1,1-Diphenyl-2-picrylhydrazyl (DPPH) radical scavenging by protein hydrolyzates from tuna cooking juice

Protease XXIII, from Aspergillus oryzae, was used to hydrolyze tuna cooking juice at 37°C for up to 6 h. The hydrolyzate obtained at the degree of hydrolysis of 25.68% (after hydrolysis for 2.5 h) displayed the highest 1, 1-diphenyl-2-picrylhydrazyl (DPPH) scavenging effect, reaching 82.19%. Six major fractions (A, B, C, D, E, and F) of this hydrolyzate were obtained by Sephadex G-25 column chromatography using a 0.05 M phosphate buffer (pH 6.5) as the mobile phase. All six fractions displayed a scavenging effect for the DPPH radical, but the scavenging effect was only obvious in two fractions (B and C). After the solid content of hydrolyzates was concentrated from one to five times, the scavenging effect of the DPPH radical increased from 17% to 75% for fraction B, and from 13% to 66% for fraction C. Seven anti-oxidative peptides were isolated from the hydrolyzates (mixture of B and C fractions) by reversed-phase HPLC. The peptide sequences comprised four to eight amino acid residues, including Val, Ser, Pro, His, Ala, Asp, Lys, Glu, Gly, or Tyr.