Investigation of non-volatile metabolite variations during round green tea processing and effect of pan-frying degree using untargeted metabolomics and objective quantification.

Round green tea (RGT) presents unique properties and is widely distributed in China, and during processing, it undergoes dynamic changes in non-volatile metabolites (NVMs), which are poorly understood. Utilizing UHPLC-Q-Exactive/MS analysis, this study comprehensively characterized 216 NVMs during RGT processing and identified fixation and pan-frying as key processes influencing NVMs. Additionally, 23 key differential NVMs were screened, with amino acid and flavonoid metabolism highlighted as key metabolic pathways for RGT taste and color quality. The impact of pan-frying degree on shape, color, and taste was also explored. Moderate pan-frying led to optimal results, including a tight and round shape, green and bright color, mellow and umami taste, and reduced astringent and bitter taste NVMs, including epigallocatechin gallate, procyanidin B2, myricetin 3-O-galactoside, quinic acid, strictinin, phenylalanine, and theobromine. This study addresses the NVM research gap in RGT processing, thus providing a technical foundation for the precision-oriented processing of high-quality tea.

Evaluation of the quality grade of Congou black tea by the fusion of GC-E-Nose, E-tongue, and E-eye.

In the present study, the comprehensive quality of Congou black tea (CBT) including aroma, taste, and liquid color was investigated by a combination of gas chromatography electronic nose (GC-E-Nose), electronic tongue (E-tongue), and electronic eye (E-eye). An excellent discrimination of different quality grades of CBT was accomplished through the fusion of GC-E-Nose, E-tongue, and E-eye combined with orthogonal partial least squares discriminant analysis, with parameters of R2Y = 0.803 and Q2 = 0.740. Moreover, the quantitative evaluation of CBT quality was successfully achieved by partial least squares regression analysis, with the absolute error within 1.39 point, and the relative error within 1.62%. Additionally, 12 key variables were screened out by stepwise multiple linear regression analysis, which significantly contributed to the comprehensive quality score of CBT. Our results suggest that the fusion of multiple intelligent sensory technologies offers great potential and practicability in the quality evaluation of black tea.

Targeted quantitative metabolomic and flavor objective quantification technique reveal the impact mechanism of shaking on black tea quality and non-volatile metabolites.

Shaking constitutes a pivotal technique for enhancing black tea quality; nevertheless, its impact on the transformation mechanism of non-volatile metabolites (NVMs) in black tea remains obscure. The present study aimed to investigate the impact of shaking-withering methods (SWM) and traditional-withering methods (TWM) on black tea quality and NVMs conversion. A total of 57 NVMs and 14 objective quantitative indicators were obtained. SWM enhanced sweetness and umami taste, as well as appearance and liquor color brightness of black tea. Eight key differential NVMs were identified by multivariate statistical and dose over threshold value analysis. Metabolic pathway and evolution law analysis revealed that SWM enhanced the oxidation of catechins and flavonol glycosides, promoted the decarboxylation of glutamic acid, then facilitated the formation of theaflavin-3,3'-digallate, finally enhanced the taste and color quality of black tea. This study offers theoretical guidance and technical support for the targeted processing of high-quality black tea.

Antiurolithiatic effect of triptonide in ethylene glycol-induced urolithiasis in rats.

Urolithiasis is one of the most prevalent benign urological disorders globally with a high incidence rate. Male Sprague-Dawley rats were chemically induced to have urolithiasis and treated with triptonide and the standard antiurolithic drug cystone. Kidney weight was measured to detect calculi formation, and urinary parameters such as pH, 24-h urine volume, and protein content were measured to analyze the urolithiasis induction in rats. The inorganic ions, organic solutes, antioxidant levels, and inflammatory cytokines were measured in the experimental rats. Triptonide treatment significantly modulated the urinary pH, decreased the protein concentration, and increased the urinary outflow in urolithiasis induced rats. It also significantly decreased the urinary excretion of calcium and phosphorous and increased the excretion of magnesium, potassium, sodium, creatinine, and uric acid. SOD, CAT, and GPx levels were increased in triptonide-treated rats, and it significantly reduced the MDA levels. Triptonide treatment also decreased the levels of inflammatory cytokines and prevented the renal tissue from inflammation. To conclude, our results prove that triptonide significantly prevents calculi formation and protects renal tissue from urolithiasis-induced damage in rats. Further studies may prove triptonide a potent alternative to currently available antiurolithic drugs.

