GC-MS and LC-MS/MS metabolomics revealed dynamic changes of volatile and non-volatile compounds during withering process of black tea

Metabolomic analysis elucidates the dynamic changes in aroma compounds and the milk aroma mechanism across various portions of tea leaves during different stages of Oolong tea processing

This study investigated the dynamics of aroma compounds in different locations of tea leaves at various stages of the Oolong tea-making process via metabolomics analysis and ribonucleic acid (RNA) gene transcriptome analysis of metabolism-related enzymes. In addition, this study focused on examining the composition and metabolic synthesis pathways of milk flavor compounds during the processing of Jin Xuan Oolong tea. This study showed that a total of 57 aroma compounds were identified, whereas the abundance of the heat map showed a decreasing abundance of these compounds from the first leaves to the stems. The milky aroma compounds were divided into two groups based on changes during the leaf-stirring process (shaking). Specifically, hexanal, 1-octen-3-ol, and trans-2-decanal decreased throughout this process. In contrast, heptanal, limonene, and jasmone increased, producing Oolong tea with a milky fragrance. Moreover, the results of this study on gene expressions of metabolic enzymes and fatty acid contents indicated the milky flavor compounds were derived from fatty acid metabolism. Therefore, this study provides theoretical support and information on the knowledge of Oolong tea processing, which potentially allows the tea industry to improve the quality of the tea to bring this fantastic flavor to consumers.

Improving flavor of Wuyi rock tea processed from rain-soaked leaves by optimizing withering conditions

Rainy weather restricts the formation of high-quality Wuyi rock tea (WRT). Herein, an optimized withering process for rain-soaked leaves was developed using response surface methodology. Results showed that increasing the withering temperature, relative humidity, and withering time from 25 °C to 40 °C, 80 % to 97 %, and 3 to 6 h, respectively, effectively improved the sensory qualities of the optimized primary WRT (WRTO) prepared from rain-soaked leaves compared with those before optimization. The high content of soluble sugars, L-theanine, catechins, esters, alcohols, terpenoids, ketones, aldehydes and aromatics contributed significantly to the formation of the unique flavor of WRTO, which was significantly increased after optimizing the withering process. The flavor wheel of WRT-O was constructed, and its unique flavor was dominated by thickness and smoothness taste and floral, fruity, and sweet aroma. This study offers a theoretical reference for quality control of WRT produced from rain-soaked leaves.

Deep Learning-Assisted Multiplexed Electrochemical Fingerprinting for Chinese Tea Identification

Selectively differential identification of natural components with similar chemical structures in complex matrices is still a challenging task by conventional analytical strategies. Herein, we developed a landmark (DaXing airport)-inspired laser engraving sensor array that combined multiplex electrochemical fingerprinting technology with a one-dimensional convolutional neural network (1D-CNN) for rapidly precise detection of three tea polyphenols and the differentiation of 24 distinct types of Chinese teas. This sensing strategy employs a diverse array of three different working electrode configurations as a multivariate sensor (bare electrode, nanoenzyme electrode, and bioenzyme electrode), generating distinct electrochemical fingerprints in complex samples. By utilizing a self-designed 1D-CNN algorithm for feature extraction, the identification of electrochemical fingerprints is significantly improved, thereby enhancing the predictive accuracy for tea polyphenols and Chinese teas. This platform successfully achieves detection of three tea polyphenols, distinguishing six Chinese tea series and 24 tea varieties with accuracy rates of 98.84 and 97.68%, respectively. Notably, the deep learning-assisted multiplexed electrochemical fingerprinting technique achieves better accuracy for tea identification compared with other representative machine learning methods. This advancement offers a rapid and reliable approach to enhancing the development of identification and authentication processes for agricultural products.

Enhancement of flavor components of oolong tea and dark tea based on graphene heating film

Reheating is crucial for improving tea quality, and graphene heating film provides a stable, uniform heating surface. This study used graphene heating film to heat oolong and dark tea at medium (M, 65 °C) and high (H, 75 °C) temperatures for 10, 20, and 30 min to assess the impact on flavor compounds. The results showed that the optimal parameters are as follows: the content of ester catechins decreased, the content of non-ester catechins increased, and the concentrations of woody and fruity compounds (Cedrol, Limonene, trans-Isoeugenol, Indole) significantly increased at M10 or H10 in oolong tea. The ester catechin content decreased at H20, the non-ester catechin content increased at M20, and the concentration of Floral compounds (trans-β-ionone) increased at H30 in dark tea. This study explores the potential of graphene heating film in tea processing, offering a theoretical basis for new technology in tea flavor enhancement.

Influence of Different Shaping Techniques on the Aroma Quality and Volatile Metabolites of Green Tea Revealed by Gas Chromatography Electronic Nose and Gas Chromatography-Tandem Mass Spectrometry

The shaping process is recognized as a crucial step in the manufacturing of green tea. However, its influence on aroma quality remains unclear. In this study, the effects of four shaping techniques, including flat green tea (FGT), straight green tea (SGT), phoenix green tea (PGT), and curled green tea (CGT), on the aroma quality and volatile metabolites of green tea were investigated by gas chromatography electronic nose (GC-E-Nose) and gas chromatography-tandem mass spectrometry (GC-MS/MS). The findings indicated that distinct shaping processes significantly influenced the development of the aroma quality and aroma components of green tea. The PGT processing facilitated the attainment of superior aroma quality of green tea. In total, 60 volatile components were identified by GC-MS/MS, with 54 of these compounds being consistently detected across four different shaping techniques. In particular, the PGT processing method was effective in yielding elevated levels of alcohols, esters and ketones. Moreover, 20 key odorants were screened out, with (E,E)-2,4-decadienal, (E,E)-2,4-nonadienal, phenylethyl alcohol, and benzeneacetaldehyde proven to be substantial contributors to the overall aromas of green tea under diverse shaping procedures. These key odorants were primarily derived from lipid degradation and the Maillard reaction. GC-E-Nose served as a significant adjunct to sensory evaluation, enabling the swift differentiation of green tea samples that have undergone various shaping processes. These findings offer both theoretical and technical perspectives that may guide the creation of innovative green tea products distinguished by their unique shapes.

