Tea Aroma Research Articles

Lifestyle of Women In Tea Garden Community: A Systematic Literature Review

Tea is integral part of our society. Popularity of tea as a beverage was established by the British East India Company. However, the soothing aroma and delicate beauty of tea conceal the harsh reality of the heavy labor of tea garden workers, specifically women. More than fifty percent of workers in tea industry are women. So, the economic role of women in tea industry is very crucial. In the tea garden community women are the primary breadwinners and men livelihood depend on them. They manage both domestic responsibilities and work in tea estate from early in the morning to evening. Despite this, in their community women receive limited recognition and value. They also struggle for decent education, healthcare, living conditions, and safety. To better understand their circumstances, a systematic review was conducted to provide an overview of lifestyle of the female tea garden community. Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) was used to identify, screening the article then eligible articles were included. A total number of 932 studies were eligible for systematic review. Most of the studies were obtained from Google Scholar, followed by Science Direct and Eric. Only 16 studies were included in our study. Based on these studies, educational and financial condition are the major factor that effect their lifestyle. Studies pointed out tea community women are in most vulnerable position. Every aspect of their lifestyle is filled with difficulties from their early marriage to discrepancies in wages. So, there is a need for evidence based, comprehensive intervention procedures to uplift the women’s lifestyle of tea community.

Effectiveness of Brewing Time Antioxidant Functional Tea Drink from Forest Plant Leaves Of Sapar (Fordia splendidissima (Miq) Buijsen)

radiation, fast food, limited exercise time, stress due to work cannot be avoided, and also from the results of oxidation processes in the body. The development of degenerative diseases caused by free radicals can be inhibited by antioxidant compounds which are able to ward off free radicals. Therefore, the body needs important substances - antioxidants - that help protect it from attacks by free radicals and radical compounds. At certain concentrations, antioxidants can inhibit or slow down the damage caused by oxidative processes. Brewing time has an important role in determining the taste, aroma and active compound content of tea. The need for clear guidance regarding brewing times is becoming increasingly important, especially with the increasing interest in premium tea drinks and the influence of healthy lifestyles. This research aims to know the relationship between brewing time and tea quality in terms of dissolved antioxidant bioactivity content. This research activity tested the antioxidant activity of Sapar leaf tea with different brewing times, namely 3, 5, 10, 15, 20 and 30 minutes. Antioxidant activity testing uses the DPPH (1,1-Diphenyl-2-picrylhydrazy,) method. From the test results it was found that Sapar leaf tea (Fordia splendidissima (Miq) Buijsen) with a brewing time of 3 minutes had the highest antioxidant bioactivity with a radical inhibition value of 81.46% and the antioxidant bioactivity decreased as the brewing time for the leaf tea became longer.

Differences in the Quality Components of Wuyi Rock Tea and Huizhou Rock Tea.

Different origins and qualities can lead to differences in the taste and aroma of tea; however, the impacts of origin and quality on the taste and aroma characteristics of Wuyi rock tea and Huizhou rock tea have rarely been studied. In this study, high-performance liquid chromatography (HPLC), gas chromatography-mass spectrometry (GC-MS), and sensory evaluation methods were used to compare the quality components of Wuyi rock tea and Huizhou rock tea. The sensory evaluation showed that they each have their own characteristics, but the overall acceptability of Wuyi rock tea is ahead of Huizhou rock tea (p < 0.01). Biochemical experiments showed that HT was the highest in water leachables, about 43.12%; WT was the highest in tea polyphenols, about 14.91%; WR was the highest in free amino acids, about 3.38%; and the six rock teas had different health benefits. High-performance liquid chromatography showed that the theanine contents of WS and WR were 0.183% and 0.103%, respectively, which were much higher than those of other varieties. The OPLS-DA model predicted the factors that caused their different tastes, in order of contribution: CG > ECG > caffeine > EGCG > theanine. Ten volatile substances with OAV ≥ 1 and VIP > 1 were also found, indicating that they contributed greatly to the aroma characteristics, especially hexanoic acid, hexyl ester, and benzyl nitrile. The results of the correlation analysis showed that theanine was significantly correlated with taste (p < 0.05), and hexanoic acid, hexyl ester, and benzyl nitrile were significantly correlated with smell (p < 0.05). Substances such as theanine, hexanoic acid, hexyl ester, and benzyl nitrile give them their unique characteristics. Analysis of the differences in the quality components of the six rock teas can provide reference value for the cultivation and processing of rock teas.

