Enzymatic Reaction-Related Protein Degradation and Proteinaceous Amino Acid Metabolism during the Black Tea (Camellia sinensis) Manufacturing Process

Dynamic changes of key metabolites in Longjing green tea during processing revealed by widely targeted metabolomic profiling and sensory experiments

In this study, widely targeted metabolomics and chemometrics were utilized to comprehensively analyse the formation of taste compounds in Longjing green tea. A total of 580 non-volatile metabolites were identified by using ultra-performance liquid chromatography-electrospray ionization-tandem mass spectrometry, and alterations in three metabolic pathways were investigated. Notably, the fixation process reduced phosphatidic acid levels, resulting in the formation of lyso-phosphatidylcholine and lyso-phosphatidylethanolamine, as well as the release of esterified polyunsaturated fatty acids. Baiye No.1 had high levels of L-glutamic acid and l-glutamine, while Longjing 43 showed elevated levels of flavones. Correlation analysis and sensory verification indicated that the specific concentration of L-leucine could decrease the umami of the tea. These findings advance our understanding of Longjing green tea quality improvement and cultivar development.

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.

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

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

Key Factors of Quality Formation in Wuyi Black Tea during Processing Timing

As the most consumed tea in the world, all kinds of black tea are developed from Wuyi black tea. In this study, quality components, regulatory gene expression, and key enzyme activity during the processing were analyzed to illustrate the taste formation of WBT. Withering mainly affected the content of amino acids, while catechins and tea pigments were most influenced by rolling and the pre-metaphase of fermentation. Notably, regulatory gene expression was significantly down-regulated after withering except for polyphenoloxidase1, polyphenoloxidase2, leucoanthocyanidin dioxygenase, chalcone isomerase, and flavonoid 3', 5'-hydroxylase. Co-expression of flavonoid pathway genes confirmed similar expression patterns of these genes in the same metabolic pathway. Interestingly, rolling and fermentation anaphase had a great effect on polyphenol oxidase, and fermentation pre-metaphase had the greatest effect on cellulase. Since gene regulation mainly occurs before picking, the influence of chemical reaction was greater during processing. It was speculated that polyphenol oxidase and cellulase, which promoted the transformation of quality components, were the key factors in the quality formation of WBT. The above results provide theoretical basis for the processing of WBT and the reference for producing high-quality black tea.

Rolling forms the diversities of small molecular nonvolatile metabolite profile and consequently shapes the bacterial community structure for Keemun black tea

The detailed dynamics of small molecular nonvolatile chemical and bacterial diversities, as well as their relationship are still unclear in the manufacturing process of Keemun black tea (KMBT). Herein, mass spectrometry-based untargeted metabolomics, Feature-based Molecular Networking (FBMN) and bacterial DNA amplicon sequencing were used to investigate the dense temporal samples of the manufacturing process. For the first time, we reveal that the pyrogallol-type catechins are oxidized asynchronously before catechol-type catechins during the black tea processing. Rolling is the key procedure for forming the small molecular nonvolatile metabolite profile (SMNMetProf), increasing the metabolite richness, and then shaping the bacterial community structure in the KMBT manufacturing process, which decreases both molecular weight and molecular polarity of the small molecular nonvolatile metabolites. The SMNMetProf of black tea is formed by the endogenous enzymatic oxidation of tea leaves, rather than bacterial fermentation.

Effect of the type of brewing water on the sensory and physicochemical properties of light-scented and strong-scented Tieguanyin oolong teas

Variations in the quality of brewing water profoundly impact tea flavor. This study systematically investigated the effects of four common water sources, including pure water (PW), mountain spring water (MSW), mineral water (MW) and natural water (NW) on the flavor of Tieguanyin tea infusion. Brewing with MW resulted in a flat taste and turbid aroma, mainly due to the low leaching of tea flavor components and complex interactions with mineral ions (mainly Ca2+, Mg2+). Tea infusions brewed with NW exhibited the highest relative contents of total volatile compounds, while those brewed with PW had the lowest. NW and MSW, with moderate mineralization, were conducive to improving the aroma quality of tea infusion and were more suitable for brewing both aroma types of Tieguanyin. These findings offer valuable insights into the effect of brewing water on the sensory and physicochemical properties of oolong teas.

Re-rolling treatment in the fermentation process improves the taste and liquor color qualities of black tea

Fermentation is a vital process occurred under the premise of rolling affecting black tea quality. Theoretically, re-rolling during fermentation will remodel the biochemical conditions of tea leaves, and thus influence black tea quality. Herein, we studied the effect of re-rolling on black tea taste and liquor color. Sensory evaluation showed that re-rolling significantly weakened the astringency taste and improved the redness and luminance of liquor. With re-rolling, the color attributes of a* and L* and the contents of theaflavins and thearubigins were significantly improved. Metabolomics analysis showed that the contents of 110 non-volatile compounds were significantly different among black teas with different rolling treatments. In summary, re-rolling accelerated the oxidation of polyphenols into pigments, the hydrolysis of proteins into amino acids, and the metabolism of alkaloids, organic acids, glycosidically-bound volatiles, and lipids during the fermentation period. Our study provided a novel and simple way to improve black tea quality.

