Abstract
Grape (Vitis vinifera) is one of the most cultivated fruit crops in the world, with an approximate annual production of ∼64 million metric tons in 2010 (OIV, 2011). Grapes composition in polyphenols and their extractability which is far from complete and typically reaching only 30–40% depend on grape varieties, vineyard location and the technological parameters during wine making process including destemming, crushing, maceration and pressing. Therefore, grape pomace potentially constitutes a very abundant and relatively inexpensive source of a wide range of polyphenols including monomeric and oligomeric flavan-3-ols (proanthocyanidins) as well as anthocyanins (glucosides, acetylated glucosides and coumarylic glucosides). Moreover, it has been evaluated as a potential source of antioxidant polyphenols which could be used as nutraceuticals or food additives. Actually, phenolic compounds are known to have some health benefits such as a chemopreventive role toward cardiovascular, cancer, and degenerative diseases. In order to valorize wine by-products from Rhone Valley area, grape and pomace seeds and skins from red wine cultivars at maturity from the vintage 2009 and 2010 (Grenache, Syrah, Carignan, Mourvédre, Counoise and Alicante) have been characterised for their phenolic contents (total phenol contents, tannin and anthocyanin contents - total and individuals; quantification of monomeric and oligomeric proanthocyanidins as well as some anthocyanins (glucosides, acetylated glucosides and coumarylic glucosides)). Ratio of initial phenolic compounds from grape to pomace was also estimated. The comparison of several wine industry by-products with their respective grapes provided evidence that grape seed and skin pomace extracts still contained appreciable amounts of flavanol-3-ols and anthocyanins even after the fermentation process. Quantitative and qualitative distribution of polyphenols in grape pomaces showed significant differences through varieties. Seed extracts from grapes and pomaces contain exceptionally high amounts of total polyphenols than skin's extracts. This study evidenced seeds from Grenache, Syrah and Alicante and skins from Syrah, Carignan and Alicante as the most interesting fractions to be valorized because of their richest contents in polyphenols compared to the other assessed fractions and varieties. This work further supports that grape pomaces obtained after vinification still retained a significant amount of polyphenols of which level depends largely on the vintage. The use of this by-product would constitute a promising natural source of available polyphenols which could be included in nutraceutical formulation. Activity effects of grape by-products on a chronic disease model with hypertension are given.