Peptides from the tryptic hydrolysate of cartilaginous proteins ofRaja porosa and their antioxidant activities

In the experiment, cartilaginous proteins of Raja porosa were prepared using guanidine-HCl extraction and acetone precipitation, and two antioxidant peptides (RCPE-A and RCPE-B) were subsequently isolated from the tryptic hydrolysates of cartilaginous proteins using ultrafiltration, anion-exchange chromatography, gel filtration chromatography and reversed phase high performance liquid chromatography (RP-HPLC). The amino acid sequences and antioxidant activities including free radical scavenging activity and lipid peroxidation inhibition were also measured. The results indicated that the amino acid sequences of RCPE-A and RCPE-B were identified as Gly-Glu-Glu-Gly-Pro-Arg-Gly (GEEGPRG) and Gly-Glu-Glu-Gly-Thr-Met-Gly-Leu (GEEGTMGL) with molecular weights of 700.71 and 792.87 u, respectively. RCPE-A and RCPE-B exhibited good scavenging activity on DPPH• (EC₅₀ 2.94 and 1.16 mg/mL), HO• (EC₅₀ 0.34 and 0.54 mg/mL), ABTS⁺• (EC₅₀ 0.34 and 0.10 mg/mL), and \rmO_2^ - • (EC₅₀ 0.11 and EC₅₀ 0.03 mg/mL). In addition, RCPE-A and RCPE-B were effectively against lipid peroxidation in a linoleic acid model system. The antioxidant activities of RCPE-A and RCPE-B were due to the smaller size and the presence of antioxidant amino acids including Gly, Glu, Pro, Arg, Met and/or Leu within their peptide sequences. These results suggested that RCPE-A and RCPE-B might serve as potential antioxidants and be used as food additives and functional foods.