Metagenomic insights into protein degradation mechanisms in natural fermentation of cassava leaves

Cassava (Manihot esculenta Crantz) leaves, the primary by-product of cassava processing, constitute a significant protein source, accounting for 18 to 38 percent on a dry weight basis. Despite their nutritional value, a substantial portion of these leaves is often discarded post-harvest, resulting in notable resource waste. This study employs metagenomic technology to investigate the protein degradation mechanism in cassava leaves, aiming to provide a technical reference for value-added of this by-product. Following a 36-hour period of natural fermentation, the protein degradation rate reached 58%, a phenomenon intricately linked to both the microbial community structure and its functional properties. Notably, Lactococcus and Enterobacter, recognized for their abundant protease activity, were predominant. Metagenomically assembled genomes further revealed Lactococcus's substantial role in producing flavors and active compounds, including amino acids and peptides. This study offers novel perspectives to the foodization and high-value utilization of cassava by-products, emphasizing the sustainable exploitation of biomass resources.

Physiological and Biochemical Analysis Revealing the Key Factors Influencing 2-Phenylethanol and Benzyl Alcohol Production in Crabapple Flowers

Floral scent (FS) plays a crucial role in the ecological functions and industrial applications of plants. However, the physiological and metabolic mechanisms underlying FS formation remain inadequately explored. Our investigation focused on elucidating the differential formation mechanisms of 2-phenylethanol (2-PE) and benzyl alcohol (BA) by examining seven related enzyme concentrations and the content of soluble sugar, soluble proteins, carbon (C) and nitrogen (N), as well as the C/N ratio. The findings revealed that the peak content of 2-PE in M. 'Praire Rose' and BA in M. 'Lollipop' occurred during the end flowering stage (S4) and flowering stage (S3) periods, respectively. The enzyme concentration change trends of phenylpyruvate decarboxylase (PDL), phenylacetaldehyde reductase (PAR), soluble protein, C, N, and C/N ratio changes during the S3-S4 period in M. 'Praire Rose' and M. 'Lollipop' were entirely opposite. Correlation and PCA analysis demonstrated that the content of CYP79D73 (a P450) and N, and the C/N ratio were key factors in 2-PE production in M. 'Praire Rose'. The production of BA in M. 'Lollipop' was more influenced by the content of phenylacetaldehyde synthase (PAAS), CYP79D73, and soluble sugar. As CYP79D73 exits oppositely in correlation to 2-PE (M. 'Praire Rose') and BA (M. 'Lollipop'), it is hypothesized that CYP79D73 was postulated as the primary factor contributing to the observed differences of 2-PE (M. 'Praire Rose') and BA (M. 'Lollipop') formation. These results carry significant implications for crabapple aromatic flower breeding and the essential oil industry etc.

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.

Effects of Vine Water Status on Malate Metabolism and γ-Aminobutyric Acid (GABA) Pathway-Related Amino Acids in Marselan (Vitis vinifera L.) Grape Berries

Malic acid is the predominant organic acid in grape berries, and its content is affected by abiotic factors such as temperature (fruit zone microclimate) and water (vine water status). The objectives of this study were to explore the potential mechanisms behind the effects of vine water status on the biosynthesis and degradation of berry malic acid and the potential downstream effects on berry metabolism. This study was conducted over two growing seasons in 2021 and 2022, comprising three watering regimes: no water stress (CK), light water stress (LWS), and moderate water stress (MWS). Compared to CK, a significantly higher level of malic acid was found in berries from the MWS treatment when the berry was still hard and green (E-L 33) in both years. However, water stress reduced the malic acid content at the ripe berry harvest (E-L 38) stage. The activities of NAD-malate dehydrogenase (NAD-MDH) and pyruvate kinase (PK) were enhanced by water stress. Except for the E-L 33 stage, the activity of phosphoenolpyruvate carboxylase (PEPC) was reduced by water stress. The highest phosphoenolpyruvate carboxykinase (PEPCK) activity was observed at the berry veraison (E-L 35) stage and coincided with the onset of a decrease in the malate content. Meanwhile, the expression of VvPEPCK was consistent with its enzyme activity. This study showed that water stress changed the content of some free amino acids (GABA, proline, leucine, aspartate, and glutamate), two of which (glutamate and GABA) are primary metabolites of the GABA pathway.

