Tea Leaves - Originating from the mystical leaves of the East, South Asia, and South America, tea has a long history and encompasses vast diversity. Within it lies infinite secrets, waiting for us to decipher. To explore and decode the mysteries of tea, we should start with its chemical composition.
The taste of tea is a comprehensive reflection of the variations in dozens of flavor compounds. Different types of tea exhibit different tastes due to variations in the types, quantities, and proportions of flavor components present. Tea leaves contain a rich array of substances, and to date, more than 700 known compounds have been identified and isolated from tea leaves.
Moisture content (75% to 78%)
Moisture is an essential component in the life processes of tea plants and serves as an important medium for the chemical changes that occur during tea processing. The changes in color, aroma, and flavor of tea leaves during the tea-making process are closely related to changes in moisture content. Therefore, monitoring the variation in moisture content is an important biochemical indicator for controlling tea quality.
The moisture content of fresh tea leaves generally ranges from 75% to 78%. It varies depending on factors such as the age of the leaves, tea plant varieties, and seasons. Generally, tender buds and leaves, leaves harvested during rainy or spring seasons, and large-leaf varieties tend to have higher moisture content. On the other hand, older leaves, medium to small-leaf varieties, and leaves harvested during dry or sunny seasons have lower moisture content.
Tea polyphenols (comprising 20% to 35% of the dry matter)
Tea polyphenols are a group of polyphenolic compounds primarily composed of catechins found in tea plants. They are also known as "tannins" or "tea tannins." Tea polyphenols can be categorized into four major classes: catechins, flavones and flavonols, anthocyanins and proanthocyanidins, and phenolic acids and their derivatives.
Tea polyphenols are an important class of compounds that distinguish tea from other plants, and they are the primary components responsible for the health benefits of tea. The content of tea polyphenols generally ranges from 20% to 35% of the dry matter in tea leaves. The levels of polyphenols in tea leaves are influenced by various factors such as the environment, tea plant varieties, and the degree of leaf maturity.
Among the total tea polyphenols, catechins account for approximately 70% and are crucial in determining the color, aroma, and taste of tea leaves.
Protein (comprising 20% to 30% of the dry matter)
The protein content in tea leaves accounts for 20% to 30% of the dry matter, but only 1% to 2% of the protein is soluble in water and directly available for utilization. This soluble protein fraction is one of the components that contribute to the taste of tea infusion.
Amino acids (comprising 1% to 4% of the dry matter)
Amino acids are fundamental components of proteins, accounting for 1% to 4% of the dry matter in tea leaves. In tea, 26 different amino acids have been identified, including theanine, glutamate, and aspartate. The levels of various amino acids in tea show distinct seasonal variations, with a higher total amino acid content in spring, lower in autumn, and intermediate in summer. This is one of the reasons why spring tea has a fresher taste.
Amino acids are considered precious in tea because they significantly contribute to the refreshing taste. They not only help balance the bitterness of polyphenols and caffeine but also contribute to the development of diverse and captivating aromas. Amino acids are an indispensable component of high-quality tea.
Alkaloids (comprising 2% to 5% of the dry matter)
Alkaloids found in tea leaves include caffeine, theobromine, and theophylline. Among them, caffeine is the most abundant, comprising approximately 2% to 5% of the dry matter, while the other alkaloids are present in trace amounts.
Caffeine is responsible for the bitterness in tea. The content of caffeine varies significantly in different parts of the tea plant, with higher amounts in the leaves and lower amounts in the stems. The caffeine content decreases as the leaves age, and it also shows noticeable variations with seasons, generally higher in summer tea compared to spring tea.
Caffeine is readily soluble in water and is an important contributor to the taste of tea. It can also serve as one of the distinguishing features to differentiate genuine tea from counterfeit products. Caffeine has various pharmacological effects on the human body, such as providing stimulation, diuretic properties, promoting blood circulation, and aiding digestion.
Carbohydrates (comprising 20% to 25% of the dry matter)
The carbohydrates found in tea leaves include monosaccharides, oligosaccharides, polysaccharides, and small amounts of other types of sugars. They account for approximately 20% to 25% of the dry matter.
Monosaccharides and disaccharides, also known as soluble sugars, are easily soluble in water and make up about 0.8% to 4% of the tea leaf composition. They are one of the substances that contribute to the taste of tea. Polysaccharides in tea leaves include substances such as starch, cellulose, hemicellulose, and lignin. They account for more than 20% of the dry matter in tea leaves and are insoluble in water. Polysaccharides are important components for assessing the tenderness of tea leaves. Tea leaves with lower tenderness have higher polysaccharide content, while leaves with higher tenderness have lower polysaccharide content.
Pectin (comprising 4% of the dry matter)
Substances like pectin in tea leaves are metabolic byproducts of sugars, comprising approximately 4% of the dry matter. The presence of pectin facilitates the hand-rolling process during tea processing and is associated with the viscosity of the tea infusion. Water-soluble pectin is one of the main components that contribute to the thickness and glossiness of the tea infusion.
