Chinese dark Tea (China dark teas, CDTs), one of the six major types of tea, has a drinking history spanning nearly a thousand years. It is a unique type of tea in China and belongs to the post-fermentation category.
Dark teas are typically made from coarse and aged raw materials, resulting in large leaves with long stems. The manufacturing process often involves prolonged heap fermentation, which gives the leaves a predominantly dark brown, oily black, or brownish-green color, and the liquor a deep red or reddish-brown hue. The unique pile-fermentation process creates its distinctive aged fragrance quality.
The processing of dark tea can be divided into two types: one involves withering, rolling, pile-fermentation, and initial drying, followed by sifting, steaming, and compression into shape; the other directly uses dark tea or sun-dried Green Tea as raw materials for pile-fermentation and color development, after which it undergoes sifting and steaming for compression.
The classification and quality characteristics of different types of dark tea were summarized in previous articles, which can be found in past posts titled “Origins, Varieties, and Characteristics of Dark Tea” and “Studies on Quality Differences Among Different Types of Chinese Dark Tea.”
I. Functional Components of Dark Tea
In addition to having a higher content of gallic acid (GA) compared to green tea, the flavanol components in dark tea are generally lower. The amino acid content in dark tea is also significantly lower than in other types of tea. Theaflavins, one of the essential functional components of dark tea, play a crucial role in the liquor color and taste, with an average content of about 12%. Flavonoids in dark tea primarily consist of quercetin and myricetin, with an average total content of approximately 0.9%. The phenolic acid content varies greatly among different dark teas, averaging around 9 mg/g. Dark tea contains rich amounts of Caffeine and some pyrimidine compounds, such as thymidine and uracil, which are characteristic substances of dark tea. Dark tea is rich in mineral elements, with lead, copper, barium, and calcium being the most abundant, exceeding those in other types of tea. The fluoride content in dark tea varies significantly depending on the region, likely due to differences in soil and environment.
The chemical composition of dark tea is complex and diverse. To date, there is no comprehensive experiment that specifically describes its important functional components, which remains a blind spot in our understanding of dark tea. However, the unique quality and significant Health benefits of dark tea have driven researchers to explore its main functional components and health mechanisms. Major functional components of dark tea are shown in Table 1.
Major functional components of dark tea are shown in Table 1
II. Health Benefits of Dark Tea
As living standards improve, healthy lifestyles and scientific health preservation are receiving increasing attention. “Healthy China 2030” has become a national strategy. In recent years, researchers have used cell cultures, animal models, and human clinical trials to reveal at the molecular, tissue, individual, and population levels that dark tea has beneficial effects in regulating metabolic syndrome and gastrointestinal function, with particular emphasis on its hypoglycemic and lipid-lowering effects. The health benefits of dark tea will be one of the research hotspots in the 21st century regarding tea and health.
☀ Lipid-Lowering and Weight Loss
Recent studies have revealed that dark tea has good lipid-lowering and weight loss effects. However, given the multitude of components in dark tea, the specific substances responsible for these lipid-lowering effects remain unknown.
☀ Hypoglycemic Effects
A diet high in fat and sugar has led to the widespread prevalence of diabetes, which has become a common and highly prevalent disease. There are historical records in China of the hypoglycemic effects of aged tea leaves, and the hypoglycemic effect of yellow tea has been confirmed. Similarly, dark tea, made from aged tea leaves, has similar functions. Xu et al. found that consuming Pu'er tea polysaccharides (20-40 mg/kg body weight) had a significant hypoglycemic effect. Polysaccharides may be the primary hypoglycemic substance, but the mechanism of action requires further research.
☀ Hypotensive Effects
Hypertension is a significant risk factor for cardiovascular disease, and effective control of blood pressure can significantly reduce the incidence of cardiovascular diseases. Traditional Chinese medicine believes that tea can help lower blood pressure. Modern medicine has proven that moderate and sustained tea consumption habits have a mild blood pressure-lowering effect, and many epidemiological surveys show that long-term tea drinking is beneficial for maintaining stable blood pressure in the elderly.
Bioactive compounds in tea, such as caffeine and polyphenols, can relax the walls of blood vessels in experimental animals, increase the effective diameter of blood vessels, and lower blood pressure through vasodilation. Tea pigments exhibit significant fibrinolytic, anti-coagulant, and anti-platelet aggregation activities, inhibiting the proliferation of arterial smooth muscle cells, indicating that tea has good hypotensive effects. L-theanine, which has attracted much attention in recent years for its blood pressure-lowering effects, can inhibit blood pressure increases by activating dopaminergic neurons. Japanese researchers have developed a γ-aminobutyric acid (GABA) tea (2 mg/g) with a significant blood pressure-lowering effect.
☀ Gastrointestinal Function Regulation
The gut microbiota plays a critical role in regulating various physiological processes in mammals. The gut microbiota is involved in many important physiological functions, such as food digestion and metabolism, immune responses, and inflammation. Many studies have found that Fu brick tea has a significant effect on regulating gastrointestinal function and gut microbiota. Eurotium cristatum, a beneficial fungus that forms the unique quality of Fu brick tea, is widely recognized for its safety. This fungus secretes polysaccharides and statins like lovastatin, which have multiple biological activities.
Pigments (such as theaflavins), beneficial fungi, phospholipids, caffeine, soluble sugars, and other substances in dark tea may play a key role in regulating the gut, affecting the gut microbiota and gut structure.
☀ Antioxidant Effects
Dark tea is rich in secondary metabolites. Analyzing the antioxidant activity of dark tea, such as free radical scavenging capacity (ABTS), ferric reducing antioxidant power (FRAP), and HepG2 cell antioxidant activity (CAA), shows that different dark teas have varying antioxidant activities, with significant variations in activity.
The free radical theory of aging suggests that the continuous production of free radicals within the human body leads to oxidative damage and chain reactions that harm cells and tissues, accelerating the aging process. Antioxidants in dark tea, such as catechins, tea pigments, and flavonoids, have the ability to scavenge free radicals, which may be the material basis for the antioxidant and anti-aging effects of dark tea.
☀ Additional Studies Have Shown That Dark Tea Also Has Protective Effects on the Kidneys and Liver.
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