Rigidity, conformation, and solvation of native and oxidized tannin macromolecules in water-ethanol solution

Abstract

We studied by light scattering and small angle x-rays scattering (SAXS) conformations and solvation of plant tannins (oligomers and polymers) in mixed water-ethanol solutions. Their structures are not simple linear chains but contain about 6% of branching. Ab initio reconstruction reveals that monomers within a branch are closely bound pairwise. The chains are rather rigid, with the Kuhn length b = 13+/-3 nm, corresponding to about 35 linearly bound monomers. Contribution of solvation layer to SAXS intensity varies in a nonmonotonic way with ethanol content phi(A), which is an indication of amphipathic nature of tannin molecules. Best solvent composition phi(A)(B) is a decreasing function of polymerization degree N, in agreement with increasing water solubility of tannins with N. Polymers longer than b present a power-law behavior I approximately Q(-d) in the SAXS profile at high momentum transfer Q. The monotonic decrease in d with increasing phi(A) (from 2.4 in water to 1.9 in ethanol) points that the tannins are more compact in water than in ethanol, presumably due to attractive intramolecular interactions in water. Tannins were then oxidized in controlled conditions similar to real biological or food systems. Oxidation does not produce any intermolecular condensation, but generates additional intramolecular links. Some oxidation products are insoluble in water rich solvent. For that reason, we identify these species as a fraction of natural tannins called "T1" in the notation of Zanchi et al. [Langmuir 23, 9949 (2007)]. Within the fraction left soluble after oxidation, conformations of polymeric tannins, despite their higher rigidity, remain sensitive to solvent composition.

Applying Nanoparticle Tracking Analysis to Characterize the Polydispersity of Aggregates Resulting from Tannin–Polysaccharide Interactions in Wine-Like Media

“…It would be expected that the larger aggregates detected by DLS and NTA represented colloidally dispersed particles. According to Zanchi et al [31,32], tannins which form aggregates between 12 and 60% v / v ethanol are preferentially solvated in ethanol, and that the proportion falling into this class may be enhanced by oxidation. The phloroglucinolysis conversion yield for ST was 67% (Supplementary Table S1), and it might be hypothesized that the uncharacterized portion indicates the presence of oxidized tannins in ST.…”

Wine and Grape Tannin Interactions with Salivary Proteins and Their Impact on Astringency: A Review of Current Research

“…An increase in protein precipitation with ethanol concentration of 13% compared with aqueous solutions may relate to the change in solubility of the formed protein-tannin complexes [ 112 ]. Zanchi and colleagues demonstrated differences in ethanol solubility in a mixture of grape-seed tannins due to both self-aggregation [ 114 , 115 ] and PRP-tannin aggregation [ 33 ], which is likely to relate to differences in the structure of the tannins. Changes in solubility of tannins in wine may also influence the resulting astringency [ 115 ].…”

Immobilization of flavan-3-ols onto sensor chips to study their interactions with proteins and pectins by SPR

“…Therefore, the higher association of apple pectins with DP2 could be due to both parameters (conformation of apple pectins and a higher availability of binding sites of dimer). Regarding flavan-3-ol oligomers, the number of catechol groups immobilized was unknown and the conformation is fully different from that of monomer and dimer, notably with increased rigidity [32], while orientation with the respect to the surface remains unknown. Associations, both with pectins or proteins, were not correlated to the number of hydroxyl groups of polyphenols immobilized contrary to the work of Jean-Gilles et al [33] but rather in the conformation adopted by polyphenols.…”