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

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

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

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

Characteristic volatile compounds of white tea with different storage times using E-nose, HS-GC-IMS, and HS-SPME-GC-MS.

This paper studied the influence of storage duration on the flavor profile of white tea in detail, with samples produced between 2020 and 2023. Sensory evaluation was performed by quantitative descriptive analysis (QDA), followed by an in-depth aroma components analysis employing an electronic nose (E-nose), headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS), and headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). The QDA findings revealed a gradual transition in the flavor profile of white tea during storage, shifting from sweet, fruity, and floral to more herbal and stale characteristics. E-nose could well distinguish white tea with different storage times. A total of 55 and 53 volatile compounds were identified by HS-GC-IMS and HS-SPME-GC-MS, respectively. The orthogonal partial least squares-discriminant analysis models, based on HS-GC-IMS (R2Y=0.998, Q2=0.987) and HS-SPME-GC-MS (R2Y=0.984, Q2=0.993), successfully distinguished white tea samples stored for different storage times. Furthermore, 14 and 8 key compounds were screened based on the double variable criterion of one-way analysis of variance (p<0.05) and variable importance in projection (VIP) >1.2, and their content changes were also compared. It is the gradual decrease of important aroma components such as 2-hexenal, 2-methyl-2-hepten-6-one, linalool, and geraniol, which are positively correlated with sweet, fruity, and floral aromas, and the gradual increase of hexanoic acid, thiophene, propanoic acid, dimethyl disulfide, and borneyl acetate, which are positively correlated with herbal and stale flavor, that leads to the changes in flavor and aroma of white tea during storage. The results of the study provided a reference for elucidating the aroma characteristics of white tea at different storage times as well as a theoretical basis for the quality control of white tea.

Improving Quality Profiles of Summer-Autumn Tea Through the Synergistic Fermentation with Three Fungal Strains

The co-fermentation of summer-autumn tea with Aspergillus niger and Eurotium cristatum effectively reduces bitterness and astringency, enhances flavor and quality, and increases market appeal and economic value. This study investigated the dynamic changes in metabolites, flavor characteristics and quality indicators of summer-autumn tea during fermentation. Using headspace solid-phase microextraction gas chromatography (HS-SPME-GC-MS), 96 key metabolites were identified, significantly enhancing the tea's aroma and flavor. On the fourth day of fermentation, the content of ester catechins (EGCG, ECG) decreased by 79.44% and 79.57%, respectively, while non-ester catechins (EGC, C, EC) increased by 175.47%, 228.18%, and 138.73%, respectively. Additionally, the gallic acid content increased by 755.58%, along with rises in free amino acids and soluble sugars. Sensory evaluation focused on taste, soup color, and aroma, resulting in a total score of 80.67. The intensity of astringency, bitterness, and sourness in the tea infusion gradually decreased, while sweetness, umami, and aroma intensified. These findings underscore the significant role of the synergistic action of the three strains in developing the unique flavor profile of summer-autumn tea during fermentation. This research lays the foundation for quality control and resource development in the processing of summer-autumn tea.

Role of Aspergillus tubingensis M16 in the quality development of instant Sichuan south-road dark tea produced by submerged fermentation

Sichuan South-road Dark Tea (SSDT) is a popular health drink in southwest China. To make its consumption more convenient, instant SSDT (ISSDT) was produced from Maozhuang tea and Aspergillus tubingensis M16 through submerged fermentation. Integrated analysis of metabolomics, proteomics, sensory quality and the unique glycoside hydrolase (GH) gene expression revealed that the ISSDT fermented by A. tubingensis M16 has a distinctive SSDT flavor with excellent aged tea aroma and mellow taste. A. tubingensis M16 induced significant changes in flavonoids, organooxygen compounds, carboxylic acids, benzene and substituted derivatives, etc., especially a sharp reduction of certain bitterness- and astringency-related chemicals in ISSDT broth. A large number of microbial extracellular GHs showed a higher abundance in the fermented ISSDT broth than in A. tubingensis M16 thallus, which, together with certain glycosyltransferase and other enzymes, encompassing alpha-galactosidase, beta-glucosidase, glucan endo-1,6-glucosidase, rhamnogalacturonase, UDP-glucose: glycoprotein glucosyltransferase, threonine aldolase, etc., were hypothesized to be highly involved in the flavonoid transformation, carbohydrates and carbohydrate conjugates metabolism, glycosides compounds conversion, and amino acid-related metabolism of ISSDT. Moreover, the expression of unique GH genes of A. tubingensis M16 was significantly up-regulated in the fermentative anaphase. A. tubingensis M16 seems to be an important functional microbe for producing ISSDT or other SSDT-related products.