Volatolomics-assisted characterization of the key odorants in green off-flavor black tea and their dynamic changes during processing.

Aroma plays a pivotal role in the quality of black tea. However, the acceptability of black tea is greatly limited by the green off-flavor (GOF) resulting from the inappropriate processing control. In this study, the key odorants causing GOF were investigated by volatolomics, and their dynamic changes and formation pathways were in-depth understood. Significant alterations in volatile metabolites were observed in the withering stage. A total of 14 key odorants were identified as contributors to GOF, including 2-methylpropanal, 3-methylbutanal, 1-hexanol, nonanal, (E, E)-2,4-heptadienal, benzaldehyde, linalool, (E, E)-3,5-octadiene-2-one, ß-cyclocitral, phenylacetaldehyde, (E, E)-2,4-nonadienal, methyl salicylate, geraniol, and ß-ionone. Among them, (E, E)-2,4-heptadienal (OAV = 3913), characterized by fatty, green, and oily aromas, was considered to be the most important contributor causing GOF. Moreover, it was found that lipid degradation served as the primary metabolic pathway for GOF. This study provides a theoretical foundation for off-flavor control and quality improvement of black tea.

Comprehensive investigation on the dynamic changes of volatile metabolites in fresh scent green tea during processing by GC-E-Nose, GC-MS, and GC × GC-TOFMS.

Processing technology plays a crucial role in the formation of tea aroma. The dynamic variations in volatile metabolites across different processing stages of fresh scent green tea (FSGT) were meticulously tracked utilizing advanced analytical techniques such as GC-E-Nose, GC-MS, and GC × GC-TOFMS. A total of 244 volatile metabolites were identified by GC-MS and GC × GC-TOFMS, among which 37 volatile compounds were concurrently detected by both methods. Spreading and fixation stages were deemed as pivotal processes for shaping the volatile profiles in FSGT. Notably, linalool, heptanal, 2-pentylfuran, nonanal, ß-myrcene, hexanal, 2-heptanone, pentanal, 1-octen-3-ol, and 1-octanol were highlighted as primary contributors to the aroma profiles of FSGT by combining odor activity value assessment. Furthermore, lipid degradation and glycoside hydrolysis were the main pathways for aroma formation of FSGT. The results not only elucidate the intricate variations in volatile metabolites but also offer valuable insights into enhancing the processing techniques for improved aroma quality of green tea.

Key umami taste contributors in Longjing green tea uncovered by integrated means of sensory quantitative descriptive analysis, metabolomics, quantification analysis and taste addition experiments.

Umami taste is a key criteria of green tea quality evaluation. The aim of this study was to comprehensively explore the key umami taste contributors in Longjing tea. The taste and molecular profiles of 36 Longjing green tea infusions were characterized by sensory quantitative descriptive analysis and LC-MS based metabolomics, respectively. By uni-/multi-variate statistical analysis, 84 differential compounds were screened among tea infusions with varied umami perceptions. Among them, 17 substances were identified as candidate umami-enhancing compounds, which showed significant positive correlations with umami intensities. Their natural concentrations were accurately quantified, and their umami taste-modifying effects were further investigated by taste addition into glutamic acid solution. Glutamic acid, aspartic acid, glutamine, theanine, phenylalanine, histidine, theogallin, galloylglucose, 1,2,6-trigalloylglucose significantly enhanced the umami taste. This study uncovered for the first time of some bitter amino acids and galloylglucose homologous series as important umami-enhancers, which provided a novel perspective into the tea taste.

Uncovering the Dynamic Alterations of Volatile Components in Sweet and Floral Aroma Black Tea during Processing.

Aroma is an indispensable factor that substantially impacts the quality assessment of black tea. This study aims to uncover the dynamic alterations in the sweet and floral aroma black tea (SFABT) throughout various manufacturing stages using a comprehensive analytical approach integrating gas chromatography electronic nose, gas chromatography-ion mobility spectrometry (GC-IMS), and gas chromatography-mass spectrometry (GC-MS). Notable alterations in volatile components were discerned during processing, predominantly during the rolling stage. A total of 59 typical volatile compounds were identified through GC-IMS, whereas 106 volatile components were recognized via GC-MS throughout the entire manufacturing process. Among them, 14 volatile compounds, such as linalool, ß-ionone, dimethyl sulfide, and 1-octen-3-ol, stood out as characteristic components responsible for SFABT with relative odor activity values exceeding one. This study serves as an invaluable theoretical platform for strategic controllable processing of superior-quality black tea.

