The structure, viscoelasticity and charge of potato peptides adsorbed at the oil-water interface determine the physicochemical stability of fish oil-in-water emulsions

We investigated the role of the interfacial properties of ten synthetic potato peptides (previously identified by bioinformatics) to physically and oxidatively stabilize 5 wt% fish oil-in-water emulsions (pH 7). Peptides alpha 10, alpha 12, gamma 1, gamma 75 and gamma 76 adopted a predominantly a-helical conformation (48-57%) at the interface leading to poor inter-peptides interactions as well as weak and stretchable interfaces (E-d* < 12mN/m). Peptides beta 22, beta 27, gamma 36 and gamma 38 displayed a significantly higher degree of interfacial inter-peptide interaction, resulting in stiff and solid-like interfaces (E-d*, = 35 - 45 mN/m). beta 22 and gamma 36 peptides re-arranged at the interface adopting a highly beta-strand structure (63-65%). Emulsions stabilized with all peptides showed high physical stability during one week (D-3,D-2 at day 1 = 0.134-0.175 mu m), except from the ones stabilized with beta 27 that had creaming after day 1, or beta 22 that destabilized during storage. Emulsions stabilized with peptides exhibiting negative surface charge at pH 7 (alpha 12, beta 22, gamma 1, 775, gamma 76, gamma 36 and 740) (zeta potential: -50.9 to -69.5 mV) showed the lowest oxidative stability due to the attraction of cationic metal ions that catalyzed lipid oxidation. In contrast, emulsions stabilized with peptides having positive surface charge at pH 7 (alpha 10, beta 27 and gamma 38) (zeta potential: 11.6-42.8 mV) showed high oxidative stability (i.e., by repulsion of cationic metal ions), independently of the peptide length, secondary structure at the interface, or viscoelasticity of the interfacial layer. Hence, this work advances our understanding of the relation between interfacial properties of peptide layers and the physicochemical stability of emulsions.