Identification and characterization of antioxidant peptides obtained by gastrointestinal digestion of amaranth proteins

• Amaranth proteins were subjected to a simulated gastrointestinal digestion.
• RP-HPLC fractions from gastrointestinal digests were evaluated by ORAC method.
• Antioxidant peptides from 11S globulin were identified by LC–MS/MS and synthesized.
• Structure–activity relationships were analyzed.

The objective of the present work was to separate and identify antioxidant peptides from a simulated gastrointestinal digest (Id) from Amaranthus mantegazzianus proteins (I), which has previously been demonstrated to have this activity. I and Id were separated by preparative RP-HPLC. Fractions were evaluated by the ORAC method and the more active ones were analyzed by LC–MS/MS. Each fraction presented diverse peptides from different proteins, most of them from the 11S globulin. After grouping the peptides from 11S globulin according to their overlapping sequences, and based on previous information about structure–activity relationships, ten sequences were synthesized, in order to evaluate their antioxidant activity. Four peptides presented interesting activity: AWEEREQGSR > YLAGKPQQEH ∼ IYIEQGNGITGM ∼ TEVWDSNEQ. They exhibited some of the structural characteristics already known to demonstrate this activity, all of them containing at least one bulky aromatic residue. All belonged to little structured, internal or exposed regions of the acid subunit of the 11S globulin.