Contents of ɑ-dicarbonyl compounds in commercial black tea and affected by the processing.

The species and contents of ɑ-dicarbonyls in commercial black tea were examined, along with the effects of the manufacturing process and drying temperature on the formation of ɑ-dicarbonyls. Ten ɑ-dicarbonyls were quantified in commercial and in-process black tea samples by using UPLC-MS/MS and their derived quinoxalines. The ɑ-dicarbonyls content in commercial black tea decreased significantly (p < 0.05) in the following order: 3-deoxyglucosone > glucosone > 3-deoxypentosone = threosone > galactosone ≥ methylglyoxal = glyoxal ≥ 3-deoxygalactosone = 3-deoxythreosone = diacetyl. Except for 3-deoxyglucosone and 3-deoxygalactosone, a further eight ɑ-dicarbonyls were identified in all manufacturing steps of black tea. Except for the drying step, the rolling and fermenting played important roles in the formation of ɑ-dicarbonyls. The total contents of ɑ-dicarbonyls in black tea infusion ranged from 16.48 to 75.32 µg/g based on our detected ten ɑ-dicarbonyls.

Recent Advances in 2-Keto-l-gulonic Acid Production Using Mixed-Culture Fermentation and Future Prospects.

Vitamin C, also known as ascorbic acid, is an essential vitamin that cannot be synthesized by the human body and must be acquired through our diet. At present, the precursor of vitamin C, 2-keto-l-gulonic acid (2-KGA), is typically produced via a two-step fermentation process utilizing three bacterial strains. The second step of this traditional two-step fermentation method involves mixed-culture fermentation employing 2-KGA-producing bacteria (Ketogulonicigenium vulgare) along with associated bacteria. Because K. vulgare has defects in various metabolic pathways, associated bacteria are needed to provide key substances to promote K. vulgare growth and 2-KGA production. Unlike previous reviews where the main focus was the interaction between associated bacteria and K. vulgare, this Review presents the latest scientific research from the perspective of the metabolic pathways associated with 2-KGA production by K. vulgare and the mechanism underlying the interaction between K. vulgare and the associated bacteria. In addition, the dehydrogenases that are responsible for 2-KGA production, the 2-KGA synthesis pathway, strategies for simplifying 2-KGA production via a one-step fermentation route, and, finally, future prospects and research goals in vitamin C production are also presented.

Objective quantification technique and widely targeted metabolomic reveal the effect of drying temperature on sensory attributes and related non-volatile metabolites of black tea.

Drying temperature (DT) considerably affects the flavor of black tea (BT); however, its influence on non-volatile metabolites (NVMs) and their correlations remain unclear. In this study, an objective quantification technique and widely targeted metabolomics were applied to explore the effects of DT (130 °C, 110 °C, 90 °C, and 70 °C) on BT flavor and NVMs conversion. BT with a DT of 90 °C presented the highest umami, sweetness, overall taste, and brightness color values. Using the weighted gene co-expression network and multiple factor analysis, 455 sensory trait-related NVMs were explored across six key modules. Moreover, 169 differential NVMs were screened, and flavonoids, phenolic acids, amino acids, organic acids, and lipids were identified as key differential NVMs affecting the taste and color attributes of BT in response to DT. These findings enrich the BT processing theory and offer technical support for the precise and targeted processing of high-quality BT.

Copper in Cancer: from transition metal to potential target.

