Synergistic Inhibition of Lipid Oxidation by Pea Protein Hydrolysate Coupled with Licorice Extract in a Liposomal Model System

Fourteen pea protein hydrolysates (PPHs) were prepared using different proteases and tested for antioxidant activity in a liposomal model system under oxidative stress (100 mu M FeCl3/2 mM ascorbate). Almost all PPHs inhibited lipid oxidation, and those prepared from heated protein with Flavourzyme (Fla-PPH) or Protamex (Pro-PPH) were the most effective. Remarkable synergistic effects were observed on both Fla-PPH and Pro-PPH with licorice extract (LE). Electron microscopy revealed a self assembled network that appeared to provide crucial protection of liposome against oxidation. The presence of LE enhanced the antioxidant potential by producing a more compact network apparently via PPH-LE complexation. Zeta potential measurements suggested electrostatic interactions are important driving forces for the accumulation of active peptides at the liposome interface. Peptides rich in leucine; lysine, glutamic acid, glutamine, valine, or proline with a hydrophobic N-terminus, as identified by mass spectrometry, were implicated in the antioxidative protection.