Astringency flavanols

Tea oxidation is generally referred to as fermentation because of the erroneous early conception of black tea production as a microbial process.66 Not until 1901 was there recognition of the process as one dependent on an enzymically catalyzed oxidation.67 This step and further reactions result in the conversion of the colorless flavanols to a complex mixture of orange-yellow to red-brown substances and an increase in the amount and variety of volatile compounds. Extract of oxidized leaf is amber-colored and less astringent than the light yellow-green extract of fresh leaf and the flavor profile is considerably more complex. 

The combination of caffeine with the oxidation products of gallated flavanols produces the characteristic described as tangy astringency , probably equivalent to the term briskness applied by professional tea-... 

The organoleptic properties of black tea depend to a considerable extent on the astringency resulting from the interaction of caffeine with the oxidized galloyl ester of the flavanols. The aroma components of black tea also constitute a unique flavor profile that blends well with the taste of the nonvolatile materials. The caffeine provides a moderate level of stimulation, which adds further to the appeal of the beverage, although tea has been shown to provide relaxation as well as revival of character.119... 

The astringency of wine tannin fractions appears to be correlated to the content of flavanol units released after thiolysis regardless of their environment in the original mol-ecules. Anthocyanins contributed neither bitterness nor astringency. Whether incorporation of anthocyanin moieties in tannin-derived structures affects their interactions with proteins and taste properties remains to be investigated. 

Dianthrone derivatives Hypericin, pseudohypericin, anthranol, photohypericin, hypericodehydrodianthrone Flavanols Catechin polymers (condensed tannins), leucocyanidin, epicatechin Photodynamic, antidepressant [monoamine oxidase inhibitor (MAOI)], antiviral Astringent, anti-inflammatory, styptic, antiviral... 

Among polyphenolic compounds, two types of flavonoids, the anthocyanins and flavanols (i.e., catechins, proanthocyanidins, condensed tannins), are particularly relevant to the quality of red wines, as they are key compounds for color definition and astringency. Other flavonoids such as flavonols may have some influence on color and bitterness, although they are present in red wines in much lower amounts. Phenolic acids and hydrolysable tannins, released from barrel wood, may also have an influence on wine taste and color, and hydroxycinnamoyl derivatives from grape must are involved in the oxidative browning of white wines together with flavanols. Besides, some of these perceptions may be modified by other sensory characteristics (e.g. sourness, sweetness) related to other wine components (Preys et al. 2006). 

Anthocyanins, flavanols and phenolic acids are the main polyphenols of grapes and grape-derived foods, responsible for their major organoleptic properties. Anthocyanins are directly involved in the color of most red fruits including grapes (7) while flavanols are thought to make an important contribution to the astringency and bitterness of plant derived foods (2,3). 

These natural compounds are of particular relevance due to their biological activities that contribute to the therapeutic properties attributed to some plants, especially those highlighted since many years ago by the traditional Chinese medicine. These features make flavanols a particular target of the pharmaceutical industry. Besides this, flavanols are also responsible for some antioxidant and sensorial properties presented in fruits and fruit-derived products. The astringency sensation is one of those properties resulting from the interaction between flavanols and salivary proteins in the oral cavity. On the other hand, flavanols can also... 

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