Edwin Haslam

Polyphenol complexation—some thoughts and observations

Abstract Current views and opinions on polyphenol (tannin)-protein complexation are outlined. ‘Structure-activity’ relationships are delineated as are experimental approaches which seek to define the modes and sites of binding of ligand (polyphenol) to the receptor (protein). A model for polyphenol-protein complexation is proposed.

Polyphenols, astringency and proline-rich proteins

Recent, NMR and precipitation, studies of molecular recognition of proline-rich proteins and peptides by plant polyphenols are described and rationalized. The action of polysaccharides and caseins in the moderation of the astringent response, which is engendered by polyphenols present in foodstuffs and beverages, is described. The possible influence of plant cell wall glycoproteins on the process of lignification is discussed in the light of the observed affinity of phenolic substrates for prolyl residues in protein structures.

Natural astringency in foodstuffs — A molecular interpretation

The structures of plant polyphenols (vegetable tannins) are briefly reviewed. Their interactions with proteins, polysaccharides, and the alkaloid caffeine are discussed at the molecular level, and these fundamental properties are related to the quality of astringency that polyphenols possess. The various ways in which astringency may be modified and ultimately lost are outlined in relation to the aging of red wines, the formation of nonbiological hazes in beers and lagers, and the ripening of fruit.

Plant proanthocyanidins. Part I. Introduction; the isolation, structure, and distribution in nature of plant procyanidins

The isolation and determination of structure of some plant procyanidins in their free phenolic forms are described. The distribution of procyanidins in the tissues of twenty-nine plant species has been examined and the biogenetic implications of this study are briefly discussed.

Thoughts on thearubigins

The chemistry underlying the changes which occur during tea leaf fermentation is reviewed and used as a basis for proposals for the structure of thearubigins, the major pigments of black teas.

Symmetry and promiscuity in procyanidin biochemistry

Abstract The occurrence and significance of procyanidins in the plant kingdom are reviewed. Stages in the elucidation of the structure and the stereochemistry of the procyanidins are outlined. Preferred helical conformations for the procyanidins, arising from the steric hindrance to rotation about the interflavan bond, are described. Biosynthetic studies are discussed and a theory of procyanidin metabolism is proposed.

Polyphenol interactions. Part 1. Introduction; some observations on the reversible complexation of polyphenols with proteins and polysaccharides

Early studies of the interactions between polyphenols and proteins are reviewed. The complexation of some simple phenols and a group of biosynthetically inter-related esters of gallic acid with bovine serum albumin (BSA) is examined by equilibrium dialysis and microcalorimetry. The phenomenon is pH dependent. The results indicate that molecular size and conformational flexibility of the polyphenol substrate lead to enhanced interactions with the protein. Preliminary studies with polysaccharides indicate that the binding here is pH independent. These studies suggest that whilst the binding of polyphenols to these macromolecules is influenced by similar structural features the ability of the polysaccharide to form structures which encapsulate the polyphenol is, in this instance, a further critical feature of the complexation.

Plant polyphenols (syn. vegetable tannins) and chemical defense-A reappraisal.

Many of the hypotheses adumbrated to rationalize the role of natural products in plant-herbivore interactions have focused attention on plant polyphenols (syn., vegetable tannins). Contemporary interpretations of the importance of plant polyphenols rest largely on the assumption that they act via their capacity to bind to proteins. The central proposition of plant-herbivore interactions, namely that plants, as a response to environmental pressures, have evolved the strategem of a chemical armory appropriate to the challenges they face, is examined in the context of plant polyphenols—their ability to complex to protein and their possible function as structural polymers.

Polyphenol interactions: astringency and the loss of astringency in ripening fruit☆

Abstract The inhibition of the enzyme β-glucosidase by natural polyphenolic substrates is described. The kinetic data suggest that the pattern of inhibition w

Tannin interactions with a full‐length human salivary proline‐rich protein display a stronger affinity than with single proline‐rich repeats

The protein IB5 has been purified from human parotid saliva. This protein contains several repeats of a short proline‐rich sequence. Dissociation constants have been measured at several discrete binding sites using 1H‐NMR for the hydrolysable tannins (polyphenols) ( , and and the condensed proanthocyanidin (−)‐epicatechin. The dissociation constants for trigalloyl glucose and pentagalloyl glucose were 15 × 10−5 and 1.7 × 10−5 M, respectively, which are 115 and 1660 times stronger than those previously measured under the same conditions for a single repeat of a mouse salivary proline‐rich protein. The increase in affinity is ascribed to intramolecular secondary interactions, which are strengthened by the rigidity of the interacting molecules.