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

As albino tea under the geographical protection of agricultural products, Zheng'an Bai tea is not only rich in amino acids, polyphenols and other beneficial components for the human body, but also its leaf color will turn green as the temperature gradually rises, thus causing changes in the quality characteristics of tea leaves. However, these changing characteristics have not yet been revealed. In-depth quality analysis was carried out on the fresh leaves of Zheng'an Bai tea at four different developmental stages and four samples from the processing stage through extensive targeted metabolomics and SPME-GC-MS analysis. In this study, a total of 573 non-volatile metabolites were detected from the fresh leaves and processing samples of Zheng'an Bai tea, mainly including 96 flavonoids, 75 amino acids, 56 sugars and alcohols, 48 terpenoids, 46 organic acids, 44 alkaloids, and 39 polyphenols and their derivatives. In fresh leaves, the most significant differential metabolites (VIP > 1, p < 0.05) among different samples mainly include substances such as ethyl gallate, theaflavin, isovitexin and linalool, while the main differential metabolites of samples in the processing stage include alkaloids, polyphenols and flavonoids such as zarzissine, methyl L-Pyroglutamate, theaflavin 3,3'-digallate, euscaphic acid and ethyl gallate. Overall, substances such as sugars and alcohols, alkaloids and polyphenols show the greatest differences between fresh leaves and the processing process. Meanwhile, 97 kinds of volatile metabolites were detected in these samples, most of which had a higher content in the fresh leaves. Moderate spreading is conducive to the release of the aroma of tea leaves, but fixation causes a sharp decrease in the content of most volatile metabolites. Ultimately, 9 volatile substances including geraniol, linalool, nerolidol, jasmone, octanal, 1-Nonanal, heptaldehyde, methyl salicylate and 1-Octen-3-ol were identified as the key aroma components (OAV >1) of Zheng'an Bai tea. In conclusion, this study has for the first time comprehensively revealed the quality change characteristics of fresh leaves at different developmental stages and during the processing of Zheng'an Bai tea, and provided a foundation for further process improvement.

Impact of spreading time on flavor quality in Duyun Maojian summer green tea

Duyun Maojian (DYMJ) is a prestigious green tea in China. The summer tea has higher tea polyphenols contents than spring tea, which reduces the green tea flavor quality and limits utilization of summer tea. Spreading is an important technology for optimizing tea quality, but its effect on DYMJ summer green tea is still unclear. In this study, we employed transcriptomics and volatile metabolomics to investigate the effect of spreading times (0, 1, 2, 3, 4, 5, 6, 7 h) on the flavor quality of DYMJ summer green tea. Sensory evaluation showed that the best taste was obtained at 4 h of spreading time. All indexes of main taste compounds reached peaking within 3–5 h (except for catechin). At 3–5 h of spreading time, important aromatic compounds with distinct floral and fruity flavors (such as phenylethanol, geraniol and cis-jasmone) were highest. Correlation analysis showed that there was a significant relationship between the main taste components and the tea aroma. In addition, transcriptomic analysis suggests that pathways related to hormone signaling and flavonoid biosynthesis in tea plants may play a key role in tea spreading. This study provides a theoretical framework for the processing of DYMJ summer green tea.

Multiomics correlation analysis on the mechanism of flavor substance formation during the processing of "Huanong 53″ black tea

A comprehensive investigation was conducted using targeted metabolomics, transcriptomics, and GC-MS techniques to study the dynamic changes in volatile and non-volatile metabolites, as well as gene transcription levels, in five processing stages of 'Huanong 53′ black tea (Camellia sinensis). A total of 2062 metabolites were identified, with flavonoids (428) and amino acids and their derivatives (194) being the main categories. The types and contents of flavor characteristic components of black tea changed most significantly during the withering and fermentation stages. Key elements of tea aroma composition, including linalool, benzeneacetaldehyde, and geraniol were found to correspond significantly with specific transcripts annotated as linalool synthase, aromatic aminotransferase, and geraniol diphosphate synthase, respectively. Throughout processing, a decrease in catechins and concomitant increase in oxidized catechin dimers, such as theaflavin (TF), was positively correlated with down-regulated flavonoid pathway gene expression and up-regulated expression of putative TF biosynthetic genes, including laccases, polyphenol oxidase, and a wide range of peroxidases. This study provides a comprehensive perspective on the changes in metabolites during black tea processing, and contributes to the research on improving black tea quality and the suitability of tea varieties for processing.

