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Review

The Chemistry, Sensory Properties and Health Benefits of Aroma Compounds of Black Tea Produced by Camellia sinensis and Camellia assamica

by
Asma Parveen
,
Chun-Yin Qin
,
Feng Zhou
,
Guoping Lai
,
Piaopiao Long
,
Mengting Zhu
,
Jiaping Ke
* and
Liang Zhang
*
State Key Laboratory of Tea Plant Biology and Utilization, Anhui Agricultural University, Hefei 230036, China
*
Authors to whom correspondence should be addressed.
Horticulturae 2023, 9(12), 1253; https://doi.org/10.3390/horticulturae9121253
Submission received: 11 October 2023 / Revised: 2 November 2023 / Accepted: 20 November 2023 / Published: 22 November 2023
(This article belongs to the Special Issue Medicinal, Aromatic, Spice Plants: Biodiversity, Phytochemistry, Bioactivity and Their Processing Innovation)
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Abstract

:
Black tea is frequently consumed worldwide and is renowned for having a distinctive scent. The volatile chemicals in tea are responsible for its aroma, which is important for sensory quality. The enzymatic and non-enzymatic processes that produce the compounds endowing black tea with its distinctive aroma are complex. Black tea is well known for its robust and complex aroma, which can vary based on the type of tea leaves used and processing technologies used. During the production of black tea, several intricate biological and chemical processes contribute to the aroma’s development. Different volatile chemicals are generated during the processing of black tea, which includes withering, rolling, fermentation (enzymatic oxidation), and drying. Various methods have been used to analyze and describe the aroma of black tea. Different methods, such as gas chromatography-mass spectrometry, olfactometry, and solid phase extraction, have been used to assess the fragrance of black tea. These methods evaluate characteristics including fruity, flowery, woody, malty, spicy, and smoky flavors. Phenyl ethyl alcohol, one-octen-3-ol, trans-linalool oxide (furanoid), geraniol, and nonanal are major aroma-active compounds in black tea. Sensory analytic techniques are used to assess black tea’s flavor and scent qualities. This assessment helps figure out the tea’s quality, unique characteristics, and even some unpleasant attributes. Black tea is mostly made from Camellia sinensis and Camellia assamica tea varieties. These two varieties, members of the Camellia genus, differ in their development patterns, leaf sizes, and chemical makeup, impacting how black tea’s scent is formed. When evaluating black tea made from Camellia sinensis and assamica, sensory analysis involved assessing the aroma when the tea was dry and, after brewing, noting any differences from other teas. This review focused on how key aromatic compounds are formed during the tea manufacturing process by Camellia sinensis and Camellia assamica black tea.

1. Introduction

Tea, a widely enjoyed beverage with numerous health advantages, is produced from the leaves and leaf buds of flowering plants categorized within the Camellia genus, which belongs to the Theaceae family. Tea plants used for producing various types of tea have generally been categorized into two primary varieties: Camellia sinensis var. sinensis, which is grown in temperate climates, and Camellia sinensis var. assamica, which is grown in tropical climates. More and more genetic research has clearly clarified that southwest China is an important origin of tea plants [1,2]. In the UK, Sealy named the tea plant “Camellia sinensis (L.) O. Kuntze” and identified two variations: “var. sinensis” (small-leaf variant) and “var. assamica” (large-leaf variant). The scientific name “Camellia sinensis (L.) O. Kuntze” has remained consistent despite subsequent studies [3].
Tea cultivation is rooted in southwest China, particularly Yunnan Province, where the tradition of brewing tea infusion is believed to have originated thousands of years ago [4]. Diverse manufacturing processes yield over 300 distinct tea varieties from Camellia sinensis leaves. Briefly, tea can be divided into six categories: green tea, white tea, yellow tea, oolong tea, black tea, and dark tea. Therein, black tea production involves the maceration of fresh tea leaves, resulting in the distinctive pigments of black tea, namely theaflavins (TFs) and thearubigins (TRs). These compounds form through the oxidation and polymerization of catechins during tea manufacturing [5]. Black tea covers over 70% of tea production worldwide (Figure 1) [6]. In addition, black tea is particularly popular in Europe and North America [7]. Worldwide, black tea production will reach 4.17 million tons in 2023, up 2.9% annually [8].
Tea’s aroma is a pivotal factor significantly influencing the character and quality of a tea [9]. Research has meticulously explored fluctuations in the levels of volatile compounds and aroma precursors throughout the fermentation phase of black tea [10,11]. The chemical composition of black tea remains dynamic during tea processing. Black tea’s volatile compounds primarily stem from the oxidation, degradation, and hydrolysis of aroma precursors, such as carotenoids, unsaturated fatty acids, and glycosidic aroma compounds [12]. The polyphenol oxidation process during black tea fermentation is not only critical in producing black tea pigments, but also participates in the formation of aroma compounds [13].
The cultivar, growing environment, and processing all result in the variances in volatile chemicals between different types of tea [14,15,16]. Overall, a complex process involving the interaction of numerous chemicals during tea production brings about the essential fragrance constituents of black tea scent. Black teas have a large number of volatile flavor compounds, although only a small number of them have an odor. Odor Activity Values (OAVs) are used to determine the overall aromatic quality of a substance. Such volatile flavor compounds are considered to be key volatile chemicals, active compounds, or key odorants [17,18].
The idea of tea sensory evaluation and human response are closely associated since sensory tests typically involve the use of the eyes, tongue, and nose. We are able to evaluate the sensory characteristics of product color, appearance, and taste of dry tea and its infusion. Therefore, it becomes appropriate to employ a technique to assess the qualities of the product and consumer acceptability using the senses. Tea aroma, a vital aspect of sensory quality, relies on volatile compounds. Quality attributes for aroma compounds are defined by a taste panel and, on occasion, by analytical methods such as mass spectrometry, gas chromatography, olfactometry (GC-MS/O), and electronic nose, in accordance with established protocols for sensory evaluation. Tea aroma, a vital aspect of sensory quality, relies on volatile compounds. Quality attributes for aroma compounds are defined using methods such as taste panels and analytical techniques like gas chromatography and mass spectrometry (Table 1). The five phases of tea preparation were examined for variations in volatile and non-volatile chemicals using GC–MS based metabolomic analyses [11].
This article details the sensory analysis methods used to assess the black tea scent profile. It explains the various scent constituents and how they impact the flavor of the tea. Additionally, this study highlights the importance of sensory analysis in establishing tea quality. The interactions between the manufacturing processes, including withering, rolling, fermentation, and drying, are also covered in this paper. In addition, this article also discusses the different aroma characteristics and chemical compositions of black tea made from Camellia sinensis and Camellia assamica (Figure 2), comparing the different types and concentrations of volatile chemicals. This study sheds important light on how different species of tea plants affect the scent that results. We used a thorough strategy with targeted keywords and reviewed multiple databases to achieve a thorough data collection process. The following keywords were utilized, either singly or in combination: processing, fermentation (enzymatic oxidation), black tea, aroma, molecular sensory, quantitative descriptive analysis, aroma extraction dilution analysis, and aroma production mechanism. These keywords were chosen because they were pertinent to the subject of our study and the particular goals we had in mind. The electronic bibliographic databases PubMed, ScienceDirect (Elsevier), Springer, and Nature yielded 466 articles when searched; after removing duplicates, the number of entries was reduced to 389. 108 records remained after the 389 records were sifted using preset inclusion criteria. These databases were chosen because they have a history of holding top-notch research articles on the topics we are interested in. Within these databases, we used advanced search capabilities and search filters to focus our search and find the most pertinent articles. To make sure that our information processing was accurate and consistent, we used standardized data extraction methodologies. We are sure that our strategy has allowed us to gather an extensive and thorough dataset to back up the research results.