In recent years, with the continuous in-depth exploration of the molecular mechanisms of tumorigenesis, numerous potential new targets for cancer treatment have been identified, some of which have been further developed in clinical practice and have produced positive outcomes. Notably, researchers' initial motivation for studying copper metabolism in cancer stems from the fact that copper is a necessary trace element for organisms and is closely connected to body growth and metabolism. Moreover, over the past few decades, considerable progress has been made in understanding the molecular processes and correlations between copper and cancer. Certain achievements have been made in the development and use of relevant clinical medications. The concept of "cuproptosis," a novel concept that differs from previous forms of cell death, was first proposed by a group of scientists last year, offering fresh perspectives on the targeting capabilities of copper in the treatment of cancer. In this review, we introduced the fundamental physiological functions of copper, the key components of copper metabolism, and a summary of the current research contributions on the connection between copper and cancer. In addition, the development of new copper-based nanomaterials and their associated mechanisms of action are discussed. Finally, we described how the susceptibility of cancer cells to this metallic nutrition could be leveraged to further improve the existing cancer treatment paradigm in the new setting.

The influence of rolling pressure on the changes in non-volatile compounds and sensory quality of congou black tea: The combination of metabolomics, E-tongue, and chromatic differences analyses.

Rolling represents an essential stage in congou black tea processing. However, the influence of rolling pressure on tea flavor and non-volatile compounds remains unclear. Herein, a combination of untargeted metabolomics, tea pigments quantification, E-tongue, colorimeter and sensory evaluation was used to evaluate the effect of rolling pressure on black tea quality. As the rolling pressure increased, theaflavins (TFs), thearubigins (TRs), and theabrownins (TBs) significantly elevated. The tea metabolic profiles fluctuated and 47 metabolites were identified as key differential metabolites including flavan-3-ols, flavonol/flavone glycosides, phenolic acids, amino acids. These substances altered possibly due to the variations in enzymatic oxidation of tea phenolics and amino acids. Overall, black tea with moderate rolling pressure presented higher sweetness, lower bitterness, and higher quality index (10 TFs + TRs)/TBs. The results were verified by a validation batch. This study provided new insights into the regulation of rolling pressure and a guidance for black tea processing.

Effect of shaking on the improvement of aroma quality and transformation of volatile metabolites in black tea.

Shaking is an innovative technology employed in black tea processing to enhance flavor. However, the effects of shaking on the evolutionary mechanisms of volatile metabolites (VMs) remain unclear. In this study, we compared the effects of a shaking-withering method with those of traditional withering on the flavor and VMs transformation of black tea. The results showed that black tea treated with shaking exhibited excellent quality with floral and fruity aroma. Based on gas chromatography-tandem mass spectrometry, 128 VMs (eight categories) were detected. Combining variable importance projection with odor activity value analysis, eight key differential VMs were identified. Shaking could promote the oxidative degradation of fatty acids and carotenoids and modulate the biosynthesis of terpenoids to facilitate the formation of floral/fruity VMs (such as (Z)-hexanoic acid-3-hexenyl ester, ethyl hexanoate, trans-ß-ionone, and decanal). Our findings provide theoretical guidance for the production of high-quality black tea with floral and fruity aromas.

Effects of electromagnetic roller-hot-air-steam triple-coupled fixation on reducing the bitterness and astringency and improving the flavor quality of green tea.

Despite the importance of fixation in determining green tea quality, its role in reducing the bitter and astringent taste of this beverage remains largely unknown. Herein, an electromagnetic roller-hot-air-steam triple-coupled fixation (ERHSF) device was developed, and its operating parameters were optimized (steam volume: 20 kg/h; hot-air temperature: 90 °C; hot-air blower speed: 1200 r/min). Compared with conventional fixation treated samples, the ratio of tea polyphenols to free amino acids and ester-catechins to simple-catechins in ERHSF-treated samples was reduced by 11.0% and 3.2%, reducing bitterness and astringency of green tea; amino acids, soluble sugars, and chlorophyll contents were significantly increased, enhancing the freshness, sweetness, and greenness; the color indexes, such as L/L* value of brightness and -a/-a* value of greenness, were also improved, and ERHSF-treated samples had the highest sensory scores. These results provided theoretical support and technical guidance for precise quality improvement of summer-autumn green tea.

In vitro assembly of the trehalose bi-enzyme complex with artificial scaffold protein.

