Characterization of Soluble Glycoproteins in Red Wine

Abstract

Red table wines, made annually from Muscat Bailey A grapes from 1981 to 1992 and aged in bottles for up to 12 years, were analyzed for soluble proteins and heat stability. The soluble protein content ranged from 33 to 87 mg/L, with an average of 57 mg/L. Heating of the wines at 80°C for six hours followed by cooling at 4°C for 17 hours resulted in the formation of slight turbidity and in only small or no decreases in proteins, ranging from 0 to 23%. Soluble proteins were isolated from the wine made in 1991 by precipitation with ammonium sulfate and fractionated by chromatography on Sephadex G-100 and by preparative polyacrylamide gel electrophoresis. The red wine contained at least seven soluble protein fractions with molecular weights of 25.5 or 30.0 K daltons; their isoelectric pHs were between 3.6 and 4.7. The protein fractions obtained were glycoproteins and were composed of moieties of proteins (88.9% to 94.4% of the total) and neutral sugars (5.6% to 11.1%). The fractions were rich in aspartic acid, serine, glutamic acid, and glycine as amino acids, and glucose and mannose as sugars.