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Flavor Compounds in Tea: Formation, Transformation and Health Beneficial Effects

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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Natural Products Chemistry".

Deadline for manuscript submissions: closed (31 December 2022) | Viewed by 35560

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Special Issue Editors

Dr. Jianhui Ye

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Guest Editor

Tea Research Institute, Zhejiang University, Hangzhou 310013, China
Interests: tea polyphenols; tea volatiles; flavonoid biosynthesis; tea processing; tea chemistry; bioactivities; tea health benefits
Special Issues, Collections and Topics in MDPI journals

Dr. Liang-Yu Wu

E-Mail Website
Guest Editor

College of Horticulture, Fujian Agriculture and Forestry University, Fuzhou 350002, China
Interests: tea chemistry

Special Issue Information

Dear colleagues,

As a widely consumed beverage over the world, the growth of tea plants, the processing methods of teas, and their health benefits have been generating attention within both academia and industry. Tea contains various types of flavor matters, such as tea polyphenols, alkaloids, amino acids and volatiles, not only endowing teas with a unique taste and characteristic aroma but also contributing to their health benefits. The constitutions of flavor compounds are impacted by tea cultivars, agronomical practices, processing and storage. Many flavor compounds in teas are thermolabile or susceptible, which are transformed during processing and storage resulted in the generation of new compounds not originating from tea leaves. In recent years, multi-omics technology and an advanced data analysis approach have been applied to deepen our understanding of tea growth, tea processing and tea health benefits. More compounds are being discovered and their associations with the sensory profiles of teas as well as bioactivities are being investigated.

This Special Issue aims to collect research articles and review papers on the flavor compounds in teas, including their biosynthesis and regulation in tea plants, transformations during tea processing, as well as bioactivities and health benefits. Papers describing the formation, transformation or health benefits of specific flavor molecules are especially welcome.

Dr. Jianhui Ye
Dr. Liang-Yu Wu
Guest Editors

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Keywords

polyphenols
alkaloids
amino acids
volatiles
cultivation and breeding
tea processing
bioactivities
health beneficial effects

Published Papers (11 papers)

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Research

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13 pages, 1826 KiB

Open AccessArticle

Sensory-Guided Identification and Characterization of Kokumi-Tasting Compounds in Green Tea (Camellia sinensis L.)

by Jiachun Lu, Yanyan Cao, Yani Pan, Sifan Mei, Gang Zhang, Qiang Chu and Ping Chen

Molecules 2022, 27(17), 5677; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27175677 - 02 Sep 2022

Cited by 3 | Viewed by 1710

Abstract

The chemical substances responsible for the kokumi taste of green tea infusion are still unclear. Here, we isolated the kokumi compound-containing fractions from green tea infusion through ultrafiltration, and the major kokumi compounds were characterized as γ-Glu-Gln and γ-Glu-Cys-Gly (GSH) through ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS). The results indicated that peptides and amino acids were essential compounds in the kokumi-enriched fractions for conducting the sense of kokumi. L-theanine had an enhancing effect on the kokumi taste of green tea infusion, which was confirmed in the sensory reconstitution study. Thus, peptides, especially γ-Glu-Gln and GSH, are the major kokumi compounds in green tea infusion, which has the potential of improving the flavor of tea beverages. Full article

(This article belongs to the Special Issue Flavor Compounds in Tea: Formation, Transformation and Health Beneficial Effects)

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15 pages, 4008 KiB

Open AccessArticle

The Dynamic Change in Fatty Acids during the Postharvest Process of Oolong Tea Production

by Zi-Wei Zhou, Qing-Yang Wu, Yun Yang, Qing-Cai Hu, Zong-Jie Wu, Hui-Qing Huang, Hong-Zheng Lin, Zhong-Xiong Lai and Yun Sun

Molecules 2022, 27(13), 4298; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27134298 - 04 Jul 2022

