This work aims to compare the chemical composition and anti-inflammatory effects on RAW264.7 macrophages of Keemun black tea stems and leaves. A total of 50 volatile compounds were identified in tea stems and leaves, and aldehydes, alcohols, and esters were the main volatile compound categories. There were 11 key volatile compounds, including geraniol, benzeneacetaldehyde, methyl salicylate, linalool, etc. contributed to distinguishing the tea stems from the tea leaves. In the quantitative and liquid chromatography-mass spectrometry (LC-MS)-based metabolomics analysis, higher contents of amino acids, monosaccharides, and quinic acids were found in stems than those in leaves. Inversely, higher contents of tea pigments, flavan-3-ols, gallic acid, purine alkaloids, and flavonol glycosides were present in tea leaves than in stems. LC-MS-based metabolomics also revealed that organic acids were the most critical non-volatile compounds responsible for the differences between tea stems and leaves. Furthermore, tea stems had better inhibiting effects of pro-inflammatory cytokines (interleukin (IL)-1β and IL-6) in lipopolysaccharide-challenged RAW264.7 macrophages than tea leaves, while no significant differences exist between leaves and stems for inhibiting the secretion of tumor necrosis factor α (TNF-α) and NO. In conclusion, our results support using Keemun black tea stems as a novel source of anti-inflammatory compounds.

Catechins are the primary polyphenols in tea. Enzymatic oxidation models of (-)-epicatechin (EC) and (-)-epigallocatechin gallate (EGCG) with different proportions were established to investigate the formation mechanism of oxidation products and their relationship to color characteristics. Their oxidation products were analyzed by liquid chromatography tandem mass spectrometry (LC-MS) combined with UV-visible spectrometry. These products were quantified by LC-MS and performed correlation coefficient analysis of color. The results indicated that single oxidation of EGCG dominated the whole reaction when EGCG had high proportions in the reaction mixture, promoting the formation of red pigments such as dehydrotheasinensin AQ and theacitrinin B. When EC with high ratios, the oxidation pathways preferred utilizing both EC and EGCG, promoting the formation of yellow pigments such as theaflavin and theadibenzotropolone A. This study provided the detailed oxidation mechanism of EC and EGCG mixture, suggesting that the proportions of catechol-type and pyrogallol-type catechins markedly affected the direction of enzymatic oxidation reaction and further influenced the color formation.

Green tea (GT) and its polyphenols (TP) possess excellent antioxidant properties and have the potential to inhibit the formation of heterocyclic aromatic amines (HAAs) in thermally processed meat products. However, their effects on the formation HAAs in roasted pork remain unclear. The study investigated the effect of green tea (GT), TP, and epigallocatechin gallate (EGCG) at additive levels of 0.05%, 0.25%, and 0.5% on the formation of HAAs, antioxidant capacity and quality characteristics during the roasting of pork patties at 250°C. Low levels of GT (0.05%, and 0.25%) and EGCG (0.05%) slightly inhibited the formation of HAAs (MeIQx, 4,8-DiMeIQx, PhIP), with inhibition rates for MeIQx, 4,8-DiMeIQx, and PhIP ranging from 4.70%–8.32% (except for 0.05% GT), 6.15%–16.19%, and 5.69%–24.69%, respectively, while the other groups (0.5% GT, 0.05% TP, 0.25% TP, 0.5% TP, 0.25% EGCG, and 0.5% EGCG) promoted the formation of HAAs. Patties with higher levels of HAAs showed greater consumption of precursors (glucose, free amino acids, and creatine) and protein oxidation. Despite this, all three additives enhanced antioxidant activities (DPPH, ABTS, FRAP) and lipid oxidation stability dose-dependently. Additionally, the additives reduced the luminance (L*), redness (a*), and yellowness (b*) of roasted pork patties. TP and EGCG caused more weight loss in patties and negatively affected their texture, whereas GT had no significant effect on these parameters. Overall, EGCG (0.05%, and 0.25%) had the greatest impact on the formation of HAAs, antioxidant capacity, and quality characteristics of roasted pork patties, followed by TP (0.05%, and 0.25%) and GT (0.05%, and 0.25%). These findings suggest that the addition of low levels of GT (0.05%, and 0.25%) can inhibit HAAs formation, enhance antioxidant capacity, and maintain the quality characteristics of roasted pork patties, whereas the addition of TP and EGCG (0.05%, 0.25%, and 0.5%) is not an effective method for improving quality characteristics and inhibiting HAAs formation in roasted pork patties.

