Insight into the volatile profiles of four types of dark teas obtained from the same dark raw tea material

Microbial and chemical diversity analysis reveals greater heterogeneity of Liubao tea than ripen Pu-erh tea

Liubao tea and ripen Pu-erh tea are representatives of dark tea in southern China. The two dark teas are famous for unique flavors, but confusingly different in development status of tea industry. In this study, microbial DNA amplification sequencing and mass spectrometry-based untargeted metabolomics were applied to observe significant differences in microbial community structure and metabolite profile between the two teas. The Shannon indices of fungi and metabolites in Liubao tea are higher than those in ripen Pu-erh tea. The dominant bacterial and fungal genera, as well as microbial biomarkers of Liubao tea and ripen Pu-erh tea were identified. The combined statistical and molecular networking analysis shows flavan-3-ols as the discriminating features between metabolite profiles of the two dark teas in level of metabolite family. More importantly, the α and β diversity analysis reveals higher pairwise Shannon index differences and Canberra distances of both microbes and metabolites in Liubao tea than those in ripen Pu-erh tea, indicating greater heterogeneity, or lower quality stability of Liubao tea products. These findings illustrate way to improve protocols of Liubao tea processing, and show urgency of involving molecular networking in workflow of metabolomics research.

The unique aroma of ripened Pu-erh tea, Liupao tea and Tietban tea: Associated post-fermentation condition and dominant microorganism with key aroma-active compound

Dark tea with a unique aroma is a particular type of tea. Post-fermentation is the key manufacturing process that forms a unique aroma, distinguishing dark tea from other types of tea. Different post-fermentation conditions may be the reason for forming unique aromas in various dark teas. Microbial community and composition during post-fermentation are the main contributors to the formation of characteristic aroma in various dark teas. In this paper, we illustrated the differences in fermentation length, pile temperature and water content of ripened Pu-erh tea, Liupao tea and Tibetan tea during post-fermentation, and only six dominant microorganisms and six key aroma-active compounds were found to be consistent among the three dark teas. Furthermore, we elaborated on the correlations between key aroma-active compounds and core functional microorganisms during post-fermentation. Exploring these interrelationships during post-fermentation is crucial and worthwhile to maintain the stability of the aroma quality of the three dark teas.

Multi-Omics analysis reveals the sensory quality and fungal communities of Tibetan teas produced by wet- and dry-piling fermentation

Ya'an Tibetan tea, a dark tea with a rich historical heritage, is typically processed using two primary piling fermentation methods: wet piling with rolled leaves (moisture content around 60%) and dry piling with sun-dried or baked green tea leaves (moisture content below 30%). This study employed sensory evaluation, targeted and non-targeted metabolomics, and fungal Internal Transcribed Spacer (ITS) sequencing to investigate changes in quality components and fungal composition in Tibetan tea processed by both wet and dry-piling methods. The results revealed that 3,7-Dimethyl-1,5,7-octatriene-3-ol and D-limonene were identified as key volatile metabolites contributing to the aroma variations between the dry and wet-piled teas. More pronounced differences were observed in non-volatile components, with 407 differential metabolites identified between the wet- and dry-piled teas. Linear discriminant analysis effect size (LEfSe) identified Rhizomucor, Aspergillus, Thermomyces, Setophoma, and Debaryomyces as the key fungal genera with significant differences between the two piling methods, also dominating in abundance and playing a crucial role in the fermentation process of Tibetan tea. Correlation analysis between microbial communities and differential metabolites showed that Debaryomyces, Thermomyces, and Setophoma were significant contributors to the aroma differences between the teas produced by the two piling methods, while Rhizomucor and Aspergillus had a greater influence on non-volatile metabolites. Since Rhizomucor and Aspergillus were the most dominant fungi in the wet (63.05%) and dry-piled (68.70%) samples, respectively, and showed opposite correlations with major non-volatile differential metabolites, they may underlie the flavor differences between the two piled teas, such as mellowness, thickness, and sweet aftertaste. This study sheds light on the chemical and fungal mechanisms underlying the quality formation of Ya'an Tibetan tea processed by wet and dry piling methods, providing theoretical guidance for the improvement, standardization, and potential enhancement of production efficiency of Ya'an Tibetan tea production.

Dynamics of linalool and its derivatives enantiomers in Camellia sinensis var. A ssamica "Hainan dayezhong"

We here analyzed changes in the proportion and content of chiral isomers of linalool and its derivatives in "Hainan dayezhong" throughout its life cycle from tea tree growth and tea manufacturing to brewing. The chiral isomers of aromatic compounds present in fresh tea leaves were found to undergo substantial diurnal and seasonal changes during tea tree growth, and their proportions varied slightly across different leaf positions. The chiral isomer content of linalool and its derivatives was consistently higher in stems than in leaves. Pest and disease stress significantly increased the proportion and content of type-R aroma. The proportion of chiral isomers underwent no considerable change during black tea manufacturing. However, their content varied dramatically among different processes. Diversity in the proportion and content of chiral isomers was observed in the wild tea tree. Further research should focus on breeding "Hainan dayezhong" wild resources to generate clones with high aroma quality.

Characterization of primary aroma compounds in Pu-erh raw tea sourced from various regions using gas chromatography-mass spectrometry and headspace solid-phase microextraction

The assessment of aroma plays a crucial role in determining the characteristics and quality of Pu-erh tea. The volatile compounds present in Pu-erh raw tea sourced from five regions in Yunnan Province have been studied using gas chromatography-mass spectrometry (GC-MS) in conjunction with headspace solid phase microextraction (HS-SPME). A total of 69 aroma-active compounds were identified, with alcohols, ketones, and aldehydes being the predominant component types. Furthermore, notable variations were observed among four pairs of volatile terpenoid enantiomers. Significant discrimination was achieved using orthogonal partial least squares discrimination analysis (R(x2) = 0.926, R(y2) = 0.843, Q2 = 0.501). Moreover, 33 important differential compounds were identified based on variable importance in the projection values (VIP > 1.0) and one-way ANOVA analysis (p < 0.05). Subsequently, a KEGG pathway analysis was conducted, revealing enrichment pathways primarily focused on the mevalonate pathway, steroid biosynthesis, and fatty acid biosynthesis. Ultimately, the key volatile compounds and major aroma-contributing compounds were successfully identified.

