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16 pages, 3131 KiB

Open AccessArticle

Comparison of Untargeted and Markers Analysis of Volatile Organic Compounds with SIFT-MS and SPME-GC-MS to Assess Tea Traceability

by Marine Reyrolle, Valérie Desauziers, Thierry Pigot, Lydia Gautier and Mickael Le Bechec

Foods 2024, 13(24), 3996; https://doi.org/10.3390/foods13243996 - 11 Dec 2024

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Abstract

Tea is one of the most consumed beverages in the world and presents a great aromatic diversity depending on the origin of the production and the transformation process. Volatile organic compounds (VOCs) greatly contribute to the sensory perception of tea and are excellent [...] Read more.

Tea is one of the most consumed beverages in the world and presents a great aromatic diversity depending on the origin of the production and the transformation process. Volatile organic compounds (VOCs) greatly contribute to the sensory perception of tea and are excellent markers for traceability and quality. In this work, we analyzed the volatile organic compounds (VOCs) emitted by twenty-six perfectly traced samples of tea with two analytical techniques and two data treatment strategies. First, we performed headspace solid-phase microextraction gas chromatography–mass spectrometry (HS-SPME-GC-MS) as the most widely used reference method for sanitary and quality controls of food. Next, we analyzed the samples with selected-ion flow-tube mass spectrometry (SIFT-MS), an emerging method for direct analysis of food products and aroma. We compared the performances of both techniques to trace the origin and the transformation processes. We selected the forty-eight most relevant markers with HS-SPME-GC-MS and evaluated their concentrations with a flame ionization detector (FID) on the same instrument. This set of markers permitted separation of the origins of samples but did not allow the samples to be differentiated based on the color. The same set of markers was measured with SIFT-MS instrument without success for either origin separation or color differentiation. Finally, a post-processing treatment of raw data signals with an untargeted approach was applied to the GC-MS and SIFT-MS dataset. This strategy allowed a good discrimination of origin and color with both instruments. Advantages and drawbacks of volatile profiles with both instruments were discussed for the traceability and quality assessment of food. Full article

(This article belongs to the Special Issue Tea: Processing Techniques, Flavor Chemistry and Health Benefits)

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13 pages, 5501 KiB

Open AccessArticle

Determination of Geographical Origin of Southern Shaanxi Congou Black Teas Using Sensory Analysis Combined with Gas Chromatography–Ion Mobility Spectrometry

by Fei Yan, Xiaohua Chen, Dong Qu, Wei Huang, Lijuan He, Tian Wan, Lijun Zhang, Qi Wang and Ching Yuan Hu

Foods 2024, 13(23), 3904; https://doi.org/10.3390/foods13233904 - 3 Dec 2024

Viewed by 718

Abstract

Southern Shaanxi is one of China’s high-quality congou black tea production areas. However, the differences in geography, cultivation, and management techniques and production processes lead to uneven qualities of southern Shaanxi congou black tea in different production areas. This study used sensory analysis [...] Read more.

Southern Shaanxi is one of China’s high-quality congou black tea production areas. However, the differences in geography, cultivation, and management techniques and production processes lead to uneven qualities of southern Shaanxi congou black tea in different production areas. This study used sensory analysis combined with gas chromatography–ion mobility spectrometry (GC-IMS) to determine southern Shaanxi congou black teas’ geographical origin and volatile fingerprints to prevent economic losses caused by fraudulent labeling. A total of 61 volatile compounds were identified and quantified by GC-IMS. Three main aroma types were found by sensory analysis coupled with significant difference analysis, and a clear correlation between volatile compounds, aroma type, and geographical origin was found by sensory and gallery plot analysis. The black tea with a green/grassy-roast aroma type was mainly distributed in production areas with an altitude of 400–800 m and 1-pentanol, cyclohexanone, 1-penten-3-one, 2-heptanone, dihydroactinidiolide and butyrolactone were the key aroma markers. The black teas produced in production areas with an altitude of 800–1000 m mainly presented strong honey and caramel-like aromas, and sotolone, furaneol, and phenylacetaldehyde played an important role. These results will be helpful for discriminating black tea from different tea production areas in southern Shaanxi. Full article

