Analysis of Chemical Components in Tea and Their Significance

Types and content: Polyphenols are the most abundant and important components in tea. They mainly include catechins, flavonoids, and phenolic acids. Catechins account for a large proportion of polyphenols in tea. For example, in green tea, the content of catechins can reach 15% - 30% of the dry weight of tea leaves. Different types of tea have different polyphenol compositions and contents.

Significance in tea quality: Polyphenols play a crucial role in the color, taste, and antioxidant properties of tea. In green tea, the high content of unoxidized catechins gives it a fresh and astringent taste and a green color. In black tea, during the fermentation process, catechins are oxidized into theaflavins and thearubigins, which are responsible for the red - brown color and mellow taste of black tea. In addition, polyphenols have strong antioxidant properties, which can help prevent oxidation and deterioration of tea during storage.

Health effects: Polyphenols have been proven to have many health benefits. They can scavenge free radicals in the body, reduce the risk of chronic diseases such as cardiovascular diseases and cancer, and improve the body's immune function.

Main amino acids in tea: The main amino acids in tea include theanine, glutamate, and aspartate. Theanine is the most characteristic amino acid in tea, accounting for about 50% - 70% of the total free amino acids in tea.

Significance in tea quality: Amino acids contribute to the freshness and umami taste of tea. In spring - harvested tea leaves, the content of amino acids is relatively high, which makes spring tea taste more fresh and mellow. They also play a role in the aroma formation of tea, reacting with other components during the processing to produce unique aroma compounds.

Health effects: Theanine has been shown to have a calming and relaxing effect. It can cross the blood - brain barrier, regulate neurotransmitters in the brain, and help reduce stress and improve sleep quality.

Content and distribution: Caffeine is one of the important components in tea. The content of caffeine in tea leaves is usually between 2% - 5%. It is mainly distributed in the young leaves and buds of tea plants.

Significance in tea quality: Caffeine gives tea a certain degree of bitterness. However, in high - quality tea, the bitterness of caffeine is balanced with the sweetness and umami of other components, resulting in a harmonious taste. Caffeine also has a stimulating effect, which can refresh the mind.

Health effects: Moderate intake of caffeine can improve mental alertness, increase metabolism, and relieve fatigue. However, excessive intake may cause side effects such as insomnia, palpitations, and increased heart rate.

Types and formation: Tea contains a large number of volatile compounds, which are responsible for its unique aroma. These compounds include alcohols, esters, aldehydes, and ketones. They are formed during the growth, processing, and storage of tea. For example, during the withering and fermentation processes, many new volatile compounds are generated through enzymatic reactions and chemical reactions.

Significance in tea quality: The types and contents of volatile compounds determine the aroma type and quality of tea. Different types of tea have different characteristic aroma profiles. For example, jasmine tea has a strong floral aroma due to the addition of jasmine flowers during processing, while oolong tea has a complex floral - fruity aroma formed during its unique semi - fermentation process.