Changes in the key odorants of loose-leaf dark tea fermented by Eurotium cristatum during aging for one year: Focus on the stale aroma

Aging process has been recognized as one of the means to improve the quality of microbial fermented teas. The evolution of the characteristic stale aroma, a key odorant of microbial fermented tea, throughout the aging process remains unknown. To investigate the changes in key odorants of the fermented tea during aging, the loose-leaf dark tea (LDT) used in this study was prepared by solid-state fermentation using Eurotium cristatum and was aged for 0, 3, 6, 9, 12 months, producing varied aged LDT samples. Quantitative descriptive analysis (QDA) showed that the intensity of stale aroma in the LDT increased gradually during aging for one year. The volatile compounds from different aged samples were extracted using solvent-assisted flavor evaporation (SAFE) combined with liquid-liquid extraction, and ninety-six aroma-active compounds were further identified by gas chromatography-mass spectrometry/olfactometry (GC - MS/O) combined with modified detection frequency (MF) values. Among them, alcohols and esters showed an increasing trend, while nitrogenous compounds showed a decreasing trend during aging. The stale aroma attribute of the LDT were closely associated with several key odorants produced from the biotransformation by Eurotium cristatum, including cedrol, β-ionone, 1-octen-3-one, 1-octen-3-ol, and 4-vinylguaiacol, their aroma contributions were confirmed by further addition tests. These findings provide a theoretical basis for the future optimization of the aging process of fermented tea.

Effect of inoculation with different Eurotium cristatum strains on the microbial communities and volatile organic compounds of Fu brick tea

Eurotium cristatum is the primary fungus in Fu brick tea (FBT) and plays a crucial role in its special flavor. This study investigated the effect of inoculation with different E. cristatum strains (i.e., ZJ, GX, GZ, HN, and SX) on the microbial communities and volatile organic compounds (VOCs) of FBT. A total of 113 VOCs were identified in all samples, with the concentration of VOCs (alcohols, aldehydes, and ketones) significantly higher in GXE FBT than in other samples. The core VOCs of GXE (19), GZE (16), HNE (19), SXE (15), and ZJE (13) FBT were identified using orthogonal partial least squares discriminant analysis and relative odor activity value (ROAV) analysis. Methional (a27), butanal (a41), 1-octen-3-one (a69), and ethyl acetate (a77) were key markers for inoculated FBTs, and 1-octen-3-ol, dimethyl disulfide, and acetoin-M were the specific markers of HNE. Linalool and (E)-2-octenal were particularly prominent in GXE, and isoamyl acetate-D was an important aroma component of GZE. Differences in microbial diversity were observed among the different inoculated fermented FBTs, and E. cristatum inoculation remarkably influenced the richness and diversity of bacterial communities. The VOCs were closely associated with fungi and bacteria, and 19 potentially dominant microorganisms (10 fungal and 9 bacterial genera) correlated with VOCs were identified. Among them, Aspergillus (fungi) and Pseudomonas (bacteria) exerted the greatest role. The FBT inoculated with E. cristatum from ZJ had the highest content of theaflavins and theabrownins, which intensified the red and yellow colors of the tea. E. cristatum greatly decreased the free amino acids and fatty acids, contributing to the aroma formation of FBT. Therefore, inoculating FBT with E. cristatum remarkably influenced the microbial communities and improved its flavor profile. This work provides a theoretical foundation on the role of E. cristatum in the formation and regulation of FBT flavor.

Sensomics-assisted analysis unravels the formation of the Fungus Aroma of Fu Brick Tea

Fu Brick Tea (FBT) is characterized by Fungus Aroma (FA), which determines the quality of FBT products. However, the aroma constituents and their interactive mechanism for FA remain unclear. In this study, the FBT sample with the optimal FA characteristics was selected from 29 FBTs. Then, 19 components with OAV ≥ 1 were identified as the odorants involved in the FA formation. The aroma recombination test suggested that the FA was potentially produced by the synergistic interplay among the 15 key odorants, including (E,E)-2,4-heptadienal, (E,E)-2,4-nonadienal, (E)-2-nonenal, (E,Z)-2,6-nonadienal, (E)-2-octenal, (E)-β-ionone, 4-ketoisophorone, dihydroactinidiolide, (E)-β-damascenone, 1-octen-3-ol, linalool, geraniol, heptanal, hexanal, and phenylacetaldehyde. And, the synergistic effects between them were preliminarily studied by aroma omissions, such as modulatory effects, masking effects, compensatory effects, and novelty effects, ultimately contributing to the FA. In all, this work helps us better understand the formation of the FA and provides a basis for the improvement of FBT production technology.

Revealing the differences in aroma of black tea under different drying methods based on GC-MS, GC-O

Drying greatly affects the aroma of black tea. In this study, the differences in aroma of black tea under hot-air drying (HD), sun drying (SD), and pan-fired drying (PD) were investigated through quantitative descriptive analysis. Headspace solid-phase microextraction and solvent assisted flavor evaporation combined with gas chromatography-mass spectrometry and gas chromatography-olfactory were used to analyze the overall aroma profile of black tea. Aroma extract dilution analysis and odor activity values revealed that 15 aroma-active compounds led to differences in aroma, namely linalool, geraniol, phenylethyl alcohol, phenylacetaldehyde, (Z) -linalool oxide (furanoid), β-damascenone, dimethyl sulfide, methional, 2-methylbutanal, 3-methylbutanal, methyl salicylate, β-myrcene, hexanal, 1-octen-3-ol, and heptanal. Among them, geraniol, linalool, and methional significantly enhanced the floral and roasty aroma of HD, while hexanal enhanced the green aroma of SD. Finally, our results were validated through aroma recombination and addition experiments. This study provides a theoretical basis for improving the aroma of black tea.

HS-SPME-GC-MS untargeted metabolomics reveals key volatile compound changes during Liupao tea fermentation

This study used headspace solid-phase microextraction-gas chromatography-mass spectrometry and multivariate statistical analysis to comprehensively analyze the volatile components in Liupao tea samples throughout fermentation. In total, 1009 volatile organic compounds were detected and identified, including terpenoids, heterocyclic compounds, esters, ketones, hydrocarbons, alcohols, aromatics, and acids. Principal component and hierarchical cluster analyses, characterize the volatile components of Liupao tea samples were characterized at various fermentation stages. Orthogonal partial least squares discriminant analysis identified 248 differentiating compounds (VIP ≥ 1, P < 0.05, and |Log2FC| ≥ 1.0) during fermentation. K-means clustering analysis showed that 11 metabolites increased significantly throughout the fermentation process, whereas 31 metabolites decreased continuously. Annotation of these differential compounds revealed significant changes in sensory flavor characteristics in "green, sweet, fruity, floral, and woody" flavors. The results demonstrated significant variations in the volatile components of Liupao tea fermentation, along with notable changes in flavor characteristics.

