Protein Binding and Astringent Taste of a Polymeric Procyanidin, 1,2,3,4,6-Penta-O-galloyl-β-d-glucopyranose, Castalagin, and Grandinin

Abstract

The objective of the present investigation was to examine oral astringency and protein binding activity of four structurally well-defined tannins, namely procyanidin (epicatechin 16 (4→8)catechin), pentagalloyl glucose (1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose), castalagin, and grandinin, representing the three main structural categories of tannins, the proanthocyanidins, the gallotannins, and the ellagitannins. Astringency threshold and dose response were determined by the half-tongue test using a trained human panel. Protein binding stoichiometry and relative affinity were determined using radioiodinated bovine serum albumin in precipitation or competitive binding assays. Procyanidin and pentagalloyl glucose were perceived as highly astringent compounds and had relatively steep dose response curves but castalagin and grandinin had a lower mass threshold for detection. In vitro, procyanidin was the most effective protein precipitating agent, and grandinin the least. Increasing the temperature increased protein precipitation by the hydrolysable tannins, especially grandinin. All four polyphenols had higher relative affinity for proline-rich proteins than for bovine serum albumin.

Anti-Cancer, Anti-Diabetic and Other Pharmacologic and Biological Activities of Penta-Galloyl-Glucose

“…In accordance with this generalization, PGG has higher affinity for the proline-rich protein gelatin than for other globular proteins such as serum albumin(88). Detailed NMR studies of the interaction between PGG and proline rich peptides suggest a stacking interaction between adjacent galloyl rings on the polyphenolic and proline residues of the peptide(89).…”

“…Therefore, the long-term safety of PGG for cancer chemoprevention still needs to be rigorously established. Since PGG is astringent(88) and inhibits human salivary α-amylase(82), potential negative effect on starch digestion and food taste should be considered during preclinical or clinical studies.…”

“…Hoffman et al studied the astringency threshold and dose-response of PGG using the half-tongue test within a trained human panel (88). The taste threshold concentration for the astringent sensation induced by PGG in aqueous solution (pH 4.5) was 1.8 μM.…”

Interaction of phenolic compounds with bovine serum albumin (BSA) and α-amylase and their relationship to astringency perception

“…In this way, several studies have been performed to correlate or predict the astringency by certain techniques based on the in vitro reactivity of polyphenols towards different proteins (Canon, Giuliani, Paté, & Sarni-Manchado, 2010;Fia, Dinnella, Bertuccioli, & Monteleone, 2009;Mateus & De Freitas, 2001;McRae et al, 2010;Monteleone, Condelli, Dinnella, & Bertuccioli, 2004;Obreque-Slier, López-Solís, Peña-Neira, & Zamora-Marín, 2010;Papadopoulou & Frazier, 2004;Papadopoulou, Green, & Frazier, 2005;Petrovic, 2009). Fluorescence quenching and nephelometry are commonly used for this purpose (Carvalho et al, 2006;De Freitas, Carvalho, & Mateus, 2003;Hofmann et al, 2006;Papadopoulou & Frazier, 2004;Soares, Gonçalves, Fernandes, Mateus, & de Freitas, 2009). Nephelometry is a particularly simple method that allows direct estimation of the amount of protein/tannin complexes (Mateus, Pinto, Ruão, & de Freitas, 2004).…”

The Chemistry and Chemical Ecology of Ellagitannins in Plant–Insect Interactions: From Underestimated Molecules to Bioactive Plant Constituents

“…With these functional assays, two samples might show very different tannin contents even though their true tannin content is the same: the assay result depends on the types of tannin (active or less active protein precipitants) present. This problem is especially pronounced with samples containing mainly monomeric C-glycosidic ellagitannins (ETs), since it is known that the loss of conformational flexibility decreases the affinity of tannins towards proteins and that C-glycosidic ETs present one of the most rigid tannin subgroups (Baxter et al, 1997;Kilkowski & Gross, 1999;Hofmann et al, 2006;Deaville et al, 2007). For this reason, samples that mainly contain gallotannins (GTs) or proanthocyanidins are expected to give a much higher yield in the protein-precipitation assays than C-glycosidic ETs.…”