The Combination of Shaking and Yellow-Light Withering Promote the Volatile Aroma Components and the Aroma Quality of Black Tea

The application of shaking during the withering process has been shown to significantly enhance the floral aroma of black tea. However, prior to this study, there was limited research on the effects of shaking combined with other withering treatments on the aroma components of black tea. In this study, the aroma attributes of black teas processed with shaking combinations of yellow-light or high-temperature withering (YLS, HTS, and HYS) were evaluated through sensory evaluation, and the volatile composition and identification of key aroma compounds in black teas and in-process withered tea leaves were analyzed by gas chromatography-mass spectrometry (GC-MS). The results indicated that black teas subjected to different shaking combinations exhibited a distinct floral aroma with higher volatile compound content, with the YLS treatment showing the most significant aroma improvement. Eight volatile compounds with relative odor activity values (rOAV) > 1 were identified from 53 differential volatile compounds in black tea under different shaking combinations as the most important contributors to aroma quality. Linalool, trans-β-Ionone, α-cedrene, and nonanal were identified as key floral volatiles with high rOAVs. Their concentrations in YLS were notably higher compared to those in S, both in withered tea leaves (with the exception of trans-β-Ionone) and in the final dry black teas, suggesting that there may be a synergistic effect between the yellow-light withering and the shaking process in enhancing these key floral compounds. Overall, this study found that shaking combined with yellow-light withering can improve the aroma composition and quality of black tea, providing a theoretical basis and practical guidance for the production and optimization of high-aroma black tea.

Comparison of volatile compounds among different types of Tieguanyin oolong tea using DHI-GC-MS

Depending on the manufacturing process, Tieguanyin tea (TGY) is classified into three main groups, light flavor type (LFT), heavy flavor type (HFT), and stale flavor type (SFT). However, the compositions and contents of volatile compounds among TGY types were still unclear. This study aimed to develop an efficient method for the nonselective determination of volatile compounds in teas via direct-headspace injection coupled with gas chromatography mass spectrometry (DHI-GC-MS), and to perform a comprehensive comparison among these teas. One hundred and twelve volatile compounds belonging to 9 classes were identified. Among them, 33 common volatiles from 4 categories (aldehydes, alcohols, ketones, and acids) were the dominant volatiles and accounted for 71.5%, 73.0%, and 71.8% of the total amount in LFT, HFT, and SFT, respectively. E-Nerolidol, ethanol, acetic acid, and some volatiles with five and six-carbon chains were the key chemicals to distinguish three different TGY teas. With PLS-DA analysis, distinct differences among different groups were observed. The results generated from this study may offer valuable insights for better grading of TGY teas.

Microbiome Flora and Metabolomics Analysis of Mung Bean Sour Liquid in Luoyang, China

In order to reveal the fermentation microflora and fermentation metabolites of traditional mung bean sour liquid (MBSL) in Luoyang area, China, this experiment was sampled from four administrative districts of Luoyang, and volatile metabolites and non-targeted metabolites were detected and analyzed by HS-SPME-GC-MS and LC-MS, and bacterial and fungal sequencing were analyzed by Illumina MiSeq high-throughput sequencing technology. And the correlation between microorganisms and metabolites was conducted. The results showed that 42 volatiles were detected in four MBSL samples named Jianxi (JX), Liujia (Liu), LiJia (LJ), Majia (MJ), with 11 identical volatile flavor subtances, and the highest content of esters was found in JX, Liu, and LJ, and the highest content of acids was found in MJ. A total of 1703 non-targeted metabolites were identified, and there were more types of amino acids, carbohydrates, fatty acids and their complexes, flavonoids, carbonyl compounds, and organic acids, accounting for 40.93%. High-throughput sequencing results showed that there were nine bacterial and fungal genera with an average abundance of more than 1%, and the dominant genera mainly belonged to lactic acid bacteria and yeast. The composition of dominant genera was different in different workshop samples, and the abundance of fungal genera differed greatly. Among the volatile substances, Methyleugenol, a volatile component, was related to more bacteria, and ketones and hydrocarbons may be more closely associated with bacteria. Acetic acid and Oxalic acid may be more closely related to fungi, while some esters were more closely related to both fungal and bacterial genera. For non-target metabolites, amino acid and alcohol metabolites may be more influenced by bacteria, and organic acids and flavonoids may be more influenced by fungi.

Dynamics of microbial communities and metabolites during the fermentation of Ningxia goji berry wine: An integrated metagenomics and metabolomics approach

Ningxia Goji Berry Wine (NGBW), a traditional Chinese fermented beverage, exhibits complex flavor quality changes during fermentation, the mechanisms of which remain insufficiently elucidated. This study aimed to elucidate the dynamic shifts in physicochemical properties, metabolites, and microbial communities throughout the controlled fermentation process of NGBW. Metabolomic analysis identified 8 key differential volatile metabolites (VOCs) and 406 differential non-volatile metabolites. The enrichment analysis of KEGG metabolic pathways revealed that, during the fermentation of NGBW, ten critical metabolic pathways-Purine metabolism, Glycine, Serine, and Threonine metabolism, Galactose metabolism, and the Citric Acid (TCA) Cycle-play essential roles. Amplicon sequencing indicated that 25 bacterial genera dominated the microbial ecosystem (relative abundance ≥ 0.1 %). Spearman correlation analysis revealed significant associations between 5 core microorganism and flavor compounds, and 25 core microbes with non-volatile metabolites, suggesting their pivotal roles in flavor formation. This study provides a theoretical basis for optimizing the fermentation process and enhancing the flavor quality of NGBW.

Comprehensive metabolite profiling reveals the dynamic changes of volatile and non-volatile metabolites in albino tea cultivar 'Ming guan' (MG) during white tea withering process

'Ming guan'(MG), an elite albino cultivar deriving from the progeny of the traditional albino cultivar 'Bai jiguan', is a promising candidate for white tea production due to its favorable amino acid to phenol ratio. In this study, a comprehensive metabolomics analysis using ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) and headspace solid-phase microextraction-gas chromatography mass spectrometry (HS-SPME-GC-MS) were conducted to reveal the dynamic changes of non-volatile and volatile organic compounds (VOCs) throughout the withering processing of MG white tea. Meanwhile, multivariate statistical analyses were applied to screen for the characteristic components in the flavor and aroma of MG white tea. A total of 625 non-volatile metabolites and 118 VOCs were determined, of which 90 non-volatile metabolites (VIP ≥ 1, FC ≥ 2 or ≤ 0.5) were identified as key flavor components significantly changed throughout the withering process. The relative odor activity value (ROAV) analysis highlighted 22 VOCs (ROAV ≥ 1) with substantial effect on aroma formation, of which geraniol, (E)-2-hexenal, 4-methoxy-benzaldehyde and guaiacol emerging as the most key aroma constituents of MG white tea, endowing MG white tea with fruity and floral odor notes. This study offered a comprehensive investigation into metabolite changes in MG white tea, contributing valuable insights for the innovation of new white tea products utilizing albino tea plant mutants.