Sensory-directed flavor analysis reveals the improvement in aroma quality of summer green tea by osmanthus scenting

Flower scenting is an effective way to enhance the aroma of green tea (GT), including those osmanthus scented green tea (OSGT). However, the mechanism of aroma enhancement by scenting is still unclear. Here, the volatiles of GT, OSGT, and osmanthus were detected by GC-MS. The total volatile content of OSGT was significantly increased compared to GT, with the flowery and coconut aromas enhanced. Furthermore, 17 of 139 volatiles were responsible for the enhancement by GC-olfactometry and their absolute odor activity values (OAVs). Aroma recombination, omission and addition experiments showed that dihydro-β-ionone, (E)-β-ionone, (E, E)-2,4-heptadienal, geraniol, linalool, α-ionone, and γ-decalactone were the key aroma volatiles with flowery or coconut aromas. Additionally, the dynamics of the key volatiles (OAVs >1) from different scenting durations were analyzed, proving that the optimal duration was 6-12 h. This study provides new insight into the mechanism of aroma formation during OSGT production.

Aqueous extract of fermented Eucommia ulmoides leaves alleviates hyperlipidemia by maintaining gut homeostasis and modulating metabolism in high-fat diet fed rats

BACKGROUND

As a traditional Chinese medicinal herb, the lipid-lowing biological potential of Eucommia ulmoides leaves (EL) has been demonstrated. After fermentation, the EL have been made into various products with lipid-lowering effects and antioxidant activity. However, the anti-hyperlipidemic mechanism of fermented Eucommia ulmoides leaves (FEL) is unclear now.

PURPOSE

To evaluate the effects of FEL on hyperlipidemia and investigate the mechanism based on regulating gut homeostasis and host metabolism.

METHODS

Hyperlipidemia animal model in Wistar rats was established after 8 weeks high-fat diet (HFD) fed. The administered doses of aqueous extract of FEL (FELE) were 128, 256 and 512 mg/kg/d, respectively. Serum biochemical parameters detection, histopathological sections analysis, 16S rDNA sequencing of gut microbiota and untargeted fecal metabolomics analysis, were performed to determine the therapeutic effects and predict related pathways of FELE on hyperlipidemia. The changes of proteins and genes elated to lipid were detected by Immunofluorescence (IF) and quantitative real-time polymerase chain reaction (qRT-PCR).

RESULTS

56 Components in FELE were identified by UPLC-MS, with organic acids, flavonoids and phenolic acids accounting for the majority. The intervention of FELE significantly reduced the body weight, lipid accumulation and the levels of total cholesterol (TC), triglycerides (TG), and low-density lipoprotein-cholesterol (LDL-C) in hyperlipidemia rats, while increased the level of High-density lipoprotein-cholesterol (HDL-C). Meanwhile, FELE improved the inflammatory makers and oxidative stress factors, which is tumor necrosis factor-α (TNF-α), monocyte chemotactic protein-1 (MCP-1), interleukin-6 (IL-6), malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT). These results demonstrated that FETE can effectively reduce blood lipids and alleviate inflammation and oxidative damage caused by hyperlipidemia. Mechanistically, FELE restore the homeostasis of gut microbiota by reducing the Firmicutes/Bacteroidetes ratio and increasing the abundance of probiotics, especially Lactobacillus, Rombousia, Bacteroides, Roseburia, Clostridia_UCG-014_Unclassified, while modulated metabolism through amino acid, bile acid and lipid-related metabolism pathways. In addition, the Pearson correlation analysis found that the upregulated bilirubin, threonine, dopamine and downregulated lipocholic acid, d-sphingosine were key metabolites after FELE intervention. IF and qRT-PCR analysis showed that FELE upregulated the expression of fatty acid oxidation proteins and genes (PPARα, CPT1A), bile acid synthesis and excretion proteins and genes (LXRα, CYP7A1, FXR), and downregulated the expression of adipogenic gene (SREBP-1c) by regulating gut microbiota to improve metabolism and exert a lipid-lowering effect.

CONCLUSION

This work filled the lipid-lowering mechanism gap of FEL. FELE can improve HFD-induced hyperlipidemia by regulating the gut microbiota homeostasis and metabolism. Thus, FEL has the potential to develop into the novel raw material of lipid-lowering drugs.

Insight into the chemical compositions of Anhua dark teas derived from identical tea materials: A multi-omics, electronic sensory, and microbial sequencing analysis

Anhua dark teas (DTs), including Tianjian tea, Qianliang tea, Hei brick tea, and Fu brick tea, are unique fermented teas from China's Anhua County; yet their chemical composition differences remain unclear. Herein, metabolomics, volatolomics, and electronic sensory assessments were employed to analyze and compare chemical compositions and sensory characteristics of five types of Anhua DTs. All of these teas were derived from identical tea materials. Chemical compositions differed significantly among Anhua DTs, with Tianjian tea remarkable. Long-lasting fermentation and complex processing methods led to transformation of multiple compounds, particularly catechins. Eighteen volatile compounds with OVA > 1 were key aroma contributors in Anhua DTs. Internal transcribed spacer and 16S ribosomal DNA sequencing showed that Eurotium, Pseudomonas, and Bacillus are dominant microorganisms in Anhua DTs. Furthermore, this study unveiled notable differences in chemical compositions between Anhua DTs and five other traditional types of tea. This research enhances our understanding of Anhua DTs processing.

Effects of Monascus purpureus on ripe Pu-erh tea in different fermentation methods and identification of characteristic volatile compounds

The present study aimed to explore the key volatile compounds (VCs) that lead to the formation of characteristic flavors in ripe Pu-erh tea (RIPT) fermented by Monascus purpureus (M. purpureus). Headspace solid-phase microextraction coupled with gas chromatography/mass spectrometry (HS-SPME-GC-MS), orthogonal partial least square-discriminant analysis (OPLS-DA) were employed for a comprehensive analysis of the VCs present in RIPT fermented via different methods and were further identified by odor activity value (OAV). The VCs 1,2-dimethoxybenzene, 1,2,3-trimethoxybenzene, (E)-linalool oxide (pyranoid), methyl salicylate, linalool, β-ionone, β-damascenone were the key characteristic VCs of RIPT fermented by M. purpureus. OAV and Gas chromatography-olfactometry (GC-O) further indicated that β-damascenone was the highest contribution VCs to the characteristic flavor of RIPT fermented by M. purpureus. This study reveals the specificities and contributions of VCs present in RIPT under different fermentation methods, thus providing new insights into the influence of microorganisms on RIPT flavor.

