelioration. However, previous studies usually performed a high-dose EGCG administration, whereas the insecurity was arisen in recent researches. In this study, we treated obese rats with an elaborate dose-40 mg/kg EGCG, 20 mg/kg caffeine, and the coadministration of them as low dose, which were similar to the daily intake; 160 mg/kg EGCG as high dose, which was the maximum safe dose had touched the contentious edge. The results suggested that the coadministration of EGCG and caffeine exerted more remarkable function on suppressing body weight gain, reducing white adipose tissue weight and decreasing the energy intake than single use. This may be due to the variation in serum lipid profile, oxidative stress, and adipose-derived and inflammatory cytokines. The pathological micrographs showed long-term high-fat diets caused severe NAFLD, but it was ameliorated at different levels by all of the administrations. In summary, low dose of EGCG or caffeine only showed a mild effect of anti-obesity and NAFLD amelioration. The coadministration of them could exert a superior curative effect as well as high dose EGCG but no anxiety regarding safety.