When drinking tea, the sensitive tongue quickly conveys the flavors in the tea soup to the brain, leading to feelings of satisfaction or enjoyment. But what substances are responsible for the tastes perceived by the tongue? Science-loving editor specially invites friends to popularize some hard knowledge about drinking tea!
The flavor substances in tea soup can be summarized as: sugars, amino acids, phenolic compounds and their oxidation products (mainly tea polyphenols), purine alkaloids (primarily caffeine), organic acids, and tea saponins. Among these, tea polyphenols, amino acids, and caffeine have the greatest impact on tea leaves quality. The taste of tea is a comprehensive response of human taste organs to the flavor components in tea. Therefore, the amounts of various flavor components and changes in their proportions all affect the taste of the tea soup.
1. Astringency —— Phenolic Substances and Their Oxides
Among the phenolic substances in tea soup, catechins have the highest content. Esterified catechins present a bitter and astringent taste with strong convergence. The astringency felt upon sipping some tea soups is mainly because esterified catechins react with proteins in the oral mucosa to form impermeable substances, causing收敛. From a sensory perspective, astringency is also produced by stimulating touch nerve endings.
2. Bitterness —— Purine Substances (Mainly Caffeine)
Among the purine substances contained in tea leaves, caffeine is the main flavor-presenting substance, which exhibits bitterness. Due to its volatility when heated, its content shows a clear downward trend during multiple infusions of tea. Because caffeine stimulates the central nervous system, while also activating cerebral cortex cells and stimulating gastric juice and bile secretion, it is the main substance forming people's preference for tea.
Anthocyanins in tea soup are also a source of bitterness. When the anthocyanin content in tea soup exceeds its threshold, the tea soup has a noticeable bitter taste. A 150-milliliter tea soup containing 15 milligrams of anthocyanins has a distinct bitter taste. Purple buds contain 1% or even more anthocyanins. Summer tea, due to strong light exposure, has high anthocyanin content and more purple buds, which is also why summer tea is often more bitter and astringent and of poorer quality.
3. Freshness —— Amino Acids
Green tea taste requires mellow, sweet, and refreshing qualities, among which the sweet and refreshing口感 are related to amino acids in tea leaves. There are many types of amino acids in tea leaves, and their presented characteristics also vary. The highest content is theanine, which is also a unique amino acid in tea. The amino acids with relatively high content in tea mainly include glutamic acid, aspartic acid, arginine, glutamine, asparagine, etc. In terms of the taste characteristics of each amino acid, not all amino acids present freshness; most amino acids are sweet or bitter.
According to relevant reports, most L-type amino acids are bitter, a few are sweet or fresh; D-type amino acids are all sweet. The amino acids that constitute proteins in nature are all L-type. Therefore, the amino acids obtained from protein hydrolysis in tea leaves mostly impart a bitter taste to the tea soup. Although the configuration of free amino acids in tea leaves is difficult to determine, it is certain that the taste quality they impart to the tea soup is not only freshness but also bitterness and sweetness. These different taste qualities, through different combinations and comprehensive effects, constitute the various different 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 contained in tea leaves. The sugar content is not high, but due to the different perception thresholds of the human taste organs for sweet and bitter tastes and the different sensing locations for different tastes, the small amount of sugar in the tea soup presents a stronger perception after people feel slight bitterness. The synergistic effect of sweetness and bitterness produces the pleasant feeling when tasting tea. The tea soup also contains a certain amount of pectin and glycosides of phenolic substances, which also play a role in the formation of the tea soup's taste. Water-soluble pectin can give the tea soup a thick and mellow口感.