Extensive targeted metabolomics analysis reveals the identification of major metabolites, antioxidants, and disease-resistant active pharmaceutical components in Camellia tuberculata (Camellia L.) seeds

Sect. tuberculata plant belongs to the Camellia genus and is named for the "tuberculiform protuberance on the surface of the ovary and fruit". It is a species of great ornamental value and potential medicinal value. However, little has been reported on the metabolites of C. tuberculata seeds. Therefore, this study was conducted to investigate the metabolites of C. tuberculata seeds based on UPLC/ESI-Q TRAP-MS/MS with extensively targeted metabolomics. A total of 1611 metabolites were identified, including 107 alkaloids, 276 amino acids and derivatives, 283 flavonoids, 86 lignans and coumarins, 181 lipids, 68 nucleotides and derivatives, 101 organic acids, 190 phenolic acids, 10 quinones, 4 steroids, 17 tannins, 111 terpenoids, and 177 other metabolites. We compared the different metabolites in seeds between HKH, ZM, ZY, and LY. The 1311 identified different metabolites were classified into three categories. Sixty-three overlapping significant different metabolites were found, of which lignans and coumarins accounted for the largest proportion. The differentially accumulated metabolites were enriched in different metabolic pathways between HKH vs. LY, HKH vs. ZM, HKH vs. ZY, LY vs. ZY, ZM vs. LY and ZM vs. ZY, with the most abundant metabolic pathways being 4, 2, 4, 7, 7 and 5, respectively (p < 0.05). Moreover, among the top 20 metabolites in each subgroup comparison in terms of difference multiplicity 7, 8 and 13. ZM and ZY had the highest phenolic acid content. Ninety-six disease-resistant metabolites and 48 major traditional Chinese medicine agents were identified based on seven diseases. The results of this study will not only lead to a more comprehensive and in-depth understanding of the metabolic properties of C. tuberculata seeds, but also provide a scientific basis for the excavation and further development of its medicinal value.

A comprehensive multi-omics analysis, integrating proteomics and metabolomics, was employed to elucidate tea-induced stewed beef quality change mechanisms

To better understand the functional mechanism of four types of tea (green tea, black tea, jasmine tea, and dark tea) on the quality of stewed beef, changes in quality characteristics, proteomics, and metabolomics were investigated. Adding these four tea types decreased the pH value, L* value, shear force, and hardness of the stewed beef. Among these groups, black tea (BT) significantly improved the tenderness of the stewed beef. They have substantially impacted pathways related to protein oxidative phosphorylation, fatty acid degradation, amino acid degradation, and peroxisomes in stewed beef. The study identified that Myosin-2, Starch binding domain 1, Heat shock protein beta-6, and Myosin heavy chain four are significantly correlated with the quality characteristics of tea-treated stewed beef, making them potential biomarkers. Green tea (GT), black tea (BT), jasmine tea (JT), and dark tea (DT) led to the downregulation of 20, 36, 38, and 31 metabolites, respectively, which are lipids and lipid-like molecules in the stewed beef. The co-analysis of proteomics and metabolomics revealed that differential proteins significantly impacted metabolites associated with carbohydrates, amino acids, lipids, and other nutrients. This study determined the effects of four types of tea on the quality of stewed beef and their underlying mechanisms, providing valuable insights for applying of tea in meat products. At the same time, it can offer new ideas for developing fresh meat products.

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.

Insights into the effects of fixation methods on the sensory quality of straight-shaped green tea and dynamic changes of key taste metabolites by widely targeted metabolomic analysis

Fresh leaves of Echa 1 were fixed by roller, steam/hot air and light-wave, and the effects of the three fixation methods on the chemical characteristics of straight-shaped green teas (GTs) were studied by widely targeted metabolomic analysis. 1001 non-volatile substances was identified, from which 97 differential metabolites were selected by the criteria of variable importance in projection (VIP) > 1, p < 0.05, and |log2(fold change)| > 1. Correlation analysis indicated that 14 taste-active metabolites were the major contributors to the taste differences between differently processed GTs. High-temperature fixation induces protein oxidation or degradation, γ-glutamyl peptide transpeptidation, degradation of flavonoid glycosides and epimerization of cis-catechins, resulting in the accumulation of amino acids, peptides, flavonoids and trans-catechins, which have flavor characteristics such as umami, sweetness, kokumi, bitterness and astringency, thereby affecting the overall taste of GTs. These findings provided a scientific basis for the directional processing technology of high-quality green tea.

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.

A systemic review on Liubao tea: A time-honored dark tea with distinctive raw materials, process techniques, chemical profiles, and biological activities

Liubao tea (LBT) is a unique microbial-fermented tea that boasts a long consumption history spanning 1500 years. Through a specific post-fermentation process, LBT crafted from local tea cultivars in Liubao town Guangxi acquires four distinct traits, namely, vibrant redness, thickness, aging aroma, and purity. The intricate transformations that occur during post-fermentation involve oxidation, degradation, methylation, glycosylation, and so forth, laying the substance foundation for the distinctive sensory traits. Additionally, LBT contains multitudinous bioactive compounds, such as ellagic acid, catechins, polysaccharides, and theabrownins, which contributes to the diverse modulation abilities on oxidative stress, metabolic syndromes, organic damage, and microbiota flora. However, research on LBT is currently scattered, and there is an urgent need for a systematical recapitulation of the manufacturing process, the dominant microorganisms during fermentation, the dynamic chemical alterations, the sensory traits, and the underlying health benefits. In this review, current research progresses on the peculiar tea varieties, the traditional and modern process technologies, the substance basis of sensory traits, and the latent bioactivities of LBT were comprehensively summarized. Furthermore, the present challenges and deficiencies that hinder the development of LBT, and the possible orientations and future perspectives were thoroughly discussed. By far, the productivity and quality of LBT remain restricted due to the reliance on labor and experience, as well as the incomplete understanding of the intricate interactions and underlying mechanisms involved in processing, organoleptic quality, and bioactivities. Consequently, further research is urgently warranted to address these gaps.