Versatile Effects of GABA Oolong Tea on Improvements in Diastolic Blood Pressure, Alpha Brain Waves, and Quality of Life

Emerging evidence has demonstrated that using a new manufacturing technology to produce γ-aminobutyric acid (GABA)-fortified oolong (GO) tea could relieve human stress and exert versatile physiological benefits. The purpose of this human study was to investigate the therapeutic effects of daily GO tea consumption on improvements in blood pressure, relaxation-related brain waves, and quality of life (QOL) over a period of 28 consecutive days. Total polyphenols, major catechins, and free amino acids were analyzed via an HPLC assay. Changes in heart rate, blood pressure, α brain waves (index of relaxation), and the eight-item QOL score were investigated on days 0, 7, 14, 21, and 28. The chemical analysis results showed that GO tea contained the most abundant amino acids and GABA, contributing to the relaxation activity. Among all study participants, the daily consumption of GO tea could reduce systolic blood pressure on day 21 and diastolic blood pressure on day 28 (p < 0.05 for both). For participants with pre-hypertension, GO tea could effectively reduce heart rate and systolic and diastolic blood pressure on day 28 (p < 0.05). At the end of the study, incremental changes in alpha brain waves and QOL scores were also demonstrated (p < 0.05 for both). This study suggests that GO tea might potentially serve as a natural source for alternative therapy to improve blood pressure, stress relief, and QOL.

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.

Growth substrates alter aboveground plant microbial and metabolic properties thereby influencing insect herbivore performance

The gut microbiome of plant-eaters is affected by the food they eat, but it is currently unclear how the plant metabolome and microbiome are influenced by the substrate the plant grows in and how this subsequently impacts the feeding behavior and gut microbiomes of insect herbivores. Here, we use Plutella xylostella caterpillars and show that the larvae prefer leaves of cabbage plants growing in a vermiculite substrate to those from plants growing in conventional soil systems. From a plant metabolomics analysis, we identified 20 plant metabolites that were related to caterpillar feeding performance. In a bioassay, the effects of these plant metabolites on insects' feeding were tested. Nitrate and compounds enriched with leaves of soilless cultivation promoted the feeding of insects, while compounds enriched with leaves of plants growing in natural soil decreased feeding. Several microbial groups (e.g., Sporolactobacillus, Haliangium) detected inside the plant correlated with caterpillar feeding performance and other microbial groups, such as Ramlibacter and Methylophilus, correlated with the gut microbiome. Our results highlight the role of growth substrates on the food metabolome and microbiome and on the feeding performance and the gut microbiome of plant feeders. It illustrates how belowground factors can influence the aboveground properties of plant-animal systems, which has important implications for plant growth and pest control.

Properties investigations of rape stalks fermented by different salt concentration: Effect of volatile compounds and physicochemical indexes

In order to find out the effect of salt concentration on fermented rape stalks, the physicochemical quality and volatile components was investigated using high performance liquid chromatography (HPLC) and headspace solid phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS). The results showed that there were abundant kinds of free amino acids (FAAs) in all samples, mainly presenting sweet, umami and bitter taste. Through taste activity value (TAV), His, Glu, and Ala contributed significantly to the taste of the sample. 51 volatile components were identified, of which the relative contents of ketones and alcohols were high. By the relative odor activity value (ROAV) analysis, the main components that had a great impact on the flavor were phenylacetaldehyde, β-Ionone, ethyl palmitate and furanone. Adjusting the appropriate salt concentration for fermentation could improve the comprehensive quality of fermented rape stalks and promote the development and utilization of rape products.

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.

Multiomics provides insights into the succession of microbiota and metabolite during plant leaf fermentation

The quality of fermented plant products is closely related to microbial metabolism. Here, the associations of bacterial communities, metabolites, and functional genes were explored using multi-omics techniques based on plant leaf fermentation systems. The results showed significant changes in the structure of the microbial community, with a significant decrease in Firmicutes and a significant increase in Proteobacteria. In addition, the concentration of metabolites with antibacterial, antioxidant and aroma properties increased significantly, enhancing the quality of the fermented plant leaves. Integrated macrogenomic and metabolomic analyses indicated that amino acid metabolism could be key metabolic pathway affecting fermentation quality. Actinobacteria, Proteobacteria, Firmicutes were actively involved in tyrosine metabolism (ko00350) and phenylalanine metabolism (ko00360), and are presumed to be the major groups responsible for synthesizing growth and flavor compounds. This study emphasized the important role of microorganisms in the changes of metabolites during the fermentation of plant leaves.