The aroma formation from fresh tea leaves of Longjing 43 to finished Enshi Yulu tea at an industrial scale

BACKGROUND

Enshi Yulu tea (ESYL) is the most representative of steamed green tea in China, but its aroma formation in processing is unclear. Thus, the ESYL volatiles during the whole industrial processing were investigated using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry.

RESULTS

A total of 134 volatiles were identified. Among these, 31 differential volatiles [P < 0.05 and variable importance in projection (VIP) > 1] and 25 key volatiles [relative odor activity value (rOAV) and/or the ratio of each rOAV to the maximum rOAV (ROAV) > 1.0] were screened out, wherein β-ionone and nonanal were the most key odorants. Besides, the sensory evaluation combined with multivariate statistical analysis of volatiles pinpointed spreading, fixation, first drying, and second drying as the key processing steps that have a pronounced influence on the aroma quality of ESYL. Furthermore, the oxidative degradation of unsaturated fatty acids, synthesis of monoterpenes, and degradation of carotenoids were the main metabolic pathway for the formation of key odorants.

CONCLUSION

The study provides comprehensive insights into the volatile characteristics during the industrial processing of ESYL and promote our understanding of the aroma formation in steamed green teas. © 2024 Society of Chemical Industry.

Different smoking processes with the special fuel rods: Impart a smoky aroma to Souchong black tea

The smoky scent is the most distinctive feature for Souchong black tea. To reduce the dependence on pinewood in the smoking process of Souchong black tea, it is crucial to find an effective alternative smoking material. Five black tea samples were prepared via using specially designed fuel rods as the smoking material in this study. Sensory analysis showed that DS (smoking at the drying stage) had the most favorable aroma, featuring a pleasant smoky aroma with floral and fruity notes. 69 volatile compounds were detected in five tested samples. Key volatiles such as β-caryophyllene, nerolidol, guaiacol, and α-terpineol, known for their woody or smoky aroma, were prominent in both DS and TS (the traditional Lapsang Souchong process) samples (OAV > 1, VIP > 1 and P < 0.05). However, DS exhibited significantly lower concentration of these volatiles than TS, giving it a more pleasant aroma. Additionally, phenylethyl alcohol and α-farnesene were characteristic volatiles in FS (smoking at the fermentation stage) and DS, imparting a sweet, mildly smoky aroma. Therefore, using these specialized fuel rods to smoking process at drying stage is an optimal method for processing Souchong black tea. These findings provide a theoretical foundation for stabilizing Souchong black tea quality, promoting green and low-carbon tea production methods.

Untargeted metabolite profiling reveals metabolic disorders in livers of rats with mepiquat exposure

Mepiquat is a contaminant produced in thermal-processed food. It can induce spleen and liver injury. However, the mechanism that mepiquat induced hepatotoxicity remains unclear. In this study, a ultra-performance liquid chromatography-mass spectrometry (UPLC-MS/MS)-based metabolomic analysis of livers in rats was performed to explore metabolic alterations. Our results demonstrated that there were 36 differential metabolites. Eleven major disordered metabolic pathways were found. Network analysis of differential metabolites and metabolic pathways indicated that glutamic acid was a possible key upregulated metabolite. It participated in nine metabolic networks. Glutathione and l-proline may be key downregulated metabolites. They were involved in eight and seven metabolic pathways, respectively. Compared with the control group, serum concentrations of alanine aminotransferase, aspartate aminotransferase, and total bile acid in high dosage group increased significantly. In addition, histopathological analysis showed liver injury in rats with mepiquat exposure. These data were consistent with results of metabolomics. Our results offered new insights for molecular mechanism of liver toxicity induced by mepiquat. PRACTICAL APPLICATION: Mepiquat is a contaminant formed in thermal-processed food. It can induce spleen and liver injury. Our results offered new insights for molecular mechanism of liver toxicity induced by mepiquat. It will provide important information for official limits of mepiquat in foods.

Metabolomics reveals a differential attitude in phytochemical profile of black tea (Camellia Sinensis Var. assamica) during processing

Black tea's quality and flavor are largely influenced by its processing stages, which affect its volatile and non-volatile phytochemicals. This study aimed to optimized black tea manufacturing by investigating withering time, fermentation time, and temperature's impact on sensory quality. Using a U*15 (157) uniform design, optimal conditions were determined: 14 h of withering, 5.6 h of fermentation, and a 34 °C temperature. A verification experiment analyzed the volatile and non-volatile profiles. HPLC, GC-MS, and LC-MS revealed dynamic changes in phytochemicals. Among 157 VOCs and 2642 metabolites, 19 VOCs (VIP > 1.5) were crucial for aroma, while 50 (VIP > 1.5, p < 0.01) characteristic metabolites were identified. During processing, fragrant volatile compounds like linalool oxides, geraniol, benzeneacetaldehyde, benzaldehyde, methyl salicylate, and linalyl acetate increased, contributing to rose and honey like aromas. These changes were crucial in developing the characteristic flavor and color of black tea. Twenty-four new compounds formed, while 80 grassy odor volatiles decreased. Non-volatile metabolites changed notably, with decreased catechins and increased gallic acid. Theaflavin compounds rose initially but declined later. This study outlines metabolite changes in Yunkang 10 black tea, crucial for flavor enhancement and quality control.

HS-SPME-GC-MS combined with relative odor activity value identify the key aroma components of flowery and fruity aroma in different types of GABA tea

Anaerobic processing is a crucial factor influencing the formation of flavor quality in Gamma-aminobutyric acid (GABA) tea. In this study, headspace solid-phase microextraction combined with gas chromatography and mass spectrometry was employed to explore the flavor characteristics of different types of GABA tea. We utilized multivariate analyses to identify at least 146 volatile components (VOCs) across 12 functional groups in the GABA tea samples via principal component analysis (PCA). At least 40 differential VOCs were screened from the GABA tea samples via orthogonal partial least squares-discriminant analysis. Subsequently, a minimum of four VOCs were identified in the GABA tea samples via the Pearson correlation coefficient combined with relative odor activity values as potential markers for flowery and fruity aromas, clarifying the impact of the VOCs on these characteristics. The results of this study provide a theoretical basis for understanding the formation of flowery and fruity flavor characteristics in GABA tea.

