Denaturation and Digestion Increase the Antioxidant Capacity of Proteins

Abstract

It has been estimated and demonstrated that the antioxidant capacity of proteins is increased as a result of digestion in the gastrointestinal tract, which can be contributed by denaturation and digestion. This study aimed to evaluate the effect of denaturation and proteolytic digestion on the antioxidant activity of bovine serum albumin (BSA) and chicken egg white proteins in model systems. Denaturation with an anionic detergent (sodium dodecyl sulfate) and digestion with papain and trypsin increased the antioxidant activity/capacity of the proteins, apparently due to the increased exposure of amino acid residues responsible for the antioxidant activity of proteins (tyrosine, tryptophan, cysteine, histidine, arginine, and cystine in the ABTS● decolorization assay; cysteine, tryptophan, tyrosine, and cystine in the FRAP assay). As the increase in the protein antioxidant activity/capacity was limited in extent, it does not invalidate the use of the antioxidant capacity of proteins to be consumed as a rough measure of their antioxidant capacity after modifications in the gastrointestinal tract.

Formation of a Purple Product upon the Reaction of ABTS Radicals with Proteins

“…The color disappeared gradually after ~10 min, presumably decomposed via redox cycling. Differences in the spectra of the laccase-ABTS • adduct (λ max = 575 nm) and for the tyrosine-ABTS adduct (λ max = 555 nm) of ABTS • and free tyrosine formed in a reaction catalyzed by laccase were ascribed to the influence of the protein environment [18]. The reaction of ABTS with lipocalin α1-microglobulin, also leading to the formation of a purple product, conditioned by the formation of ABTSadducts to at least two tyrosine residues in the protein molecule, was also reported [19].…”

“…Tyrosine residues are one of the amino acid residues most susceptible to oxidative modifications, including one-electron oxidations [23]. Tyrosine radicals, if formed in proteins, are able to form adducts with various radicals [18]. Tyrosine nitration proceeds via the formation of tyrosyl radicals and the subsequent reaction of these radicals with • NO 2 .…”