2. The Main Aroma Compounds of Black Tea

Extensive research has delved into the chemical composition of tea leaves, with the primary constituents belonging to the polyphenol group accounting for 18 to 36% of the dry weight. Additionally, C. sinensis encompasses many chemical constituents, including methylxanthines, amino acids, chlorophyll, carotenoids, lipids, carbohydrates, vitamins, and an impressive roster of over 600 volatile compounds. The chemical composition of black tea comprises both volatile and non-volatile compounds. In tea, volatile organic components (VOCs) exist in exceedingly small quantities, comprising a mere 0.01% of the total dry weight. Despite their minuscule presence, these compounds profoundly influence tea products’ flavor due to their remarkably low threshold values and high odor units [34,35,36]. Some studies revealed volatile flavor compounds with floral and pleasant odor features like geraniol, phenyl ethyl alcohol, β-ionone, and linalool [26].
According to Wang et al. [27], distinctive volatile compounds can distinguish between various black teas. For instance, Indian black teas contain linalool, pentanoic acid, and hexanoic acid, while Chinese black teas feature phenylethyl alcohol. Sri Lankan black teas, on the other hand, are characterized by 1-methyl-naphthalene and β-ionon. Kangra orthodox black tea contains several major volatile constituents, including geraniol, linalool, (Z/E)-linalool oxides, (E)-2-hexenal, phytol, β-ionone, hotrienol, methylpyrazine, and methyl salicylate [36]. A comparative analysis of gas chromatography-olfactometry (GC-O) and odor activity value (OAV) calculations revealed specific odorants that significantly define distinct tea categories. Methyl salicylate in Ceylon tea, (E)-2-octenal in Assam tea (Camellia assamica), benzeneacetaldehyde in Keemun tea (Camellia sinensis), and linalool and trans-linalool oxide (furanoid) in Darjeeling tea (Camellia sinensis) emerged as the most definitive odor contributors in their respective tea categories [37].
According to certain researchers’ findings, compounds like linalool oxide I, II, and III, E,E-2,4-nonadienal,4,5-dimethyl-3-hydroxy-2,5-dihydrofuran-2-one, 1-octen-3-one, E,Z-2,6-nonadienal, and bis(2-methyl-3-furyl) disulfide displayed higher odor activity values in tea infusions, imparting floral, fatty, caramel, mushroom, cucumber, and cooked beef-like aromas. Overall, floral, mushroom-like, and caramel-like scents predominated in Hanzhong (Camellia sinensis) black tea infusions [20]. Su et al. [38] highlighted the positive influence of geraniol, linalool, and methyl salicylate on preserving the floral flavor characteristic of Keemun black tea. Steeping temperature plays a critical role in shaping the aroma of Yingde black tea infusion, as confirmed by a study combining instrumental analysis and sensory evaluations [39]. Xinyang black tea (XYBT) is recognized for its honey sugar-like aroma, a feature developed during fermentation.
Study have found that (E,E,Z)-2,4,6-nonatrienal is the primary odorant component of Darjeeling black tea [37]. The main aroma volatiles found in black tea are geraniol, linalool, (Z/E)-linalool oxides, (E)-2-hexenal, phytol, β-ionone, hotrienol, methylpyrazine and methyl salicylate [36].
Some researchers have also extensively demonstrated that Yunnan Congou black teas of varying grades exhibited similar aroma compositions but differed significantly in content. Superior Yunnan Congou black tea showcased higher levels of linalool, linalool oxide, α-terpineol, and geraniol than their inferior counterparts. Conversely, inferior Yunnan black tea had elevated levels of leaf aldehyde, benzaldehyde, and benzeneacetaldehyde. In conclusion, higher grade Yunnan Congou black tea exhibited superior fragrance quality. In contrast, all grades of Congou black tea have a robust fragrance, strong aroma, and distinctive taste compared to Dianhong black tea. Essential aroma-active compounds responsible for the fundamental Congou black tea aroma included linalool, (E)-furan linalool oxide, (Z)-pyran linalool oxide, methyl salicylate, β-myrcene, and phenylethyl alcohol, as identified through GC-O analysis of representative samples [40,41].
According to Wang et al. [31], phenylethyl alcohol, geraniol, linalool, α-ionone, cis-3-hexenyl hexanoate, and methyl salicylate play pivotal roles as major contributors to the floral fragrance of black tea. Notably, they are prominent in Jinxuan, Longjing, and Baihaozao varieties, constituting a substantial proportion of their aroma profiles. Sensory-directed aroma recombination and omission tests further confirmed the importance of phenylacetaldehyde, linalool, geraniol, and 3-ethyl-2,5-dimethylpyrazine in shaping the sensory characteristics of high-grade Dianhong black tea, which is dominated by floral, sweet, and caramel-like odors [42]. Moreover, linalool and benzeneacetaldehyde play significant roles in creating the sweet aroma of Assam black tea. These compounds exhibit significantly high OAVs and contribute to the sweet and floral attributes of the tea’s aroma [25]. Black teas with a sweat and floral aroma had much higher alcohol content than those with a sweet aroma alone. Linalool and its oxides, known as linalool oxides, were among the newly found alcohol components and were crucial odorants for black tea, which adds flowery and citrus flavors. Lilac, citrus, and mushrooms are among the scents connected to oct-1-en-3-ol, created by the oxidative breakdown of linoleic acid [39]. According to Schuh and Schieberle [37], black tea contains several aroma-active compounds, including geraniol, phenyl ethyl alcohol, methyl salicylate, phenylacetaldehyde, (E)-2-octenal, linalool, 1-octen-3-ol, benzyl alcohol, (Z)-jasmone, trans-linalool oxide (furanoid), and trans-β-ionone [25,43]. Linalool oxide has a sweet scent, while geraniol, phenylacetaldehyde, benzaldehyde, methyl salicylate, phenyl ethanol, and hexanal have a flowery fragrance. Additionally, as indicated, the ingredients give black tea its characteristic scent [44]. Forty-six aroma substances were identified in the two cultivars through GC-MS analysis, with nine exhibiting significant differences. These include heptaldehyde, furfural, 2,2,6-trimethylcyclohexanone, 2-pentadec-2-enylfuran, cis-3-hexenyl acetate, carveol, methyl salicylate, 5-methyl-2-hexanone, and hexanal in black tea from the Yunnan, Fujian, and Yichang regions [45].
The chemical compounds responsible for flavor and aroma in black tea are as follows: linalool and linalool oxide are responsible for the sweet flavor and citrus/lemon odor. Geraniol attributed rose odor and a floral flavor, and phenyl acetaldehyde is associated with distinctive hyacinth notes and floral flavors. Benzaldehyde brings fruity and almond smells—the fruity and minty smell given off by methyl salicylate, while phenyl ethanol is the source of the fruity and honey smell. Hexanal brings the grassy and fresh smell [46].
The color and taste of black tea are associated with TFs and TRs produced by catechins as they oxidize. They are responsible for giving black tea the dark color and astringent taste. Linalool is responsible for a floral and sweet aroma in black tea. Black tea has undergone complete fermentation (enzymatic oxidation), and its floral aroma contributes significantly to the aroma’s complexity. This article examines some of the most significant major fragrance components and their manufacturing technique (Table 2 and Figure 3).
Black tea produced by Camellia sinensis and Camellia assamica contains a variety of fragrance components, including:
➢
The floral-smelling molecule linalool is typically found in black tea, among other forms of tea. It improves the overall flavor and aroma of the tea.
➢
Another floral component found in black tea is geraniol. It has a rose-like scent and enhances the tea’s fragrant profile.
➢
Black tea contains a chemical called cis-jasmone, which has a fruity scent. It contributes to the tea’s characteristic aroma.
➢
Black tea typically contains the chemical methyl salicylate, which smells like wintergreen. It imparts a pleasant, minty undertone to the entire smell.
➢
Black tea contains the chemical trans-2-hexenal, which has a grassy, green scent. It adds to the tea’s energizing, earthy aroma.
➢
Black tea includes a component known as furfural, which has a distinctive caramel aroma. It imparts a sweet and roasted note to the entire scent.
➢
Black tea is given a sweet and floral aroma with benzyl alcohol.
➢
Black tea contains benzyl acetate, which contributes to black tea’s fruity and floral aroma.