Cited by 8 | Viewed by 1900

Abstract

As important factors to oolong tea quality, the accumulation and dynamic change in aroma substances attracts great attention. The volatile composition of oolong tea is closely related to the precursor contents. Fatty acids (FAs) and their derivatives are basic components of oolong tea fragrance during the postharvest process. However, information about the precursors of FAs during the postharvest process of oolong tea production is rare. To investigate the transformation of fatty acids during the process of oolong tea production, gas chromatograph–flame ionization detection (GC-FID) was conducted to analyze the composition of FAs. The results show that the content of total polyunsaturated FAs initially increased and then decreased. Specifically, the contents of α-linolenic acid, linoleic acid and other representative substances decreased after the turn-over process of oolong tea production. The results of partial least squares discrimination analysis (PLS-DA) showed that five types of FAs were obviously impacted by the processing methods of oolong tea (VIP > 1.0). LOX (Lipoxygenase, EC 1.13.11.12) is considered one of the key rate-limiting enzymes of long-chain unsaturated FAs in the LOX-HPL (hydroperoxide lyase) pathway, and the mechanical wounding occurring during the postharvest process of oolong tea production greatly elevated the activity of LOX. Full article

(This article belongs to the Special Issue Flavor Compounds in Tea: Formation, Transformation and Health Beneficial Effects)

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15 pages, 3556 KiB

Open AccessArticle

Identification of Key Aroma Compounds Responsible for the Floral Ascents of Green and Black Teas from Different Tea Cultivars

by Qi-Ting Fang, Wen-Wen Luo, Ya-Nan Zheng, Ying Ye, Mei-Juan Hu, Xin-Qiang Zheng, Jian-Liang Lu, Yue-Rong Liang and Jian-Hui Ye

Molecules 2022, 27(9), 2809; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27092809 - 28 Apr 2022

Cited by 11 | Viewed by 2560

Abstract

Chemicals underlying the floral aroma of dry teas needs multi-dimensional investigations. Green, black, and freeze-dried tea samples were produced from five tea cultivars, and only ‘Chunyu2’ and ‘Jinguanyin’ dry teas had floral scents. ‘Chunyu2’ green tea contained the highest content of total volatiles (134.75 μg/g) among green tea samples, while ‘Jinguanyin’ black tea contained the highest content of total volatiles (1908.05 μg/g) among black tea samples. The principal component analysis study showed that ‘Chunyu2’ and ‘Jinguanyin’ green teas and ‘Chunyu2’ black tea were characterized by the abundant presence of certain alcohols with floral aroma, while ‘Jinguanyin’ black tea was discriminated due to the high levels of certain alcohols, esters, and aldehydes. A total of 27 shared volatiles were present in different tea samples, and the contents of 7 floral odorants in dry teas had correlations with those in fresh tea leaves (p < 0.05). Thus, the tea cultivar is crucial to the floral scent of dry tea, and these seven volatiles could be promising breeding indices. Full article

(This article belongs to the Special Issue Flavor Compounds in Tea: Formation, Transformation and Health Beneficial Effects)

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14 pages, 3169 KiB

Open AccessArticle

Effect of Yellowing Duration on the Chemical Profile of Yellow Tea and the Associations with Sensory Traits

by Fang-Yuan Fan, Sen-Jie Zhou, Hong Qian, Bang-Zheng Zong, Chuang-Sheng Huang, Ruo-Lan Zhu, Hao-Wei Guo and Shu-Ying Gong

Molecules 2022, 27(3), 940; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27030940 - 29 Jan 2022

Cited by 13 | Viewed by 3294

Abstract

The yellowing process is the crucial step to form the characteristic sensory and chemical properties of yellow tea. To investigate the chemical changes and the associations with sensory traits during yellowing, yellow teas with different yellowing times (0–13 h) were prepared for sensory evaluation and chemical analysis. The intensities of umami and green-tea aroma were reduced whereas sweet taste, mellow taste and sweet aroma were increased under long-term yellowing treatment. A total of 230 chemical constituents were determined, among which 25 non-volatiles and 42 volatiles were the key chemical contributors to sensory traits based on orthogonal partial least squares discrimination analysis (OPLS-DA), multiple factor analysis (MFA) and multidimensional alignment (MDA) analysis. The decrease in catechins, flavonol glycosides and caffeine and the increase in certain amino acids contributed to the elevated sweet taste and mellow taste. The sweet, woody and herbal odorants and the fermented and fatty odorants were the key contributors to the characteristic sensory feature of yellow tea with sweet aroma and over-oxidation aroma, including 7 ketones, 5 alcohols, 1 aldehyde, 5 acids, 4 esters, 5 hydrocarbons, 1 phenolic compound and 1 sulfocompound. This study reveals the sensory trait-related chemical changes in the yellowing process of tea, which provides a theoretical basis for the optimization of the yellowing process and quality control of yellow tea. Full article