Effects of solid-state fermentation with Bacillus subtilis LK-1 on the volatile profile, catechins composition and antioxidant activity of dark teas

In this study, the solid-state fermentation (SSF) of dark tea was carried out using Bacillus subtilis LK-1, which was isolated from Fu brick tea (FBT). The effects of SSF with B. subtilis on volatile organic compounds (VOCs), non-volatile metabolites, and antioxidant activities of dark tea was investigated. A total of 45 VOCs were identified, primarily consisting of ketones (18), hydrocarbons (8), aldehydes (7), and alcohols (6). Following fermentation, the content of key odor active substances such as linalool, β-ionone, and 3,5-octadiene-2-one significantly increased, resulting in an enhanced floral and fruity aroma of dark tea. Furthermore, new flavor substances like geranyl isovalerate and decanal were produced during SSF, enriching the aroma profile of dark tea. Non-ester catechins demonstrated a drastic increase, while ester catechins remarkably decreased after SSF. Furthermore, SSF led to a slight decrease in the total polyphenols content and antioxidant activity of dark tea. There is a close relationship between VOCs and the main non-volatile metabolites during SSF. Overall, this study highlighted the great impact of SSF with B. subtilis on the metabolites of dark tea and provided valuable insights into the role of bacteria in shaping the metabolite profile of FBT.

Metabolome and Microbiome Analysis to Study the Flavor of Summer Black Tea Improved by Stuck Fermentation

Tea is the most popular and widely consumed beverage worldwide, especially black tea. Summer tea has a bitter and astringent taste and low aroma compared to spring tea due to the higher content of polyphenols and lower content of amino acids. Microbial fermentation is routinely used to improve the flavor of various foods. This study analyzed the relationship between the quality of black tea, metabolic characteristics, and microbial communities after microbial stuck fermentation in summer black tea. Stuck fermentation decreased the bitterness, astringency sourness, and freshness, and increased the sweetness, mellowness, and smoothness of summer black tea. The aroma also changed from sweet and floral to fungal, with a significant improvement in overall quality. Metabolomics analysis revealed significant changes in 551 non-volatile and 345 volatile metabolites after fermentation. The contents of compounds with bitter and astringent taste were decreased. Sweet flavor saccharides and aromatic lipids, and acetophenone and isophorone that impart fungal aroma showed a marked increase. These changes are the result of microbial activities, especially the secretion of extracellular enzymes. Aspergillus, Pullululanibacillus, and Bacillus contribute to the reduction of bitterness and astringency in summer black teas after stuck fermentation, and Paenibacillus and Basidiomycota_gen_Incertae_sedis contribute positively to sweetness. In addition, Aspergillus was associated with the formation of fungal aroma. In summary, our research will provide a suitable method for the improvement of tea quality and utilization of summer tea, as well as provide a reference for innovation and improvement in the food industry.

Dynamical changes of tea metabolites fermented by Aspergillus cristatus, Aspergillus neoniger and mixed fungi: A temporal clustering strategy for untargeted metabolomics

Dark tea fermentation involves various fungi, but studies focusing on the mixed fermentation in tea remain limited. This study investigated the influences of single and mixed fermentation on the dynamical alterations of tea metabolites. The differential metabolites between unfermented and fermented teas were determined using untargeted metabolomics. Dynamical changes in metabolites were explored by temporal clustering analysis. Results indicated that Aspergillus cristatus (AC) at 15 days, Aspergillus neoniger (AN) at 15 days, and mixed fungi (MF) at 15 days had respectively 68, 128 and 135 differential metabolites, compared with unfermentation (UF) at 15 days. Most of metabolites in the AN or MF group showed a down-regulated trend in cluster 1 and 2, whereas most of metabolites in the AC group showed an up-regulated trend in cluster 3 to 6. The three key metabolic pathways mainly composed of flavonoids and lipids included flavone and flavonol biosynthesis, glycerophospholipid metabolism and flavonoid biosynthesis. Based on the dynamical changes and metabolic pathways of the differential metabolites, AN showed a predominant status in MF compared with AC. Together, this study will advance the understanding of dynamic changes in tea fermentation and provide valuable insights into the processing and quality control of dark tea.

Aroma characterisation of Liu-pao tea based on volatile fingerprint and aroma wheel using SBSE-GC-MS

Liu-pao tea (LPT) has unique aroma characteristics, and is a special microbial fermented tea produced using dark raw tea (LPM) as its raw material. In this study, stir bar sorptive extraction (SBSE) combined with gas chromatography-mass spectrometry (GC-MS) was applied to investigate the volatiles of 16 LPTs and 6 LPMs. Moreover, variations in volatile profiles between LPTs and LPMs were explored. Results showed that a total of 132 volatile compounds were identified from LPTs. The volatile fingerprint was constructed with a similarity ranged from 0.85 to 0.99. Furthermore, twenty-six aroma compounds were selected to depict the molecular aroma wheel of LPT. Multivariate statistical analysis revealed that the contents of 24 aroma compounds changed significantly (P < 0.05) when LPMs were processed into LPTs. These results reveal the volatile profiles of LPTs and aroma composition changes during microbial fermentation process, which might provide chemical basis of the aroma quality of LPT.

Characterization of volatile metabolites in Pu-erh teas with different storage years by combining GC-E-Nose, GC-MS, and GC-IMS

Storage time is one of the important factors affecting the aroma quality of Pu-erh tea. In this study, the dynamic changes of volatile profiles of Pu-erh teas stored for different years were investigated by combining gas chromatography electronic nose (GC-E-Nose), gas chromatography-mass spectrometry (GC-MS), and gas chromatography-ion mobility spectrometry (GC-IMS). GC-E-Nose combined with partial least squares-discriminant analysis (PLS-DA) realized the rapid discrimination of Pu-erh tea with different storage time (R2Y = 0.992, Q2 = 0.968). There were 43 and 91 volatile compounds identified by GC-MS and GC-IMS, respectively. A satisfactory discrimination (R2Y = 0.991, and Q2 = 0.966) was achieved by using PLS-DA based on the volatile fingerprints of GC-IMS. Moreover, according to the multivariate analysis of VIP > 1.2 and univariate analysis of p < 0.05, 9 volatile components such as linalool and (E)-2-hexenal were selected as key variables to distinguish Pu-erh teas with different storage years. The results provide theoretical support for the quality control of Pu-erh tea.