Evaluation of the phytochemical, bioactive compounds and descriptive sensory of encapsulated lingzhi (Ganoderma lucidum) extracts with combined wall materials for masking effect on the perception of off-flavour and bitterness

Lingzhi mushroom (Ganoderma lucidum) is known as a medicinal mushroom that can be utilized in various functional foods available in the market, including powders, dietary supplements, and tea. However, its use is limited due to factors such as bitterness, flavour, and astringency. The objective of this study is to characterize and quantify the sensory profile of Lingzhi mushroom samples (fresh, dried and Lingzhi extracts) using quantitative descriptive analysis and investigate the physicochemical and sensory properties of encapsulated Lingzhi extracts using different ratios of wall material (maltodextrin, gum Arabic and modified starch from rice flour). The optimal ratio for encapsulation involved 32.75 % maltodextrin, 42.25 % gum Arabic, and 25 % modified starch w/w. Three parallel experiments were performed under practical conditions, resulting in average encapsulation efficiencies of 88.39 ± 0.09 % for flavonoids 89.53 ± 0.06 % for polysaccharides and 0.31 ± 0.01 of water activity. The sensory descriptive analysis indicated the following ratings: brown sugar aroma (4.36 ± 0.17), earthy aroma (22.04 ± 0.12), nutty aroma (2.00 ± 0.01), fresh mushroom aroma (11.18 ± 0.19), dried Lingzhi aroma (3.08 ± 0.13), black tea aroma (4.50 ± 0.19), salty taste (1.00 ± 0.01), earthy flavour (23.14 ± 0.22) and Mushroomy (after taste) (2.06 ± 0.09), respectively. The flavour identified of Lingzhi extracts and encapsulated by gas chromatography electronic nose (GC-E-Nose). The result showed ten flavour compounds (Acetaldehyde, Methanethiol, Propanal, propane-2-one, Methyl acetate, 2-methyl propanal, Ethyl Acetate, Heptane, 1-Butanamine, 2-methyl butanal, Thiophene). Optimizing the encapsulation conditions has a significant impact on reducing off-flavours and bitterness. Comparing the flavour profiles of Lingzhi extracts with encapsulated Lingzhi extracts using gas chromatography electronic nose (GC-E-Nose). Encapsulation technology represents a burgeoning field that holds immense potential in ensuring the stability of functional ingredients and facilitating their incorporation into instant beverage products.

Comprehensive analysis reveals the contribution of “rolling-anaerobic” processing to the improved aroma, taste and color of GABA black tea

GABA black tea (GABT), produced by the combination of anaerobic treatment and Chinese traditional black tea processing technology, has a unique flavor and health benefits. However, how to manufacture high-quality GABT efficiently is the major challenge for this area. In this study, a processing improvement of multiple rolling-anaerobic treatment cycle was applied to prepare tailored GABTs, and their comprehensive quality including aroma, taste and color were analyzed. The sensory evaluation results showed that the improvement significantly optimized the overall GABT quality. The accumulation of linalool oxide Ⅰ, citronellol, etc. was the main reason for the superior aroma of tailored GABT, while the dynamic changes of sweet/umami amino acids, catechins and tea pigments played critical roles in the GABT taste and color quality formation during processing. Furthermore, correlation analysis was applied to determine the contribution of various processing steps. These findings provide a novel manufacturing method for high-quality GABT products.

The Effect of Temperature and Humidity on Yellow Tea Volatile Compounds during Yellowing Process.

Yellowing is the key processing technology of yellow tea, and environmental conditions have a significant impact on the yellowing process. In this study, volatile compounds of the yellowing process under different environmental conditions were analyzed by GC-MS. Results showed that a total of 75 volatile compounds were identified. A partial least squares discriminant analysis (PLS-DA) determined that 42 of them were differential compounds, including 12 hydrocarbons, 8 ketones, 8 aldehydes, 6 alcohols, and 8 other compounds, and compared the contents of differential compounds under the conditions of 40 °C with 90% humidity, 50 °C with 50% humidity, and 30 °C with 70% humidity, then analyzed the variation patterns of hydrocarbons under different yellowing environmental conditions. A 40 °C with 90% humidity treatment reduced the content of more hydrocarbons and increased the aldehydes. The content of 3-hexen-1-ol was higher when treated at 50 °C with 50% humidity and was consistent with the results of sensory evaluation. This study could provide a theoretical basis for future research on the aroma of yellow tea.

