Wine polysaccharides play an important role in wine aroma and flavor perception. The interaction of polysaccharides with wine aroma may depend on the physical and chemical properties of aroma, structure, and composition of polysaccharides. In addition, wine polysaccharides are closely related to the mouthfeel perceptions due to their interactions with excess tannins and pigments, which further affects the sensation of astringency, sweetness, and body of the wine. However, the actual cause and mechanisms are not well studied. Hence, it is essential to research wine polysaccharide composition. GC or GC-MS can analyze polysaccharide composition after methanolysis and silylation. Methanolysis conditions were investigated using lactose under acidic conditions (0.5 M HCl ) in methanol at 75, 80, and 85 οC for 16, 18, and 20 hrs. After the methanolysis, an aliquot of 0.2 mL internal standard myo-inositol in pyridine (0.1 mg/mL) was added, and the mixture was dried under a flow of nitrogen gas. For silylation, 0.1 mL 1-(trimethylsilyl)imidazole (TMSI) was added and incubated at 80 οC for 30 min. The characteristic peaks of sugars were identified by GC-MS with an HP-5MS column. It was found that methanolysis was temperature and time-dependent, lactose was methanolyzed completely at 85 οC, higher than reported in the literature. Sugar standards (glucose, xylose, mannose, arabinose, galactose, rhamnose, fucose, glucuronic acid and galacturonic acid) and Pinot noir grape polysaccharides were methanolized by 0.5 M HCl/MeOH at 85 οC for 18 h and derivatized by TMSI. Under these conditions, glucose mainly gave alpha- and beta-methyl-tetrakis-O-(trimethylsilyl) glucopyranoside. In contrast, galactose gave both furanosides and pyranosides. Similarly, arabinose gave mixtures of alpha-/beta-1-methyl-O-tris-(3-methylsilyl)-arabinofuranosides and alpha-/beta-1-methyl-O-tris-(3-methylsilyl) arabinopyranosides. GC-MS analysis showed that Pinot noir grape polysaccharides were composed mainly of glucose, arabinose, rhamnose, galactose, mannose, galacturonic acid and xylose.

Pinot noir grape polysaccharide analysis by GC-MS after methanolysis and silylation

ACS Spring Meeting 2021

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