Total polyphenols content, antioxidant activity and stability of a grape pomace incorporated in animal feed

Abstract

Grape pomace (GP), resulting from wine making, is rich in antioxidant polyphenols originating from the input material, the grapes. Because of the high production volumes of grape pomace, environmental impact and nutritional content, new ways for its valorization are experimented. In order to incorporate it in animal feed (cow and pig), we determined its content in total polyphenols by the Folin Ciocalteu method, the antioxidant activity by the DPPH assay and its stability using the UV-Vis spectroscopy for different extraction media. In terms of total polyphenols the acetone extraction was the best (4667.1 mg GAE/100g sample) comparing with ethanol and water (2140.4 mg GAE/100g sample respectively 2083.9 mg GAE/100g sample), and the ruminal fluid (732.9 mg GAE/100g sample) and pepsin (712.2 mg GAE/100g sample). The highest antioxidant activity expressed as an antiradical activity against the DPPH radical, was registered for the acetone extract (32.8 μM Trolox Equivalents(TE)), followed by the ethanol (6.5 μM TE) and water extraction equal with pepsin extraction (4 μM TE), and the mixture of ruminal fluid (0.5 μM TE). The results show that even though the extraction of polyphenols in organic solvents is the best, when applied to the digestive media the situation changes. In both ruminal fluid and pepsin were measured almost the same amount of total polyphenols but the antioxidant activity was much lower in the ruminal fluid - 8 times lower. The UV-Vis spectroscopy shows that the acetone extract is stable over time when kept at – 20 ͦC