Tea trichomes were regarded as an essential evaluation index for reflecting tea flavor quality in terms of aroma and influence on infusion color. This study reveals the impact of golden oxidized trichomes on the color, volatile and non-volatile metabolites of black teas through comparative metabolomics combined quantitative analysis on hongbiluo (trichomes-deficiency black teas), hongjinluo (trichomes-rich black teas), and trichomes (from hongjinluo). Forty-six volatile components were detected using headspace solid-phase microextraction gas chromatography-mass spectrometry, while the results suggested that the contribution of trichomes to black teas is limited. A total of 60 marker non-volatile compounds were identified, including catechins, catechin oxidation products, flavonoid glycosides, organic acids, hydrolysable tannins and amino acids. Notably, p-coumaroyl-kaempferol glucosides, and catechin dimers demonstrated high levels in independent trichomes and showed a positive correlation with the brightness and yellow hue of black tea infusions, specifically kaempferol 3-O-di-(p-coumaroyl)-hexoside. Furthermore, results from fractional extraction analysis of separated trichomes provided that N-ethyl-2-pyrrolidinone-substituted epicatechin gallates, acylated kaempferol glycosides, and chromogenic catechins dimers, such as theaflavins, were primary color contributors in oxidized trichomes. Especially, we found that epicatechin gallate (ECG) and its derivates, 3'-O-methyl-ECG and N-ethyl-2-pyrrolidinone-substituted ECG, highly accumulated in trichomes, which may be associated with the varieties of hongbiluo and hongjinluo black teas. Eventually, addition tests were applied to verify the color contribution of trichome mixtures. Our findings employed comprehensive information revealing that golden oxidized trichomes contributed significantly to the brightness and yellow hue of black tea infusion, but their contribution to the aroma and metabolic profile is limited. These findings may contribute to the effective modulation of the infusion color during black tea production by regulating the proportion of tea trichomes or screening trichomes-rich or deficiency varieties.

The present study provided a highly efficient and systematic workflow for identifying colorants of food and beverage. Generally, the objective colorimeter and subjective human eye had different systems to identify colors, which makes the color description very challenging. Here, the Lab/LCH color system was applied to clearly illustrate color changes. Our workflow was applied to determine and verify the differential colorant substances between two groups of black tea infusions. Regarding color parameters, the infusions of black tea from Camellia sinensis and Camellia assamica differed significantly. The differential substances between black tea infusions were correlated to color parameters by mass spectrometry and nuclear magnetic resonance based multivariate statistical analysis and verified by machine learning tool. Pyroglutamic acid-glucose Amadori product, quercetin-3-O-glucoside, quinic acid and theabrownins were identified as main color contributors to black teas' color difference, which were also verified by addition test with standard black tea infusion.

A color-deepening effect of theaflavins on the theanine-glucose thermal reaction model was revealed. Generated chromogenic intermediates in the initial stage and an accelerated browning rate through the promoted degradation of theanine-glucose Amadori rearrangement product in the intermediate and final stages are responsible for the color-deepening effect. Four pink-to-red theaflavin-theanine intermediates were verified as theaflavinies referencing the nuclear magnetic resonance and liquid chromatography-mass spectrometry information on theaflavins and l-theanine, including one accurately identified as theaflavinie 4. Theaflavinie 4 showed two maximum absorption peaks at 401 and 506 nm with parallel intensities, which resulted in a significant dichromic color change from pale pink to orange and red. Theaflavinies also could undergo further thermal reactions to yield brown polymers under higher temperatures (130 and 140 degrees C). This research provided new insight into realizing thermally formed polymers during black tea processing, which may be formed by oxidation products and amino acids or proteins through non-enzymatic thermal reactions.

