Composition of Protein Fractions from Precipitates Formed in Muscat Bailey A Red Wines during Aging

Abstract

Muscat Bailey A red wines produced from 1981 to 1991 were stored in 1.8-L glass bottles at 15°. Precipitates were collected from the wines by centrifugation at 39, 000×g for 30 minutes and analyzed. The contents of proteins, total phenols, and neutral sugars were 19 to 88 mg/l with an average of 55 mg/l, 16 to 118 mg/l with an average of 72 mg/l, and 25 to 140 mg/l with an average of 77 mg/l, respectively. A linear correlation was observed between the turbidity of the wines and the contents of protein, total phenol, and neutral sugar in the precipitates, suggesting that the turbidity in red wine is formed by mutual interaction among proteins, phenols and neutral sugars. The 1987 wine, which exhibited nearly the average values of the wine components, was selected for further analysis. When the proteins in the wine precipitate were solubilized with pH 10.0 buffer, the recovery of solubilized proteins was about 80% of the total proteins in the precipitate. The solubilized fraction after dialysis was composed of 20% proteins, 35% total phenols and 29% neutral sugars. The 1981 and 1991 wines, which had the longest and shortest storage times, respectively, and the 1984 wine which had the highest turbidity, were chosen for fractionation of the soluble proteins and proteins from the wine precipitates, followed by amino acid analysis. There was a considerable difference in amino acid composition, especially with respect to aspartic acid, threonine, serine, and alanine, between the soluble proteins and the proteins in precipitates from the three wines.