Antioxidant Activity of Selenium-Enriched Peptides from the Protein Hydrolysate of Cardamine violifolia

Cardamine violifolia is a selenium (Se)-enriched plant found in China. In this study, the Se-enriched peptides of C. violifolia (CP) were isolated using a 1 kDa ultrafiltration membrane after enzymatic hydrolysis by alkaline and neutral proteases. The peptides were separated by DEAE-Sepharose FF anion-exchange chromatography and purified using preparative high-performance liquid chromatography (prep-HPLC). The component with the highest antioxidant activity, CPR13, was identified by comparing the 1,1-diphenyl-2-picrylhydrazyl (DPPH center dot), hydroxyl (center dot OH), 2,2 '-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS(+)center dot), and superoxide (O2-center dot) radical scavenging ability of each fraction. At a concentration of 0.1 mg/mL, the DPPH center dot, center dot OH, O2-center dot, and ABTS(+)center dot scavenging activities of CPR13 were 89.2%, 26.3%, 40.6%, and 42.9%, respectively. Amino acid sequences were obtained by liquid chromatography combined with mass spectrometry as follows: GRVGSSSC, GRAGGSYM, GHPNFKLNCSGG, GTKSCKA, ASSNARDMI, TAGGCYIPI, and KNCALQ. The seleno-amino acids were identified as selenomethionine, methylselenocysteine, and selenocysteine. Correlation analysis among organic Se content, peptide content, and antioxidant activity revealed that organic Se plays a greater role in free radical scavenging than peptides, and that the organic Se content of the Se-enriched peptides was positively correlated with their antioxidant ability (P < 0.05). It indicated that CP has a great potential as natural functional materials for dietary supplement.