Organic acids (comprising 3% of the dry matter)
Tea leaves contain a variety of organic acids, constituting approximately 3% of the dry matter. The organic acids found in tea leaves are primarily free organic acids, such as malic acid, citric acid, succinic acid, and oxalic acid. During tea processing, additional organic acids are formed, including palmitic acid, linoleic acid, and acetic acid.
Organic acids in tea leaves are one of the main components contributing to the aroma. It has been discovered that there are 25 different types of organic acids among the aromatic compounds in tea leaves. While some organic acids may not possess inherent aroma, they can transform into aromatic compounds through oxidation, such as linoleic acid. Additionally, certain organic acids act as effective adsorbents for aroma compounds, such as palmitic acid.
Lipids (comprising 8% of the dry matter)
Lipids found in tea leaves include fats, phospholipids, glycolipids, sugar esters, and sulfides, comprising approximately 8% of the dry matter. They play a positive role in the formation of tea aroma. Lipids in the protoplasm of tea plant cells have a regulatory effect on the substance permeation of human cells.
Pigments (comprising 1% of the dry matter)
The pigments in tea leaves can be categorized into liposoluble pigments and hydro soluble pigments, with their content accounting for only about 1% of the dry matter in tea leaves. Liposoluble pigments are insoluble in water and include chlorophyll, xanthophylls, and carotenoids. Hydrosoluble pigments include flavonoids, anthocyanins, and the oxidative products of tea polyphenols, such as theaflavins, thearubigins, and theabrownins.
Liposoluble pigments are the primary components responsible for the color of dry tea and the color of the tea infusion. The color of the six major tea categories is closely related to the content, composition, and transformation of pigments in tea leaves.
Aromatic compounds (comprising 0.02% of the fresh leaf total)
Aromatic compounds in tea refer to the collective term for volatile substances present in tea leaves.
Although the content of aromatic compounds in tea leaves is not high, the variety is complex. According to analysis, tea leaves typically contain more than 300 different aroma compounds. The main components of tea's aromatic compounds include alcohols, phenols, aldehydes, ketones, acids, esters, lactones, nitrogen-containing compounds, sulfur-containing compounds, hydrocarbons, and oxides, among others.
In fresh tea leaves, alcohol compounds are the predominant aromatic compounds. Low-boiling-point leaf alcohols contribute to the strong grassy aroma, while high-boiling-point compounds such as agarwood alcohol and phenethyl alcohol contribute to the fragrant and floral characteristics.
Vitamins (comprising 0.6% to 1% of the dry matter)
Tea leaves contain a rich variety of vitamins, with their content ranging from 0.6% to 1% of the dry matter. Vitamins can be classified into water-soluble and fat-soluble types.
Fat-soluble vitamins include vitamin A, vitamin D, vitamin E, and vitamin K. Among them, vitamin A is present in relatively higher amounts. Fat-soluble vitamins are insoluble in water and cannot be directly absorbed and utilized when consuming tea.
Water-soluble vitamins include vitamin C, vitamin B1, vitamin B2, vitamin B3, vitamin B5, vitamin B11, vitamin P, and inositol. Vitamin C has the highest content among water-soluble vitamins, and drinking tea can contribute to the intake of certain nutritional components.
Enzymes (several)
Enzymes are a class of biologically active proteins that serve as catalysts for various chemical reactions within organisms. They are characterized by high efficacy and strong specificity. Without enzymes, including in tea plants, all biological processes would cease to exist. The synthesis and transformation of substances in tea plants also depend on the catalytic action of enzymes.
Enzymes, as proteins, participate in a series of chemical changes caused by enzymatic activity in the life processes of tea plants and during tea processing. Therefore, they are also referred to as biological catalysts.
Enzymes are characterized by vulnerability to denaturation and inactivation under high or low temperatures. Each type of enzyme has an optimal temperature range for activity, typically between 30°C and 50°C. If enzymes become inactivated or denatured, their catalytic ability is lost.
Tea processing takes advantage of these characteristics of enzymes by using technical methods to either inhibit or activate enzyme activity. This allows for enzymatic reactions to occur according to the requirements of different tea types, resulting in the unique color, aroma, and flavor of each tea.
Inorganic compounds (comprising 3.5% to 7.0% of the dry matter)
The collective term for inorganic compounds in tea is referred to as ash content. It represents the residue of tea leaves after being incinerated at 550°C. The ash content in tea leaves accounts for 3.5% to 7.0% of the dry matter and is divided into water-soluble and water-insoluble fractions. Ash primarily consists of mineral elements and oxides.
The water-soluble fraction of ash, which can dissolve in water, makes up 50% to 60% of the total ash content. Tea leaves with good freshness tend to have higher water-soluble ash content, while coarse and aged tea or tea with a high stem content has a higher overall ash content. Ash content is one of the quality inspection indicators for exported tea, with a general requirement of not exceeding 6.5%.
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