The capacity differences of seven catechin monomers to produce colors after treating with catechin-free extract were investigated. After 240-min reaction, only (-)-epicatechin (EC) and (+)-catechin (C) presented obvious luminous red color with L* values of 63.32-71.73, a* values of 37.13-46.44, and b* values of 65.64-69.99. Meanwhile, the decrease rate of EC and C was 43.52 %-50.35 %, which were significantly lower than those of other catechin monomers (85.91 %-100 %). The oxidized products of catechin monomers were analyzed by ultra-high performance liquid chromatography-quadrupole-time of flight-mass spectrometry coupled with diode array detector, wherein dehydro-dimers and -trimers (oxidative coupling products of catechins' A-B ring) were found to be the major chromogenic compounds of EC and C. Additionally, the antioxidant capacity of catechin monomers only decreased after 30-min reaction, while along with further enzymatic reaction, catechin monomers presented comparable oxyradical scavenging ability (e.g., the DPPH inhibitory rates of catechin monomers were in the range of 24.42 %-50.77 %) to vitamin C (positive control, DPPH inhibitory rate was 27.66 %). Meanwhile, the inhibitory effects of most catechin monomers on α-glucosidase were enhanced in different degrees. These results provided basis for the development of enzymatically-oxidized catechin monomers as functional food color additives.

While key aroma and taste compounds of Keemun Congou black teas (KCBT) form during aeration and thermal stages, it is still unknown whether these processing stages also produce non-volatile color-contributing metabolites. Through integrating metabolomics with correlation and ridge regression analyses, 190 metabolites were identified as marker compounds that reclassified 15 KCBT samples collected from five processing stages into four groups. Meanwhile, the results of quantification and heatmap analysis showed that the concentrations of theaflavins and theasinensins significantly increased, as catechin decreased, after rolling, while flavonoid aglycones and polyunsaturated fatty acids increased throughout drying. Regression analysis between marker compound levels and total color difference values (∆E) revealed that the major color contributors were 3,5-dicaffeoylquinic acid, glucosyl-dehydrodigallic acid, theacitrin A, kaempferol-O-robinobioside, and (-)-epigallocatechin, with regression coefficients (absolute value) exceeding 4 × 10-2. Overall, the present study confirmed that rolling and drying were the two vital stages responsible for the color formation of KCBT.

BACKGROUND:Roasting is an essential step in making roasted teas, and its role in producing flavors has been widely studied. However, the variation of potential hazardous compounds during the tea roasting process is still vague. The present study established an effective method based on liquid chromatography-triple quadrupole-tandem mass spectrometry to simultaneously determine the variation of acrylamide (AA), 5-hydroxymethylfurfural (5-HMF), and free amino acids during the tea roasting process. Meanwhile, the effects of several tea polyphenols on the formation of AA and 5-HMF were investigated by a wet-to-dry thermal model reaction. RESULTS:Medium-temperature roasted teas had the highest levels of AA and 5-HMF, with ranges of 0.13-0.15 μg g-1 and 68.72-123.98 μg g-1, respectively. Quantitative results showed that the levels of monosaccharides and amino acids decreased during roasting, which might contribute to the formation of 5-HMF and AA. Meanwhile, the decrease of epigallocatechin gallate (EGCG), epigallocatechin (EGC), and epicatechin (EC) might be related to their inhibitory effects on 5-HMF and AA. Thermal model reaction results showed that EGCG and EC significantly inhibited 5-HMF formation with a decline rate of 33.33% and 72.22%, respectively, mainly by trapping glucose. Gallic acid (GA) also had an inhibitory effect on the formation of AA (decreased by 92.86%) and 5-HMF (44.44%), mainly through impeding the preliminary reaction of asparagine and glucose. CONCLUSION:The roasting temperature determined the levels of AA and 5-HMF in teas. Catechins inhibited the formation of 5-HMF and AA mostly through trapping monosaccharides, while the inhibitory effect of GA was achieved by impeding the reaction. © 2024 Society of Chemical Industry.

