Interactive Precipitation Between Phenolic Fractions and Peptides in Wine-Like Model Solutions: Turbidity, Particle Size, and Residual Content as Influenced by pH, Temperature and Peptide Concentration

¹ The Institute of Enology and Viticulture, Yamanashi University, Kofu, Yamanashi 400, Japan
² University of California, Davis, CA 95616-8749.

Four gelatin preparations (whole gelatin of average MW 70 000 and gelatin peptides of average MW 10 000, 5000, and 2000), three synthetic peptides (MW 2531, 1354, and 1274) composed of a repeating sequence of amino acid residues (proline, proline or hydroxyproline, and glycine), and soluble and insoluble polyvinylpyrrolidone were used. They were mixed with four phenolic fractions (dimeric, oligomeric, polymeric, and total phenol fractions from grape seeds) in aqueous 10% ethanol solutions of pH 2.5 to 4.0. After four days at 4°C, 15°C, or 25°C, the turbidity, residual phenol and peptide contents, and particle sizes of the precipitates formed in the mixtures were determined. The turbidity increased with increasing particle size and with decreasing residual phenol and peptide. Increasing the pH from 2.5 to 3.0 - 3.3 (depending on the phenolic fraction) or lowering the storage temperature resulted in increased turbidity and decreased residual phenol and peptide, but the degrees of the changes in turbidity and residual contents varied with the phenolic fraction. Increasing the amounts of large MW whole gelatin and the 2000 MW gelatin peptide from 25 to 150 mg/L resulted in increasing turbidity, increasing particle size, and decreasing residual phenols. The turbidity with the small gelatin peptide was higher than that with the large gelatin below pH 3.0 to 3.3, but above these pH values the turbidity with the latter was larger than that with the former. The phenol adsorption capacity of the small synthetic peptides was higher than that of large MW whole gelatin or the other gelatin preparations when added at the same weights, but other effects were similar. The results on the interaction between the small peptides and the phenolic fractions showed that the gelatin peptides and the synthetic peptides of low molecular weight were very effective for fining wines, at least at the same levels as whole gelatin or soluble polyvinylpyrrolidone with high affinity for phenols. The mode of association for phenol-peptide interaction and the properties of peptide chains effective for the adsorption of phenols are discussed.

Key words: phenols, peptides

Submitted on May 23, 1994