Integrated Transcriptomic and Metabolomic Analyses Reveal Changes in Aroma- and Taste-Related Substances During the Withering Process of Black Tea

Withering is one of the major processing steps critical for the quality of black tea. In this study, we investigated the mechanisms underlying the physicochemical changes in metabolites and gene expression during the withering process of black tea using metabolomic and transcriptomic approaches, respectively. Based on gas chromatography/mass spectrometry non-targeted metabolomic approaches (GC-MS) and ultra-high performance liquid chromatograph-tandem mass spectrometry (UHPLC-MS/MS), a total of 76 volatile compounds and 160 non-volatile compounds were identified from tea leaves, respectively. RNA-seq analysis revealed that the number of differentially expressed genes (DEGs) for the comparative combination of withering time (i.e., W4h, W6h, W8h, W10h, and W12h) compared with CK (i.e., fresh leaves) were 3634, 2906, 4127, 5736, and 7650, respectively. The core genes in starch metabolism, namely alpha-amylase (AMY) and beta-amylase (BAM), were upregulated as withering time increased. AMY and BAM contributed to the decomposition of starch to increase the soluble sugars. The content of tea leaf alcohols and aldehydes, which are the vital contributors for greenish aroma, gradually decreased as withering time increased due to the downregulation of associated genes while the compounds related to sweet and fruity characteristics increased due to the upregulated expression of related genes. Most DEGs involved in amino acids were significantly upregulated, leading to the increase in free amino acids content. However, DEGs involved in catechins metabolism were generally downregulated during withering, and resulted in a reduction in catechins content and the accumulation of theaflavins. The same trend was observed in alpha-linolenic acid metabolism-related genes that were downregulated and enhanced the reduction in grassy aroma in black tea. The weighted gene co-expression network analysis (WGCNA) of DEGs showed that one module can be associated with more components and one component can be regulated by various modules. Our findings provide new insights into the quality formation of black tea during the withering process.

Withering and Fermentation Affect the Transformation and Accumulation of Key Metabolites in Rougui (Camellia sinensis) for the Formation of Special Taste Characteristics

During the production of Wuyi rock tea, withering and fermentation play a crucial role in the primary processing of the tea, greatly influencing the development of its distinct taste characteristics. In this study, Rougui (Camellia sinensis) was selected as the research object to investigate the effects of withering and fermentation on metabolites and taste characteristics in tea leaves. The findings revealed that a total of 1249 metabolites were detected in Rougui leaves at various processing stages, of which only 40 key metabolites were significantly altered. The process of withering and fermentation is crucial to increase the content of organic acids, plumerane, alkaloids, nucleotides and derivatives, amino acids and derivatives, and free fatty acids in the leaves of Rougui and to decrease the content of saccharides, phenolic acids, flavonols, flavones, and flavanols, which in turn enhances the mellowness, fresh and brisk taste, and aroma of tea and attenuates the saccharides, bitterness, and astringency. Withering and fermentation had the greatest effect on the bitterness and astringency of Rougui taste characteristics, followed by mellowness. It can be seen that withering and fermentation were extremely important for the development of Rougui's special taste characteristics. The present study provides important support for optimizing Rougui processing and the formation of its special taste characteristics.

Widely targeted metabolomics and SPME-GC-MS analysis revealed the quality characteristics of non-volatile/volatile compounds in Zheng'an Bai tea

Background

As albino tea under the geographical protection of agricultural products, Zheng'an Bai tea is not only rich in amino acids, polyphenols and other beneficial components for the human body, but also its leaf color will turn green as the temperature gradually rises, thus causing changes in the quality characteristics of tea leaves. However, these changing characteristics have not yet been revealed.

Methods

In-depth quality analysis was carried out on the fresh leaves of Zheng'an Bai tea at four different developmental stages and four samples from the processing stage through extensive targeted metabolomics and SPME-GC-MS analysis.

Results

In this study, a total of 573 non-volatile metabolites were detected from the fresh leaves and processing samples of Zheng'an Bai tea, mainly including 96 flavonoids, 75 amino acids, 56 sugars and alcohols, 48 terpenoids, 46 organic acids, 44 alkaloids, and 39 polyphenols and their derivatives. In fresh leaves, the most significant differential metabolites (VIP > 1, p < 0.05) among different samples mainly include substances such as ethyl gallate, theaflavin, isovitexin and linalool, while the main differential metabolites of samples in the processing stage include alkaloids, polyphenols and flavonoids such as zarzissine, methyl L-Pyroglutamate, theaflavin 3,3'-digallate, euscaphic acid and ethyl gallate. Overall, substances such as sugars and alcohols, alkaloids and polyphenols show the greatest differences between fresh leaves and the processing process. Meanwhile, 97 kinds of volatile metabolites were detected in these samples, most of which had a higher content in the fresh leaves. Moderate spreading is conducive to the release of the aroma of tea leaves, but fixation causes a sharp decrease in the content of most volatile metabolites. Ultimately, 9 volatile substances including geraniol, linalool, nerolidol, jasmone, octanal, 1-Nonanal, heptaldehyde, methyl salicylate and 1-Octen-3-ol were identified as the key aroma components (OAV >1) of Zheng'an Bai tea.

Conclusion

In conclusion, this study has for the first time comprehensively revealed the quality change characteristics of fresh leaves at different developmental stages and during the processing of Zheng'an Bai tea, and provided a foundation for further process improvement.

Are there any differences in the quality of high-mountain green tea before and after the first new leaves unfold? A comprehensive study based on E-sensors, whole metabolomics and sensory evaluation

High-mountain green tea, where the first new leaf hasn't yet unfurled, is prized for perceived superior quality, but this hasn't yet been verified by experimentation. Electronic sensors, whole metabolomics and sensory evaluation were employed to assess the quality of yymj (tea buds with a newly unfurled leaf) and qymj (tea buds without new leaves). The qymj proved to have significant advantages in aroma, color and shape, but still had some shortcomings in umami, bitterness and sourness. Differences in the content of volatile organic compounds (including alcohols, hydrocarbons and lipids) and nonvolatile organic compounds (flavonoids, amino acids, sugars, and phenolic acids) quality of high-mountain green teas with different maturity levels and provides well explained these quality differences. This study establishes a systematic approach to study the quality of high-mountain green tea at different maturity levels, and provides important reference information for consumers, governments and tea farmers.