(This article belongs to the Special Issue Flavor Compounds in Tea: Formation, Transformation and Health Beneficial Effects)

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13 pages, 787 KiB

Open AccessArticle

Impact of Co-Delivery of EGCG and Tuna Oil within a Broccoli Matrix on Human Gut Microbiota, Phenolic Metabolites and Short Chain Fatty Acids In Vitro

by Meng Shi, Emma Watson, Michael Conlon, Luz Sanguansri and Mary Ann Augustin

Molecules 2022, 27(3), 656; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27030656 - 20 Jan 2022

Cited by 2 | Viewed by 1905

Abstract

(-)-Epigallocatechin gallate (EGCG) and tuna oil (TO) are beneficial bioactive compounds. EGCG, TO or a combination of, delivered by broccoli by-products (BBP), were added to an in vitro anaerobic fermentation system containing human fecal inocula to examine their ability to generate short-chain fatty acids (SCFA), metabolize EGCG and change the gut microbiota population (assessed by 16 S gene sequencing). Following 24 h fermentation, EGCG was hydrolyzed to (-)-epigallocatechin and gallic acid. EGCG significantly inhibited the production of SCFA (p < 0.05). Total SCFA in facal slurries with BBP or TO-BBP (48–49 µmol/mL) were significantly higher (p < 0.05) than the negative control with cellulose (21 µmol/mL). EGCG-BBP and TO-EGCG-BBP treatment increased the relative abundance of Gluconacetobacter, Klebsiella and Trabulsiella. BBP and TO-BBP showed the greatest potential for improving gut health with the growth promotion of high butyrate producers, including Collinsella aerofaciens, Bacillus coagulans and Lactobacillus reuteri. Full article

(This article belongs to the Special Issue Flavor Compounds in Tea: Formation, Transformation and Health Beneficial Effects)

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12 pages, 1219 KiB

Open AccessArticle

Green, Black and Rooibos Tea Inhibit Prostaglandin E2 Formation in Human Monocytes by Inhibiting Expression of Enzymes in the Prostaglandin E2 Pathway

by Alexander Hedbrant, Ingrid Persson, Ann Erlandsson and Jonny Wijkander

Molecules 2022, 27(2), 397; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27020397 - 08 Jan 2022

Cited by 4 | Viewed by 1724

Abstract

The formation of prostaglandin E2 (PGE2) is associated with adverse inflammatory effects. However, long-term treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) comes with risk of severe side effects. Therefore, alternative ways to inhibit PGE2 are warranted. We have investigated the effects of tea extracts and the polyphenols epigallocatechin gallate (EGCG) and quercetin on PGE2 formation, determined by immunoassay, and protein expression, determined by immunoblotting, of cytosolic phospholipase A2 (cPLA2), cyclooxygenase 2 (COX-2) and microsomal PGE synthase-1 (mPGES-1) in human monocytes. Green and black tea extracts, and with a lower potency, Rooibos tea extract, inhibited lipopolysaccharide (LPS) and calcium ionophore-induced PGE2 formation. In addition, all tea extracts inhibited the LPS-induced expression of mPGES-1, and the green and black tea extracts also inhibited, to a lesser extent, COX-2 expression. The tea extracts only marginally reduced cPLA2 expression and had no effect on COX-1 expression. EGCG, present in green and black tea, and quercetin, present in all three teas, also inhibited PGE2 formation and expression of mPGES-1, COX-2 and cPLA2. Cell-based and cell-free assays were also performed to evaluate direct effects on the enzymatic activity of COX and PGE synthases. Mainly, the cell-free assay demonstrated partial inhibition by the tea extracts and polyphenols. However, the inhibition required higher doses compared to the effects demonstrated on protein expression. In conclusion, green and black tea, and to a lesser extent Rooibos tea, are potent inhibitors of PGE2 formation in human monocytes, and mediate their effects by inhibiting the expression of the enzymes responsible for PGE2 formation, especially mPGES-1. Full article

