Astringency of Fruits and Fruit Products in Relation to Phenolic Content

Abstract

Publisher Summary This chapter briefly discusses the nature of the constituents responsible for the sensation of astringency and the physiology of the astringency sensation and the factors influencing it. Variety, maturity, and climate are known to influence the astringency of fruit. The chapter presents extensive data on the effect of seasonal conditions on the astringency of American grape juices, and also on apple juices. Certain fruits are astringent when they are unripe. During ripening on the tree or in storage, this astringency disappears. This loss in astringency may be accompanied by a change in the tannin fraction. The actual change in tannins, determined chemically, are small and may either increase or decrease. In astringent fruits, the main phenolic compounds found are flavanols. Both the flavanols and the flavan diols occur. Other major constituents of the phenolic fraction consist of the flavanols, kaempferol, quercetin, myricetin, chlorogenic acid, and the cinnarnic acids such as caffeic acid. Apart from environmental factors such as locality, season, stage of development, and mineral nutrition, which are known to affect the level of phenolic compounds in fruits, and hence astringency, various secondary treatments can decrease the degree of astringency in fruits, for example, treatment with carbon dioxide, ethylene; precipitation of the tannin with acetic acid, formaldehyde; and oxidation with ozone. Astringency may also be reduced by air drying, particularly in persimmons. If the fruit is chilled, astringency may increase. The various theories proposed to explain loss in astringency have been classified into three groups: binding, change in molecular size of the tannins, and a change in the hydroxylatzon pattern of the Phenolic Compound.