Antioxidant capacities of fractionated barley hordein hydrolysates in relation to peptide structures

Scope This study has revealed strong antioxidant activities of barley hordein hydrolysate fractions and investigated the relationships between antioxidant properties and structural features of hordein peptides. Methods and results Barley hordein fractions separated based on molecular weight and surface hydrophobicity demonstrated strong antioxidant bioactivities, especially ferrous ion chelating capacity. Structural studies revealed the poly-l-proline helix, -turn, and -sheet as the dominant structural elements in the large molecular weight fraction, while most of the small-sized peptides assumed unordered random coil conformation accompanied by a large amount of ionized carboxyl groups produced as a result of partial deamidation of glutamine residues during hydrolysis. A study of antioxidant capacity in relation to peptide structure indicated the contribution of hydrophobic residues in radical scavenging and the positive effect of ionized carboxyl groups together with Lys and Met in metal chelation activity. QPYPQ was identified as the most repeated sequence in potent RP-HPLC fractions, which might be a particular structural motif that plays a key role in scavenging free radicals. Conclusion Barley hordein with its unique sequence partitioning has potential to produce peptides with strong antioxidant bioactivities.