Aggregation of a Proline-Rich Protein Induced by Epigallocatechin Gallate and Condensed Tannins: Effect of Protein Glycosylation

Astringency is one of the most important organoleptic qualities of numerous beverages, including red wines. It is generally thought to originate from interactions between tannins and salivary proline-rich proteins (PRPs). In this work interactions between a glycosylated PRP, called II-1, and flavan-...

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Bibliographic Details
Published in:Journal of agricultural and food chemistry 2008-08, Vol.56 (15), p.6724-6732
Main Authors: Pascal, Christine, Poncet-Legrand, Céline, Cabane, Bernard, Vernhet, Aude
Format: Article
Language:English
Subjects:
animal proteins
aqueous solutions
Biological and medical sciences
Catechin - analogs & derivatives
Catechin - chemistry
Colloids - chemistry
Drug Stability
dynamic light scattering
EGCG
epigallocatechin
ethanol
flavan-3-ols
flavanols
Food Chemistry/Biochemistry
Food engineering
Food industries
Fundamental and applied biological sciences. Psychology
Glycosylation
grape seeds
Humans
Life Sciences
Light
molecular weight
proanthocyanidins
Proanthocyanidins - chemistry
proline
Proline - analysis
Proline - chemistry
Proline-rich proteins
protein aggregates
protein content
protein structure
saliva
Salivary Proteins and Peptides - chemistry
Scattering, Radiation
Seeds - chemistry
sensory properties
small-angle X-ray scattering
Solutions
solvents
tannins
Vitis - chemistry
X-Rays
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Summary:Astringency is one of the most important organoleptic qualities of numerous beverages, including red wines. It is generally thought to originate from interactions between tannins and salivary proline-rich proteins (PRPs). In this work interactions between a glycosylated PRP, called II-1, and flavan-3-ols were studied in aqueous solutions and at a colloidal level, by dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS). The flavan-3-ols were a monomer, epigallocatechin gallate (EGCG), and polymerized flavan-3-ol fractions extracted from grape seeds. In aqueous solutions containing EGCG and protein II-1, protein aggregation took place when protein concentration and the EGCG/protein ratio exceeded a threshold. The aggregates had a small size, comparable with the dimensions of protein monomers, and formed stable dispersions (no phase separation). Most proteins remained free in solution. This behavior is in sharp contrast with the phase separation observed for nonglycoslated PRP in the same conditions. Moreover, this slight aggregation of II−I in the presence of EGCG was disrupted by the addition of 12% ethanol. Increasing the flavan-3-ol molecular weight strongly enhanced II−I/tannin aggregation: the threshold was at a lower protein concentration (0.2 mg/mL) and a lower tannin/protein ratio. Still, in most cases, and in contrast with that observed with a nonglycosylated PRP, the aggregates remained of discrete size and stable. Only at low ethanol content (2%) did the addition of tannin polymers finally lead to phase separation, which occurred when the molar ratio of tannins to proteins exceeded 12. This systematic effect of ethanol confirmed the strong effect of cosolvents on protein/tannin interactions.
ISSN:0021-8561
1520-5118
DOI:10.1021/jf800790d