Anhua dark Tea, as a typical representative of dark teas, is a post-Fermented tea obtained through microbial fermentation. Due to its unique processing techniques and specific microbial flora in the production area, Anhua dark tea possesses distinctive functional components and health attributes, making it highly favored by consumers. The main functional components of Anhua dark tea include polyphenols, alkaloids, amino acids, terpenoids, polysaccharides, and secondary metabolites from Eucommia corchorifolia. Below is a brief introduction to the functions of each component, providing new scientific evidence for the development and utilization of Anhua dark tea's functional components and their Health benefits that drive market consumption.

I. Polyphenolic Compounds

Polyphenolic compounds account for 20% to 35% of the dry weight of tea leaves, mainly including catechins, flavonols, phenolic acids, etc.

1. Catechin Compounds

Catechin compounds are the primary constituents of tea polyphenols, comprising about 60% to 80% of total polyphenolic compounds, with various biological activities such as antioxidation, lipid-lowering, weight loss, immune regulation, antiviral properties, and anticancer effects.

The content of polyphenols decreases during the processing of Anhua dark tea, and with extended fermentation time, both ester-type and non-ester-type catechins decline continuously. In Anhua dark tea, ester-type catechins are hydrolyzed into gallic acid and non-ester-type catechins under the action of microbial enzymes. Non-ester-type catechins undergo further ring cleavage, oxidation, and polymerization reactions, generating a series of catechin B-ring derivatives. Eight new catechin B-ring cleavage derivatives unique to Fu brick tea have been isolated, suggesting they may be characteristic components of the Fu brick Tea processing process. Catechin compounds form theaflavins, thearubigins, and theabrownins during processing. Theabrownins are the most predominant tea pigments in Anhua dark tea, formed by the oxidation and polymerization of catechins, theaflavins, and thearubigins. During the flowering (fungus growth) process of Fu brick tea, the contents of theaflavins and thearubigins rapidly decrease starting from the fourth day, while the theabrownin content begins to increase gradually from the second day.

Changes in the content of tea pigments during the flowering process of Fu brick tea

Additionally, several new catechin derivatives have been isolated from Fu brick tea, which possess multiple biological activities, such as Fuzhuanin A, which promotes the growth of human stem cells and prevents the misfolding of beta-amyloid proteins, and Fuzhuanin B, which inhibits HeLa cell (human cervical cancer cell) activity. Theabrownins exhibit good effects in antioxidation, lipid-lowering, and blood sugar reduction. These catechin derivatives are personalized characteristic components produced during the piling and flowering processes of Anhua dark tea and are key components contributing to its unique flavor and health benefits.

Illustration of the inhibitory effect of Fuzhuanin B on HeLa cells observed under an optical microscope (×200); Figure A is the negative control, and Figure B shows the cells after treatment with 10 μM Fuzhuanin B for 24 hours. Comparing Figures A and B clearly demonstrates the inhibitory effect of Fuzhuanin B on HeLa cells.

2. Flavonols

The flavonols in Anhua dark tea mainly include kaempferol, quercetin, myricetin, etc. Flavonols have antioxidative, lipid-lowering, hepatoprotective, and anticancer activities and are one of the most important functional components of Anhua dark tea, closely related to its flavor and health benefits. The flavonols in Anhua dark tea primarily exist as oxygenated flavonoids. However, in recent years, multiple carbon-glycosylated flavonoids, including chafurosides A, chafurosides B, and vitexin-2″-α-L-rhamnoside, have also been isolated from Fu brick tea.

Through studying changes in flavonoid content during the flowering process of Fu brick tea, it has been found that the content of flavonol compounds decreases during the piling and flowering processes of Anhua dark tea. Similar to catechin compounds, as the content of flavonol compounds declines, some flavonol derivatives are generated in Anhua dark tea. However, there is currently a lack of understanding regarding these flavonol derivatives, which requires attention and exploration.

3. Phenolic Acids

Anhua dark tea contains various phenolic acids, including gallic acid, caffeic acid, ferulic acid, salicylic acid, etc., with gallic acid being present at higher concentrations. These phenolic acids possess antioxidative, lipid-lowering, antibacterial, antiviral, and other bioactivities. Anhua dark tea also contains some phenolic acid derivatives, including 3-O-galloylquinic acid and 3-O-caffeoylquinic acid.

Studies have shown that simple phenols such as 2,5-dihydroxybenzoic acid, m-phloroglucinol, and o-phloroglucinol are formed through a series of ring cleavage, reduction, hydrolysis, decarboxylation, demethylation, and dehydroxylation reactions under the action of microbial enzymes. This process is similar to the transformation of catechins in the human intestine. Catechins are poorly absorbed in the small intestine and mostly enter the large intestine where they are decomposed and metabolized by intestinal microorganisms. Compared to larger molecular weight catechins, simple phenolic acids are more readily absorbed in the body. Therefore, the microbial fermentation of Anhua dark tea may play a role similar to that of intestinal microorganisms, breaking down catechins into simpler phenolic acids that are easier for the body to absorb. This is likely one of the important mechanisms contributing to the unique health benefits of Anhua dark tea.

II. Alkaloids

The alkaloids in Anhua dark tea are primarily purine alkaloids, with small amounts of pyrimidine alkaloids. The purine alkaloids in Anhua dark tea mainly include caffeine, theobromine, and theophylline, with caffeine having the highest content. A new alkaloid named N-(2-hydroxyphenyl)-2-pyrrolidone was isolated from Anhua Qianliang tea.

Chemical structure of N-(2-hydroxyphenyl)-2-pyrrolidone

Caffeine has a strong bitter taste and is an important component contributing to the flavor of Anhua dark tea, giving the tea infusion a bitter but sweet aftertaste along with catechins and amino acids. Caffeine is an important functional component of Anhua dark tea, possessing stimulant, fat-burning, and diuretic effects. Theophylline and theobromine have similar activities to caffeine, with theophylline possibly being stronger in heart stimulation, diuresis, and muscle relaxation, and theobromine potentially being more effective in central nervous system stimulation than caffeine and theophylline. Compared to other types of tea, the raw materials used for Anhua dark tea generally have lower grades (except for Tianjian tea), resulting in relatively lower caffeine content, which further decreases due to degradation during microbial fermentation. The low caffeine characteristic of Anhua dark tea makes it more suitable for elderly individuals and those sensitive to caffeine.

III. Amino Acids

Anhua dark tea contains over 20 types of amino acids, with Theanine being the primary amino acid and a major contributor to the fresh and refreshing taste of the tea infusion. Theanine has various benefits, including stress relief, fatigue reduction,