(This article belongs to the Special Issue Tea: Processing Techniques, Flavor Chemistry and Health Benefits)

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Geographical growing areas of southern Shaanxi congou black tea. Full article ">Figure 2
Diagram of odor perceptions and intensities of southern Shaanxi congou black tea from different tea-producing areas obtained from sensory analysis. (a) Sensory analysis diagram of ZB039, MX013 and NZ066 balck tea. (b) Sensory analysis diagram of NQ009, MX004 and LY047 balck tea. (c) Sensory analysis diagram of XX002, XX007, XX038, LY016, ZB024, NZ027, CG012 and CG048 balck tea. * Significant difference at p < 0.05. Full article ">Figure 3
Two-dimensional spectra of volatile compounds of congou black tea from different tea-producing areas in southern Shaanxi. Full article ">Figure 4
Gallery plot of the volatile compounds of congou black tea from different tea-producing areas in southern Shaanxi. Full article ">Figure 4 Cont.
Gallery plot of the volatile compounds of congou black tea from different tea-producing areas in southern Shaanxi. Full article ">Figure 5
The dendrogram was obtained by cluster analysis of the volatile components in southern Shaanxi congou black teas using the systematic clustering method. Full article ">

11 pages, 2318 KiB

Open AccessArticle

Combined Analysis of Grade Differences in Lapsang Souchong Black Tea Using Sensory Evaluation, Electronic Nose, and HS-SPME-GC-MS, Based on Chinese National Standards

by Xiaomin Pang, Zi Yan, Jishuang Zou, Pengyao Miao, Weiting Cheng, Zewei Zhou, Jianghua Ye, Haibin Wang, Xiaoli Jia, Yuanping Li and Qi Zhang

Foods 2024, 13(21), 3433; https://doi.org/10.3390/foods13213433 - 28 Oct 2024

Viewed by 769

Abstract

Tea standard samples are the benchmark for tea product quality control. Understanding the inherent differences in Chinese national standards for Lapsang Souchong black tea of different grades is crucial for the scientific development of tea standardization work. In this study, Lapsang Souchong black [...] Read more.

Tea standard samples are the benchmark for tea product quality control. Understanding the inherent differences in Chinese national standards for Lapsang Souchong black tea of different grades is crucial for the scientific development of tea standardization work. In this study, Lapsang Souchong black tea of different grades that meet Chinese national standards was selected as the research object. The aroma characteristics were comprehensively analyzed through sensory evaluation, electronic nose, and HS-SPME-GC-MS (headspace solid-phase microextraction gas chromatography–mass spectrometry). The findings indicate that the higher-grade Lapsang Souchong has a higher evaluation score. The results of electronic nose analysis indicate that the volatiles with differences in tea of different grades were mainly terpenoids and nitrogen oxides. The results of HS-SPME-GC-MS analysis show that the odor characteristics of the super-grade samples are mainly floral and fruity, and these substances mainly include D-Limonene, 3,7-dimethyl-1,6-octadien-3-ol and 3-Hydroxymandelic acid, and ethyl ester. The primary aroma characteristics of the first-grade samples are floral, sweet, woody, and green, with key contributing compounds including 2-Furanmethanol, 1-Octen-3-ol, and 5-ethenyltetrahydro-α,α,5-trimethyl-cis-, 4,5-di-epi-aristolochene. The main aroma characteristics of the second-grade samples are green, herbal scent, and fruity, and the main substances include 3,7-dimethyl-1,6-octadien-3-ol, 2,3-dimethylthiophene, Dihydroactinidiolide, and Naphthalene-1-methyl-7-(1-methylethyl)-. It is worth noting that the second-grade samples contain a large amount of phenolic substances, which are related to the smoking process during processing. This study lays a solid foundation for the preparation of tea standard samples and the construction of the tea standard system. Full article