Identifying distinct markers in two Sorghum varieties for baijiu fermentation using untargeted metabolomics and molecular network approaches

The quality of strong-flavor Baijiu, a prominent Chinese liquor, is intricately tied to the choice of sorghum variety used in fermentation. However, a significant gap remains in our understanding of how glutinous and non-glutinous sorghum varieties comprehensively impact Baijiu flavor formation through fermentation metabolites. This study employed untargeted metabolomics combined with feature-based molecular networking (FBMN) to explore the unique metabolic characteristics of these two sorghum varieties during fermentation. FBMN analysis revealed 267 metabolites within both types of fermented sorghum (Zaopei) in the cellar. Further multidimensional statistical analyses highlighted sphingolipids, 2,5-diketopiperazines, and methionine derivatives as critical markers for quality control. These findings represent a significant advancement in our understanding and provide valuable insights for regulating the quality of Baijiu flavors.

Effects of Five Different Withering Methods on the Composition and Quality of Congou Black Tea

To explore the effects of different withering methods on the quality of Congou black tea, this study focused on five different withering methods: natural withering, warm-air withering, sun-natural combined withering, sun withering, and shaking withering. Gas chromatography‒mass spectrometry (GC‒MS), high-performance liquid chromatography (HPLC), and ion-exchange chromatography techniques were used to analyze the nonvolatile and volatile components and composition of the tea. The results revealed significant differences (p < 0.05) in the contents of nonvolatile constituents including caffeine, polyphenols, soluble sugars, free amino acids and their components, theaflavins, thearubigins, and catechins among the five different withering methods, with varying degrees of correlation between these components. A total of 227 aroma compounds were detected, and significant differences in the contents of alcohols, aldehydes, and ketones were observed. A relative odor activity value (ROVA) analysis of the aroma compounds revealed that 19 compounds had an ROVA > 1. Among them, benzylaldehyde, trans-2-decenal, decanal, benzaldehyde, nonanal, hexanal, trans-linalool, and geraniol from the shaking withering method had significantly higher ROVA values than those from the other withering methods, which may be the reason for the prominent floral and fruity aroma of shaking withering. This study revealed the impact of different withering methods on the quality of Congou black tea, providing a scientific basis for the development of Congou black tea with different flavors and the improvement of Congou black tea processing techniques.

Characterization of differences in physicochemical properties, volatile organic compounds and non-volatile metabolites of prune wine by inoculation of different lactic acid bacteria during malolactic fermentation

To investigate the effects of inoculating with three strains of lactic acid bacteria on prune wine quality during malolactic fermentation, this study determined its antioxidant activity, phenolic compounds, organic acids, and volatile/non-volatile metabolites. The results showed that inoculation with Lactobacillus paracasei SMN-LBK improved the antioxidant activity and phenolic compounds of prune wine. 73 VOCs were detected in prune wine by HS-SPME-GC-MS, and VOC content increased by 4.3% and 9.1% in MLFS and MLFB, respectively. Lactobacillus delbrueckii subsp. Bulgaricus showed better potential for winemaking, and citral and 5-nonanol, were detected in the MLF samples. 39 shared differential metabolites were screened and their metabolic pathways were investigated based on nontargeted metabolomics. Differences in amino acid and flavonoid content between strains reflected their specificity in flavonoid biosynthesis and amino acid biosynthesis. These findings will provide useful information for the biochemical study and processing of prune wine.

Integrated Metabolomics and Proteomics Analysis Provides Insights into the Formation of Volatile Compounds in Three Different Polyembryonic Mango Cultivars

Understanding volatile compound formation is critical for enhancing the flavor quality of mangoes. Integrated untargeted metabolomics and proteomics were employed to explore volatile compound formation in three different polyembryonic mango cultivars ("Ah Ping," "Rosa," and "Rosigold"). A total of 87 volatile compounds were identified using SPME-GC-MS. Untargeted metabolomics and proteomics resulted in identification of 508 metabolites and 4481 proteins, respectively. Integrative analysis revealed that the volatile compound formation was influenced by fatty acids, amino acids, pentose, and hexose, as well as terpenoid metabolisms. Specifically, upward expression of core enzymes in lipoxygenanse pathway was responsible for the higher levels of some C6 and C9 volatile compounds in "Ah Ping." The differential expression of key enzymes in fatty acid degradation facilitates the varied contents of straight-chain volatile compounds. The upregulation of glutamate decarboxylase and branched-chain amino acid aminotransferase upstream of butanoate metabolism led to the highest levels of butyl esters in "Ah Ping." Furthermore, the different levels of volatile furan and pyran compounds might be attributed to differential expression of critical enzymes in pentose and hexose metabolism. These findings established a metabolic and proteomic map unraveling the biosynthesis of specific volatile compounds and provided insights into understanding the characteristic flavor of mango.

Effect of withering/spreading on the physical and chemical properties of tea: A review

Withering and spreading, though slightly differing in their parameters, share the same aim of moisture reduction in tea leaves, and they have a strong impact on the physical and chemical properties of tea. Even though researchers tend to pay close attention to the characteristic crafts of different teas, increasing investigations begin to focus on the withering process due to its profound effects on the composition and content of quality-related compounds. This review provides an overview of tea withering process to address questions comprehensively during withering. Hence, it is expected in this review to figure out factors that affect withering results, the way withering influences the physical and chemical properties of withered leaves and tea quality, and intelligent technologies and devices targeted at withering processes to promote the modernization of the tea industry. Herein, several key withering parameters, including duration, temperature, humidity, light irradiation, airflow, and more, are tailored to different tea types, demanding further exploration of advanced withering devices and real-time monitoring systems. The development of real-time monitoring technology enables objective and real-time adjustment of withering status in order to optimize withering results. Tea quality, including taste, aroma, and color quality, is first shaped during withering due to the change of composition and content of quality-related metabolites through (non)enzymatic reactions, which are easily influenced by the factors above. A thorough understanding of withering is key to improving tea quality effectively and scientifically.

Metabolomics applications for plant-based foods origin tracing, cultivars identification and processing: Feasibility and future aspects

Metabolomics, the systematic study of metabolites, is dedicated to a comprehensive analysis of all aspects of plant-based food research and plays a pivotal role in the nutritional composition and quality control of plant-based foods. The diverse chemical compositions of plant-based foods lead to variations in sensory characteristics and nutritional value. This review explores the application of the metabolomics method to plant-based food origin tracing, cultivar identification, and processing methods. It also addresses the challenges encountered and outlines future directions. Typically, when combined with other omics or techniques, synergistic and complementary information is uncovered, enhancing the classification and prediction capabilities of models. Future research should aim to evaluate all factors affecting food quality comprehensively, and this necessitates advanced research into influence mechanisms, metabolic pathways, and gene expression.

