Glycoproteins: Characterization in a Hybrid Grape Variety (Muscat Bailey A) Juice, Fermenting Must, and Resultant Red Wine

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Elucidation of the differences in properties between unstable and soluble proteins will assist in developing effective fining of wine and in breeding of grape varieties with fewer unstable proteins. Soluble proteins from juice, must pressed just after fermentation on skins, and from red wines were isolated by ammonium sulfate precipitation and fractionated by Sephadex G-100 followed by high performance liquid chromatography. At least 17, 18, and 22 protein fractions were obtained from the juice, fermenting must, and red wine samples, respectively. All of the fractions had sugars in the range of 0.3% to 33.3% of total glycoproteins (the sum of the total sugars and amino acids found in the hydrosolates). Most of the glycoproteins had less than 10% sugars. The glycoproteins differed from grape proteins, generally being rich in the amino acids aspartic acid, glycine, threonine, glutamic acid, and alanine and in the sugars arabinose, rhamnose, galactose, and glucose. Their isoelectric points and molecular weights ranged from 3.7 to 4.9 and form 12.1 to 30.8 K daltons, respectively. Differences in the HPLC patterns and in the chemical and physical properties of the protein fractions obtained revealed the presence of several individual glycoproteins, their concentrations, and occurrence of specific glycoproteins at each stage of vinification. The proportion of glycoprotein sugars decreased in the order juice proteins &gt; must proteins &gt; wine proteins — <i>i.e.</i>, degradation or modification of the sugar portions of the glycoproteins occurred during vinification. The origin of wine glycoproteins suggests roles in aging reactions and other wine characteristics.