Ripening of cv. Cabernet Sauvignon grapes: polysaccharides fractions evolution and phenolic extractability

Abstract

Polysaccharides and more specifically pectins, make up a significant portion of the cell wall material of the plant cells including the grapes. During the fruit ripening the associated softening is related to the breakdown of the cell wall polysaccharides. During this process, it is expected that polysaccharides that are soluble in red wine will be formed influencing its texture. Anthocyanins are responsible for the wine color and tannins for the astringency, body and bitterness of the wine. In the skins, these compounds are located in the cell vacuoles and the barrier that conditions their extractability is the skin cell wall that may determine the mechanical resistance, the texture and the ease of processing berries. The aim of this work was study the evolution of the polysaccharides and the anthocyanin and tannin extractability during the ripening period in Cabernet Sauvignon grapes, trying to correlate these variables. Samples were taken in a vineyard from 100% of veraison (24th February- 2014; 18.3±0.31°Brix) until technical maturity (14th April-2014; 24.4 ± 0.40°Brix). Total soluble (1) and insoluble polysaccharides (2), polysaccharides fractions by HPLC-RI (1) and anthocyanin and tannin extractability (3) were measured in five dates. Total soluble polysaccharides increase from 0.18 ± 0.03 at veraison to 0.50 ± 0.07g/g skin at technical maturity. In the same period insoluble polysaccharides decrease from 128.05 ± 9.33 to 69.00 ± 3.00 g/g skin. In the case of polysaccharides fractions (F) [neutral polysaccharides (F1), acid polysaccharides (F2) and oligosaccharides (F3)], only F2 change during the sampling dates increasing significantly its value in time. Anthocyanins and tannins increased their extractability in ≈ 18% and ≈ 10% in the sampling period, respectively. Pearson correlation coefficient between soluble polysaccharides and anthocyanin extractability was 0.86 and between soluble polysaccharides and tannin extractability was 0.76. The increase in soluble polysaccharides is closely related with anthocyanin and tannin extraction from grapes.

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