2.1. The Main Processing Technologies of Black Tea

Black tea scent is created by a complicated process that includes numerous phases and chemical reactions. Tea leaves undergo a series of steps during processing, including withering, rolling, fermentation, and drying (Figure 4).

2.1.1. Withering

Fresh tea leaves (Camellia sinensis) are first withered by being exposed to air, having their moisture content decreased from 76 to 60–62%. Enzymes (phenol oxidase) in the tea leaves break down materials, including proteins and polyphenols, during withering and producing volatile compounds. High-molecular-weight phenol oxidase forms with catechol oxidation activity are typically generated during this step [49]. The withering process in black tea manufacturing plays a pivotal role in controlling the development of terpenoids, leading to an enhanced flavor quality in brewed tea. This process significantly influences black tea’s aroma and overall sensory characteristics [50]. The withering procedure encourages the softness of the tea leaves, and postharvest enzymatic reactions start to take place, which accelerates the chemical changes [51].

2.1.2. Rolling

Rolling is the next process after withering the leaves to liberate more volatile chemicals. Tea leaves (Camellia sinensis) that have withered are ruptured during the rolling process, which also damages the tea cells and releases oxidase, which initiates oxidation. The oxidation of the green tea leaves causes them to become bright copper in color while rolling. This technique determines the black tea’s curling. The cell walls of the leaves are destroyed during this process, allowing the enzymes and other chemicals to mingle and interact more easily. Fresh tea leaves will have their surfaces curled and disrupted by a light rolling motion and most TFs are produced during rolling [52]. Black tea’s aroma is largely produced by the hydrolysis of glycosidically bound fragrance precursors because the structure of the leaf cells is changed, and the substances are completely mixed during the rolling process [53]. A deep rolling may promote the release of endogenous enzymes and tea extract, causing the tea polyphenols and polyphenol oxidase (PPO) to mix in black tea [52].

2.1.3. Fermentation (Enzymatic Oxidation)

Fermentation plays an integral role in the black tea (Camellia sinensis) manufacturing process, exerting significant influence over the ultimate quality of the finished tea product. Unfermented tea leaves undergo a remarkable transformation during this critical phase, shifting from their initial green hue to a rich, coppery brown. Simultaneously, the grassy aroma evolves into a more delicate floral scent. This transformation hinges on a complex series of biochemical reactions, with the precise timing of fermentation cessation being paramount. Proven criteria are required to conclude the fermentation at the right moment, as both under-fermentation and over-fermentation can result in a decline in the quality of the final tea product [54]. Essential oils and amino acids are some examples of volatile and non-volatile substances, respectively [55].
Fermentation is the most crucial of the various stages of black tea manufacturing. This step delves into the process of protein degradation and the metabolic pathways of proteinaceous amino acids during enzymatic reactions that occur throughout fermentation, elucidating their impact on tea quality [56,57]. Enzymatic oxidation, sometimes referred to as fermentation, is the stage of tea processing that happens when the tea leaves’ cell walls disintegrate and their interiors become airborne. Oxygen exposure triggers a chemical interaction with the polyphenol-containing organic enzymes found inside the leaves. Among these enzymes, polyphenol oxidase is the most significant. Depending on the situation, the fermentation time is a crucial parameter in the production process of black tea (Camellia assamica). Some researchers focused on compounds like TFs and TRs and found that the ideal fermentation period for black tea changes depending on the type of fresh leaves utilized [44,58]. Enzymatic processes in tea leaves accelerate during fermentation, reducing the amount of bitter and astringent chemicals [47]. An electronic nose equipped with quartz crystal microbalance sensors can be used to track the ideal period for black tea fermentation since the fermentation process alters the fragrant volatiles in the tea [56]. Although fermentation is the term used to describe the part of the tea processing where the tea is left to brown and cure, this is actually a misnomer. When biological agents like yeast or bacteria break down organic material, taste, alcohol, and carbon dioxide are produced. This is known as true fermentation.

