Valorization of grape pomace extracts against cranberry, elderberry, rose hip berry, goji berry and raisin extracts: Phytochemical profile and in vitro biological activity

The circular economy is gaining attention around the world as a sustainable approach to tackling environmental problems, promoting more responsible management of resources. The aim of this work is the valorization of grape pomace as a waste product of agrifood chain. We prepared decoction (DC), ultrasound-assisted and microwave-assisted extracts (UAE and MAE respectively) of grape pomace, determining their phytochemical profile (using HPLC-ESI-Q-TOF-MS), antioxidant activity and enzyme inhibitory effects. Then, the results were compared with those of raisins and several edible berries already present in the market. Grape pomace extracts presented the highest total phenolic content (62-68 mg gallic acid equivalents/g; mg GAE/g), whereas the concentrations in the other berries were 4-43 mg GAE/g. These results were in agreement with the higher antioxidant activity and tyrosinase inhibition observed in grape pomace compared with the other berries, except for the metal chelating activity. The main compounds in grape pomace extracts were flavonoids (particularly quercetin glycosides), followed by organic acids (citric, isocitric and gallic acids). These results open new perspectives in the development of food supplements and nutraceuticals based on grape pomace extracts.