(This article belongs to the Special Issue Tea: Processing Techniques, Flavor Chemistry and Health Benefits)

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Sensory evaluation and electronic nose analysis of three grades of Lapsang Souchong black tea. (a) Radar chart displaying sensory scores. (b,c) Electronic nose evaluation results: (b) principal component analysis (PCA) illustrating the differentiation among grades; (c) radar chart depicting sensor responses. Grades A, B, and C correspond to special grade, first grade, and second grade, respectively. Full article ">Figure 2
Analysis of volatile compounds and their classification in three grades of Lapsang Souchong black tea: (a) Doughnut chart illustrating the distribution of volatile compounds across all samples. (b) Venn diagram comparing the presence of compounds in grades A, B, and C. (c) Principal component analysis (PCA) showcasing the variance among the grades. (d) Relative abundance of various volatile compounds in grades A, B, and C. (e) Heatmap representation of the normalized relative content of each volatile compound, with rows corresponding to tea samples and columns to individual volatile components. Grades A, B, and C denote special grade, first grade, and second grade, respectively. Full article ">Figure 3
Pairwise analysis of volatile metabolites in three grades of Lapsang Souchong black tea: (a–c) OPLS-DA analysis illustrating the differences between (a) grades A and B, (b) grades A and C, and (c) grades B and C; red dots indicate metabolites with significant differences, while green dots represent those without significant differences. (d–f) Heatmaps showing the volatile compound profiles for (d) A compared to B, (e) A compared to C, and (f) B compared to C. Differential metabolites were identified based on their variable importance in projection (VIP > 1). Full article ">Figure 4
Identification of differentially volatile metabolites among grades A, B, and C: (a) OPLS-DA models assessing the goodness of fit for grades A, B, and C. (b) Validation of the OPLS-DA analysis for the three grades of Lapsang Souchong black tea. (c) Loading plot from the OPLS-DA analysis highlighting the volatile metabolites, where red dots indicate significant differences and green dots indicate non-significant differences. (d) Heatmap representing the differential metabolites across the three grades. Full article ">

17 pages, 8873 KiB

Open AccessArticle

Effect of Isolated Scenting Process on the Aroma Quality of Osmanthus Longjing Tea

by Jianyong Zhang, Yuxiao Mao, Yongquan Xu, Zhihui Feng, Yuwan Wang, Jianxin Chen, Yun Zhao, Hongchun Cui and Junfeng Yin

Foods 2024, 13(18), 2985; https://doi.org/10.3390/foods13182985 - 20 Sep 2024

Viewed by 836

Abstract

Scenting is an important process for the formation of aroma quality in floral Longjing tea. There are differences in the aroma quality of osmanthus Longjing teas processed by different scenting processes. The efficient isolated scenting method was employed to process a new product [...] Read more.