2.1.4. Drying

The last step is the drying process in black tea (Camellia sinensis), which ends the fermentation process and concentrates the volatile components that give the tea its aroma. The leaves are moved via “tiered dryers” on metal conveyor belts at the peak of the fermentation process. The tea is dried in heated air at 80–90 °C for about 20 min, which causes the cell fluid to adhere to the leaves and gives the tea its deep brown to black color. The leaves have a final humidity of between 5 and 6%.
Different drying techniques can result in the formation of various volatiles. Drying plays a crucial role in tea production as it can greatly affect the aroma of the tea due to the volatile chemicals created, altered, or lost by the tea molecules [59]. Some researchers investigated the effects of different drying techniques, such as conventional hot-air drying, microwave drying, far-infrared drying, halogen-lamp drying and halogen lamp–microwave combination drying processes in black tea. The study’s findings suggested that black tea that was microwave-treated exhibited the most favorable outcomes. In addition to flavonoids, essential oils and amino acids play pivotal roles in defining tea’s characteristic taste and aroma. Notably, the content of essential oils increases during the withering, rolling, and fermentation phases, diminishing during the drying step. However, this decline is compensated for by the Maillard reaction, an interaction between amino acids and sugars during drying that contributes positively to the tea’s flavor and color [60]. Hot-air drying is the most widely utilized drying technique for black tea. Following oxidation, rolling, and withering, hot air is used to dry the tea leaves in a regulated setting. In order to obtain the desired taste and fragrance profiles, this method is frequently used in the manufacture of black tea since it provides for fine control over temperature and humidity. Hot-air drying has gained popularity because it is more effective and can maintain consistent tea quality, even if traditional air drying is still utilized in some areas. Traditional drying techniques using hot air provide benefits such as ease of use and low cost, but have drawbacks such as extended drying times and significant nutritional loss. Drying takes place for about 10–15 min at 130–150 °C, followed by cooling outside of the drying apparatus for an hour, and finally drying for about 10 min at 80–90 °C.

2.2. The Formation Pathway of Critical Aroma Compounds

Many volatile substances, such as aldehydes, ketones, hydrocarbons, and terpenoids, contribute to black tea’s scent. These aromatic chemicals are created during tea preparation through a complicated series of chemical interactions (Figure 5). The volatile compounds that give finished teas their scents can be present in freshly picked leaves and those produced during production from precursors [12,61,62].
Volatile terpenoids (VTs), volatile fatty acid derivatives (FADVs), volatile amino acid derivatives (AADVs), and carotenoid-derived volatiles (CDVs) are the four main groups of tea volatiles based on their sources of synthesis [9,20]. When tea is processed, hydrolases like β-primeverosidase liberate volatiles typically attached to glycosidic chains in the fresh tea leaves [63]. Notably, specific compounds known as glycosidically bound volatiles (GBVs) play a significant role in the scents. According to Schwab et al. [61], these molecules consist of a sugar molecule attached to a volatile molecule. The degradation of carotenoids significantly increases the concentration of volatile flavor compounds (VFC), like β-ionone, α-ionone, β-damascone, and α-damascone, during the black tea leaf fermentation process [64].
Catechins and other flavonoids found in new tea leaves undergo oxidative degradation, which is the first step in synthesizing fragrance compounds in black tea. Tea leaves are stretched out and exposed to air when withering, which causes some of the polyphenols to oxidize partially. The polyphenol oxidase (PPO) enzyme catalyzes this oxidation process. The catechins are consequently transformed into intricate secondary metabolites like TFs and TRs. During metabolic processes, young isolated leaves undergo hydrolysis of proteins, fatty acids, glycosides, and other polysaccharides [65,66]. These compounds operate as the substance for the ultimate development of the tea’s flavors.
The taste and aroma of black tea are greatly affected by the presence of TFs and TRs. They are oxidative condensation products of catechins, diverse and highly polymerized molecules. TRs are dark brown to black pigments, whereas TFs are yellow to orange-red pigments with an astringent taste [10,67]. The tea leaves are dried and rolled in the final stage of processing, which results in the creation of scent molecules. Intriguingly, the Maillard reaction (a non-enzymatic browning reaction involving amino acids and reducing sugars) occurs during this step and produces furfural, a furan-like substance. This compound is responsible for the sweet and caramel-like fragrance that is a defining feature of black tea. Furthermore, β-cyclocitral imparts a refreshing fruity aroma to tea [22].
The fermentation process of black tea can produce many aroma components. In order to understand the creation of scent in black tea, a comprehensive analysis must be conducted to identify the key volatile molecules (FADVs, AADVs, VTs, or CDVs) involved in the fermentation process. This process is responsible for black tea’s sweet, floral, and fruity fragrances. For instance, by raising the quantity of appropriate precursors in fresh leaves by cultivation techniques, it could be used to enhance black tea’s scent quality [13].

2.3. The Variation in Critical Aroma Compounds during Processing

The quality of black tea can be enhanced by improving the processing methods. During the processing of black tea leaves (Camellia sinensis L.), intricate chemical changes take place [68]. The use of partial least-squares discriminant analysis and odor activity value analysis determined the five key components, including 3-carene, geraniol, β-myrcene, τ-cadinol, and β-ionone. In addition, a sensory investigation revealed that withering–shaking resulted in a black tea (Camellia sinensis) with a fruitier flavor while withering–withering produced a more floral taste [69].
During the rolling and fermentation of black tea (Camellia assamica), linalool, methyl salicylate, and C6-aldehydes produce a rose-like flavor, whereas unsaturated fatty acids decrease. During the withering and fermentation of black tea (Camellia assamica), trans-2-hexenal increases while cis-3-hexenal decreases [67,70]. Fruity and floral fragrances are significantly influenced by the volatile derivatives of phenylpropanoid/benzenoid [71]. According to Wang et al. [72], the fermentation process alters the chemical composition of tea, resulting in changes to its profile and volatile compounds. The sum of the five volatile chemicals (E)-benzaldehyde, indole, methyl-5-hapten-2-one, methyl salicylate, and 2-hexenal, were demonstrated to be capable of distinguishing between fermented and unfermented teas. According to Wu et al. [73], certain flavor components had dramatically different contents. Variously fermented teas suggested that certain active ingredients may distinguish different fermentation levels.
During withering, the breakdown of proteins may result in higher levels of amino acids. Proteins are broken down by an enzyme called peptidase [74]. Glycoside-bound volatiles in tea leaves (Camellia sinensis) are converted into free volatiles by β-primeverosidases, β-glucosidases, and glycosyl transferases, as extensively researched and functionally characterized [75,76]. It is essential to follow certain rules to fully appreciate the various sensory qualities of black tea, such as its color, aroma, taste, and health benefits. It is crucial to carefully monitor the fermentation process [44].

