Interactive Precipitation between Graded Peptides from Gelatin and Specific Grape Tannin Fractions in Wine-like Model Solutions

¹ Institute of Enology and Viticulture, Yamanashi University, Kofu, Japan
² Department of Viticulture and Enology, University of California, Davis, CA 95616-5270.

Peptides isolated from gelatin hydrolysates purified with repeated dialysis and gel-permeation chromatography were mixed in aqueous alcoholic solutions of tartaric acid resembling wine with monomeric catechin or dimeric and oligomeric condensed tannin fractions from grape seeds. Precipitation did not increase significantly after the first day at 15°C. Exposure to air or nitrogen in the headspace made no difference in the results in tests up to two weeks. Increasing ethanol content decreased precipitation, but glucose and KCl had no effect. Although the largest peptide fraction caused haze, the smallest peptide fraction (2000 MW) was most effective in producing clarification by precipitation. Monomeric or dimeric flavonoids did not readily precipitate with the peptides but did interfere with precipitation by tannin. Completeness of precipitation was diminished by increasing acid in the range pH 4.5 to 2.5 suggesting that hydrogen bonding, at least with regard to protonation of the phenols, is not the only mechanism.

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