Investigation of the Effect of Fragrance-Enhancing Temperature on the Taste and Aroma of Black Tea from the Cultivar Camellia sinensis (L.) O. Kuntze cv. Huangjinya Using Metabolomics and Sensory Histology Techniques

Huangjinya has recently seen widespread adoption in key tea-producing areas of China, celebrated for its unique varietal traits. Its leaves are also used to produce black tea with distinctive sensory characteristics. The fragrance-enhancing (EF) process is essential in crafting Huangjinya black tea (HJYBT) and is significant in flavor development. However, the impact of EF on non-volatile metabolites (NVMs), volatile metabolites (VMs), and their interactions remains poorly understood. This study aims to investigate how EF temperatures (60 °C, 70 °C, 80 °C, 90 °C, and 110 °C) influence HJYBT flavor transformation. Quantitative descriptive analysis revealed that EF improved the color, aroma, and appearance of tea leaves. Moreover, after an EF temperature of 80 °C, the HJYBT exhibited lower bitterness and astringency, whereas floral, sweet, and fruity aromas became stronger. However, when EF temperatures exceeded 90 °C, a pronounced burnt aroma developed, with HJYBT at 100 °C exhibiting caramel and roasted notes. Partial least squares discriminant analysis indicated that geraniol and linalool contribute to floral and fruity aromas, while 2-ethyl-6-methyl-pyrazine, furfural, and myrcene are key volatiles for caramel and roast aromas. Heptanal, methyl salicylate, α-citral, 1-hexanol, and (E)-3-hexen-1-ol were found to modify the green and grassy odor. Overall, HJYBT treated at 80 °C EF exhibited the highest umami, sweetness, floral and fruity aromas, and overall taste, exhibiting the least astringency, bitterness, and green and grassy notes. These results provide a significant theoretical basis for enhancing HJYBT quality and selecting the optimal EF method.

Dynamic Changes in Aroma Compounds during Processing of Flat Black Tea: Combined GC-MS with Proteomic Analysis.

Flat black tea (FBT) has been innovatively developed to alleviate homogenisation competition, but the dynamic changes in aroma components during the process remain unclear. This study employed HS-SPME-GC-MS to analyse the aroma components of tea samples from various processing stages of FBT, and to make a comparative assessment with conventional strip-like Congou black tea (SBT). Additionally, a proteomic analysis was conducted on fresh leaves, withered leaves, and frozen-thawed leaves. Significant changes were observed in the aroma components and proteins during the processing. The results of the multivariate and odour activity value analysis demonstrated that the principal aroma components present during the processing of FBT were linalool, (E)-2-hexen-1-al, methyl salicylate, geraniol, hexanal, benzeneacetaldehyde, (Z)-3-hexenyl butyrate, dimethyl sulphide, 2-methylbutanal, 2-ethylfuran, nonanal, nonanol, 3-methylbutanal, (Z)-3-hexen-1-ol, 2-pentylfuran, linalool oxide I, and β-myrcene. Freezing-thawing and final roasting are the key processing steps for forming the aroma quality of FBT. The final roasting yielded a considerable quantity of pyrazines and pyrroles, resulting in a high-fried aroma, but caused a significant reduction in linalool, geraniol, β-myrcene, and esters, which led to a loss of floral and fruity aromas. The freezing-thawing treatment resulted in an accelerated loss of aroma substances, accompanied by a decrease in the expression level of lipoxygenase and 2-C-methyl-D-erythritol 2,4-cyclodiphosphate synthase. The formation of aroma substances in the linoleic acid metabolic pathway and terpenoid metabolic process was hindered, which had a negative impact on tea aroma. This study elucidates the causes of unsatisfactory aroma quality in tea products made from frozen tea leaves, providing theoretical support for the utilisation of frostbitten tea leaves, and helps us to understand the mechanism of aroma formation in black tea.