2.3.1. The Effects of Manufacturing Parameters on Critical Aroma Compounds

According to the research, the quality of tea leaves changed after processing due to considerable changes in the composition and concentration of the chemicals in tea leaves [7]. Black tea processing involves several chemical reactions that significantly alter the tea’s flavor and aroma profile. Some of the essential fragrance molecules and how they change as black tea (Camellia sinensis) is processed are as follows. Linalool: A terpene alcohol called linalool is responsible for black tea’s flowery and zesty scent. During the withering process, the concentration of linalool, a flavonoid glycoside compound, rises but falls during later processing phases. As the withering process progresses, the concentration of linalool, a flavonoid glycoside compound, increases. However, during the later processing phases, it decreases [77]. Geraniol: A terpene alcohol with a rose-like scent in black tea. During withering and fermentation, geranyl pyrophosphate oxidizes to produce geraniol. Its concentration increases in the first stages of fermentation [78]. Benzaldehyde/Phenylacetaldehyde has an almond-like, sweet scent in various nuts and fruits. This compound contributes to black tea’s nutty and fruity notes in its aroma [79].
The volatility of black tea may be affected by the temperature of the fermenting process. The relative volatile content might be more volatile at higher fermentation temperatures, including alcohols and alkenes at 31 °C, and esters and alkanes at 28 °C [80]. The process of withering can significantly impact fragrance components, for instance, increasing the concentrations of nerol, hexyl alcohol, and (E)-2-hexenoic acid, as well as increasing salicylic acid, benzyl alcohol, (Z)-2-pentenol, (E)-2-hexenal, and benzaldehyde acid and other aroma compound precursors [63]. According to Vuong et al. [81], amino acids contribute significantly to black tea’s nutritional value and overall quality. Lipoprotein synthesis is also crucial for aroma compound production [82]. Lipids degrade, which results in a drop in unsaturated fatty acid content to produce fragrance chemicals through oxidative cleavage during withering [83]. According to Soheilifard et al. [84], sensory evaluations revealed that withering the tea leaves for 16 h resulted in superior sensory quality attributes in the final tea product. This rolling action facilitated the release of sap and essential oils from the tea leaves, ultimately enhancing the tea’s flavor. According to Zheng et al. [85], fermentation increased the amounts of methyl salicylate and linalool, with its distinctive scent. The amount of (E)-2-hexenal chemicals was reduced by drying [68]. During the rolling and fermentation processes, there was a concurrent increase in trans-2-hexenal, linalool, and methyl salicylate. Regrettably, most of these volatile compounds were lost during the firing [65].
The quality of black tea greatly depends on the fermentation stage during processing. The suitable temperature of 28 °C is crucial for black tea fermentation. If the fermentation is carried out at high temperatures and for a longer duration such as 2–4 h or 55–110 min, it results in black tea with high levels of TF and intense color. However, when fermentation takes place at high temperatures, it leads to higher TR and total color levels, with lower values of TF, sensory rating, and brightness. Research showed that during the drying, the final step in tea production, the tea leaves were exposed to high temperatures over an extended period. As a result, more volatile chemicals were lost during the drying process, but the overall content of volatile compounds increased [86]. The main fragrance components in tea leaves converged and gathered throughout the drying process, creating its distinctive aroma [87]. The tea’s aroma was greatly influenced by processing, and a thorough examination of how the tea aroma changed throughout processing substantially impacted how the tea was processed. The tea aroma quality formation depends on the tea leaves’ volatile compounds.

2.3.2. The Effects of Season, Horticultural Practice, and Growing Area on the Aroma Compounds

Liu et al. [88] investigated how varying seasons exhibited distinct volatile chemicals and aroma precursors of Yingde black tea (Camellia assamica). The types and quantities of volatile compounds typically exhibited a declining trend followed by an increasing trend when the harvesting season changed, confirming that the development of tea scent is a dynamic process. Moreover, using large amounts of nitrogen fertilizer raised the amount of unsaturated fatty acids and decreased the aroma of black tea. To make high-quality tea requires the provision of the necessary amounts of macronutrients, nitrogen, phosphorus, and potassium along with other minor nutrients, since the quality of tea is strongly correlated with caffeine, catechins, amino acids, and volatile compounds in harvestable tea shoots (two or three succulent leaves along with a bud) [89]. Some researchers effectively determined the distinct scent compounds linked to distinct tea origins, offering insightful information about the aroma qualities of black teas from several geographical areas [90].

2.4. The Health Benefits of Critical Aroma Compounds of Black Tea

2.4.1. Neuro-Regulation Effects

Some evidence indicates the beneficial effects of black tea (Camellia sinensis) consumption on mental alertness, planning abilities, and work-related focus [91].
The aging process represents a significant risk factor for neurodegenerative conditions such as Alzheimer’s disease (AD), Parkinson’s disease (PD), and amyotrophic lateral sclerosis (ALS). Remarkably, black tea, a caffeine beverage, exhibits an inverse association with Parkinson’s disease risk. This investigation was carried out within the context of the Singapore Chinese Health Study, scrutinizing various factors about the occurrence of Parkinson’s disease [92]. A research initiative, spearheaded by Associate Professor Louis Tan, a Senior Consultant at the Department of Neurology within the National Neuroscience Institute (NNI), in collaboration with other neurologists from NNI, found that black tea may harbor neuroprotective agents that contribute to its beneficial effects against Parkinson’s disease [93]. Regular consumption of black tea may lower the risk of developing Parkinson’s disease. The concept of combining iron chelation with antioxidant therapy emerges as a promising approach for neuroprotection. Tea flavonoids (black tea) have gained recognition for their potential to chelate divalent metals, exhibit antioxidant properties, and demonstrate anti-inflammatory effects. They possess the capacity to traverse the blood–brain barrier, guarding against neuronal death in diverse cellular and animal models of neurological diseases [93,94,95].

