Defensin protein from sweet potato (Ipomoea batatas [L.] Lam 'Tainong 57') storage roots exhibits antioxidant activities in vitro and ex vivo

► SPD1 exhibits antioxidant activities in vitro. ► SPD1 could decrease the production of intracellular peroxide in HepG2 cells ex vivo. ► SPD1 might contribute its antioxidant activities against hydroxyl and peroxyl radicals.