As the final processing step, drying temperature between 90 and 140 degrees C is usually applied to terminate enzymatic activities and improve sensory characteristics of black tea. Liquid chromatography tandem mass spectrometry (LC-MS) based non-targeted and targeted metabolomics analyses combined in vitro biological assays were adopted to investigate the chemical and biological variations after drying. Fifty-nine differentially expressed metabolites including several hydroxycinnamic acid derivatives and pyroglutamic acid-glucose Amadori rearrangement products (ARPs) were identified, the latter of which was correspondingly accumulated with increasing temperature. The levels of theaflavins (TFs), thearubigins (TRs), monosaccharides and free amino acids gradually decreased with increasing temperature. Furthermore, the bioassays of black tea showed that drying under 110 degrees C provided the highest antioxidant capacities, but the inhibitory effects on alpha-glucosidase and alpha-amylase were decreasing along with increasing drying temperature. These results are valuable for optimizing drying process to obtain superior sensory properties and preserve bioactivities of black tea.

To explore the influence of tea trichomes on the quality of white tea, liquid chromatography quadrupole time-of-flight mass spectrometry (LC-Q-TOF-MS), and headspace solid phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) were used to identify non-volatile and volatile compounds white tea without trichomes (WTwt) and pure trichomes (PT). It was found that the bitter and astringent compounds, caffeine (CAF), epigallocatechin gallate (EGCG), epicatechin gallate (ECG) and flavonol glycosides, were mainly enriched in the WTwt, with 16.3-fold, 47.1-fold and 28.7-fold decrease in CAF and EGCG and ECG, respectively, and the content of these compounds in PT were lower than the taste thresholds. In PT, kaempferol-3-O-(p-coumaroyl)-glucoside and kaempferol-3-O-(di-p-coumaroyl)-glucoside were non-volatile marker compounds, and decanal was significant aroma contributor with rOAV = 250.86. Moreover, the compounds in trichomes mainly contributed to the fruity and floral aroma of white tea, among which benzyl alcohol, (E)-geranylacetone, decanal, dodecanal and 6-methyl-5-hepten-2-one were the crucial aroma components, which were 2.1, 1.7, 1.8, 1.4 and 2.2 times as much as the WTwt in the PT, respectively. In conclusion, trichomes can improve the quality of white tea by reducing the bitterness and astringency, increasing the umami, as well as enhancing the fruity and floral aromas.

Deep eutectic solvent (DES) has been widely developed and applied in extracting the functional components of teas, however, few studies devoted to revealing the composition differences of tea extracts obtained with DES. The present study aims to study the chemical composition and bioactive differences of Dianhong congou black tea extracts prepared by eight choline chloride (ChCl)-based DES. In addition, D-101 macroporous resin was used to remove DES for bioactivity analysis. High performance liquid chromatography (HPLC) and LC-mass spectrometry (LC-MS) were applied to quantitatively and qualitatively analyze chemical composition differences of DES extracts before and after DES removal. Quantitative results showed that DES4 (composed of ChCl and ethylene glycol) was suitable for extracting catechins (e.g., the extracted level of epicatechin gallate was 8.75 mg/g), theaflavins (theaflavin-3,3 '-digallate, 1.59 mg/g), and monosaccharides (glucose, 4.97 mg/g), meanwhile DES5 (composed of ChCl and glycerol) was proved to be effective for extracting free amino acids (with highest level of theanine, 19.72 mg/g). LC-MS based metabolomics results showed that DES2 (ChCl-citric acid), DES3 (ChCl-proline), and DES4 had considerable remaining amounts of flavonoid glycosides, theasinensins, and hydrolysable tannins after DES removal. Although purified DES5 extract contained a comparable amount of these marker compounds to other purified DES extracts, its antioxidant and alpha-glucosidase inhibitory activities were the lowest among others. Combining results from above, DES4 was proved to be the optimum solvent for extracting functional components of Dianhong congou black tea. The finding provided basis for the application of DES extraction method in tea science.