2.4.2. Anti-Microbial Effects

Tea’s (Camellia sinensis) antibacterial and antioxidant properties were attributed to the main mechanism by which fermentation enhances antioxidant activity which is the production of more free and absorbable phenolic compounds and flavonoids as a consequence of tea processing. Additionally, fermentation causes the structural disintegration of plant cell walls, which releases or synthesizes a variety of antioxidant chemicals. After fermentation, the caffeine content is slightly reduced, improving the tea’s flavor. Additionally, the range of aromatic compounds expands after fermentation, giving the tea a fresh aroma [96]. These teas (Camellia sinensis) have anti-inflammatory and weight-loss properties. They also contain L-theanine, which can regulate brain activity and human attention [97]. Black tea’s caffeine might also improve mental clarity.
Maintaining a healthy gut can help prevent various illnesses and health issues. Drinking black tea (Camellia assamica) might increase the number and type of beneficial intestinal microorganisms. The tea polyphenols may serve as probiotics and food for the beneficial bacteria in the gut. Additionally, these polyphenols may stop the development of other dangerous bacteria in the gut. In addition to possibly lowering the incidence of colorectal and esophageal/stomach malignancies, black tea may help heal stomach ulcers [98]. Most bacteria have the potential to cause illnesses and even death. Black tea’s phytonutrients and antioxidants may have antibacterial characteristics [99]. Black tea (Camellia sinensis) has antioxidant and antibacterial qualities that shield against staphylococcus infections [100,101]. Black tea’s fluoride also prevents tooth caries [102]. Consequently, drinking black tea (Camellia sinensis) may also benefit oral health.
According to Del Rio et al. [103], higher dietary phenolic intake has been linked to lower risks of various chronic diseases. Tea’s antioxidant and antibacterial properties are improved after fermentation. Microbially fermented tea also possesses anti-inflammatory and weight-loss properties. Microbially fermented tea has positive medicinal and physiological benefits when consumed over time. Fermented tea’s anti-microbial qualities have a promising future in food preservation [20]. Amino acids affect the nutritional value and quality of black tea. Fermentation is the process that is most important in the creation of black tea.
Numerous studies indicate that tea can enhance psychological and neurological functions. Recent research reveals that tea catechins can enter the brain and protect neurons from cell death caused by neurological diseases. This is due to their antioxidant, anti-inflammatory, and divalent metal-chelating properties, as demonstrated in animal and cellular models [104]. As the polyphenols in black tea are said to prevent the formation of dangerous germs, drinking black tea also performs an antibacterial function [105]. Another study that showed a notable reduction in the growth of various dangerous bacteria offers further evidence of the antibacterial capability of black tea components [106].

2.4.3. Digestive Tract Protective Effects

The polyphenols in black tea (Camellia sinensis) prevent obesity by limiting fat and complex sugar digestion and absorption. Tea aroma components, notably TFs, exhibit strong antioxidant action. In the digestive system, they can aid in scavenging dangerous free radicals that can cause cell damage and raise the possibility of developing digestive problems like gastric ulcers and colorectal cancer [107].
Certain tea fragrance components, such as catechins and theanine (Camellia sinensis), have been discovered to have antibacterial activities. In the digestive tract, they can stop the formation of dangerous bacteria like Helicobacter pylori, which is linked to gastric ulcers and gastritis. Tea aroma components can support the maintenance of a healthy balance of gut flora and safeguard the digestive tract by preventing the overgrowth of these bacteria [108,109]. Theanine is crucial for the T-cell-mediated immune system’s efficient operation since it helps keep these cells activated. A biologically active substance called theine has been shown to activate the central nervous and cardiovascular systems, relax blood vessels, enhance digestion, increase circulation, and stop platelet aggregation [110].
For gastroprotective effects it has been demonstrated that tea (Camellia sinensis) aroma chemicals, such as tannins, have gastroprotective properties. They may be able to fortify the mucosal lining of the digestive tract, acting as a defense against harm from irritants and stomach acids. This step can help prevent gastroesophageal reflux disease (GERD) and stomach ulcers [111]. By encouraging the release of gastric juices, regulating intestinal flora, which lowers the risk of gastrointestinal disorders, and activating peristaltic motions, organic acids aid in digestion [110].

3. Conclusions

Tea has been made from tea (Camellia sinensis) leaves for over 50 centuries. Tea plant varieties mainly belong to two major groups: Camellia sinensis var. sinensis (CSS; Chinese type) and Camellia sinensis var. assamica (CSA; Assam type). Both types of tea have distinctive fragrance profiles that add to the special qualities of black tea. The interplay of numerous metabolic pathways is a complex process that results in the synthesis of fragrance molecules in black tea. When making black tea, the process of fermentation is essential because it causes the leaves to oxidize. This process causes some chemical molecules, like catechins, to break down while creating other ones, including TFs and TRs. These substances help give black tea its distinctive flavor and aroma.
The significant fragrance components present in various kinds of black tea belong to Camellia sinensis var. sinensis and Camellia sinensis var. assamica, covered in this article. Overall, several procedures and chemical interactions are needed to produce the scent of black tea. In conclusion, the Maillard reaction, fermentation, oxidative degradation of catechins, oxidative condensation of TFs, and TRs all contribute to creating important scent components in black tea. The essential elements of the black tea scent are currently being processed. According to sensory analysis, the scent of black tea from Camellia assamica is comparable to that of the more well-known Camellia sinensis.
➢
Notwithstanding, there are a few subtle variances in the aromatic patterns of both types of tea. For instance, black tea from Camellia assamica often has a stronger, maltier aroma than Camellia sinensis. Furthermore, according to the cultivar and specific growing conditions, Camellia assamica teas have a slightly fruity or floral aroma. Conclusively, the aroma sensory analysis of black tea from Camellia sinensis and Camellia assamica involves the analysis of volatile compounds formed during tea processing.
Numerous fragrance components in black tea have been shown to provide a range of health advantages. The aroma of black tea can activate the nervous system, increasing energy and improving mental clarity. The aromatic elements in black tea may benefit the digestive tract. They can aid in maintaining a healthy gut environment, promote healthy digestion, reduce digestive problems, including bloating and indigestion, and increase immunity. Black tea’s aromatic constituents may help to relax the body and mind. They can aid in lowering tension and stress and fostering relaxation, all of which can benefit mental health. While black tea may have many health advantages, it is crucial to remember that individual responses may differ, and excessive drinking should be avoided because it may have negative consequences, including a faster heartbeat, sleeplessness, or digestive problems. All in all, researchers, tea experts, and enthusiasts interested in black tea’s sensory evaluation and aroma development will find this review useful.

