Anti-oxidative capacity of enzymatically released peptides from soybean protein isolate

Shelf-life of dietary products and the need for health supporting functional ingredients often require components with high anti-oxidative properties. The study aimed at the characterisation of peptides with antioxidant properties from enzymatically hydrolysed soybean protein isolate. Soybean protein isolate was hydrolysed with a food grade pancreatic trypsin/chymotrypsin for industrial applications, ultrafiltered and the permeate was fractionated by size exclusion chromatography. Anti-oxidative properties of these fractions were tested in a Trolox(A (R))-equivalent-anti-oxidative capacity assay, which is based on the absorbance suppression of 2,2'-azinobis(3-ethyl benzothiazoline-6-sulfonate) radical cations by anti-oxidative substances at lambda 414 nm. The amino acid compositions and sequences of the peptide fractions were determined by liquid chromatography and mass spectrometry analysis. Compared to the intact soybean protein isolate a peptide fraction with an anti-oxidative capacity of 113 mg TEAC/g was obtained. This fraction was shown to be enriched in peptides smaller than 1 kDa with prevailing aromatic amino acid residues. Nine peptides derived from glycinin and beta-conglycinin were sequenced by tandem mass spectrometry. The particular sequences were synthesized and assayed. The synthetic peptide analogue TTYY (beta-conglycinin fragment 291-294) revealed significant radical scavenging properties of 13.6 up to 59.6% with 0.18-18 mM in a concentration dependent manner. Peptides from soybean protein isolate were shown to possess anti-oxidative capacities which might be linked to the presence of carboxy terminal tyrosine. These findings offer new functional application possibilities in nutrition, cosmetics and pharmaceuticals.