Bitterness of foodstuff may be caused either by naturally occurring bittering compounds or by chemical during storage or processing. The bitterness and astringency of tea are mainly formed by the combination of tea polyphenols, caffeine, and some amino acids.
Catechins account for approximately 70%-80% of total tea polyphenols. The main polyphenols found in tea are flavonoids. Flavonoids are a group of bioactive compounds synthesized during plant metabolism. Flavonoids contain two six-carbon rings linked by a three-carbon unit, which is also known as a chalcone structure.
Catechins (also referred to as flavanols) are bioactive compounds that are a subclass of flavonoids, and, in tea, are the main secondary metabolites. The four components in tea with the highest catechin content are epicatechin (EC), epicatechin gallate (ECg), epigallocatechin (EGC), and epigallocatechin gallate (EGCg). According to recent studies sensory evaluations indicated that the taste of catechin is bitter and astringent.
Green teas or teas made with tea leaves harvested later in the season have less theanine but more catechins and, therefore, have more astringency and bitterness. Thus, green teas or teas made with leaves harvested early in the season may have umami and sweet taste whereas green teas made with leaves harvested later in the season will be more bitter and astringent.
Another important factor affecting the bitter taste of tea is caffeine. Caffeine is the main alkaloid in tea, which generally accounts for 2%-5% of the dry weight of tea. Some studies have shown that the main flavor of caffeine is bitterness.
Bitterness of tea
