THE POTENTIAL USE OF SOLUBLE POLYSACCHARIDES TO PREVENT THE OXIDATION OF ROSÉ WINES

Abstract

Lately, rosé wine is rapidly increasing its popularity worldwide. Short-time macerations with the red skin of the grapes cause the partial extraction of anthocyanins, which are responsible for the pinkish-salmon hue of rosé wines. However, the low quantity of tannins (antioxidants) and richness in phenolic acids, which can be easily oxidized into yellowish pigments, tend to predispose rosé wines to an undesirable browning. Although the use of SO₂ for the prevention of oxidation is highly extended, this practice is expected to be reduced. Therefore, the search for alternative oenological adjuvants that prevent the oxidation and browning of rosé wines is highly desired. Thus, the aim of this work is to assess the effect of the addition of soluble polysaccharides, issued from grape pomace on the oxidation process. To do this, rosé wines were made using grapes from V. vinifera cv Syrah and employing two different maceration times: short (S, 10 min) and long (L, 2 hours).

Thus, two different wines were elaborated (SYS and SYL). Soluble polysaccharides were extracted, purified and characterized (by means of HPLC-DAD-MS and HPLC-RID) from white grape pomace and added to the rosé wines. Then, wines were submitted to an oxidation process by reaching oxygen saturation level in the solution. Wines’ phenolic composition was studied before the oxidation process and then its evolution was monitored.

The extract of polysaccharides presented three main fractions: F1 (25%) with a MW of 104 kDa; F2 (13%) with a MW of 8 kDa and F3 (62%) with a MW of 2 kDa. The polysaccharide extract was analysed by HPLC-DAD-MS after acid hydrolysis and a chemical modification reaction, in order to obtain a derivative of the monosaccharide which could be detected by UV. The main constitutive monosaccharide units detected were: galacturonic acid (26.3%), arabinose (26.2%), galactose (16%), xylose (11.4%), glucose (9.0%), mannose (6.6%), rhamnose (3.2%) and glucuronic acid (1.3%).

Two antioxidant test (FRAP and ABTS) were performed on the polysaccharide extract for the purpose of measuring its potential use as an antioxidant. Phenolic composition was analysed by HPLC-DAD-MS during the duration of the study (60 days).

Results allowed us to assess the importance of polysaccharide addition to modify the ability of rosé wines to resist oxidation, evaluating the possible application of a natural polysaccharide obtained from wine’s by-product as an oenological adjuvant.