Extraction of phenolics from Vitis vinifera wastes using non-conventional techniques

Polyphenols, the well known naturally occurring antioxidants, are the most abundant secondary metabolites in grape wastes. Herein we investigate several non-conventional extraction methods vs classic solid–liquid extraction (SLE) to obtain phenolic compounds from grape seeds and skins. We compared SLE, ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE) and high pressure and temperature extraction (HPTE) in term of extraction yield and antioxidant power of the extract. Solvent of choice between methanol and ethanol was the former, both for skins and seeds. Quali-quantitative analyses were performed using colorimetric and HPLC methods. The highest content in total polyphenols, o-diphenols and flavonoids, both for seeds (108.3, 47.0 mg_GAE g_DW⁻¹, 47.2 mg_CE g_DW⁻¹) and skins (34.2, 10.1 mg_GAE g_DW⁻¹, 21.6 mg_CE g_DW⁻¹) was obtained with HPTE working in a Parr reactor. While the highest antiradical power was determined in seeds extracts from MAE (78.6 μl_extract μg_DPPH⁻¹). Prolonged extraction times (over 30 min) further increased the amount of total polyphenols, while progressively decreased the amount of flavonoids and the antiradical power.