Comparative composition and antioxidant activity of Peptide fractions obtained by ultrafiltration of egg yolk protein enzymatic hydrolysates

Abstract

The objective of the study was to compare the antioxidant activity of two distinct hydrolysates and their peptide fractions prepared by ultrafiltration (UF) using membranes with molecular weight cut-off of 5 and 1 kDa. The hydrolysates were a delipidated egg yolk protein concentrate (EYP) intensively hydrolyzed with a combination of two bacterial proteases, and a phosphoproteins (PPP) extract partially hydrolyzed with trypsin. Antioxidant activity, as determined by the oxygen radical absorbance capacity (ORAC) assay, was low for EYP and PPP hydrolysates with values of 613.1 and 489.2 µM TE×g-1 protein, respectively. UF-fractionation of EYP hydrolysate increased slightly the antioxidant activity in permeate fractions (720.5-867.8 µM TE×g-1 protein). However, ORAC values were increased by more than 3-fold in UF-fractions prepared from PPP hydrolysate, which were enriched in peptides with molecular weight lower than 5 kDa. These UF-fractions were characterized by their lower N/P atomic ratio and higher phosphorus content compared to the same UF-fractions obtained from EYP-TH. They also contained high amounts of His, Met, Leu, and Phe, which are recognized as antioxidant amino acids, but also high content in Lys and Arg which both represent target amino acids of trypsin used for the hydrolysis of PPP.

Figure 1

Schematic representation of the process used for the dephosphorylation of EYP and PPP, the production of enzymatic hydrolysates and their UF-fractions.

Figure 2

Molecular weight distribution profile (%) of protein/peptide components in total hydrolysates (TH) and their UF-fractions prepared from egg yolk proteins hydrolyzed with Alcalase and Protease N (a) and phophoproteins hydrolyzed with trypsin (b).

Figure 3

Antioxidant activity (μM TE·g⁻¹ protein) of hydrolysates (TH) and UF-fractions prepared from egg yolk proteins (EYP) and phosphoproteins (PPP). Bars represent mean ± SD (n = 3) and statistical differences between TH and their respective UF-fractions are indicated (★ p < 0.05; ★★ p < 0.01; ★★★ p < 0.001).

Figure 4

Pooled content (% of total amino acids, protein basis) in His, Lys, Met, Leu, Phe, and Arg of egg yolk proteins (EYP), phosphoproteins (PPP), their hydrolysates and UF-fractions.