Author Contributions

Conceptualization, L.Z.; methodology, A.P.; software, A.P.; validation, A.P., J.K. and L.Z.; formal analysis, A.P.; investigation, A.P.; resources, L.Z.; data curation, A.P.; writing—original draft preparation, A.P.; writing—review and editing, A.P., C.-Y.Q., F.Z., G.L., P.L. and M.Z.; visualization, A.P. and L.Z.; supervision, L.Z.; project administration, L.Z.; funding acquisition, L.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Anhui Key Research and Development Plan (202104b11020001).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

All datasets presented in this study are included in the article.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Worldwide Tea Production in 2022.
Figure 1. Worldwide Tea Production in 2022.
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Figure 2. Morphological differences between the two varieties.
Figure 2. Morphological differences between the two varieties.
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Figure 3. Main typical aroma compounds in black tea of Camellia sinensis and Camellia assamica.
Figure 3. Main typical aroma compounds in black tea of Camellia sinensis and Camellia assamica.
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Figure 4. Tea Processing stages.
Figure 4. Tea Processing stages.
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Figure 5. The formation pathway of critical aroma compounds.
Figure 5. The formation pathway of critical aroma compounds.
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Table 1. Comparative summarization on the different extraction method of tea volatiles.
Table 1. Comparative summarization on the different extraction method of tea volatiles.
Extraction MethodTechniqueDetector/
Sensor		ApplicationReference
Solid phase extraction (SPE)GC-MS Used with SPME, and solvent-assisted flavor evaporation (SAFE), respectively, for the analysis of tea body notes, tea infusion, and dry tea aroma from six model manufacturing processes[19]
GCMass spectrometry (MS), flame ionization (FID) and olfactometry (O)Used to extract and characterize the aroma compounds in the infusion of Hanzhong black tea[20]
Solid-phase microextraction (SPME) Optimized to study the effect of grinding and brewing on tea volatiles of tea (Camellia sinensis) and SAFE applied for the analysis of tea volatiles in tea[21]
GC-MS Used to detect volatile compounds in black teas after withering–shaking and shaking–withering processing.[22]
Stir bar sorptive extraction (SBSE)GC-O, GC-MSGas chromatography-flame photometric detector (GC-FPD)Used to extracted compound of three famous black teas from around the world—Darjeeling, Keemun, and Ceylon[23]
Headspace solid-phase microextraction (HS-SPME)GC-MS Analyzed the volatile flavor compounds of 31 black tea samples from 7 districts in Guangdong[24]
GC×GC-TOF-MS combined with GC-O/GC-TOF-MS Analyzed the aroma components of 24 samples of the world’s four black teas[25]
GC-MS Aroma characteristics and volatile components of Jiangxi Congou black tea.[26]
GC-MS Analyzed volatile flavor compounds in 112 black teas from seven countries by untargeted metabolomics[27]
GC-MS, GC-O Optimized with SAFE method to analyse characteristics of key aroma compounds of three kinds of Chinese representative black tea[28]
GC-MS To extract the volatile compounds when analyzing the volatile profile of black tea[29]
Ultra-fast Gas Chromatography (UFGC) analyzerE-nose detectorUsed to identify the variations of Assam black tea (Camellia Sinensis (L.) O. Kuntze) with their aroma compounds[30]
GC×GC-TOF-MS Used to identify 158 volatile compounds during the fermentation period of black tea[13]
GC-MS, GC-O Identification of aroma-active components in black teas produced by six Chinese tea cultivars in high-latitude regions[31]
GC-MSE-noseMain aroma components and aroma differences of black tea produced from two tea cultivars, Fuyun 6 and Jinguanyin[32]
GC-MSQuartz crystal microbalance (QCM)Used to detect linalool gas in orthodox black tea[33]
Table 2. The critical aroma compounds of various types of black tea.
Table 2. The critical aroma compounds of various types of black tea.
GroupCompoundsOts (ug/L)C.sinensisC.assamicaAroma QualityIdentification References
Aldehydes(E)-2-Hexenal82✓✓Green apple-like, bitter almond-like, green grassMS, RI, STD[20,21,28,47]
Benzeneacetaldehyde52✓✓Rose-like floral, honeyMS, RI, STD[21,25,28]
Citral5✓×Fruity, citrusMS, RI, STD[24,47,48]
Benzaldehyde320✓✓Nutty, bitter almond, oily, green, floralMS, RI, STD[21,25,28]
(E,E)-2,4-heptadienal56✓×Fatty, green, vegetableMS, RI, STD[23,28]
Furfural9.56✓✓Sweet, woody, almond smellMS, RI, STD[23,28]
Hexanal2.4✓✓Fresh green grassMS, RI, STD[23,28]
Neraln.m--Lemon peel, citrusMS, RI, STD[28]
(E)-2-Pentenal310✓×FruityMS, RI, STD[20,43]
(E,E)-2,4-Nonadienal0.06✓✓FattyMS, RI, STD[20,25,37,47]
Nonanal1✓✓Floral, freshMS, RI, STD[25]
(E,Z)-2,6-Nonadienal0.0045✓✓Fresh, cucumber-likeMS, RI, STD[20,25,37,47]
(E)-2-Nonenal0.39✓✓Fatty, greenMS, RI, STD[23,25,37]
(E)-2-Octenal3✓✓Fatty, greece odorMS, RI, STD[24,25,48]
5-Methyl furfural500✓✓Sweet, mapleMS, RI, STD[28]