Analyzing the influence of withering degree on the dynamic changes in non-volatile metabolites and sensory quality of Longjing green tea by non-targeted metabolomics

Withering is an important processing stage in green tea, which contributes to the tea flavor quality. The aim of this work was to comprehensively investigate the changes of chemical features and flavor attributes in Longjing green teas produced with five different withering degrees (moisture content of 75.05, 72.53, 70.07, 68.00, and 64.78%, w.b.). Combined with human sensory evaluation, electronic tongue and chromatic differences analysis, an assessment of the relationship between the withering degree and the sensory quality of Longjing tea was obtained. By using a non-targeted metabolomics approach, 69 significantly differential metabolites were screened. As the withering degree increased, most free amino acids and catechin dimers were increased, largely attributed to the hydrolysis of proteins and catechin oxidative polymerization, respectively. The contents of organic acids as well as phenolic acids and derivatives were reduced. Interestingly, flavone C-glycosides decreased overall while flavonol O-glycosides increased. The correlation analysis revealed that metabolites such as theasinensin F, theasinensin B, theaflavin, theaflavin-3,3′-gallate, theaflavin-3′-gallate, malic acid, succinic acid, quinic acid, theanine glucoside and galloylglucose had a greater influence on the taste and color of tea infusion (|r| &gt; 0.6, p &lt; 0.05). Overall, an appropriate withering degree at a moisture content of around 70% is more favorable to enhance the Longjing tea quality. These results may enhance the understanding of green tea flavor chemistry associated with withering and provide a theoretical basis for green tea processing.

Identification of potential light deficiency response regulators in endangered species Magnolia sinostellata

Magnolia sinostellata is one of the endangered species in China and largely suffers light deficiency stress in the understory of forest. However, the weak light response molecular mechanism remains unclear. More importantly, hub genes in the molecular network have not been pinpointed. To explore potential regulators in the mechanism, weighted gene co-expression network analysis (WGCNA) was performed to analysis the trancriptome data of M. sinostellata leaves subjected to weak light with different time points. Gene co-expression analysis illustrated that module 1, 2 and 3 were closely associated with light deficiency treatment, which. Gene ontology and KEGG analyses showed that genes in module 1 mainly participated in amino and nucleotide metabolism, module 2 mostly involved in carbon fixation and module 3 mostly regulated photosynthesis related pathways, among which 6, 7 and 8 hub genes were identified, respectively. Hub genes isoform_107196 in module 1 and isoform_55976 in module 2 were unique to M. sinostellata. This study found that light deficiency inhibited photosynthesis and stress tolerance, while improved carbon metabolism and flowering related pathways in M. sinostellata, which can impact its accumulation reserves of growth and reproduction in the next season. In addition, key shade response regulators identified in this study have laid a firm foundation for further investigation of shade response molecular mechanism and protection of other shade sensitive plants.

Effects of Preharvest Shading on Dynamic Changes in Metabolites, Gene Expression, and Enzyme Activity of Three Tea Types during Processing

Preharvest shading significantly influences tea flavor. However, little attention has been given to the mechanism of shading on metabolites, genes, and enzymes in the processing of different tea types. Our study identified 1028 nonvolatile metabolites covering 10 subclasses using a widely targeted metabolome. The results show that shading had a greater effect on the compositions of amino acids, flavonoids, and theaflavins in tea leaves. The combined transcriptomics and enzyme activity analysis results indicate that the upregulated expression of asparagine, aspartate, and tryptophan synthesis genes and proteolytic enzymes promoted the accumulation of amino acids. The downregulated enzyme genes resulted in the reduction of nongalloylated catechins and flavonoid glycosides. Simultaneously, the accumulation of TFs in shaded tea was due to the enhanced enzymatic activities of polyphenol oxidase and peroxidase during processing. Theaflavin-3-3'-di-O-gallate was also significantly positively correlated with the antioxidant and hypoglycemic activities of shaded tea. The results contribute to a better understanding of how preharvest treatments influence summer tea quality.

Dynamic Analysis of Physicochemical Properties and Polysaccharide Composition during the Pile-Fermentation of Post-Fermented Tea

Ultra-high performance liquid chromatography-quadrupole-time of flight tandem mass spectrometry (UHPLC-Q-TOF-MS/MS) was used to study the diversity of tea polysaccharides and the dynamic changes in the physicochemical indexes of tea samples. FT-IR spectra and the free radical scavenging ability of tea polysaccharides, during pile-fermentation of post-fermented tea, were analyzed. The results showed that 23 saccharide co mponents in tea polysaccharides were identified: these belonged to 11 monosaccharides, 5 oligosaccharides, and 6 derivatives of monosaccharides and oligosaccharides. The abundance of oligosaccharides decreased gradually, while monosaccharides, and derivatives of monosaccharides and oligosaccharides increased gradually with the development of pile-fermentation. According to the differences in polysaccharide composition and their abundance, the tea polysaccharide samples extracted from different pile-fermentation stages could be clearly classed into three groups, W-0, W-1~W-4 and W-5~C-1. The pile-fermentation process affected the yield, the content of each component, FT-IR spectra, and the DPPH free radical scavenging ability of tea polysaccharides. Correlation analysis showed that microorganisms were directly related to the changes in composition and the abundance of polysaccharides extracted from different pile-fermentation stages. The study will further help to reveal the function of tea polysaccharides and promote their practical application as a functional food.

