Protein characterization of Roditis Greek grape variety and Sauvignon blanc and changes in certain nitrogen compounds during alcoholic fermentation

Must and wine samples of the Greek grape variety Roditis and the French one Sauvignon blanc were analysed in order to obtain further knowledge of the protein profile of Roditis and to watch the evolution of grape proteins during the alcoholic fermentation of Roditis and Sauvignon blanc musts. For these purposes protein samples were isolated from must and wine samples by ammonium sulphate precipitation and subjected to sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Eleven and nine bands with molecular weights between 11, 1 and 64,4 kDa were detected on the electrophoregramms of Roditis and Sauvignon blanc must and wine samples respectively, using Coomassie Brillant Blue R-250 and silver staining methods. Two protein fractions of must and wine samples with molecular weights of 64,4 kDa and 34,4 kDa were identified as being glycoproteins in the profile of the Greek grape variety, according to the Periodic acid-silver staining, while only one must and wine fraction of 64,4 kDa had positively react with this stain, as far as it concerns Sauvignon blare. None of the low molecular weight protein fractions found to be responsible for haze formation. A modified (Bradford) dye binding procedure was used for the determination of musts and wines soluble proteins. Free amino nitrogen and the contents of neutral and acidic polysaccharides in the protein fractions after chromatography on Sephadex G-25, were also analyzed.