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The winemaking process generates large amounts of by-products that are still a potential source of bioactive compounds to be used as functional food ingredients. This study is aimed to develop a cow milk kefir fortified with Sangiovese red grape pomace. The phenolic extracts of skins and seeds, which were obtained after infusion and ultrasound-assisted extraction (UAE), were rich in (+)-catechin (105.0±147.0 mg/L) and (-)-epicatechin (76.0±364.0 mg/L) based on HPLC-DAD analysis. The UAE-derived skin extracts were selected for their best antioxidant effectiveness and incorporated into kefir, whose functional properties have been investigated through spectrophotometric assays. The addition of UAE-derived skin extract to kefir was significantly effective in enhancing the total phenolic content (43.2 %) thus increasing the total antioxidant capacity (+47.7 %) and lowering IC50 ABTS (-36.0%) and DPPH (-31.45%). An increased inhibitory activity towards α-amylase, α-glucosidase and pancreatic lipase was also achieved by decreasing the corresponding IC50 values (69.39 and 73.01 "g/mL, respectively).