Polyphenols from grape and apple skin: A study on non-conventional extractions and biological activity on endothelial cell cultures

Grape and apple skins and seeds are rich in natural antioxidant compounds known as polyphenols. Polyphenols exhibit a wide range of beneficial biological properties acting as antioxidants and antiinflammatory that can be exploited for vascular diseases. The polyphenol content in grapes and apples depends on cultivar and growing conditions. For this study, four different cultivars of apples (Golden Delicious, Jonagold, Renetta Canada and Raventze) and three of grapes (Fumin, Premetta and Petit Rouge), typical of Aosta Valley (Italy), were harvested at commercial maturity. Skins were collected and dried. Powdered samples were extracted with methanol using microwave assisted extraction (MAE, 110 °C, 60 min) and high pressure and temperature extraction (HPTE, 150 °C, 150 min). The non-conventional methodologies were compared with the classic solid-liquid extraction (25 °C, 19 h). The extracts were characterized in terms of total polyphenols (TP) content and their antiradical power. HPLC analysis was also performed to quantify main single phenolic compounds. For grape and apple skins, the higher TP yields were obtained by HPTE using Jonagold and Premetta cultivars, respectively. In general, extraction yields of HPTE have reached values higher than 30 and 10 mg of Gallic Acid Equivalent per g of Dry Material for grape and apple skins, respectively. Moreover, the biological vaso-protective activity of apple extracts was investigated by evaluating the expression of endothelial activation markers in an in vitro model of endothelial dysfunction induced by the pro-inflammatory cytokine TNFα.