Isolation, Characterization, and Compositional Analysis of Polysaccharides from Pinot Noir Wines: An Exploratory Study

It has been reported that polysaccharides in wine can interact with tannins and other wine components and modify the sensory properties of the wine. Unfortunately, the contribution of polysaccharides to wine quality is poorly understood, mainly due to their complicated structure and varied composition. In addition, the composition and molecular structure of polysaccharides in different wines can vary greatly. In this study, the polysaccharides were isolated from pinot noir wine, then separated into high-molecular-weight (PNWP-H) and low-molecular-weight (PNWP-L) fractions using membrane-based ultrafiltration. Each polysaccharide fraction was further studied using size exclusion chromatography, UV-Vis, FT-IR, matrix-assisted laser desorption/ionization-high-resolution mass spectrometry, and gas chromatography-mass spectrometry (GC-MS). The results showed that PNWP-L and PNWP-H had different chemical properties and compositions. The FT-IR analysis showed that PNWPs were acidic polysaccharides with α- and β-type glycosidic linkages. PNWP-L and PNWP-H had different α- and β-type glycosidic linkage structures. FT-IR showed stronger antisymmetric and symmetric stretching vibrations of carboxylate anions of uronic acids in PNWP-L, suggesting more uronic acid in PNWP-L. The size exclusion chromatography results showed that over 72% of the PNWP-H fraction had molecular sizes from 25 kDa to 670 kDa. Only a small percentage of smaller molecular polysaccharides was found in the PNWP-H fraction. In comparison, all of the polysaccharides in the PNWP-L fraction were below 25 KDa, with a majority distributed approximately 6 kDa (95.1%). GC-MS sugar composition analysis showed that PNWP-L was mainly composed of galacturonic acid, rhamnose, galactose, and arabinose, while PNWP-H was mainly composed of mannose, arabinose, and galactose. The molecular size distribution and sugar composition analysis suggested that the PNWP-L primarily consisted of rhamnogalacturonans and polysaccharides rich in arabinose and galactose (PRAG). In comparison, PNWP-H were mostly mannoproteins and polysaccharides rich in arabinose and galactose (PRAG). Further research is needed to understand the impacts of these fractions on wine organoleptic properties.

Inhibition Mechanisms of Wine Polysaccharides on Salivary Protein Precipitation

In this work, high-performance liquid chromatography, fluorescence quenching, nephelometry, and sodium dodecyl sulfate polyacrylamide gel electrophoresis were used to study the effect of polysaccharides naturally present in wine [rhamnogalacturonan II (RG II) and arabinogalactan proteins (AGPs)] on the interaction between salivary proteins (SP) together present in saliva and tannins (punicalagin (PNG) and procyanidin B2). In general, the RG II fraction was more efficient to inhibit SP precipitation by tannins, especially for acidic proline-rich proteins (aPRPs) and statherin/P-B peptide, than AGPs. The RG II fraction can act mainly by a competition mechanism in which polysaccharides compete by tannin binding. However, in the presence of Na⁺ ions in solution, no RG II effect was observed on SP-tannin interactions. On the other hand, dependent upon the saliva sample as well as the tannin studied, AGPs can act by both mechanisms, competition and ternary (formation of a ternary complex with SP-tannin aggregates enhancing their solubility).

Impact of berry size at harvest on red wine composition: a winemaker's approach

BACKGROUND

A classical postulate of viticulture declares that small grape berries produce the best red wines. The popularity of this postulate among winemakers leads them to consider berry size at harvest as a tool to measure the grape's potential to obtain great red wines. To address this issue, two vineyards from the same cultivar and subjected to the same physiological conditions during growing were selected for their difference in average grape berry size at harvest. Grapes from both origins were characterized and used for red winemaking by the same way. Release of volatile compounds and phenolic compounds during the alcoholic fermentation was monitored, and the finished wines were chemically characterized.

RESULTS

Larger grapes have a lower theoretical surface-to-volume ratio but have thicker skins and a greater proportion of skins (m/m). Wines made from grapes with a greater proportion of skins contain higher amounts of phenolic compounds, terpenes, volatile acids, acetate esters and polysaccharides.

CONCLUSION

According to the results, it seems that grape skin extraction is more related to skin proportion than to berry size. Thus not always smaller grapes produce darker red wines. © 2019 Society of Chemical Industry.