Characterization of food antioxidants, illustrated using commercial garlic and ginger preparations

Methods for the characterization of antioxidants are presented and illustrated by their application to commercial garlic and ginger preparations, since it has been widely speculated that garlic and ginger might be beneficial to human health because they exert ‘antioxidant activity’. The sample of commercial ginger powder, tested at concentrations up to 5 mg/ml, inhibited the peroxidation of phospholipid liposomes, but a sample of one commercial garlic preparation was less effective. Both preparations could scavenge peroxyl radicals, but the garlic preparation was again less effective. The ginger and garlic preparations were powerful scavengers of hydroxyl radicals (OH) and were able to react with hypochlorous acid (HOCl) at a rate sufficient to protect catalase and alpha-l-antiproteinase against inactivation. However, they could also interact with iron chelates to facilitate OH generation from H2O2 (‘pro-oxidant’ activity). Ginger (but not the garlic preparation) also exerted pro-oxidant action in the bleomycin assay, accelerating damage to DNA in the presence of a bleomycin-ferric iron complex. Our results illustrate the use of antioxidant characterization methods.