Future perspectives on aptamer for application in food authentication

Food fraudulence and food contamination are major concerns, particularly among consumers with specific dietary, cultural, lifestyle, and religious requirements. Current food authentication methods have several drawbacks and limitations, necessitating the development of a simpler, more sensitive, and rapid detection approach for food screening analysis, such as an aptamer-based biosensor system. Although the use of aptamer is growing in various fields, aptamer applications for food authentication are still lacking. In this review, we discuss the limitations of existing food authentication technologies and describe the applications of aptamer in food analyses. We also project several potential targets or marker molecules to be targeted in the SELEX process. Finally, this review highlights the drawbacks of current aptamer technologies and outlines the potential route of aptamer selection and applications for successful food authentication. This review provides an overview of the use of aptamer in food research and its potential application as a molecular reporter for rapid detection in food authentication process. Developing databases to store all biochemical profiles of food and applying machine learning algorithms against the biochemical profiles are urged to accelerate the identification of more reliable biomarker molecules as aptamer targets for food authentication.

Studies on Flavor Compounds and Free Amino Acid Dynamic Characteristics of Fermented Pork Loin Ham with a Complex Starter

Staphylococcus simulans and Lactobacillus plantarum screened from Guizhou specialty food were used to prepare fermented pork loin ham. The sensory qualities and flavor profiles of fermented pork loin hams from 0 to 42 days were investigated in order to reveal the dynamics of fermented pork loin ham. The results show that total free amino acids (TFAA) content reached the highest value on the 35th day, and the umami amino acids, including aspartic acid (ASP), glutamic acid (GLU), glycine (GLY), and alanine (ALA), were the main amino acids in all periods. Notably, the RV coefficient (0.875) indicates that free amino acids (FAA) are highly correlated with the sensory score of the E-tongue. In terms of the volatile compounds identified, the esters content gradually increased between 7 and 42 days, and ethyl octanoate was the most abundant compound during all periods. These esters imparted a characteristic aroma component to the fermented pork loin ham. The most important finding was that the increase in the content of esters represented by octanoic acid-ethyl ester might be related to the increase in the content of FAA with the increase in fermentation time. Both the E-nose and E-tongue showed good discrimination ability for fermented tenderloin ham with different fermentation times, which was crucial in cases with large clusters. In addition, the multiple factor analysis (MFA) indicated that the E-nose aroma value might be the key factor in distinguishing fermented pork loin ham with different fermentation times.

Carbon and Nitrogen Metabolism Are Jointly Regulated During Shading in Roots and Leaves of Camellia Sinensis

Numerous studies have shown that plant shading can promote the quality of green tea. However, the association of shading with metabolic regulation in tea leaves and roots remains unelucidated. Here, the metabolic profiling of two tea cultivars ("Xiangfeicui" and "Jinxuan") in response to shading and relighting periods during the summer season was performed using non-targeted metabolomics methods. The metabolic pathway analyses revealed that long-term shading remarkably inhibit the sugar metabolism such as glycolysis, galactose metabolism, and pentose phosphate pathway in the leaves and roots of "Xiangfeicui," and "Jinxuan" were more sensitive to light recovery changes. The lipid metabolism in the leaves and roots of "Xiangfeicui" was promoted by short-term shading, while it was inhibited by long-term shading. In addition, the intensity of the flavonoid metabolites in the leaves and roots of "Jinxuan" were upregulated with a trend of rising first and then decreasing under shading, and five flavonoid synthesis genes showed the same trend (F3H, F3'5'H, DFR, ANS, and ANR). Simultaneously, the amino acids of the nitrogen metabolism in the leaves and roots of the two cultivars were significantly promoted by long-term shading, while the purine and caffeine metabolism was inhibited in the leaves of "Xiangfeicui." Interestingly, CsGS1.1 and CsTSI, amino acid synthase genes was upregulated in the leaves and roots of two cultivars. These results indicated that shading could participate in carbon and nitrogen metabolic regulation of both leaf and root, and root metabolism could have a positive association with leaf metabolism to promote the shaded tea quality.

Effect of red light on the composition of metabolites in tea leaves during the withering process using untargeted metabolomics

BACKGROUND

Red light withering significantly improves the sensory flavor qualities of tea, although changes in metabolites during this process have not been systematically studied until now. The present study comprehensively analyzes metabolites in withered tea leaves at 2-h intervals up to 12 h under red light (630 nm) and dark conditions using ultra performance liquid chromatography-high resolution mass spectrometry (untargeted metabolomics).

RESULTS

Ninety-four non-volatile compounds are identified and relatively quantified, including amino acids, catechins, dimeric catechins, flavonol glycosides, glycosidically-bound volatiles, phenolic acids and nucleosides. The results show that amino acids, catechins and dimeric catechins are most affected by red light treatment. Ten free amino acids, theaflavins and theasinensin A increase after red light irradiation, whereas epigallocatechin gallate and catechin fall.