Metabolomic analysis reveals the changing trend and differential markers of volatile and nonvolatile components of Artemisiae argyi with different aging years

INTRODUCTION

Artemisia argyi Folium (AAF) is a traditional medicinal herb and edible plant. Analyzing the differential metabolites that affect the efficacy of AAF with different aging years is necessary.

OBJECTIVE

The aim of the study was to investigate the changing trend and differential markers of volatile and nonvolatile metabolites of AAF from different aging years, which are necessary for application in clinical medicine.

METHODOLOGY

Metabolites were analyzed using a widely targeted metabolomic approach based on ultrahigh-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and gas chromatography tandem mass spectrometry (GC-MS).

RESULTS

A total of 153 volatile metabolites and 159 nonvolatile metabolites were identified. Principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) could clearly distinguish AAF aged for 1 year (AF-1), 3 years (AF-3), and 5 years (AF-5). Seven flavonoids and nine terpenoids were identified as biomarkers for tracking the aging years.

CONCLUSIONS

The metabolomic method provided an effective strategy for tracking and identifying biomarkers of AAF from different aging years. This study laid the foundation for analysis of the biological activity of Artemisia argyi with different aging years.

Revealing the mechanism of post-harvest processing on rose quality based on dynamic changes in water content, enzyme activity, volatile and non-volatile metabolites

Existing studies on post-harvest processing of edible roses have mainly focused on processing techniques and physicochemical properties of the final dried products, with limited studies on how changes in metabolites during processing affect the quality of these products. This study investigated changes in water content and status, enzyme activity, phenolic compounds, and volatile and non-volatile compounds during processing and revealed the mechanisms by which post-harvest processing (drying without blanching (WBD) and drying with blanching (BD)) affects the quality of dried roses by establishing their correlations. Results showed that the blanching reduced the relative content of free water and water activity, thus reducing the subsequent drying time and enzyme activity. The BD method caused higher levels of phenolic compounds than the WBD method in terms of gallic acid, ellagic acid, epicatechin, and quercetin. The OPLS-DA analysis identified 6 differential volatiles out of 72 detected volatiles, contributing to the unique aroma of dried roses by activating olfactory receptors through hydrogen bonding and hydrophobic interactions. 58 differential metabolites were screened from 964 non-volatile metabolites. KEGG pathway analysis revealed that the changes in volatile and non-volatile metabolites induced by different processing methods were due to the effect of blanching on glutathione and fatty acid metabolism. These findings provide a comprehensive understanding of how post-harvest processing affects the quality of dried roses.

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, β-cyclocitral, phenylacetaldehyde, (E, E)-2,4-nonadienal, methyl salicylate, geraniol, and β-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.

Differential metabolic networks in three energy substances of flaxseed (Linum usitatissimum L.) during germination

Germinated flaxseed (Linum usitatissimum L.) is an essential potential food ingredient, but the major energy substances (proteins, lipids, and carbohydrates) metabolites and metabolic pathways are unknown. Comprehensive metabolomic analyses were performed using Fourier transform infrared spectroscopy and high-performance liquid chromatography mass spectrometry on flaxseed from 0 to 7 d. Additionally, the critical metabolites pathways networks of three energy substances metabolites during flaxseed germination were exhibited. The results showed that arginine was the most active metabolite during germination, strongly associated with the arginine biosynthesis and arginine and proline metabolism pathways. Carbohydrates predominantly comprised sucrose on 0-3 d, which participated in galactose metabolism and starch and sucrose metabolism. The main flaxseed phospholipid molecules were phosphatidic acid, phosphatidylethanolamine, lysophosphatidic acid, and lysophosphatidylcholine during germination. This study underscores the paramount metabolic pathways in proteins, lipids and carbohydrates were arginine and proline metabolism, linoleic acid metabolism, arachidonic acid metabolism, and ascorbate and aldarate metabolism during germination.

Applications of chromatographic methods in metabolomics: A review

Chromatography is a robust and reliable separation method that can use various stationary phases to separate complex mixtures commonly seen in metabolomics. This review examines the types of chromatography and stationary phases that have been used in targeted or untargeted metabolomics with methods such as mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy. General considerations for sample pretreatment and separations in metabolomics are considered, along with the various supports and separation formats for chromatography that have been used in such work. The types of liquid chromatography (LC) that have been most extensively used in metabolomics will be examined, such as reversed-phase liquid chromatography and hydrophilic liquid interaction chromatography. In addition, other forms of LC that have been used in more limited applications for metabolomics (e.g., ion-exchange, size-exclusion, and affinity methods) will be discussed to illustrate how these techniques may be utilized for new and future research in this field. Multidimensional LC methods are also discussed, as well as the use of gas chromatography and supercritical fluid chromatography in metabolomics. In addition, the roles of chromatography in NMR- vs. MS-based metabolomics are considered. Applications are given within the field of metabolomics for each type of chromatography, along with potential advantages or limitations of these separation methods.

Combined volatile compounds and non-targeted metabolomics analysis reveals variation in flavour characteristics, metabolic profiles and bioactivity of mulberry leaves after Monascus purpureus fermentation

BACKGROUND

Mulberry leaves (MLs) are widely used in food because of their nutritional and functional characteristics. However, plant cell walls and natural bitterness influence nutrient release and the flavor properties of MLs. Liquid-state fermentation using Monascus purpureus (LFMP) is a common processing method used to improve food properties. The present study used headspace solid-phase micro extraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) and non-targeted metabolomics to examine changes in volatile and non-volatile metabolites in MLs. The transformation mechanism of LFMP was investigated by microscopic observation and dynamic analysis of enzyme activity, and changes in the biological activity of MLs were analyzed.

RESULTS

LFMP significantly increased total phenolics, total flavonoids, free amino acids and soluble sugars in MLs, at the same time as decreasing phytic acid levels. In total, 92 volatile organic compounds (VOCs) were identified and quantified. VOCs such as (2R,3R)-(-)-2,3-butanediol, terpineol and eugenol showed some improvement in the flavour characteristics of MLs. By using non-targeted metabolomics, 124 unique metabolites in total were examined. LFMP altered the metabolic profile of MLs, mainly in plant secondary metabolism, lipid metabolism and amino acid metabolism. Microscopic observation and dynamic analysis of enzyme activity indicated that LFMP promoted cell wall degradation and biotransformation of MLs. In addition, LFMP significantly increased the angiotensin I-converting enzyme and α-glucosidase inhibitory activity of MLs.

CONCLUSION

LFMP altered the flavour characteristics, metabolite profile and biological activity of MLs. These findings will provide ideas for the processing of MLs into functional foods. In addition, they also provide useful information for biochemical studies of fermented MLs. © 2023 Society of Chemical Industry.

