China is a major tea-drinking country with a rich variety of tea. The tea commonly referred to comes from the Camellia genus of the Theaceae family. Tea contains many active ingredients such as amino acids, tea polysaccharides, alkaloids, tea polyphenols, and pectins. Among them, tea polyphenols, as a natural and efficient food additive, have already been applied in the food industry.
Physical and Chemical Properties of Tea Polyphenols
Tea polyphenols are derived from tea leaves and are a mixture of various organic polyhydroxy compounds, including catechins, anthocyanins, flavonols, and phenolic acids. The main antioxidant component is catechin. Epigallocatechin gallate (EGCG) makes up 50-60%, epicatechin gallate (ECG) accounts for 15-20%, epigallocatechin makes up 10-15%, gallocatechin 6-8%, and epicatechin 4-6%. At room temperature, tea polyphenols appear as a light yellow or light green powder with astringency, and they are highly resistant to acids, remaining stable within a pH range of 2-7. Tea polyphenols exhibit some hygroscopicity and can easily discolor in alkaline environments.
Composition of Tea Polyphenols in Different Teas
Tea is typically classified into six types based on its oxidation level: unfermented green tea, lightly fermented white tea, partially fermented yellow tea, semi-fermented oolong tea, fully fermented black tea, and post-fermented dark tea. Each type of tea has unique characteristics in its processing.
In green tea production, heat treatment prevents enzymatic oxidation of green tea extract, minimizing the degradation of active substances. In the case of white tea, freshly harvested leaves and buds are immediately dried, avoiding enzyme inactivation and compound oxidation.
Compared to green tea, the production of yellow tea involves a unique process called “menhuang,” or “yellowing,” which promotes oxidation and removes the grassy aroma typical of green tea while preserving its beneficial compounds.
Oolong tea is semi-fermented with a lower enzymatic oxidation rate, offering various physiological benefits and a pleasant aroma and taste. In black tea production, fresh tea leaves are thoroughly rolled to release polyphenol oxidase, which then reacts with catechins to form other polyphenols like theaflavins and thearubigins.
Dark tea, a post-fermented tea, undergoes microbial fermentation, leading to changes in its chemical composition, such as polyphenols, polysaccharides, and caffeine.
Different processing methods lead to variations in the phenolic content of teas. The phenolic content in various tea products is shown in the table.
Functional Properties of Tea Polyphenols
Tea polyphenols exhibit various biological activities, such as antioxidant, antibacterial, and anti-mutagenic effects. EGCG, the most abundant catechin, plays a major role in antioxidant activity. The bioactivity stems from the phenolic hydroxyl groups in tea polyphenols, which function differently in various food types, making tea polyphenols widely applicable in food.
- Antioxidant Effect on Natural Oils
Tea polyphenols are natural antioxidants for oils, with an antioxidant capacity far exceeding synthetic antioxidants like butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), effectively preventing and delaying the oxidation or rancidity of lipids. - Pigment Protection
Tea polyphenols can prevent the degradation and fading of natural pigments like beta-carotene, reportedly providing 20 times the protection of vitamin C. - Deodorizing Effect
Tea polyphenols can eliminate the unpleasant odor of methyl mercaptan. In Japan, tea polyphenols are used in deodorizing chewing gum and cigarette filters to eliminate bad breath. Experimental results also show that tea polyphenols inhibit bacteria in the intestines of animals that produce foul-smelling compounds. - Antioxidant and Anti-Aging Effects
Tea polyphenols can scavenge excess free radicals in the body, slowing down aging. Their antioxidant activity is stronger than vitamin E, and they work even better when combined with vitamins C and E. - Anti-Caries Effect
Clinical evidence shows that green tea extract can strongly inhibit cariogenic bacteria, significantly reducing plaque and periodontal indices. - Antibacterial and Antiviral Properties
Polyphenols can precipitate bacterial proteins, causing them to denature and lose activity. Using tea polyphenols’ antibacterial and antiviral properties, catechins are used in air conditioning systems abroad. - Lowering Blood Lipids and Inhibiting Atherosclerosis
Tea polyphenol compounds significantly inhibit the rise of cholesterol levels in plasma and the liver, promoting the excretion of lipid compounds through feces. They not only prevent and treat atherosclerosis but also have a weight loss effect. - Various Pharmacological Effects
Tea polyphenols, especially catechin derivatives, inhibit the proliferation of cancer cells, have anti-cancer and anti-mutagenic effects, reduce the toxicity of heavy metals to the human body, and provide protection against radiation. - Application in Fish Oil Products
Tea polyphenols can effectively prevent the peroxidative decomposition of polyene esters and acids, and their antioxidant capacity is stronger than that of vitamin E. Tea polyphenol emulsions can be used in food blending oils to extend shelf life and further enhance antioxidant effects.
Applications of Tea Polyphenols in Food
- Preservation of Seafood
Bacterial infection, primarily from Pseudomonas species, is the main cause of spoilage in seafood. Green tea extract exhibits antioxidative effects in various seafood, effectively inhibiting bacterial growth, slowing lipid oxidation, and extending the shelf life of fish. - Preservation of Meat and Poultry Products
Meat and poultry products are prone to microbial growth due to high surface moisture and other characteristics, leading to spoilage. Numerous studies have shown that tea polyphenols inhibit bacteria like E. coli, Salmonella, Staphylococcus, and Bacillus subtilis. As an antioxidant, tea polyphenols eliminate harmful free radicals, inhibit bacterial growth, reduce unpleasant odors, and maintain the fresh color of meat products. - Preservation of Fruits and Vegetables
Spraying or coating low concentrations of Green tea extract on fresh fruits and vegetables inhibits bacterial growth and prolongs shelf life. The preservation mechanism is complex, with different key factors for different types of produce. - Application in Functional Foods
Functional foods are designed to improve body functions. With the development of society and living standards, consumers seek to enhance their physical health through functional foods. Green tea extract is used in products such as health beverages and milk, demonstrating anti-fatigue, anti-aging, and anti-tumor effects. - Application as a Color Preservative
Tea polyphenols act as a natural color preservative, preventing the degradation of pigments and vitamins in food. They are highly cost-effective and widely used as a color stabilizer in foods like meat products. - Application in Deodorizers
Tea polyphenols are natural deodorizers, effectively eliminating unpleasant smells in food products such as soy, fish, and meat. They are also used in candy, chewing gum, and toothpaste to reduce bad breath.