2-Methylbutanal1.5✓✓Musty, cocoaMS, RI, STD[23,28,48]
3-Methylbutanal0.5✓✓Fruity, chocolateMS, RI, STD[23,25,28,48]
2-Methylpropanal1.9✓✓Fresh aldehydeMS, RI, STD[25,48]
beta-Cyclocitral3✓×Tropical saffron, herbalMS, RI, STD[23,28]
(1R)-(-)-Myrtenaln.m--sweet, mintyMS, RI, STD[28]
2-Phenyl-2-Butenaln.m--Floral, black teaMS, RI, STD[28]
Ketones6-Methyl-5-hepten-2-one160✓✓Citrus, greenMS, RI, STD[25,28,43,47]
α-Ionone58✓×Woody, floral, violet incenseMS, RI, STD[20,24,25,28,47,48]
β-Ionone21✓✓Woody, floral, fruity, violet odorMS, RI, STD[20,23,24,25,28,37,43,47,48]
2-Nonanone5✓✓GreenMS, RI, STD[25]
Coumarinn.m--Sweet, hay, beanMS, RI, STD[23,28]
(E,E)-3,5-Octadien-2-one150✓×Fruity, greenMS, RI, STD[28,48]
3-methylnonane- 2,4-dione0.01✓✓Hay-likeMS, RI, STD[28,37]
1-Octen-3-one0.5✓✓Mushroom-likeMS, RI, STD[20,25,37,47]
β-Damascenone0.004✓×Floral, fruityMS, RI, STD[28,37]
cis-Jasmone24✓×Woody, herbalMS, RI, STD[25,28,43]
2-Heptanone0.14✓×Fruity, cheeseMS, RI, STD[28,43]
Isophoronen.m--Sweet, woodyMS, RI, STD[28]
AlcoholsLinalool19✓✓Citrus, floralMS, RI, STD[20,23,24,25,28,48]
Geraniol27✓✓Sweet floralMS, RI, STD[20,23,24,25,28,37,43,47,48]
Phenylethyl alcohol772✓✓Rose, floralMS, RI, STD[20,24,25,28,37,43,48]
(Z)-3-Hexenol70✓✓Fresh grassMS, RI, STD[25,28,37]
Benzyl alcohol11,076✓✓Floral, bitter almond-likeMS, RI, STD[20,23,24,25,28,43]
cis-Linaloloxide320✓✓Citrus, floral, sweet woodyMS, RI, STD[24,28]
Nerol528✓×Neroli, citrusMS, RI, STD[24,28]
α-Terpineol404✓✓Lilac, woody, terpeneMS, RI, STD[23,28,37,43,47]
1-Hexanol500✓✓Oily, fruityMS, RI, STD[24,28,43]
(Z)-3-Hexen-1-ol8✓×Green, grass, sweetMS, RI, STD[23,25,43]
(E)-2-hexen-1-ol1900✓✓Green, Leaf, walnut, woodyMS, RI, STD[23,24,37,43,48]
trans-Linaloloxide320✓✓Citrus, floralMS, RI, STD[25,28]
2-Pentenol400✓×FruityMS, RI, STD[28]
1-Penten-3-ol400✓×Green, radishMS, RI, STD[20,28]
2-Ethyl-1-hexanol300✓✓Citrus, sweetMS, RI, STD[28]
Furfuryl alcohol4.5×✓Sweet, caramelMS, RI, STD[28]
1-Octen-3-ol45✓✓Mushroom, earthyMS, RI, STD[20,23,25,28,43]
Hotrienol110✓✓LavenderMS, RI, STD[25,28]
AcidsBenzoic acidn.m--Faint, balsamMS, RI, STD[28]
Geranic acidn.m--Green, woodyMS, RI, STD[28]
(E)-2-Hexenoic acid1900✓✓Fruity, sweetMS, RI, STD[28]
(E)-3-Hexenoic acidn.m--Green, woodyMS, RI, STD[28]
Hexanoic acid1000✓✓Fatty, cheesy, sweet odorMS, RI, STD[24,28]
Butanoic acid1000✓×Sharp aceticMS, RI, STD[28]
EstersMethyl salicylate75✓✓Winter green-like MS, RI, STD[23,25,28,48]
Dihydroactinidiolide0.0021✓×Musk, rose-like, fruit, woodyMS, RI, STD[23,25,28,43,48]
Methyl hexanoate10✓×Fruity, pineappleMS, RI, STD[28]
Benzyl acetate30✓×Floral, fruityMS, RI, STD[28]
γ-Butyrolactone50✓✓Creamy, oilyMS, RI, STD[28]
Hydrocarbonsβ-Ocimene48✓✓Citrus, tropicalMS, RI, STD[28]
β-Myrcene1.2✓✓Pepper woody, sweet citrus, balsamic aromaMS, RI, STD[23,25,28]
D-Limonene200✓✓Citrus, orange, light flowersMS, RI, STD[23,28,48]
Styrene50✓✓Sweet floral, balsamMS, RI, STD[28,48]
Longifolenen.m--Sweet, woodyMS, RI, STD[28]
Naphthalenen.m--BalmyMS, RI, STD[28]
SulfideDimethyl sufide0.84✓✓CornMS, RI, STD[28]
Dimethyl disulfide1.1×✓Sulfurous, vegetableMS, RI, STD[25,28]
Pyrazines2-Methylpyrazine60✓✓Popcorn, nuttyMS, RI, STD[25,28]
2,6-Dimethyl pyrazine6✓×Roasted, coffee, roasted nut, roast beefMS, RI, STD[25,28]
2-Ethyl-pyrazine4✓✓Nutty, mustyMS, RI, STD[28]
Others1-Ethyl-1H-pyrrole-2-carbaldehyden.m--Burnt, roasted, smokyMS, RI, STD[28]
2-Formyl-1H-pyrrolen.m--Musty, beefyMS, RI, STD[28]
2-Acetyl pyrrolen.m--Musty, sweetMS, RI, STD[28]
2-Ethylfuran100✓✓Bread, sweetMS, RI, STD[28]
2-Pentylfuran4.8✓✓Fruity, greenMS, RI, STD[28]
Ots = Odor thresholds in water. n.m: not mentioned. × indicated this aroma compound was not detected. ✓ indicated this aroma was detected.
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Parveen, A.; Qin, C.-Y.; Zhou, F.; Lai, G.; Long, P.; Zhu, M.; Ke, J.; Zhang, L. The Chemistry, Sensory Properties and Health Benefits of Aroma Compounds of Black Tea Produced by Camellia sinensis and Camellia assamica. Horticulturae 2023, 9, 1253. https://doi.org/10.3390/horticulturae9121253

AMA Style

Parveen A, Qin C-Y, Zhou F, Lai G, Long P, Zhu M, Ke J, Zhang L. The Chemistry, Sensory Properties and Health Benefits of Aroma Compounds of Black Tea Produced by Camellia sinensis and Camellia assamica. Horticulturae. 2023; 9(12):1253. https://doi.org/10.3390/horticulturae9121253

Chicago/Turabian Style

Parveen, Asma, Chun-Yin Qin, Feng Zhou, Guoping Lai, Piaopiao Long, Mengting Zhu, Jiaping Ke, and Liang Zhang. 2023. "The Chemistry, Sensory Properties and Health Benefits of Aroma Compounds of Black Tea Produced by Camellia sinensis and Camellia assamica" Horticulturae 9, no. 12: 1253. https://doi.org/10.3390/horticulturae9121253

APA Style

Parveen, A., Qin, C. -Y., Zhou, F., Lai, G., Long, P., Zhu, M., Ke, J., & Zhang, L. (2023). The Chemistry, Sensory Properties and Health Benefits of Aroma Compounds of Black Tea Produced by Camellia sinensis and Camellia assamica. Horticulturae, 9(12), 1253. https://doi.org/10.3390/horticulturae9121253

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