Scenting is an important process for the formation of aroma quality in floral Longjing tea. There are differences in the aroma quality of osmanthus Longjing teas processed by different scenting processes. The efficient isolated scenting method was employed to process a new product of osmanthus Longjing tea in this study, and this was compared with the traditional scenting method. The volatile compounds of osmanthus Longjing tea were analyzed by a GC-MS instrument. In addition, the effects of scenting time and osmanthus consumption on the aroma quality of Longjing tea were studied. The results indicated that there were 67 kinds of volatile compounds in the osmanthus Longjing tea produced by the isolated scenting process (O-ISP), osmanthus Longjing tea produced by the traditional scenting process (O-TSP), and raw Longjing tea embryo (R), including alcohols, ketones, esters, aldehydes, olefins, acids, furans, and other aroma compounds. The proportions of alcohol compounds, ester compounds, aldehyde compounds, and ketone compounds in O-ISP were higher than in O-TSP and R. When the osmanthus consumption was increased, the relative contents of volatile aroma compounds gradually increased, which included the contents of trans-3,7-linalool oxide II, dehydrolinalool, linalool oxide III (furan type), linalool oxide IV (furan type), 2,6-Dimethyl cyclohexanol, isophytol, geraniol, 1-octene-3-alcohol, cis-2-pentenol, trans-3-hexenol, β-violet alcohol, 1-pentanol, benzyl alcohol, trans-p-2-menthene-1-alcohol, nerol, hexanol, terpineol, 6-epoxy-β-ionone, 4,2-butanone, 2,3-octanedione, methyl stearate, cis-3-hexenyl wasobutyrate, and dihydroanemone lactone. When the scenting time was increased, the relative contents of aroma compounds gradually increased, which included the contents of 2-phenylethanol, trans-3,7-linalool oxide I, trans-3,7-linalool oxide II, dehydrolinalool, isophytol, geraniol, trans-3-hexenol, β-ionol, benzyl alcohol, trans-p-2-menthene-1-ol, nerol, hexanol, terpineol, dihydroβ-ionone, α-ionone, and β-ionone,6,10. The isolated scenting process could achieve better aroma quality in terms of the floral fragrance, refreshing fragrance, and tender fragrance than the traditional scenting process. The isolated scenting process was suitable for processing osmanthus Longjing tea with high aroma quality. This study was hoped to provide a theoretical base for the formation mechanism and control of quality of osmanthus Longjing tea. Full article

(This article belongs to the Special Issue Tea: Processing Techniques, Flavor Chemistry and Health Benefits)

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16 pages, 6888 KiB

Open AccessArticle

Effects of Different Fermentation Methods on Flavor Quality of Liupao Tea Using GC-Q-TOF-MS and Electronic Nose Analyses

by Xiaohui Zhou, Di Tian, Hongjie Zhou, Rui Dong, Chenyang Ma, Ling Ren, Xueyi Yang, Qingyi Wang, Ning Chen, Liubo Yang, Xuan Tang, Yixin Bi, Yapeng Liu, Xiujuan Deng, Baijuan Wang and Yali Li

Foods 2024, 13(16), 2595; https://doi.org/10.3390/foods13162595 - 19 Aug 2024

Viewed by 1010

Abstract

To further develop Liupao tea products and enhance their flavor, this study investigated the effects of different fermentation methods on the aroma quality of Liupao tea. The aroma quality of Liupao tea was comprehensively analyzed using HS-SPME in combination with GC-Q-TOF-MS, electronic nose, [...] Read more.

To further develop Liupao tea products and enhance their flavor, this study investigated the effects of different fermentation methods on the aroma quality of Liupao tea. The aroma quality of Liupao tea was comprehensively analyzed using HS-SPME in combination with GC-Q-TOF-MS, electronic nose, and sensory evaluations. Electronic nose detection showed that the aroma fingerprints of Liupao tea samples with different fermentation methods were different. Sulfides, alcohols, ketones, and methyls were the main aroma categories affecting the aroma of the four groups of Liupao tea samples. GC-Q-TOF-MS analysis revealed significant differences in the composition of aroma components among the four fermentation methods of Liupao tea (p < 0.05). Furthermore, the total amount of aroma compounds was found to be highest in the group subjected to hot fermentation combined with the inoculation of Monascus purpureus (DMl group). Based on the OPLS-DA model, candidate differential aroma components with VIP > 1 were identified, and characteristic aroma compounds were selected based on OAV > 10. The key characteristic aroma compounds shared by the four groups of samples were 1,2,3-Trimethoxybenzene with a stale aroma and nonanal with floral and fruity aromas. The best sensory evaluation results were obtained for the DMl group, and its key characteristic aroma compounds mainly included 1,2,3-Trimethoxybenzene, nonanal, and cedrol. The results of this study can guide the development of Liupao tea products and process optimization. Full article

(This article belongs to the Special Issue Tea: Processing Techniques, Flavor Chemistry and Health Benefits)

