Characterization of dietary fiber and the in vitro indigestible fraction of grape pomace.

摘要

Grape pomace (red grape skins (RGS) and white grape skins (WGS) and seeds (WGSe)) were analysed and the composition of their in vitro indigestible fraction characterized. All samples were rich in protein (12-14% DM), fat (7-12% DM) and minerals (6-9% DM), with smaller amounts of soluble sugars (about 3% DM) and polyphenols (4-5% DM). Analysis of the indigestible fraction showed that about 17-21% of the DM were non-starch polysaccharides (NSP), mainly cellulose and pectins. Condensed tannins (CT) content was very high, ranging from 16.0% in WGSe to 26.9% in RGS. A very high percentage of the protein (up to 80%) was also indigestible in vitro, appearing as resistant protein (RP) in the fibre residue. It is concluded that over 60% of the grape pomaceDM was indigestible in vitro. This indigestible fraction was composed of dietary fibre (NSP plus lignin) as well as CT and RP. The presence of high amounts of CT and RP, unusual in most of the dietary fibre-rich vegetable products, would provide grape pomace with peculiar physiological and nutritional properties.