Danye Zhu, Armando Alcazar Magana, Yongsheng Tao, and Michael C. Qian*
*Oregon State University, 100 Wiegand Hall, Corvallis, OR 97331 (michael.qian@oregonstate.edu)

Mouthfeel is an important quality attribute of red wine. It is postulated that polysaccharides from grapes and yeasts could play an important role in wine mouthfeel. Understanding the structural characterization of polysaccharides from different sources is extremely important for wine organoleptic quality. In this study, Pinot noir grapes were broken and then extracted with hot water (90°C, 2 hr) twice to extract free sugar and highly water-soluble polysaccharide (named G1). The residues were then extracted with alkali solution (0.5 M sodium hydroxide solution with 10 mM NaBH4, 80°C, 2 hr) (named G2). The obtained supernatants were neutralized, concentrated, and centrifuged, then absolute alcohol was added to precipitate polysaccharide overnight. Ultraviolet scanning showed a unique absorption peak between 190 and 200 nm, indicating that the extracts were polysaccharides. The grape polysaccharides were methanolized by 0.5 M HCl/MeOH at 85°C for 18 hr and derivatized by 1-(trimethylsilyl)imidazole (TMSI) for gas chromatography-mass spectrometry (GC-MS) analysis. Glucose, xylose, mannose, arabinose, galactose, rhamnose, fucose, glucuronic acid, and galacturonic acid were methanolized and silylated to confirm sugar identification. Methyl-alpha- and methyl-beta-galactopyranoside and methyl-al- pha-mannopyranoside were used to verify sugar anomer distribution. GC-MS analysis revealed that G1 was composed mainly of glucose, arabinose, rhamnose, galactose, mannose, galacturonic acid, and xylose. G2 was composed primarily of arabinose, galactose, glucose, rhamnose, galacturonic acid, xylose, and mannose.

Funding Support: American Vineyard Foundation (AVF)