CHARACTERIZATION OF DIETARY FIBER AND THE IN-VITRO INDIGESTIBLE FRACTION OF GRAPE POMACE

Grape pomace [red grape skins (RGS), and white grape skins (WGS), and seeds (WGSe)] were analyzed and the chemical composition of their in v itro indigestible fraction characterized. All samples were rich in pro tein (12% - 14% dry matter), fat (7% - 12% dm), and minerals (6% - 9% dm), with smaller amounts of soluble sugars (about 3% dm) and polyphen ols (4-5% dm). Analysis of the indigestible fraction showed that about 17% to 21% of the dry matter were non-starch polysaccharides (NSP), m ainly cellulose and pectins. Condensed tannins (CT) content was very h igh, ranging from 16.0% in WGSe to 26.9% in RGS. A very high percentag e of the protein (up to 80%) was also indigestible in vitro, appearing as resistant protein (RP) in the fiber residue. In conclusion, over 6 0% of the grape pomace dry matter was indigestible in vitro. This indi gestible fraction was composed of dietary fiber (NSP plus lignin) as w ell as CT and RP. The presence of high amounts of CT and RP, unusual i n most of the dietary fiber-rich vegetable products, would provide gra pe pomace with peculiar physiological and nutritional properties.