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Figure 1
Aroma profile of different Liupao teas by QDA. (a) Electronic nose odor fingerprints of different Liupao tea (b). Full article ">Figure 2
Proportion of volatile components in four types of tea samples (a) Histogram of the total concentration of volatile compounds of four samples (ns: p > 0.05, * p < 0.05, **: p < 0.01, ***: p < 0.001) (b). Volatile aroma species of four groups samples (c). Four groups of samples of different types of aroma content line chart (d). Full article ">Figure 3
Scatter plot of PCA model scores of volatile compounds of tea samples. (a) Hierarchical cluster analysis (HCA) plot. (b) OPLS–DA model score of volatile compounds of tea samples. (c) Permutation test for validation of OPLS–DA model. (d) Differential compounds VIP value plot (Cl vs. CMl). (e) Differential compounds’ VIP value plot Cl vs. Dl). (f) Differential compounds’ VIP value plot (CMl vs. DMl). (g) Differential compounds’ VIP value plot (Dl vs. DMl). (h) Screening criterion for differential aroma compounds with VIP > 1, p < 0.05 and top 20 VIP ranking. Full article ">Figure 4
Flavor wheel of key volatile compounds in the four types of Liupao tea samples. DMl group (a); Dl group (b); Cl group (c); CMl group (d); cumulative quantitative bar chart of OAV (e). Full article ">Figure 5
The key volatile compounds in the four types of samples (OAV > 10). Full article ">Figure 6
Pathways for the formation of key characteristic aromatic compounds. Full article ">

19 pages, 3432 KiB

Open AccessArticle

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

by Yanqin Yang, Qiwei Wang, Jialing Xie, Yuliang Deng, Jiayi Zhu, Zhongwen Xie, Haibo Yuan and Yongwen Jiang

Foods 2024, 13(5), 728; https://doi.org/10.3390/foods13050728 - 28 Feb 2024

Cited by 5 | Viewed by 1718

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Tea: Processing Techniques, Flavor Chemistry and Health Benefits)

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Graphical abstract

Graphical abstract
Full article ">Figure 1
PLS-DA of SFABT over the entire manufacturing process via the GC-E-Nose. (A) Scores of PLS-DA (R2Y = 0.963 and Q2 = 0.869). (B) Cross-validation by a 200-fold permutation test (R2 = 0.357 and Q2 = −0.626). Full article ">Figure 2
Fingerprints of SFABT during the entire manufacturing process obtained from GC-IMS: (A) two-dimensional topographic plot and (B) difference comparison plots. Full article ">Figure 3
Fingerprints of SFABT during the entire manufacturing process obtained from GC-IMS. (A) Fingerprints of all the samples. The suffix -M represents a monomer of volatile components, while the suffix -D represents a dimer. (B) Scores of PLS-DA with R2Y = 0.996 and Q2 = 0.992. (C) Cross-validation through a 200-fold permutation examination, yielding an R2 score of 0.169 and Q2 at −0.688. Full article ">Figure 4
The volatiles identified throughout the entirety of the manufacturing process for SFABT via GC-MS. (A) Comparative proportions of volatiles across distinct categories. (B) Dynamic alterations of various volatile classifications throughout the complete manufacturing process. Full article ">Figure 5
The results of multivariate statistical analysis obtained from GC-MS. (A) Scores of OPLS-DA (R2Y = 0.695 and Q2 = 0.655). (B) Cross-validation through a 200-fold permutation examination, yielding an R2 score of 0.38 and Q2 at −0.764. (C) Heat map analysis. Full article ">Figure 6
Possible formation mechanisms of key odorants in SFABT. Full article ">

14 pages, 6154 KiB

Open AccessArticle

Comparative Metabolomics Study of Four Kinds of Xihu Longjing Tea Based on Machine Fixing and Manual Fixing Methods

by Hongchun Cui, Yuxiao Mao, Yun Zhao, Haitao Huang, Junfeng Yin, Jizhong Yu and Jianyong Zhang

Foods 2023, 12(24), 4486; https://doi.org/10.3390/foods12244486 - 14 Dec 2023

Cited by 2 | Viewed by 1269

Abstract

China Xihu Longjing tea is famous for its good flavor and quality. However, information on its related metabolites, except for flavonoids, is largely deficient. Different processing methods for China Xihu Longjing tea fixing—by machines at both the first and second step (A1), first [...] Read more.

