Purification and identification of antioxidant peptides from round scad (Decapterus maruadsi) hydrolysates by consecutive chromatography and electrospray ionization-mass spectrometry.

Round scad (Decapterus maruadsi) was hydrolyzed with a double-enzyme (a mixture of neutrase and trypsin) to obtain antioxidant peptides. The round scad hydrolysates obtained by 5-h hydrolysis (RSH) displayed the strongest antioxidant activities, which could scavenge the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, the hydroxyl radical, and exhibit reducing power. RSH was further separated into four fractions by using an ultrafiltration membrane system, and low-molecular-weight fraction RSH-IV (<5 kDa) showed the highest antioxidant activities. Fraction RSH-IV was then purified with gel filtration chromatography followed by reverse high-performance liquid chromatography (RP-HPLC). The sequence of the purified antioxidant peptide was identified as Lys-Gly-Phe-Arg (506 Da) by liquid chromatography/electrospray ionization tandem mass spectrometry (LC-MS/MS). Additionally, the purified peptide could scavenge DPPH radical at IC50 value of 0.13 mg/mL, and it showed a 49.08-fold higher DPPH radical scavenging activity compared with that of the crude RSH. The results suggest that antioxidant peptides obtained from round scad (Decapterus maruadsi) could be a good source of natural antioxidant.