Formation of aroma characteristics driven by volatile components during long-term storage of An tea

The aim of this study was to reveal the molecular basis of aroma changes during storage of An tea (AT). The key volatile compounds in AT were screened using SPME-GC-MS and SPE-GC-MS analytical techniques in combination with odor activity value (OAV) and flavor dilution factor (FD). The results showed that with the increase of storage time the stale and woody aromas were revealed. Esters, acids and hydrocarbons are the main types of volatile compounds in AT, and their content accounts for 52.69 %-61.29 % of the total volatile compounds. The key volatile compounds with stale and woody aromas during AT storage were obtained by OAV value and FD value, namely ketoisophorone (flavor dilution factor, FD = 64), linalool oxide C (FD = 64), 1-octen-3-ol (OAV > 1, FD = 32), 1,2-dimethoxybenzene (FD = 16), naphthalene (OAV > 1, FD = 32), 3,4-dimethoxytoluene (FD = 16), and 1,2,3-trimethoxybenzene (FD = 8). Our research provides a scientific basis and insights for the improvement of quality during the storage of dark tea.

Changes in the volatile compounds and characteristic aroma during liquid-state fermentation of instant dark tea by Eurotium cristatum

Instant dark tea (IDT) was prepared by liquid-state fermentation inoculating Eurotium cristatum. The changes in the volatile compounds and characteristic aroma of IDT during fermentation were analyzed using gas chromatography-mass spectrometry by collecting fermented samples after 0, 1, 3, 5, 7, and 9 days of fermentation. Components with high odor activity (log₂^FD ≥ 5) were verified by gas chromatography-olfactometry. A total of 107 compounds showed dynamic changes during fermentation over 9 days, including 17 alcohols, 7 acids, 10 ketones, 11 esters, 8 aldehydes, 37 hydrocarbons, 4 phenols, and 13 other compounds. The variety of flavor compounds increased gradually with time within the early stage and achieved a maximum of 79 compounds on day 7 of fermentation. β-Damascenone showed the highest odor activity (log₂^FD = 9) in the day 7 sample, followed by linalool and geraniol. These results indicate that fungal fermentation is critical to the formation of these aromas of IDT.

Characterization of the Aroma Profiles of Guangdong Black Teas Using Non-Targeted Metabolomics

Guangdong black teas have diverse flavors and aromas. To explore the molecular basis of these aromas, we extracted and analyzed the volatile flavor compounds of 31 black tea samples from 7 districts (Yingde, Luokeng, Renhua, Meizhou, Chaozhou, Lianshan, and Heyuan) in Guangdong Province with headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS). Then, 135 volatile flavor compounds (VFCs) were identified and grouped into 12 classes according to their chemical structure. Notably, alcohols accounted for 31.40-44.43% of total VFCs. The score plot of supervised partial least squares-discriminant analysis (PLS-DA) revealed good discrimination for most black tea samples. Additionally, 64 compounds with variable importance in projection > 1.0 were identified as differential odorants. Through an odor activity value analysis, eight volatile compounds were identified as the key active differential VFCs: linalool, methyl salicylate, phenylethyl alcohol, p-cresol, 3-methyl-butanoic acid, geraniol, benzaldehyde, and benzeneacetaldehyde. Thus, benzeneacetaldehyde and linalool in YJ-Yingde samples, benzaldehyde in Luokeng samples with an almond-like aroma, phenylethyl alcohol in the Heyuan samples, and p-cresol and 3-methyl-butanoic acid in the Chaozhou samples were the key volatile flavor compounds that could differentiate local black teas from other black teas. These findings will enrich the research in tea aroma chemistry and provide a method for identifying the origins of Guangdong black teas.

Headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS) and odor activity value (OAV) to reveal the flavor characteristics of ripened Pu-erh tea by co-fermentation

Introduction

Pu-erh tea is a geographical indication product of China. The characteristic flavor compounds produced during the fermentation of ripened Pu-erh tea have an important impact on its quality.

Methods

Headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS) and odor activity value (OAV) is used for flavor analysis.

Results

A total of 135 volatile compounds were annotated, of which the highest content was alcohols (54.26%), followed by esters (16.73%), and methoxybenzenes (12.69%). Alcohols in ripened Pu-erh tea mainly contribute flower and fruit sweet flavors, while methoxybenzenes mainly contribute musty and stale flavors. The ripened Pu-erh tea fermented by Saccharomyces: Rhizopus: Aspergillus niger mixed in the ratio of 1:1:1 presented the remarkable flavor characteristics of flower and fruit sweet flavor, and having better coordination with musty and stale flavor.

Discussion

This study demonstrated the content changes of ripened Pu-erh tea’s flavor compounds in the fermentation process, and revealed the optimal fermentation time. This will be helpful to further understand the formation mechanism of the characteristic flavor of ripened Pu-erh tea and guide the optimization of the fermentation process of ripened Pu-erh tea.

Understanding of formation and change of chiral aroma compounds from tea leaf to tea cup provides essential information for tea quality improvement

Abundant secondary metabolites endow tea with unique quality characteristics, among which aroma is the core component of tea quality. The ratio of chiral isomers of aroma compounds greatly affects the flavor of tea leaves. In this paper, we review the progress of research on chiral aroma compounds in tea. With the well-established GC-MS methods, the formation of, and changes in, the chiral configuration of tea aroma compounds during the whole cycle of tea leaves from the plant to the tea cup has been studied in detail. The ratio of aroma chiral isomers varies among different tea varieties and finished teas. Enzymatic reactions involving tea aroma synthases and glycoside hydrolases participate the formation of aroma compound chiral isomers during tea tree growth and tea processing. Non-enzymatic reactions including environmental factors such as high temperature and microbial fermentation involve in the change of aroma compound chiral isomers during tea processing and storage. In the future, it will be interesting to determine how changes in the proportions of chiral isomers of aroma compounds affect the environmental adaptability of tea trees; and to determine how to improve tea flavor by modifying processing methods or targeting specific genes to alter the ratio of chiral isomers of aroma compounds.