CONCLUSION

The present study provides a comprehensive and systematic profile of the dynamic effects of red light on withering tea and a rationale for its use in tea processing quality control. © 2021 Society of Chemical Industry.

The chemistry, processing, and preclinical anti-hyperuricemia potential of tea: a comprehensive review

Hyperuricemia is an abnormal purine metabolic disease that occurs when there is an excess of uric acid in the blood, associated with cardiovascular diseases, hypertension, gout, and renal disease. Dietary intervention is one of the most promising strategies for preventing hyperuricemia and controlling uric acid concentrations. Tea (Camellia sinensis) is known as one of the most common beverages and the source of dietary polyphenols. However, the effect of tea on hyperuricemia is unclear. Recent evidence shows that a lower risk of hyperuricemia is associated with tea intake. To better understand the anti-hyperuricemia effect of tea, this review first briefly describes the pathogenesis of hyperuricemia and the processing techniques of different types of tea. Next, the epidemiological and experimental studies of tea and its bioactive compounds on hyperuricemia in recent years were reviewed. Particular attention was paid to the anti-hyperuricemia mechanisms targeting the hepatic uric acid synthase, renal uric acid transporters, and intestinal microbiota. Additionally, the desirable intake of tea for preventing hyperuricemia is provided. Understanding the anti-hyperuricemia effect and mechanisms of tea can better utilize it as a preventive dietary strategy.HighlightsHigh purine diet, excessive alcohol/fructose consumption, and less exercise/sleep are the induction factors of hyperuricemia.Tea and tea compounds showed alleviated effects for hyperuricemia, especially polyphenols.Tea (containing caffeine or not) is not associated with a higher risk of hyperuricemia.Xanthine oxidase inhibition (reduce uric acid production), Nrf2 activation, and urate transporters regulation (increase uric acid excretion) are the potential molecular targets of anti-hyperuricemic effect of tea.About 5 g tea intake per day may be beneficial for hyperuricemia prevention.

Impact of prolonged withering on phenolic compounds and antioxidant capability in white tea using LC-MS-based metabolomics and HPLC analysis: Comparison with green tea

Contents of 20 bioactive compounds in 12 teas produced in Xinyang Region were determined by high performance liquid chromatography. Ultra-high performance liquid chromatography-quadrupole time of flight-mass spectrometry was developed for untargeted metabolomics analysis. Antioxidant activities were measured by 4 various assays. Those teas could be completely divided into green and white tea through principal component analysis, hierarchical cluster analysis and orthonormal partial least squares-discriminant analysis (R²Y = 0.996 and Q² = 0.982, respectively). The prolonged withering generated 472 differentiated metabolites between white and green tea, prompted significant decreases (variable importance in the projection > 1.0, p-value < 0.05 and fold change > 1.50) of most catechins and 8 phenolic acids to form 4 theaflavins, and benefited for the accumulation of 17 flavonoids and flavonoid glycosides, 8 flavanone and their derivatives, 20 free amino acids, 12 sugars and 1 purine alkaloid. Additionally, kaempferol and taxifolin contributed to 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging ability of white tea.

Black tea aroma formation during the fermentation period

The present study aimed to systematically investigate black tea aroma formation during the fermentation period. In total, 158 volatile compounds were identified. Of these, most amino acid-derived volatiles (AADVs) and carotenoid-derived volatiles (CDVs) showed significant increases, while fatty acid-derived volatiles (FADVs) and volatile terpenoids (VTs) displayed diverse changes during the fermentation period. During this time, fatty acids, amino acids, carotenoids, and glycosidically bound volatiles (GBVs, especially primeverosides) were found to degrade to form aroma components. Further, equivalent quantification of aroma showed that the intensity of green scent was notably decreased, while the intensities of sweet and floral/fruity scents were greatly increased and gradually dominated the aroma of tea leaves. AADVs and CDVs were shown to make greater contributions to the formation of sweet and floral/fruity scents than VTs. Our study provides a detailed characterization of the formation of sweet and floral/fruity aromas in black tea during the fermentation period.

Solid-state fermentation by Aspergillus niger and Trichoderma koningii improves the quality of tea dregs for use as feed additives

This study evaluated the ability of Aspergillus niger and Trichoderma koningii to improve the quality of tea dregs (TDs) through solid-state fermentation as well as the value of the fermented tea dregs (FTDs) produced for use as bio-feed additives. After fermentation, FTDs differed in color and structure. Fermentation with A. niger and T. koningii increased the contents of crude protein, crude fiber, neutral detergent fiber, and acid detergent fiber of TDs. Compared to the unfermented group, the contents of reducing sugar, total flavonoids, total polyphenols, and theasaponins were increased in A. niger FTDs, while in T. koningii FTDs caffeine was completely degraded, the theasaponins were lower, and the contents of reducing sugar and caffeine higher. Regarding free amino acids, A. niger FTDs had the highest content of total amino acids, total essential amino acids, total non-essential amino acids, total aromatic amino acids, total branched-chain amino acids, and total non-protein amino acids, and all types of essential amino acids, followed by T. koningii FTDs and the control TDs. Fungal fermentation had similar effects on the content of various hydrolytic amino acids as those on above free amino acids, and increased the content of bitter and umami components. The composition of essential amino acids of TDs or FTDs was similar to that of the standard model, except for sulfur-containing amino acids and isoleucine. Solid-state fermentation with A. niger and T. koningii effectively improved the nutritional value of TDs, increased the contents of functional substances, and improved the flavor of TDs. This study demonstrated a feasible approach to utilize TDs that not only increases animal feed resources, but also reduces the production of resource waste and pollution.

