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 α10, α12, γ1, γ75 and γ76 adopted a predominantly α-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 β22, β27, γ36 and γ38 displayed a significantly higher degree of interfacial inter-peptide interaction, resulting in stiff and solid-like interfaces (E _d ^∗=35−45mN/m). β22 and γ36 peptides re-arranged at the interface adopting a highly β-strand structure (63–65%). Emulsions stabilized with all peptides showed high physical stability during one week (D _3,2 at day 1 = 0.134–0.175 μm), except from the ones stabilized with β27 that had creaming after day 1, or β22 that destabilized during storage. Emulsions stabilized with peptides exhibiting negative surface charge at pH 7 (α12, β22, γ1, γ75, γ76, γ36 and γ40) (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 (α10, β27 and γ38) (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.