Effects of Maturity and Processing on the Volatile Components, Phytochemical Profiles and Antioxidant Activity of Lotus (Nelumbo nucifera) Leaf

In this study, fresh lotus leaves at two maturity stages were processed to tea products by different methods (white-tea process, green-tea process and black-tea process). The volatile compounds, phytochemical profiles and antioxidant activities of lotus-leaf tea were investigated. A total of 81 volatile components were identified with HS-GC-IMS. The mature lotus-leaf tea showed more volatile compounds than the tender lotus-leaf tea. The lotus leaf treated with the white-tea process had more aroma components than other processing methods. In addition, six types of phenolic compounds, including luteolin, catechin, quercetin, orientin, hyperoside and rutin were identified in the lotus-leaf tea. The mature leaves treated with the green-tea process had the highest levels of TPC (49.97 mg gallic acid/g tea) and TFC (73.43 mg rutin/g tea). The aqueous extract of lotus-leaf tea showed positive scavenging capacities of DPPH and ABTS radicals, and ferric ion reducing power, whereas tender lotus leaf treated with the green-tea process exhibited the strongest antioxidant activity. What is more, the antioxidant activities had a significant positive correlation with the levels of TPC and TFC in lotus-leaf tea. Our results provide a theoretical basis for the manufacture of lotus-leaf-tea products with desirable flavor and health benefits.

Characterization and modelling of odor-active compounds release behavior from Fu-brick tea during boiling-water extraction by molecular sensory science approach

The odor-active compounds in Fu-brick tea and their release behaviors during boiling-water were studied. Fifty-one odor-active compounds were identified, and their release behaviors were identified by continuously recovering 16 sections of condensed water combined with sensory, instrumental, and nonlinear curve fitting analysis. The odor intensities of condensed water and the concentrations of odor-active compounds could be significantly fitted (p < 0.01) to power-function type curves. Hydrocarbons showed the fastest release rate, while organic acids showed the slowest. The release rates had very little correlation with their concentrations, molecular weights, and boiling points. Most odor-active compounds (≥70 %) released need to evaporate more than 24 % of the added water during boiling-water extraction. Meanwhile, on the basis of odor activity value (OAV) calculation, the aroma recombination experiments were performed to explore the odor-active compounds that made major contributions to the formation of the aroma profile of each condensed water.

Heimao tea polysaccharides ameliorate obesity by enhancing gut microbiota-dependent adipocytes thermogenesis in mice fed with high fat diet

Heimao tea (HMT) is a kind of fermented dark tea that has various health benefits. However, the available information regarding the anti-obesity effect of HMT and its active ingredients is still limited. Herein, we extracted the polysaccharides from Heimao tea (HMTP) and evaluated the anti-obesity effect and the underlying mechanism of HMTP. 12-Week administration of HMTP ameliorated lipid accumulation in the adipose tissue and improved glucolipid metabolism in high-fat diet (HFD)-fed mice. HMTP also induced browning of inguinal white adipose tissue (iWAT) and enhanced the thermogenic activity of interscapular brown adipose tissue (iBAT) by upregulating the expression of a series of thermogenic genes, such as Ucp1, Prdm16, and Pgc1α. Interestingly, the anti-obesity effect of HMTP was closely associated with altered relative abundance of the gut microbes, especially Dubosiella and Romboutsia, with significant increases, in which the abundance of Dubosiella and Romboutsia was negatively correlated with the body weight (r = -0.567, p < 0.05; r = -0.407, p < 0.05) and positively correlated with the iBAT index (r = 0.520, p < 0.05; r = 0.315, p < 0.05). Our data suggest that the alteration of the gut microbiota may play a critical role in HMTP-induced iWAT browning and iBAT activation, and our findings may provide a promising way for preventing obesity.

Physicochemical and Colon Cancer Cell Inhibitory Properties of Theabrownins Prepared by Weak Alkali Oxidation of Tea Polyphenols

Existing studies on the biological activity of theabrownins are not based on their free state but on the complexes of theabrownins, polysaccharides, proteins, and flavonoids. In this study, theabrownins (TBs-C) were prepared by weak alkali oxidation of tea polyphenols. The ultraviolet-visible scanning spectrum of TBs-C showed two characteristic absorption peaks at 203 and 270 nm. The zeta potential of the TBs-C aqueous solution was negative, and the values varied from - 6.26 to -19.55 mV with a solution pH of 3-9. Storage conditions of pH 5.0-7.0 and around 25 °C were beneficial for the physical and chemical stability of the TBS-C solution. Cells were treated with series concentrations and examined by MTT, HE staining, PI immunofluorescence staining, flow cytometry, and real-time PCR to investigate the antiproliferative effect of TBs-C on human colon cancer HT-29 cells. The results showed that TBs-C, particularly at 500 µg/mL, inhibited cell growth. TBs-C induced HT-29 cell apoptosis, as confirmed by morphological changes, nucleus propidium iodide staining, and distributions of the cell cycle. The apoptotic mechanism may be due to the intracellular redox imbalance induced by TBs-C.

Identification of aroma-active compounds responsible for the floral and sweet odors of Congou black teas using gas chromatography-mass spectrometry/olfactometry, odor activity value, and chemometrics

BACKGROUND

Floral and sweet odors are two typical characteristic aromas of Congou black tea, but their aroma-active compounds are still unclear. Characterizing the key aroma-active compounds can provide a theoretical foundation for the practical aroma quality evaluation of Congou black tea and directional processing technology of high-quality black tea with floral or sweet odors. Gas chromatography-olfactometry (GC-O) combined with odor activity value (OAV) is often used to screen key aroma-active substances, but the interaction between aroma components and their impact on the overall sensory quality is ignored. Therefore, in this study, OAV combined with variable importance in projection (VIP) and Spearman correlation analysis (SCA) were used to characterize the aroma-active components of Congou black teas with floral and sweet odors.

RESULTS

Eighty-five volatiles were identified in these samples using gas chromatography-mass spectrometry (GC-MS). Twenty-three compounds were identified as potential markers for the floral and sweet odors of Congou black teas from orthogonal partial least squares discriminant analysis (OPLS-DA). Eighteen compounds were selected as candidate aroma compounds based on GC-O analysis and OAV calculations. In addition, 26 compounds were screened as crucial aroma compounds based on SCA. Finally, 19 compounds were evaluated as key aroma compounds by the comprehensive evaluation of VIP, OAV, and SCA. Terpenoids are the main active compounds that contribute to the floral odor of Congou black tea, whereas aldehydes are the key compounds for the sweet odor.

CONCLUSION

The proposed method can effectively screen the aroma-active compounds and can be used for comprehensive quality control of products. © 2022 Society of Chemical Industry.