Introduction: Trehalose is a significant rare sugar known for its stable properties and ability to protect biomolecules from environmental factors. Methods: In this study, we present a novel approach utilizing a scaffold protein-mediated assembly method for the formation of a trehalose bi-enzyme complex. This complex consists of maltooligosyltrehalose synthase (MTSase) and maltooligosyltrehalose trehalohydrolase (MTHase), which work in tandem to catalyze the substrate and enhance the overall catalytic efficiency. Utilizing the specific interaction between cohesin and dockerin, this study presents the implementation of an assembly, an analysis of its efficiency, and an exploration of strategies to enhance enzyme utilization through the construction of a bi-enzyme complex under optimal conditions in vitro. Results and Discussion: The bi-enzyme complex demonstrated a trehalose production level 1.5 times higher than that of the free enzyme mixture at 40 h, with a sustained upward trend. Compared to free enzyme mixtures, the adoption of a scaffold protein-mediated bi-enzyme complex may improve cascade reactions and catalytic effects, thus presenting promising prospects.

Comprehensive investigation on flavonoids metabolites of Longjing tea in different cultivars, geographical origins, and storage time.

In this study, four kinds of Longjing tea, the famous flat green tea and the protected geographical indication product in China, were used to explore the quality difference of the same green tea due to the cultivar, geographic origin, and storage time under the premise of consistent picking conditions and processing technology using the widely targeted metabolomics. Results showed that 483 flavonoid metabolites with 10 subgroups of flavonoids were screened and 118 differential flavonoid metabolites were identified. The number and subgroups of differential flavonoid metabolites produced by different cultivars of Longjing tea were the largest, followed by storage time, and third by the geographic origin. Glycosidification and methylation or methoxylation were the main structural modifications of differential flavonoid metabolites. This study has enriched the understanding of the effects of the cultivar, the geographic origin, and the storage time on the flavonoid metabolic profiles of Longjing tea, and provided worthy information for the traceability of green tea.

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.

The Integration of Metabolomics, Electronic Tongue, and Chromatic Difference Reveals the Correlations between the Critical Compounds and Flavor Characteristics of Two Grades of High-Quality Dianhong Congou Black Tea.

Tea's biochemical compounds and flavor quality vary depending on its grade ranking. Dianhong Congou black tea (DCT) is a unique tea category produced using the large-leaf tea varieties from Yunnan, China. To date, the flavor characteristics and critical components of two grades of high-quality DCT, single-bud-grade DCT (BDCT), and special-grade DCT (SDCT) manufactured mainly with single buds and buds with one leaf, respectively, are far from clear. Herein, comparisons of two grades were performed by the integration of human sensory evaluation, an electronic tongue, chromatic differences, the quantification of major components, and metabolomics. The BDCT possessed a brisk, umami taste and a brighter infusion color, while the SDCT presented a comprehensive taste and redder liquor color. Quantification analysis showed that the levels of total polyphenols, catechins, and theaflavins (TFs) were significantly higher in the BDCT. Fifty-six different key compounds were screened by metabolomics, including catechins, flavone/flavonol glycosides, amino acids, phenolic acids, etc. Correlation analysis revealed that the sensory features of the BDCT and SDCT were attributed to their higher contents of catechins, TFs, theogallin, digalloylglucose, and accumulations of thearubigins (TRs), flavone/flavonol glycosides, and soluble sugars, respectively. This report is the first to focus on the comprehensive evaluation of the biochemical compositions and sensory characteristics of two grades of high-quality DCT, advancing the understanding of DCT from a multi-dimensional perspective.

Characterization of the key odorants in floral aroma green tea based on GC-E-Nose, GC-IMS, GC-MS and aroma recombination and investigation of the dynamic changes and aroma formation during processing.

To characterize the key odorants of floral aroma green tea (FAGT) and reveal its dynamic evolution during processing, the volatile metabolites in FAGT during the whole processing were analyzed by integrated volatolomics techniques, relative odor activity value (rOAV), aroma recombination, and multivariate statistical analysis. The volatile profiles undergone significant changes during processing, especially in the withering and fixation stages. A total of 184 volatile compounds were identified (∼53.26% by GC-MS). Among them, 7 volatiles with rOAV > 1 were identified as characteristic odorants of FAGT, and most of these compounds reached the highest in withering stage. According to the formation pathways, these key odorants could be divided into four categories: fatty acid-derived volatiles, glycoside-derived volatiles, amino acid-derived volatiles, and carotenoid-derived volatiles. Our study provides a comprehensive strategy to elucidate changes in volatile profiles during processing and lays a theoretical foundation for the targeted processing of high-quality green tea.