Wine polysaccharides modulating astringency through the interference on interaction of flavan-3-ols and BSA in model wine

Polysaccharides and flavan-3-ols from Cabernet Sauvignon wine were isolated and then characterized by high performance liquid chromatography coupled with diode array detector (HPLC-DAD), high performance size exclusion chromatography (HPSEC) and HPLC-MS. The influence of purified polysaccharides on the aggregation of flavan-3-ols-proteins were investigated using fluorescence spectroscopy, circular dichroism (CD) and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) to evaluate the co-effect of polysaccharides on wine astringency. The results indicated that mannoproteins (MPs) and rhamnogalacturonans II (RG II) were the major polysaccharides to significantly alter the interaction of flavan-3-ols with bovine serum albumin (BSA). The interaction of polysaccharides-flavan-3-ols-BSA was enhanced with the concentration (from 0.2 to 0.6 g/L) of the studied polysaccharides. Furthermore, the reaction of BSA-flavan-3-ols was strengthened in the absence of polysaccharides when percentage of galloylation (%G) was higher (11.29). When mean degree of polymerization (mDP) of flavan-3-ols was from 5.14 to 6.88, the secondary structure of proteins was changed from mainly α-helix to random curl and the formation of protein precipitation increased. This work pointed out that the important property of polysaccharides and different structural characteristic flavan-3-ols are able to modulate wine astringency perception.