The linoleic acid reaction models were set at 150 degrees C for 120 min, and its oxidation process was monitored by nuclear magnetic resonance (NMR) and gas chromatography-mass spectrometry (GC-MS). Results showed that no furan was formed from linoleic acid without heating, while furan accumulated throughout the heating process. Linoleic acid ran out within 30 min, which indicated that furan was formed mainly from the intermediate oxidation products of linoleic acid after 30 min. It should be noticed that the content of (E,E)-2,4-decadienal reached maximum once the linoleic acid ran out and then decreased with the formation of furan. Multivariate statistical analysis suggested that (E,E)-2,4-decadienal was the most important aldehyde related to furan formation during linoleic acid oxidation. To prove this assumption, the variation of furan from (E,E)-2,4-decadienal reaction models heating at 150 degrees C for 60 min was also studied. Results showed that the content of furan increased with the oxidation of (E,E)-2,4-decadienal. Furthermore, NMR and GC-MS data proved that (E,E)-2,4-decadienal could be oxidized to 4,5-epoxy-(E)-2-decenal. In conclusion, our results supported (E,E)-2,4-decadienal and trans-4,5-epoxy-(E)-2-decenal as critical intermediate products of furan formation from linoleic acid oxidation.

It is now widely recognized that gut microbiota plays a critical role not only in the development and progression of diseases, but also in its susceptibility to dietary patterns, food composition, and nutritional intake. In this comprehensive review, we have compiled the latest findings on the effects of food nutrients and bioactive compounds on the gut microbiota. The research indicates that certain components, such as unsaturated fatty acids, dietary fiber, and protein have a significant impact on the composition of bile salts and short-chain fatty acids through catabolic processes, thereby influencing the gut microbiota. Additionally, these compounds also have an effect on the ratio of Firmicutes to Bacteroides, as well as the abundance of specific species like Akkermansia muciniphila. The gut microbiota has been found to play a role in altering the absorption and metabolism of nutrients, bioactive compounds, and drugs, adding another layer of complexity to the interaction between food and gut microbiota, which often requires long-term adaptation to yield substantial outcomes. In conclusion, understanding the relationship between food compounds and gut microbiota can offer valuable insights into the potential therapeutic applications of food and dietary interventions in various diseases and health conditions.

Black tea cream down can be separated into the resoluble (RS) and irresoluble (IS) parts. The irresoluble part hardly dissolves in boiling water after it forms in tea infusion, thus it is an indelible particle in the tea beverage industry. In the current work, we qualitatively and quantitatively analyzed the differences of chemical composition between these two parts. The results showed that the irresoluble cream down contained theaflavins and caffeine, but only dissolved in DMSO rather than boiling water. The irresoluble cream down contained higher levels of Al, Ca, Fe, and Cu mineral elements than resoluble cream down. The elemental analysis also indicated that irresoluble cream down was composed of more hydrogen element than resoluble cream down. The Fourier transform infrared (FT-IR) spectroscopy analysis confirmed that the irresoluble cream down spectrum presented two critical differential absorption peaks at 2919 and 2850 cm-1, which were attributed to the saturated carbon moiety of organic compounds. Moreover, we compared the effects of four metal ions (including Al3+, Ca2+, Fe3+, and Cu2+) on the formation of cream particle, and found that Al3+ had the strongest contribution to the particle formation of cream down. Meanwhile, caffeine also contributed to the particle formation of cream down as a secondary role.

Different from post-fermented teas, pickled tea is a unique processed tea of fresh leaves of Camellia sinensis var. assamica under anaerobic fermentation. It is mainly consumed in ethnic minority areas in southwest China. The chemical characteristics of pickled tea during processing were studied by mass spectrometry-based metabolomics and quantitative determination. Metabolomics results showed that a total of 44 marker compounds, including flavan-3-ols, organic acids, glycosides, and flavonoids were identified in pickled tea during fermentation. Thereinto, galloylated catechins were mainly degraded or oxidated into the corresponding nongalloylated cat-echins and theaflavins. Caffeine and theobromine slightly varied, while organic acids markedly varied during the whole processing. In addition, butanedioic, lactic, and gallic acid were found as the main organic acids in pickled tea and their contents were 220 +/- 9, 177 +/- 21, and 172 +/- 6 mu g/g, respectively. The inhibitory effects of pickled tea samples on alpha-amylase and alpha-glucosidase were also investigated and subsequently analyzed with respect to chemical-biological activities correlation. The results showed that glycosides and most organic acids were key alpha-amylase inhibitors, while catechins and flavonoids were key alpha-glucosidase inhibitors. The present study aimed to comprehensively explore the chemical variation of pickled tea during processing, and key inhibitors of alpha-glucosidase and alpha-amylase.