The R2R3 Transcription Factor CsMYB59 Regulates Polyphenol Oxidase Gene CsPPO1 in Tea Plants (Camellia sinensis)

Polyphenol oxidase (PPO) plays a role in stress response, secondary metabolism, and other physiological processes during plant growth and development, and is also a critical enzyme in black tea production. However, the regulatory mechanisms of PPO genes and their activity in tea plants are still unclear. In this study, we measured PPO activity in two different tea cultivars, Taoyuandaye (TYDY) and Bixiangzao (BXZ), which are commonly used to produce black tea and green tea, respectively. The expression pattern of CsPPO1 was assessed and validated via transcriptomics and quantitative polymerase chain reaction in both tea varieties. In addition, we isolated and identified an R2R3-MYB transcription factor CsMYB59 that may regulate CsPPO1 expression. CsMYB59 was found to be a nuclear protein, and its expression in tea leaves was positively correlated with CsPPO1 expression and PPO activity. Transcriptional activity analysis showed that CsMYB59 was a transcriptional activator, and the dual-luciferase assay indicated that CsMYB59 could activate the expression of CsPPO1 in tobacco leaves. In summary, our study demonstrates that CsMYB59 represents a transcriptional activator in tea plants and may mediate the regulation of PPO activity by activating CsPPO1 expression. These findings provide novel insights into the regulatory mechanism of PPO gene in Camellia sinensis, which might help to breed tea cultivars with high PPO activity.

Effects of Long-Term Non-Pruning on Main Quality Constituents in 'Dancong' Tea (Camellia sinensis) Leaves Based on Proteomics and Metabolomics Analysis

'Dancong' tea is a famous traditional Oolong tea. In order to keep the original taste of "ancient tea trees", most of the 'Dancong' tea plants are planted in a single plant pattern without pruning. The objective of this study was to explore the effects of long-term non-pruning on main quality constituents in 'Dancong' tea. The results showed that the contents of free amino acids, chlorophylls, and floral-honey aromatic substances in tea leaves of unpruned tea plants were higher than those in every year pruned tea plants, while the catechin content in leaves of pruned tea plants was higher than that in leaves of unpruned tea plants. Quantitative proteomics analysis showed that most enzymes involved in biosynthesis of catechins were downregulated in leaves of unpruned tea plants. Five proteins involved in chlorophyll metabolism and 12 proteins related to photosynthesis were upregulated, and the results suggested that higher chlorophyll content and more efficient photosynthetic energy conversion may be important for the higher accumulation of special quality components in leaves of unpruned tea plants. The findings of this study will advance our understanding of the mechanism of formation of different metabolites in leaves of unpruned and pruned tea plants.

NMR, RP-HPLC-PDA-ESI-MSn, and RP-HPLC-FD Characterization of Green and Oolong Teas (Camellia sinensis L.)

Untargeted (NMR) and targeted (RP-HPLC-PDA-ESI-MSⁿ, RP-HPLC-FD) analytical methodologies were used to determine the bioactive components of 19 tea samples, characterized by different production processes (common tea and GABA tea), degrees of fermentation (green and oolong teas), and harvesting season (autumn and spring). The combination of NMR data and a multivariate statistical approach led to a statistical model able to discriminate between GABA and non-GABA teas and green and oolong teas. Targeted analyses showed that green and GABA green teas had similar polyphenol and caffeine contents, but the GABA level was higher in GABA green teas than in regular green tea samples. GABA oolong teas showed lower contents of polyphenols, caffeine, and amino acids, and a higher content of GABA, in comparison with non-GABA oolong teas. In conclusion, the results of this study suggest that the healthy properties of teas, especially GABA teas, have to be evaluated via comprehensive metabolic profiling rather than only the GABA content.

Assessment of quality and safety of meats from various animal species in the Shuchinsk-Burabay resort zone, Kazakhstan

Aim:

This study aimed to determine the food safety and protein adequacy of meats from various animals in the Shuchinsk-Burabay resort zone.