(This article belongs to the Special Issue Flavor Compounds in Tea: Formation, Transformation and Health Beneficial Effects)

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14 pages, 4661 KiB

Open AccessArticle

Screening the Key Region of Sunlight Regulating the Flavonoid Profiles of Young Shoots in Tea Plants (Camellia sinensis L.) Based on a Field Experiment

by Jing Jin, Yi-Qing Lv, Wei-Zhong He, Da Li, Ying Ye, Zai-Fa Shu, Jing-Na Shao, Jia-Hao Zhou, Ding-Mi Chen, Qing-Sheng Li and Jian-Hui Ye

Molecules 2021, 26(23), 7158; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26237158 - 26 Nov 2021

Cited by 9 | Viewed by 1730

Abstract

Both UV and blue light have been reported to regulate the biosynthesis of flavonoids in tea plants; however, the respective contributions of the corresponding regions of sunlight are unclear. Additionally, different tea cultivars may respond differently to altered light conditions. We investigated the responses of different cultivars (‘Longjing 43’, ‘Zhongming 192’, ‘Wanghai 1’, ‘Jingning 1’ and ‘Zhonghuang 2’) to the shade treatments (black and colored nets) regarding the biosynthesis of flavonoids. For all cultivars, flavonol glycosides showed higher sensitivity to light conditions compared with catechins. The levels of total flavonol glycosides in the young shoots of different tea cultivars decreased with the shade percentages of polyethylene nets increasing from 70% to 95%. Myricetin glycosides and quercetin glycosides were more sensitive to light conditions than kaempferol glycosides. The principal component analysis (PCA) result indicated that shade treatment greatly impacted the profiles of flavonoids in different tea samples based on the cultivar characteristics. UV is the crucial region of sunlight enhancing flavonol glycoside biosynthesis in tea shoots, which is also slight impacted by light quality according to the results of the weighted correlation network analysis (WGCNA). This study clarified the contributions of different wavelength regions of sunlight in a field experiment, providing a potential direction for slightly bitter and astringent tea cultivar breeding and instructive guidance for practical field production of premium teas based on light regimes. Full article

(This article belongs to the Special Issue Flavor Compounds in Tea: Formation, Transformation and Health Beneficial Effects)

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19 pages, 3047 KiB

Open AccessArticle

Effects of Light Intensity and Spectral Composition on the Transcriptome Profiles of Leaves in Shade Grown Tea Plants (Camellia sinensis L.) and Regulatory Network of Flavonoid Biosynthesis

by Jian-Hui Ye, Yi-Qing Lv, Sheng-Rui Liu, Jing Jin, Yue-Fei Wang, Chao-Ling Wei and Shi-Qi Zhao

Molecules 2021, 26(19), 5836; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26195836 - 26 Sep 2021

Cited by 37 | Viewed by 3514

Abstract

Black net shade treatment attenuates flavonoid biosynthesis in tea plants, while the effect of light quality is still unclear. We investigated the flavonoid and transcriptome profiles of tea leaves under different light conditions, using black nets with different shade percentages, blue, yellow and red nets to alter the light intensity and light spectral composition in the fields. Flavonol glycosides are more sensitive to light intensity than catechins, with a reduction percentage of total flavonol glycosides up to 79.6% compared with 38.7% of total catechins under shade treatment. A total of 29,292 unigenes were identified, and the KEGG result indicated that flavonoid biosynthesis was regulated by both light intensity and light spectral composition while phytohormone signal transduction was modulated under blue net shade treatment. PAL, CHS, and F3H were transcriptionally downregulated with light intensity. Co-expression analysis showed the expressions of key transcription factors MYB12, MYB86, C1, MYB4, KTN80.4, and light signal perception and signaling genes (UVR8, HY5) had correlations with the contents of certain flavonoids (p < 0.05). The level of abscisic acid in tea leaves was elevated under shade treatment, with a negative correlation with TFG content (p < 0.05). This work provides a potential route of changing light intensity and spectral composition in the field to alter the compositions of flavor substances in tea leaves and regulate plant growth, which is instructive to the production of summer/autumn tea and matcha. Full article

