Tea The flavor compounds in tea soup can be summarized as: sugars, amino acids, phenolic substances and their oxidation products (mainly tea polyphenols), purine alkaloids (mainly caffeine), organic acids, and tea saponins. Among them, tea polyphenols, amino acids, and caffeine have the greatest impact on tea quality. The taste of tea is a comprehensive response of the human taste organs to the flavor components in tea. Therefore, the content of each flavor component and the changes in their proportions will affect the taste of tea soup.

1) Astringency — Phenolic substances and their oxides

The phenolic substances in tea soup are mainly catechins. Ester-type catechins present a bitter and astringent taste with strong astringency. The astringent taste caused by some tea soups is mainly because ester-type catechins react with oral mucosa proteins to form impermeable substances, causing astringency. From a sensory perspective, astringency is also produced by stimulating the nerve endings of the sense of touch.

2) Bitterness — Purine substances (mainly caffeine)

Among the purine substances in tea, caffeine is the main flavor compound, presenting a bitter taste. Due to its volatility when heated, its content decreases significantly during multiple infusions. Caffeine has a stimulating effect on the central nervous system and also stimulates the activity of brain cortex cells, gastric juice, and bile secretion, making it a major substance that forms people's preference for tea.

Anthocyanins in tea soup are also a source of bitterness. When the content of anthocyanins in tea soup exceeds its threshold, the tea soup has an obvious bitter taste. When 150 ml of tea soup contains 15 mg of anthocyanins, the bitterness is evident. Purple buds contain 1% or even more anthocyanins. Summer tea, due to strong light exposure, has a high anthocyanin content, resulting in many purple buds, which is also the reason why summer tea is often bitter and astringent and of poor quality.

3) Umami — Amino acids

Green tea requires a mellow and refreshing taste, and both the sweet and fresh sensations are related to the amino acids in tea. There are many types of amino acids in tea, each presenting different characteristics. The most abundant is theanine, an amino acid unique to tea. Other amino acids with higher content in tea include glutamic acid, aspartic acid, arginine, glutamine, and asparagine. Regarding the taste characteristics of each amino acid, not all amino acids present umami; most amino acids present a sweet or bitter taste. According to relevant reports, L-type amino acids mostly present a bitter taste, while a few present a sweet or umami taste; D-type amino acids all present a sweet taste. In nature, the amino acids that make up proteins are all L-type. Therefore, the amino acids obtained from protein hydrolysis in tea mostly give a bitter taste to the tea soup. Although the configuration of free amino acids in tea is difficult to determine, it is certain that they do not only give umami to the tea soup but also bitterness and sweetness. These different tastes, through different proportions and comprehensive effects, constitute the various taste characteristics of tea soup.

4) Sweetness — Sugars and other substances

The sugars that present sweetness in tea soup are mainly soluble sugars such as monosaccharides and disaccharides in tea. The content of sugars is not high, but due to the different thresholds of human taste organs for sweet and bitter tastes and the different positions of taste perception, a small amount of sugar in tea soup produces a stronger sensation after people perceive a slight bitterness. The synergistic effect of sweetness and bitterness produces a pleasant feeling when tasting tea. Tea soup also contains a certain amount of pectin and phenolic glycosides, which also contribute to the formation of tea soup taste. Water-soluble pectin can give tea soup a thick and mellow taste.

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