Materials and Methods:

Samples of meat were collected from markets “Zhomart” and “Kausar.” Two hundred and ninety-eight samples of meat were obtained: beef - 166, horse - 42, pork - 67, mutton - 8, and poultry - 15. From each carcass, part of the carcass, point samples were taken to form an average sample and conduct research. Analyses used inductively coupled plasma mass spectrometry and liquid chromatography. The determination of amino acid composition was carried out following the chromatographic method for determining the amino acid composition of meat proteins.

Results:

The quality of meats from the resort zone was lower than recommended due to the reduced content of essential amino acids, including valine, lysine, isoleucine, and phenylalanine. Concentrations of heavy metals and radionuclides did not exceed maximum permissible limits, and trace concentrations of arsenic, cadmium, and lead were detected in all meat samples, except beef. The latter meat showed increased concentrations of mercury.

Conclusion:

In terms of quality indicators, all types of meat met standards; however, pork protein displayed the most favorable amino acid composition, both for content of essential amino acids and the ratio of amounts of essential to non-essential amino acids. For content of heavy metals, poultry and pork meats were safest.

HS-SPME and GC/MS volatile component analysis of Yinghong No. 9 dark tea during the pile fermentation process

Each type of tea has a unique volatile profile due to its variety, processing technologies and origin. Using HS-SPME and GC/MS, we analyzed the changes of volatile components in cultivar Yinghong No. 9 during pile-fermentation every 10 days. A total of 94 compounds showed significant differences during a total of 60 days mainly including alkanes, ketones, esters, terpenes, aromatics and heterocyclic compounds. Interestingly, 13 metabolites were progressively reduced during the first 20 days and remained unchanged in subsequent procedures, while 17 metabolites remained unchanged in the early stage and progressively increased during the last 20 days of pile fermentation, indicating that they are characteristic volatile compounds of raw material sun-dried green tea and dark tea, respectively. β-ionone, phenylethyl alcohol, and a-ionone could be the top three contributed aroma compounds in the final dark tea. Our study provides a theoretical basis for process and quality improvement of Yinghong No. 9.

Molecular and Biochemical Characterization of Jasmonic Acid Carboxyl Methyltransferase Involved in Aroma Compound Production of Methyl Jasmonate during Black Tea Processing

Methyl jasmonate (MeJA), a volatile organic compound, is a principal flowery aromatic compound in tea. During the processing of black tea, MeJA is produced by jasmonic acid carboxyl methyltransferase (JMT) of the jasmonic acid (JA) substrate, forming a specific floral fragrance. CsJMT was cloned from tea leaves; the three-dimensional structure of CsJMT was predicted. Enzyme activity was identified, and protein purification was investigated. Site-directed deletions revealed that N-10, S-22, and Q-25 residues in the beginning amino acids played a key functional role in enzyme activity. The expression patterns of CsJMT in tea organs differed; the highest expression of CsJMT was observed in the fermentation process of black tea. These results aid in further understanding the synthesis of MeJA during black tea processing, which is crucial for improving black tea quality using specific fragrances and could be applied to the aromatic compound regulation and tea breeding improvement in further studies.

Using near-infrared hyperspectral imaging with multiple decision tree methods to delineate black tea quality

The evaluation of tea quality tended to be subjective and empirical by human panel tests currently. A convenient analytical approach without human involvement was developed for the quality assessment of tea with great significance. In this study, near-infrared hyperspectral imaging (HSI) combined with multiple decision tree methods was utilized as an objective analysis tool for delineating black tea quality and rank. Data fusion that integrated texture features based on gray-level co-occurrence matrix (GLCM) and short-wave near-infrared spectral features were as the target characteristic information for modeling. Three different types of supervised decision tree algorithms (fine tree, medium tree, and coarse tree) were proposed for the comparison of the modeling effect. The results indicated that the performance of models was enhanced by the multiple perception feature fusion. The fine tree model based on data fusion obtained the best predictive performance, and the correct classification rate (CCR) of evaluating black tea quality was 93.13% in the prediction process. This work demonstrated that HSI coupled with intelligence algorithms as a rapid and effective strategy could be successfully applied to accurately identify the rank quality of black tea.

Metabolomics combined with proteomics provides a novel interpretation of the changes in nonvolatile compounds during white tea processing

In this study, metabolomics and proteomics were employed to investigate the change mechanism of nonvolatile compounds during white tea processing. A total of 99 nonvolatile compounds were identified, among which the contents of 13 free amino acids, caffeine, theaflavins, 7 nucleosides and nucleotides, and 5 flavone glycosides increased significantly, while the contents of theanine, catechins, theasinesins, 3 proanthocyanidins, and phenolic acids decreased significantly during the withering period. The results of proteomics indicated that the degradation of proteins accounted for the increase in free amino acid levels; the weakened biosynthesis, in addition to oxidation, also contributed to the decrease in flavonoid levels; the degradation of ribonucleic acids contributed to the increase in nucleoside and nucleotide levels during the withering period. In addition, the drying process was found to slightly promote the formation of white tea taste. Our study provides a novel characterization of white tea taste formation during processing.