Fruit astringent taste

The strongly astringent taste of persimmon fruits arises from soluble tannins that accumulate in large specialized cells called tannin cells. In this chapter, some chemical properties of persimmon tannins, an outline of simple and reliable methods for estimation of the degree of astringency and the amount of tannins, and some aspects of the physiological changes in the tannin contents of persimmon fruits will be described. 

The Folin-Ciocalteau (FC) procedure is one of the standard procedures in wine analysis, as well as in tea analysis (Wiseman et al., 2001). One drawback in interpretation is that different classes of phenolics have varying taste attributes, and tests for chemical astringency based on precipitation of proteins have been recently developed (Adams et al., 1999). In addition, if the food product contains sugar, it can mask the bitterness and astringency, as observed in ripe fresh fruit, sweetened chocolates, and tea. 

Features A tree-like shrub, ten to twenty feet high. Fruit shiny black, sweet and edible. Young bark glossy purplish-brown, with scattered warts. Old bark greyish-brown, inner surface white. Fracture short. Root bark cinnamon colour. Taste bitter, astringent. 

L-Tartaric acid is an abundant constituent of many fruits such as grapes and bananas and exhibits a slightly astringent and refreshing sour taste. It is one of the main acids found in wine. It is added to other foods to give a sour taste and is normally used with other acids such as citric acid and malic acid as an additive in soft drinks, candies, and so on. It is produced by acid hydrolysis of calcium tartrate, which is prepared from potassium tartrate obtained as a by-product during wine production. Optically active tartaric acid is used for the chiral resolution of amines and also as an asymmetric catalyst. 

The flavonols and their glycosides contribute to specific taste characteristics such as bitterness and astringency in berry fruits and their products (Shahidi and Naczk, 1995). The molecular structure of flavonols lacks the conjugated double bonds of the anthocyanins, and they are thereby colorless. They may, however, contribute to discoloration of berry fruits, as they are readily oxidized by O-phenoloxidase in the presence of catechin and chlorogenic acid. Discoloration may also occur as a consequence of complex formation with metallic ions. On the other hand, the flavonol glycoside rutin is known to form complexes with anthocyanins, thus stabilizing the color of these compounds. 

The basic varieties, sweet and sour cherry, have been crossed to over 600 types. The taste of the stone fruits is acid, sweet and slightly astringent. The balance depends on the ripeness and especially on the species. The flavour is fresh, fruity, green, floral and slightly spicy and develops a strong bitter almond, benzaldehyde character when crushed. 

Irregular flaky or bladdery, 1-1.5 cm long and 0.5-1 cm wide. Externally purplish-red to purplish-black, shrunken, lustrous. Sometimes with a rounded scar of persistent calyx at the apex and a scar of fruit stalk at the base. Texture soft. Odour, slight taste, sour, astringent and slightly bitter. 

The taste of fruits is influenced by phenolic compounds. The presence of tannins yields an astringent, harsh taste, similar to an unripe apple (or an apple variety suitable only for processing). Table quality apples are low in phenolic compounds. Flavanones (naringin, neohesperidin) are the bitter compounds of citrus fruits. 

Soluble pectins bind polyphenols, quench their astringent effect and, thus, contribute to the mild taste of ripe fruits. 

Monomeric units of condensed tannins, which lack their astringent and bitter taste, are colourless catechins, also known as 3-hydroxyflavans or flavan-3-ols (8-305). They are intermediates in the biosynthesis of other flavonoids. Flavan-3-ols are found in virtually all fruits, vegetables and other plant materials. Their structure depends on the stereochemistry of the flavan-3-ol units, the number of hydroxyl groups, the stereochemistry of mutual bonds of units forming oligomers, the degree of polymerisation... 

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