Ostrich (Struthio camelus) egg white (OEW) proteinswere hydrolyzed using various proteases (α-chymotrypsin, pepsin, trypsin and papain). Antioxidant activities of hydrolysates were evaluated using 1, 1-diphenyl- 2-picrylhydrazyl (DPPH) radical scavenging and iron chelating activity. The hydrolysate obtained by trypsin exhibited the highest antioxidant activity. This hydrolysate was passed through an ultrafiltration membrane with a 3 kDa-cut off, and the resulting filtrate was purified using reversed-phase high performance liquid chromatography (RP-HPLC). Eight peptide fractions were separated and their antioxidant activities were tested. The results showed that the F6 fraction possessed the highest antioxidant activity in the inhibition of linoleic acid autoxidation (86.4% at 20 μg/ml), scavenging activity for DPPH radical (81% at 200 μg/ml) and 2, 2-azino-bis (3-ethylbenzothiazoline-6-sulphonicacid) diammonium salt (ABTS) radical (37.6% at 90.9 μg/ml). In addition, the iron chelating activity, hydroxyl radical scavenging and reducing power of the F6 fraction were 20% at 317.5 μg/ml, 28.6% at 163.9 μg/ml and 0.083 at 113.6 μg/ml, respectively. The peptide sequence was found to be LTEQESGVPVMK (with a molecular mass of 1317.65 Da) using mass spectrometry. The results suggest that the digestion of OEWproteins by trypsin protease could be exploited to produce natural antioxidants.

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