CHARACTERIZATION OF SOLUBLE GLYCOPROTEINS IN RED WINE

Red table wines, made annually from Muscat Bailey A grapes from 1981 t o 1992 and aged in bottles for up to 12 years, were analyzed for solub le proteins and heat stability. The soluble protein content ranged fro m 33 to 87 mg/L, with an average of 57 mg/L. Heating of the wines at 8 0-degrees-C for six hours followed by cooling at 4-degrees-C for 17 ho urs resulted in the formation of slight turbidity and in only small or no decreases in proteins, ranging from 0 to 23%. Soluble proteins wer e isolated from the wine made in 1991 by precipitation with ammonium s ulfate and fractionated by chromatography on Sephadex G-100 and by pre parative 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 mo ieties 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, gluta mic acid, and glycine as amino acids, and glucose and mannose as sugar s.