China Xihu Longjing tea is famous for its good flavor and quality. However, information on its related metabolites, except for flavonoids, is largely deficient. Different processing methods for China Xihu Longjing tea fixing—by machines at both the first and second step (A1), first step by machine and second step by hand (A2), first step by hand and second step by machine (A3), and by hand at both the first and second step (A4)—were compared using a UHPLC–QE–MS-based metabolomics approach. Liquid chromatography–mass spectrometry was used to analyze the metabolic profiles of the processed samples. A total of 490 metabolites (3 alkaloids, 3 anthracenes, 15 benzene and substituted derivatives, 2 benzopyrans, 13 coumarins and derivatives, 128 flavonoids, 4 furanoid lignans, 16 glycosides and derivatives, 5 indoles and derivatives, 18 isocoumarins and derivatives, 4 chalcones and dihydrochalcones, 4 naphthopyrans, 3 nucleosides, 78 organic acids and derivatives, 55 organooxygen compounds, 5 phenols, 109 prenol lipids, 3 saccharolipids, 3 steroids and steroid derivatives, and 17 tannins) were identified. The different metabolic profiles were distinguished using PCA and OPLS-DA. There were differences in the types and contents of the metabolites, especially flavonoids, furanoid lignans, glycosides and derivatives, organic acids and derivatives, and organooxygen compounds. There was a positive correlation between flavonoid metabolism and amino acid metabolism. However, there was a negative correlation between flavonoid metabolism and amino acid metabolism, which had the same trend as prenol lipid metabolism and tannins. This study provides new valuable information regarding differences in the metabolite profile of China Xihu Longjing tea processed based on machine fixing and on manual fixing methods. Full article

(This article belongs to the Special Issue Tea: Processing Techniques, Flavor Chemistry and Health Benefits)

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11 pages, 1503 KiB

Open AccessArticle

Compositions and Antioxidant Activity of Tea Polysaccharides Extracted from Different Tea (Camellia sinensis L.) Varieties

by Kunyue Xiao, Yutao Shi, Sisi Liu, Yuqiong Chen, Dejiang Ni and Zhi Yu

Foods 2023, 12(19), 3584; https://doi.org/10.3390/foods12193584 - 27 Sep 2023

Cited by 2 | Viewed by 1880

Abstract

Tea polysaccharide (TPS) is a bioactive compound extracted from tea. It has raised great interest among researchers due to its bioactivity. However, few studies focused on the diversity of TPS in its compositions and antioxidant activity. This study collected 140 different tea varieties [...] Read more.

Tea polysaccharide (TPS) is a bioactive compound extracted from tea. It has raised great interest among researchers due to its bioactivity. However, few studies focused on the diversity of TPS in its compositions and antioxidant activity. This study collected 140 different tea varieties from four tea germplasm gardens in China, and their TPSs in tea shoots were extracted. The extraction efficiency, composition contents, including neutral sugar, uronic acid, protein, and tea polyphenols, and the scavenging abilities of hydroxyl radical (·OH) and superoxide radical (O2-·) of 140 TPSs were determined and analyzed. The results showed significant differences in the compositions and antioxidant activities of TPS extracted from different tea varieties. By applying hierarchical clustering analysis (HCA), we selected nine tea varieties with high TPS extraction efficiency and 26 kinds of TPS with high antioxidant capacity. Full article

(This article belongs to the Special Issue Tea: Processing Techniques, Flavor Chemistry and Health Benefits)

