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

Due to the seasonality of its production and 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 recent years, due to the increased general sensitivity to issues like the sustainability of agro-industrial production and the growing consumer demand for the use of natural versus synthetic compounds. This 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 polyphenols (NEPP) linked to fiber were quantified as condensed tannins 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, the dietary fiber of skins may be more interesting due to the higher NEPP content than in seeds; moreover, the winemaking technique influenced the quantity and characteristics of skin fiber, which contained SDF, almost absent in seeds.