Polyphenolic Profile and Dietary Fiber Content of Skins and Seeds from Unfermented and Fermented Grape Pomace

Due to the seasonality of its production and to its polluting characteristics, the management and disposal of large amounts of grape pomace (GP) produced worldwide every year can pose a significant economic and environmental challenge. The research on the possible exploitation of GP for various purposes has been constantly growing during the last years, due to the increased general sensibility on issues like sustainability of agro-industrial production and to the growing consumer demand for the use of natural versus synthetic compounds. The work concerned the determination of the polyphenolic profile and the dietary fiber content of skins and seeds from unfermented and fermented white and red grape pomace of different cultivars, sampled from local wineries in the Piedmont area (Italy) after winemaking. A double extraction was performed to maximize the extraction of polyphenols from grape pomace flours. The extractable polyphenols content (EPP) was determined in the extracts, while the non-extractable condensed tannins (NEPP) linked to the fiber were quantified in the residue after extraction. The total dietary fiber (TDF) was determined for skins and seeds; limited to skins, the analysis was extended to the distinction between soluble and insoluble dietary fiber (SDF and IDF). The polyphenolic and dietary fiber content was significantly higher in seeds than in skins. However, from a nutritional point of view, skins dietary fiber may be more interesting due to the higher NEPP content than seeds; moreover, the winemaking technique influenced the quantity and characteristics of skins fiber, which contained SDF, almost absent in seeds.