Astringency proteins structures

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. 

Data for the metabolites in plasma are generally for the unbound forms, but there is ample evidence that PPT bind noncovalently to proteins. Most studies on PPT-protein interaction have focused on protein utilization or astringency but a few studies have addressed binding to plasma proteins and lipoproteins. " " Strongest binding has been associated with 1,2-dihydroxyphenols and proline-rich proteins such as those character-istic of human saliva and structure-activity relationships have been reported. 

Tannins are used in medicine primarily because of their astringent properties, which are due to the fact that they react with the proteins of the layers of tissue with which they come into contact. Tannins are known to tan the outermost layer of the mucosa and to render it less permeable and more resistant to chemical and mechanical injury or irritation however, the correlation between the molecular structures of tannins and the astringent/antiulcer activity is not known. 

The sensation of astringency is felt differently by tasters [86] probably due to differences in individuals saliva in terms of its protein composition [11, 47]. Astringency is also affected by the structure of the phenolic compounds [88], pH [89], the presence of other substances [90-92], and viscosity [11]. In fact it is believed that complex beverages such as wine and beer have subtle sub-qualities of sensorial descriptors related to astringency (soft, grainy, harsh, green, chalky, etc.), that are not perceived in tannin model solutions, which could be due to the presence of other molecules [87]. 

Recent progress in the characterization of numerous tannins has enabled the investigation of the biological activities of these compounds on the basis of structural differences in a way similar to that used for die other types of natural organic compounds such as alkaloids, terpenoids and flavonoids. Besides astringency, a fundamental property of tannins, based on strong affinity to biopolymers such as proteins and polysaccharides, various biological and pharmaceutical activities beneficial to human healdi, have been found. 

Collectively these results complement those of Hagerman and Butler (31) who, in a separate study, showed that conformationally mobile proteins - as opposed to those with a tightly coiled secondary structure - have high affinities for polyphenols. Complimentarity between the polydentate ligand (polyphenol) and receptor (protein) is thus maximized by conformational flexibility in both components. In this context the comparatively lower astringency of the proantho-cyanidins (3) may, in part, be explicable in terms of the conformational restraints imposed by restricted rotation about the repeating inter-flavan bonds (40). 

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