(This article belongs to the Special Issue Flavor Compounds in Tea: Formation, Transformation and Health Beneficial Effects)

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11 pages, 12682 KiB

Open AccessCommunication

Effect of Ferrous Ion on Heat-Induced Aroma Deterioration of Green Tea Infusion

by Ying Gao, Jie-Qiong Wang, Jian-Xin Chen, Fang Wang, Gen-Sheng Chen, Jun-Feng Yin and Yong-Quan Xu

Molecules 2021, 26(14), 4255; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26144255 - 13 Jul 2021

Cited by 7 | Viewed by 2220

Abstract

Aroma deterioration is one of the biggest problems in processing tea beverages. The aroma of tea infusion deteriorates fast during heat sterilization and the presence of ferrous ion (Fe²⁺) aggravates it. The underlying mechanism remains unveiled. In this study, Fe²⁺ was verified to deteriorate the aroma quality of green tea infusion with heat treatment. Catechins were necessary for Fe²⁺-mediated aroma deterioration. By enhancing the degradation of catechins, Fe²⁺ dramatically increased the production of hydrogen peroxide (H₂O₂). Fe²⁺ and H₂O₂ together exacerbated the aroma of green tea infusion with heat treatment. GC-MS analysis revealed that the presence of Fe²⁺ enhanced the loss of green/grassy volatiles and promoted the formation of new volatiles with diversified aroma characteristics, resulting in a dull scent of green tea infusion. Our results revealed how Fe²⁺ induced aroma deterioration of green tea infusion with heat treatment and could help guide tea producers in attenuating the aroma deterioration of tea infusion during processing. Full article

(This article belongs to the Special Issue Flavor Compounds in Tea: Formation, Transformation and Health Beneficial Effects)

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Review

Jump to: Research

16 pages, 1222 KiB

Open AccessReview

Beneficial Effects of Green Tea EGCG on Skin Wound Healing: A Comprehensive Review

by Fa-Wei Xu, Ying-Li Lv, Yu-Fan Zhong, Ya-Nan Xue, Yong Wang, Li-Yun Zhang, Xian Hu and Wei-Qiang Tan

Molecules 2021, 26(20), 6123; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26206123 - 11 Oct 2021

Cited by 39 | Viewed by 6518

Abstract

Epigallocatechin gallate (EGCG) is associated with various health benefits. In this review, we searched current work about the effects of EGCG and its wound dressings on skin for wound healing. Hydrogels, nanoparticles, micro/nanofiber networks and microneedles are the major types of EGCG-containing wound dressings. The beneficial effects of EGCG and its wound dressings at different stages of skin wound healing (hemostasis, inflammation, proliferation and tissue remodeling) were summarized based on the underlying mechanisms of antioxidant, anti-inflammatory, antimicrobial, angiogenesis and antifibrotic properties. This review expatiates on the rationale of using EGCG to promote skin wound healing and prevent scar formation, which provides a future clinical application direction of EGCG. Full article

(This article belongs to the Special Issue Flavor Compounds in Tea: Formation, Transformation and Health Beneficial Effects)

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14 pages, 993 KiB

Open AccessReview

Antiviral Effects of Green Tea EGCG and Its Potential Application against COVID-19

by Ying-Qi Wang, Qing-Sheng Li, Xin-Qiang Zheng, Jian-Liang Lu and Yue-Rong Liang

Molecules 2021, 26(13), 3962; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26133962 - 29 Jun 2021

Cited by 36 | Viewed by 7318

Abstract

(–)-Epigallocatechin-3-O-gallate (EGCG), the most abundant component of catechins in tea (Camellia sinensis (L.) O. Kuntze), plays a role against viruses through inhibiting virus invasiveness, restraining gene expression and replication. In this paper, the antiviral effects of EGCG on various viruses, including DNA virus, RNA virus, coronavirus, enterovirus and arbovirus, were reviewed. Meanwhile, the antiviral effects of the EGCG epi-isomer counterpart (+)-gallocatechin-3-O-gallate (GCG) were also discussed. Full article

(This article belongs to the Special Issue Flavor Compounds in Tea: Formation, Transformation and Health Beneficial Effects)

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