Thermochemical reactions in tea drying shape the flavor of tea: A review

Drying is the final and essential step in tea processing. It contributes a lot to the formation of tea flavor quality by a series of complicated and violent thermochemical reactions, such as degradation reaction, Maillard reaction, redox reaction, isomerization reaction, etc. However, the mechanism of specific thermochemical reaction is unclear. Here, by comprehensively summarizing the thermochemical reactions of the main chemicals, including polyphenols, lipids, amino acids and carbohydrates, etc., during tea drying with particularly focus on their contributions of thermal drying on the flavor including color, aroma, and taste, we found that thermal degradation is the dominant thermochemical reaction, directly affecting the taste and color of tea, and thermal oxidation of lipids and Maillard reaction mainly contribute to form tea aroma. More interesting was that high temperature enhanced nucleophilicity of phenolics, allowing them to easily trap carbonyl substances to form small molecular adducts (i.e. EPSFs) or polymers, which could interfere other thermochemical reactions, and then alter the flavor quality of tea. Over all, this review provides updated scientific evidence for in-depth exploration of thermochemical reactions towards tea precision processing.

Developed metabolomics approach reveals the non-volatile color-contributing metabolites during Keemun congou black tea processing

While key aroma and taste compounds of Keemun Congou black teas (KCBT) form during aeration and thermal stages, it is still unknown whether these processing stages also produce non-volatile color-contributing metabolites. Through integrating metabolomics with correlation and ridge regression analyses, 190 metabolites were identified as marker compounds that reclassified 15 KCBT samples collected from five processing stages into four groups. Meanwhile, the results of quantification and heatmap analysis showed that the concentrations of theaflavins and theasinensins significantly increased, as catechin decreased, after rolling, while flavonoid aglycones and polyunsaturated fatty acids increased throughout drying. Regression analysis between marker compound levels and total color difference values (∆E) revealed that the major color contributors were 3,5-dicaffeoylquinic acid, glucosyl-dehydrodigallic acid, theacitrin A, kaempferol-O-robinobioside, and (−)-epigallocatechin, with regression coefficients (absolute value) exceeding 4 × 10−2. Overall, the present study confirmed that rolling and drying were the two vital stages responsible for the color formation of KCBT.

Hyperspectral guidance for summer tea processing: Enhancing taste and aroma through short‐term cycled heaping

AbstractTo reduce the unpleasant flavor in tea infusion made from summer fresh leaves and lessen tea resource wastage, a short‐term cycled heaping method, addressing the temperature/moisture variations during prolonged heaping, was introduced to produce high‐quality yellow tea with significantly enhanced taste and aroma. Furthermore, a hyperspectral approach was developed to anticipate such improvements. Specifically, short‐term cycled heaping reduced summer tea's astringency and bitterness while increasing sweetness. Using near‐infrared spectroscopy, the multiplicative scatter correction (MSC)–support vector machine (SVM) model predicted tea umami with 66.25% precision and richness with 77.64% accuracy via standard normal variate (SNV)–SVM, based on epigallocatechin (EGC), epicatechin (EC), and gallocatechin gallate (GCG) variations. Aroma enhancement was forecasted by a hyperspectral–electronic nose regression model, achieving over 81.50% prediction accuracy for summer tea aromas in the visible spectrum and surpassing 73.45% in the near‐infrared domain, primarily attributed to pentanal, propanal, toluene, ethyl propionate, and 2,3‐pentanedione variations. Overall, hyperspectral‐guided summer tea processing, particularly for summer‐harvested leaves, shows potential in offering a valuable screening tool, enhancing quality, and efficiency in the tea industry and promoting sustainable development.

Revealing the differences in aroma of black tea under different drying methods based on GC–MS, GC-O

Drying greatly affects the aroma of black tea. In this study, the differences in aroma of black tea under hot-air drying (HD), sun drying (SD), and pan-fired drying (PD) were investigated through quantitative descriptive analysis. Headspace solid-phase microextraction and solvent assisted flavor evaporation combined with gas chromatography–mass spectrometry and gas chromatography-olfactory were used to analyze the overall aroma profile of black tea. Aroma extract dilution analysis and odor activity values revealed that 15 aroma-active compounds led to differences in aroma, namely linalool, geraniol, phenylethyl alcohol, phenylacetaldehyde, (Z) -linalool oxide (furanoid), β-damascenone, dimethyl sulfide, methional, 2-methylbutanal, 3-methylbutanal, methyl salicylate, β-myrcene, hexanal, 1-octen-3-ol, and heptanal. Among them, geraniol, linalool, and methional significantly enhanced the floral and roasty aroma of HD, while hexanal enhanced the green aroma of SD. Finally, our results were validated through aroma recombination and addition experiments. This study provides a theoretical basis for improving the aroma of black tea.