Contribution of specific amino acid and secondary structure to the antioxidant property of corn gluten proteins

The composition, structure, and proper positioning of amino acid in a peptide are closely related to its antioxidant activity. In this study, we purified antioxidant peptides from corn protein hydrolysates (CPH) and identified novel antioxidant peptides from fraction CPH2-III as Ala-Gly-Ile/Leu-Pro-Met (AGI/LPM; 487.62 Da) and His-Ala-lle/Leu-Gly-Ala (HAI/LGA; 467.53 Da). AGLPM and HALGA exhibited better oxygen radical absorbance capacities than AGIPM and HAIGA did (P < 0.05), as assessed using HepG2 cells with the cellular antioxidant activity assay (CAA) and electron spin resonance (ESR) spectroscopy. Finally, the secondary structure was determined using circular dichroism (CD). ESR showed that the AGLPM and HALGA peptides had the strongest abilities to scavenge hydroxyl radicals, by 79.41 +/- 1.41% and 75.16 +/- 2.26%, respectively. Thus, corn gluten meal could be used as a potential source of antioxidant peptides for food applications. Additionally, the amino acid Leu compared with Ile may be a critical factor contributing to strong antioxidant activity than the Ile in the peptide sequence (not C-terminus or N-terminus) and CD showed that the lower alpha-helix and random coil are the main causes.