Not only do flavan-3-ols participate in the formation of chromogenic oxidation products such as theaflavins, but chlorogenic acid (3-caffeoylquinic acid, CQA) is also involved in the enzymatic oxidation during black tea processing. The critical oxidation product of CQA and (-)-epigallocatechin (EGC) were identified as an adduct containing benzobicyclo[3.2.2]nonenone structure, which was named as the dichlorogeniccatechin (DCGC) oligomer. It was composed of two molecules of CQA and one molecule of EGC. The effects of the initial reactant ratio and reaction time on the generation of DCGC were also analyzed. A high proportion of CQA promoted the production of DCGC, but a high proportion of EGC inhibited the DCGC formation. In addition, the content of DCGC in Keemun black tea during processing was determined. The content of DCGC highly increased after withering but decreased after drying. This study provides a new perspective for the investigation of other oxidation oligomers in black tea.

With the development of metabolomics analytical techniques, relevant studies have increased in recent decades. The procedures of metabolomics analysis mainly include sample preparation, data acquisition and pre-processing, multivariate statistical analysis, as well as maker compounds' identification. In the present review, we summarized the published articles of tea metabolomics regarding different analytical tools, such as mass spectrometry, nuclear magnetic resonance, ultraviolet-visible spectrometry, and Fourier transform infrared spectrometry. The metabolite variation of fresh tea leaves with different treatments, such as biotic/abiotic stress, horticultural measures, and nutritional supplies was reviewed. Furthermore, the changes of chemical composition of processed tea samples under different processing technologies were also profiled. Since the identification of critical or marker metabolites is a complicated task, we also discussed the procedure of metabolite identification to clarify the importance of omics data analysis. The present review provides a workflow diagram for tea metabolomics research and also the perspectives of related studies in the future.

N-ethyl-2-pyrrolidinone-substituted flavan-3-ols (EPSFs) were prepared by an in vitro model reaction, and the taste thresholds of EPSFs and their dose-over-threshold factors in large-leaf yellow tea (LYT) were investigated. The effects of initial reactant ratios, reaction temperatures and time, pH values, and water addition on the yield of EPSFs were explored. The contents of EPSFs during roasting were determined by liquid chromatography quadrupole time-of-flight mass spectrometry (LC-Q-TOF-MS). When the initial ratio of (-)-epigallocatechin gallate (EGCG) to theanine was 1:2 and roasted under 120 °C for 120 min, the contents of EPSFs were the highest. The bitterness and astringency thresholds of four EPSF isomers were measured by the half-tongue method, of which EPSF2 and EPSF3 had higher thresholds than EGCG. In LYT, four EPSFs had lower bitterness and astringency dose-over-threshold factors than EGCG. This study suggested that the reduction of bitterness and astringency of tea after roasting may be mainly due to the formation of EPSFs.

A statistical optimization study was used to maximize the extraction of bioactive compounds and antioxidant activity from green tea derived from purple leaves of Camellia sinensis var. assamica. Simultaneous optimization was applied, and a combination of 60 °C, 15 min, and a mass-solvent ratio of 1 g of dehydrated purple leaves to 62.3 mL of an ethanol/citric acid solution, were determined as the ideal extraction conditions. The optimized extract of purple tea leaves (OEPL) contained showed stability in relation to variations in pH, and lyophilized OEPL exerted cytotoxic and antiproliferative effects against cancerous cells (A549 and HCT8), demonstrated antimicrobial activity towards Listeria monocytogenes (ATCC 7644), Staphylococcus aureus (ATCC 13565) and Staphylococcus epidermidis (ATCC 12288), inhibition of α-amylase and α-glycosidase enzymes and reduced the release of pro-inflammatory cytokines (TNF-α, CXCL2/MIP-2, and IL-6) in lipopolysaccharides-stimulated RAW 264.7 macrophages. Thus, our results provide a broad assessment of the bioactivity of "green" extracts obtained by a simple and low-cost process using non-toxic solvents, and they have the potential to be used for technological applications.