Proline astringency

Even higher proline contents have been reported in salivary PRPs these can contain 40-45 mol% proline and also have a substantial amount of glutamine. This protein binds ingested polyphenols, which precipitates the PRPs and removes the lubrication these normally provide. The result is the sensation of astringency (Green, 1993 Haslam and Lilley, 1988). 

Luck, G. et ak. Polyphenols, astringency and prolin-rich proteins. Phytochemistry 37, 357, 1994. 

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. 

Thus, Tressl et al.219 characterised eight 2-(l-pyrrolidinyl)-2-cyclopentenones and 11 cyclopcnt(/ )azcpin-8( lf/)-oncs from proline-monosaccharide and proline-cyclic enolone systems. The compounds possessed bitter tastes, with the former exhibiting concomitant astringency. The bitter thresholds in water of Structure 33 and 34 were 50 and 10 ppm, respectively. 

Luck G, Liao H, Murray NJ, Grimmer HR, Warminski EE, Williamson MP, Lilley TH, Haslam E Polyphenols, astringency and proline-rich proteins. Phytochemistry 1994 37 357-371. 

Collectively these results fully complement those of Hagerman and Butler who showed that proline-rich and conformationally mobile proteins have high affinities for polyphenols and that, on occasion, such proteins may be preferentially precipitated in presence of other proteins. Complementarity between the polydentate ligand (polyphenol) and the receptor (protein) is maximized by conformational flexibility in both components. The results also show that there is a very wide variability in the protein-complexing capabilities of the polyphenolic end-products of gallic acid metabolism (Fig. 19), There is no clearly consistent pattern nor is there evident any discernable correlation between the apparent metabolic cost to the plant of its synthesis of a particular polyphenol and that polyphenol s astringency, i.e. its ability to complex with protein. 

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