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, β-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.

Understanding the dynamic changes of volatile and non-volatile metabolites in black tea during processing by integrated volatolomics and UHPLC-HRMS analysis

Processing technology has an important effect on the flavor quality of black tea. However, the dynamic changes of volatile and non-volatile metabolites in black tea during processing are poorly understood. In this study, the volatile and non-volatile compounds during black tea processing were comprehensively characterized by integrated volatolomics and UHPLC-Q-Exactive/MS analysis. Volatile and non-volatile metabolites changed continuously throughout the processing process, especially during the withering stage. A total of 178 volatile metabolites and 103 non-volatile metabolites were identified. Among them, 11 volatile components with relative odor activity value greater than 1 (including dimethyl sulfide, 3-methylbutanal, 2-methylbutanal, β-myrcene, β-ocimene, linalool, methyl salicylate, β-cyclocitral, β-citral, citral, and β-ionone) were regarded as key aroma-active components responsible for finished black tea with sweet aroma. This study provides a comprehensive understanding of dynamic evolution trajectory of volatile and non-volatile metabolites during processing, which lays a theoretical foundation for the targeted processing of high-quality black tea.

Exploration of Raw Pigmented-Fleshed Sweet Potatoes Volatile Organic Compounds and the Precursors

Sweet potato provides rich nutrients and bioactive substances for the human diet. In this study, the volatile organic compounds of five pigmented-fleshed sweet potato cultivars were determined, the characteristic aroma compounds were screened, and a correlation analysis was carried out with the aroma precursors. In total, 66 volatile organic compounds were identified. Terpenoids and aldehydes were the main volatile compounds, accounting for 59% and 17%, respectively. Fifteen compounds, including seven aldehydes, six terpenes, one furan, and phenol, were identified as key aromatic compounds for sweet potato using relative odor activity values (ROAVs) and contributed to flower, sweet, and fat flavors. The OR sample exhibited a significant presence of trans-β-Ionone, while the Y sample showed high levels of benzaldehyde. Starch, soluble sugars, 20 amino acids, and 25 fatty acids were detected as volatile compounds precursors. Among them, total starch (57.2%), phenylalanine (126.82 ± 0.02 g/g), and fatty acids (6.45 μg/mg) were all most abundant in Y, and LY contained the most soluble sugar (14.65%). The results of the correlation analysis revealed the significant correlations were identified between seven carotenoids and trans-β-Ionone, soluble sugar and nerol, two fatty acids and hexanal, phenylalanine and 10 fatty acids with benzaldehyde, respectively. In general, terpenoids and aldehydes were identified as the main key aromatic compounds in sweet potatoes, and carotenoids had more influence on the aroma of OR than other cultivars. Soluble sugars, amino acids, and fatty acids probably serve as important precursors for some key aroma compounds in sweet potatoes. These findings provide valuable insights for the formation of sweet potato aroma.

Effect of cooking methods on metabolites of deep purple-fleshed sweetpotato

The effects of different cooking methods on purple-fleshed sweetpotato (PFSP) metabolites were systematically explored, containing the changes of starch, soluble sugar, volatile organic compounds and non-target metabolites after steaming, boiling and baking. Compared to raw samples, the steamed samples showed the greatest changes in starch (degraded from 53.01% to 39.5%) and soluble sugar content (increased from 11.82% to 29.08%), while the baked samples showed insignificant changes in starch (51.06%). In total, 64 volatile organic compounds were identified in PFSP, with aldehydes decreasing and terpenes increasing after cooking. However, most of them were low in content and contributed weak aroma for PFSP. More importantly, 871 non-volatile metabolites were detected in PFSP, and 83.5% of which were well-preserved after cooking, while most of the changes were concentrated in phenylpropanoids, amino acids and carbohydrates. This study enriches the understanding of quality changes after PFSP cooking and helps consumers choose the right cooking method.

The novel nematicide chiricanine A suppresses Bursaphelenchus xylophilus pathogenicity in Pinus massoniana by inhibiting Aspergillus and its secondary metabolite, sterigmatocystin

Introduction

Pine wilt disease (PWD) is responsible for extensive economic and ecological damage to Pinus spp. forests and plantations worldwide. PWD is caused by the pine wood nematode (PWN, Bursaphelenchus xylophilus) and transmitted into pine trees by a vector insect, the Japanese pine sawyer (JPS, Monochamus alternatus). Host infection by PWN will attract JPS to spawn, which leads to the co-existence of PWN and JPS within the host tree, an essential precondition for PWD outbreaks. Through the action of their metabolites, microbes can manipulate the co-existence of PWN and JPS, but our understanding on how key microorganisms engage in this process remains limited, which severely hinders the exploration and utilization of promising microbial resources in the prevention and control of PWD.

Methods

In this study we investigated how the PWN-associated fungus Aspergillus promotes the co-existence of PWN and JPS in the host trees (Pinus massoniana) via its secondary metabolite, sterigmatocystin (ST), by taking a multi-omics approach (phenomics, transcriptomics, microbiome, and metabolomics).

Results

We found that Aspergillus was able to promote PWN invasion and pathogenicity by increasing ST biosynthesis in the host plant, mainly by suppressing the accumulation of ROS (reactive oxygen species) in plant tissues that could counter PWN. Further, ST accumulation triggered the biosynthesis of VOC (volatile organic compounds) that attracts JPS and drives the coexistence of PWN and JPS in the host plant, thereby encouraging the local transmission of PWD. Meanwhile, we show that application of an Aspergillus inhibitor (chiricanine A treatment) results in the absence of Aspergillus and decreases the in vivo ST amount, thereby sharply restricting the PWN development in host. This further proved that Aspergillus is vital and sufficient for promoting PWD transmission.

Discussion

Altogether, these results document, for the first time, how the function of Aspergillus and its metabolite ST is involved in the entire PWD transmission chain, in addition to providing a novel and long-term effective nematicide for better PWD control in the field.

Comprehensive applications of metabolomics on tea science and technology: Opportunities, hurdles, and perspectives

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.