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Review

Jump to: Research

21 pages, 1634 KiB

Open AccessReview

Research Progress on the Effect and Mechanism of Tea Products with Different Fermentation Degrees in Regulating Type 2 Diabetes Mellitus

by Guangneng Li, Jianyong Zhang, Hongchun Cui, Zhihui Feng, Ying Gao, Yuwan Wang, Jianxin Chen, Yongquan Xu, Debao Niu and Junfeng Yin

Foods 2024, 13(2), 221; https://doi.org/10.3390/foods13020221 - 10 Jan 2024

Cited by 3 | Viewed by 3312

Abstract

A popular non-alcoholic beverage worldwide, tea can regulate blood glucose levels, lipid levels, and blood pressure, and may even prevent type 2 diabetes mellitus (T2DM). Different tea fermentation levels impact these effects. Tea products with different fermentation degrees containing different functional ingredients can [...] Read more.

A popular non-alcoholic beverage worldwide, tea can regulate blood glucose levels, lipid levels, and blood pressure, and may even prevent type 2 diabetes mellitus (T2DM). Different tea fermentation levels impact these effects. Tea products with different fermentation degrees containing different functional ingredients can lower post-meal blood glucose levels and may prevent T2DM. There are seven critical factors that shed light on how teas with different fermentation levels affect blood glucose regulation in humans. These factors include the inhibition of digestive enzymes, enhancement of cellular glucose uptake, suppression of gluconeogenesis-related enzymes, reduction in the formation of advanced glycation end products (AGEs), inhibition of dipeptidyl peptidase-4 (DPP-4) activity, modulation of gut flora, and the alleviation of inflammation associated with oxidative stress. Fermented teas can be used to lower post-meal blood glucose levels and can help consumers make more informed tea selections. Full article

(This article belongs to the Special Issue Tea: Processing Techniques, Flavor Chemistry and Health Benefits)

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The formation factors of T2DM. High-sugar and high-fat diet (HS-HFD). Downward arrow means down-regulation. Full article ">Figure 2
The regulatory effect of different fermented teas on organs of patients with T2DM. Epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), epicatechin (EC); theaflavin (TF-1), theaflavin-3-gallate (TF-3), theaflavin-3′-gallate (TF-3′), theaflavin-3-3′-gallate (TF-3-3′); glucose transporters (GLUTs); calmodulin-dependent protein kinase kinase 2 (CaMKK2) -adenosine monophosphate activates protein kinases (AMPK); insulin receptor substrate 1/phosphoinositide 3-kinase/protein kinase B (IRS1/PI3K/AKT); sirtuin 6/adenosine monophosphate activated protein kinase/sterol regulatory element-binding protein-1/fatty acid synthase (SIRT6/AMPK/SREBP-1/FASN); dipeptidyl peptidase-4 (DPP-4); sodium-glucose cotransporter-2 (SGLT2); short-chain fatty acids (SCFAs). Downward arrow means down-regulation. Upward arrow means up-regulation. Full article ">Figure 3
Mechanism of different fermentation degree tea in balancing postprandial blood glucose. (A): Inhibition of digestive enzymes. (B): Effect on glucose transport. (C): Inhibition of gluconeogenesis pathway. (D): Inhibition of formation of AGEs. (E): Inhibition of DPP-4 activity. (F): Regulation of gut microbiota. Blood glucose levels (BGL); glucokinase (GK); glycogen synthase kinase (GSK); pyruvate carboxylase (PC); phosphoenolpyruvate carboxy kinase (PEPCK); gructose-1,6-bisphosphatase (FBP); glucose-6-phosphatase (G6P); glyoxal (GO), methylglyoxal (MGO),3-meoxyglucosone (3-DG); superoxide dismutase (SOD); catalase (CAT); glutathione (GSH); glutathione peroxidase (GSH-PX). Downward arrow means down-regulation. Upward arrow means up-regulation. Full article ">

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