Chromatographic-Based Platforms as New Avenues for Scientific Progress and Sustainability

Chromatography was born approximately one century ago and has undergone outstanding technological improvements in innovation, research, and development since then that has made it fundamental to advances in knowledge at different levels, with a relevant impact on the well-being and health of individuals. Chromatography boosted a comprehensive and deeper understanding of the complexity and diversity of human-environment interactions and systems, how these interactions affect our life, and the several societal challenges we are currently facing, namely those related to the sustainability of our planet and the future generations. From the life sciences, which allowed us to identify endogenous metabolites relevant to disease mechanisms, to the OMICS field, nanotechnology, clinical and forensic analysis, drug discovery, environment, and "foodprint", among others, the wide range of applications of today's chromatographic techniques is impressive. This is fueled by a great variability of powerful chromatographic instruments currently available, with very high sensitivity, resolution, and identification capacity, that provide a strong basis for an analytical platform able to support the challenging demands of the postgenomic and post COVID-19 eras. Within this context, this review aims to address the great utility of chromatography in helping to cope with several societal-based challenges, such as the characterization of disease and/or physiological status, and the response to current agri-food industry challenges of food safety and sustainability, or the monitoring of environmental contamination. These are increasingly important challenges considering the climate changes, the tons of food waste produced every day, and the exponential growth of the human population. In this context, the principles governing the separation mechanisms in chromatography as well the different types and chromatographic techniques will be described. In addition, the major achievements and the most important technological advances will be also highlighted. Finally, a set of studies was selected in order to evince the importance of different chromatographic analyses to understand processes or create fundamental information in the response to current societal challenges.

Identification and characterization of the key volatile flavor compounds in black teas from distinct regions worldwide

Volatile flavor compounds in 112 black teas from seven countries were analyzed by untargeted metabolomics using headspace solid-phase microextraction and gas chromatography-mass spectrometry (HS-SPME/GC-MS). Multivariate statistical analysis and odor activity values (OAVs) were used to classify these samples and identify key odorants. A total of 140 volatile flavor compounds (VFCs), including 12 different groups, were identified, and alcohols were prevalent in China and India samples, accounting for 40.83% and 34.96% of the total VFCs, respectively. Eight volatile compounds with OAVs > 1 were identified as key active differential odorants in Chinese, Indian, and Sri Lankan samples, including linalool, pentanoic acid, methyl salicylate, hexanoic acid, 1-methyl-naphthalene, phenylethyl alcohol, geraniol, and β-ionone. Linalool, pentanoic acid, and hexanoic acid in Indian black teas, phenylethyl alcohol in Chinese black teas, and 1-methyl-naphthalene, β-ionone in Sri Lankan black teas could be used to discriminate different black tea groups. A total of 12-14 VFCs with OAVs > 1 were identified as key active aromatics in Chinese black tea sample. Linalool and benzeneacetaldehyde in Yingde (Guangdong) black tea, methyl salicylate in Taiwanese samples, and benzeneacetic acid in Anhui black tea could be used as biomarkers to distinguish them from other Chinese samples. Sensory evaluation results showed that most black teas presented the common sweet, floral odors, which were consistent with GC-MS analysis. These results will contribute to characterize the odor metabolome of black teas and provide biochemical basis for identifying the authenticity of different black teas. PRACTICAL APPLICATION: Linalool, pentanoic acid, and hexanoic acid in Indian black teas, phenylethyl alcohol in Chinese black teas, 1-methyl-naphthalene, β-ionone, and methyl salicylate in Sri Lankan black teas could be used to discriminate black teas from the three countries. Linalool and benzeneacetaldehyde in Yingde black teas, methyl salicylate in Taiwanese black teas, and benzeneacetic acid in Anhui black tea are the potential biomarkers to distinguish these teas from other Chinese black teas.

Salting-out re-distillation combined with sensory-directed analysis to recover odor-active compounds for improving the flavor quality of instant Pu-erh tea

The objective of this study was to develop an effective recovery technology of odor-active compounds (OACs) to improve the flavor quality of instant Pu-erh tea (IPT) based on their released behaviors. Salting-out re-distillation (SRD) combined with sensory-directed analysis was developed. The contributing factors, including the soaking time of tea, recovery volume of condensed water of first distillation, amount of sodium chloride, recovery volume of condensed water of SRD, and re-use times of sodium chloride, were studied systematically. Under optimized conditions, 41 OACs were recovered in the first distillation, and the total recovery rate was 83.94%. Forty-one OACs were recovered via SRD, and the total recovery rate reached 72.29%, significantly better than membrane method (33.46%). The IPT prepared by adding OACs that recovered via SRD showed strong aroma attributes intensities and good coordination. This developed method can provide a more effective scheme to improve the flavor quality of IPT.

Effects of electrostatic spray drying on the sensory qualities, aroma profile and microstructural features of instant Pu-erh tea

The sensory qualities, aroma profile, and microstructural features of instant Pu-erh teas (IPTs) produced by electrostatic spray drying (ESD) were evaluated by sensory and instrumental analyses and compared with those produced by other drying methods (freeze-drying [FD], vacuum drying [VD], and conventional spray drying [CSD]). The sensory qualities of ESDIPT were similar to those of FDIPT, and better than those of VDIPT and CSDIPT. Eighty-eight volatiles were detected in all IPTs, and 45 odor-active compounds were captured. Most of their OAVs were higher in ESDIPT than in VDIPT and CSDIPT but were lower than those in FDIPT. Dihydro-β-ionone had the highest OAV. Aroma recombination experiments were performed to verify the identification results. ESDIPT was present in the shape of microspheres with many regular concave surfaces, which was different from those treated by other drying methods. In terms of sensory quality and productivity, ESD would be a potential method for IPT production.

Hypolipidaemic and antioxidant effects of various Chinese dark tea extracts obtained from the same raw material and their main chemical components

In order to investigate the hypolipidaemic and antioxidant effects of various dark teas produced from different post-fermentation using the same raw material, a hyperlipidaemia zebrafish model combined with binding bile salts assay and antioxidant assays were performed in this study. Results showed that the hypolipidaemic effect of dark tea extracts increased significantly (p < 0.05) while the antioxidant ability decreased sharply compared with raw material. Particularly, Liupao tea (50%) and Pu-erh tea (48%) showed promising hypolipidaemic potential; however, the antioxidant capacity of Pu-erh tea decreased (31-49%) most dramatically. Besides, the levels of total polyphenols and catechins decreased sharply, but theabrownin, gallic acid, and caffeine increased significantly after post-fermentation. Moreover, the potential mechanisms of regulating hyperlipidaemia by dark tea extracts were discussed. These results suggest that microbial fermentation significantly affects the bioactivity of dark teas, and provide theoretical basis for processing and improving of dark tea products for hyperlipidaemia therapy.