Characterizing and Decoding the Effects of Different Fermentation Levels on Key Aroma Substances of Congou Black Tea by Sensomics

Fermentation is the key technology for black tea aroma formation. The key aroma substances of black tea at different fermentation stages (unfermented (WDY), underfermented (F1H), fully fermented (F4H), and overfermented (F8H)) were characterized by the methodology of Sensomics. Aroma extract dilution analysis was performed on volatile fractions extracted by using solvent-assisted flavor evaporation and solid-phase microextraction, yielding 93 odor-active areas. Internal standard method plus stable isotope dilution analysis was used for quantitative analysis. The omission experiment identified 23 aroma substances. Further reduction and addition experiments revealed phenylacetaldehyde, (E,E)-2,4-heptadienal, geraniol, linalool, β-damascenone, 2-methylbutyraldehyde, dimethyl sulfide, and isovaleraldehyde with odor activity values (OAV) > 100 as the characteristic aroma components of F4H and also as the main contributors to aroma differences between different fermentation degrees. The green odor of (E,E)-2,4-heptadienal was highlighted in WDY and F1H relative to that in F4H due to the lower contribution of phenylacetaldehyde and β-damascenone in the former two samples. Additionally, excessive OAV increase of fatty aldehydes in F8H masked its similar floral and fruity aroma.

Untargeted Metabolomics and Physicochemical Analysis Revealed the Quality Formation Mechanism in Fermented Milk Inoculated with Lactobacillus brevis and Kluyveromyces marxianus Isolated from Traditional Fermented Milk

Traditional fermented milk from the western Sichuan plateau of China has a unique flavor and rich microbial diversity. This study explored the quality formation mechanism in fermented milk inoculated with Lactobacillus brevis NZ4 and Kluyveromyces marxianus SY11 (MFM), the dominant microorganisms isolated from traditional dairy products in western nan. The results indicated that MFM displayed better overall quality than the milk fermented with L. brevis NZ4 (LFM) and K. marxianus SY11 (KFM), respectively. MFM exhibited good sensory quality, more organic acid types, more free amino acids and esters, and moderate acidity and ethanol concentrations. Non-targeted metabolomics showed a total of 885 metabolites annotated in the samples, representing 204 differential metabolites between MFM and LFM and 163 between MFM and KFM. MFM displayed higher levels of N-acetyl-L-glutamic acid, cysteinyl serine, glaucarubin, and other substances. The differential metabolites were mainly enriched in pathways such as glycerophospholipid metabolism, arginine biosynthesis, and beta-alanine metabolism. This study speculated that L. brevis affected K. marxianus growth via its metabolites, while the mixed fermentation of these strains significantly changed the metabolism pathway of flavor-related substances, especially glycerophospholipid metabolism. Furthermore, mixed fermentation modified the flavor and quality of fermented milk by affecting cell growth and metabolic pathways.

Chemical Analysis of Various Tea Samples Concerning Volatile Compounds, Fatty Acids, Minerals and Assessment of Their Thermal Behavior

Tea is the most consumed drink worldwide due to its pleasant taste and various beneficial effects on human health. This paper assesses the physicochemical analysis of different varieties of tea (leaves, flowers, and instant) after prior drying and fine grinding. The thermal decomposition behavior of the tea components shows that the tea has three stages of decomposition, depending on temperature. The first stage was attributed to the volatilization of water, while the second stage involved the degradation of volatiles, polyphenols, and fatty acids. The degradation of cellulose, hemicellulose, and lignin content occurs at the highest temperature of 400 °C in the third stage. A total of 66 volatile compounds, divided into eight classes, were identified in the tea samples. The volatile compounds were classified into nine odor classes: floral, fruity, green, sweet, chemical, woody, citrus, roasted, and alcohol. In all flower and leaf tea samples, monounsaturated (MUFAs), polyunsaturated (PUFAs), and saturated fatty acids (SFAs) were identified. A high content of omega-6 was quantified in acacia, Saint John's Wort, rose, and yarrow, while omega-3 was found in mint, Saint John's Wort, green, blueberry, and lavender samples. The flower and leaf tea samples studied could be a good dietary source of polyphenolic compounds, essential elements. In instant tea samples, a low quantity of polyphenols and major elements were identified. The physicochemical analysis demonstrated that both flower and leaf teas have high-quality properties when compared to instant tea.

Application of Multi-Perspectives in Tea Breeding and the Main Directions

Tea plants are an economically important crop and conducting research on tea breeding contributes to enhancing the yield and quality of tea leaves as well as breeding traits that satisfy the requirements of the public. This study reviews the current status of tea plants germplasm resources and their utilization, which has provided genetic material for the application of multi-omics, including genomics and transcriptomics in breeding. Various molecular markers for breeding were designed based on multi-omics, and available approaches in the direction of high yield, quality and resistance in tea plants breeding are proposed. Additionally, future breeding of tea plants based on single-cellomics, pangenomics, plant-microbe interactions and epigenetics are proposed and provided as references. This study aims to provide inspiration and guidance for advancing the development of genetic breeding in tea plants, as well as providing implications for breeding research in other crops.

Effects of Sun Withering Degree on Black Tea Quality Revealed via Non-Targeted Metabolomics

In this study, the effects of different sun withering degrees (75% (CK), 69% (S69), 66% (S66), 63% (S63), and 60% (S60) water content in the withered leaves) on black tea sensory quality were investigated by means of sensory evaluation plus metabolomics analysis. Sensory evaluation results showed higher sensory quality scores for the black tea in S69-S66, due to better freshness, sweeter taste, and a sweet and even floral and fruity aroma. Additionally, 65 non-volatile components were identified using Ultra Performance Liquid Chromatography-Quadrupole-Time of Flight-Mass Spectrometry (UPLC-Q-TOF/MS). Among them, the content increase of amino acids and theaflavins was found to promote the freshness and sweetness of black tea. The aroma of tea was analyzed using combined Solvent Assisted Flavor Evaporation-Gas Chromatography-Mass Spectrometry (SAFE-GC-MS) and Headspace-Solid Phase Micro Extract-Gas Chromatography-Mass Spectrometry (HS-SPME-GC-MS), and 180 volatiles were identified, including 38 variable importance in projection (VIP) > 1 (p < 0.05) and 25 Odor Activity Value (OAV) > 1 volatiles. Statistical analysis revealed 11 volatiles as potential major aroma differential metabolites in black tea with a different sun withering degree, such as volatile terpenoids (linalool, geraniol, (E)-citral, and β-myrcene), amino-acid-derived volatiles (benzeneethanol, benzeneacetaldehyde, and methyl salicylate), carotenoid-derived volatiles (jasmone and β-damascenone), and fatty-acid-derived volatiles ((Z)-3-hexen-1-ol and (E)-2-hexenal). Among them, volatile terpenoids and amino acid derived volatiles mainly contributed to the floral and fruity aroma quality of sun-withered black tea.