Mixed interfaces comprising pea proteins and phosphatidylcholine: A route to modulate lipid oxidation in emulsions?

Many food emulsions, such as mayonnaise or infant formula, are stabilized by combinations of proteins and phospholipids that are concomitantly present at the oil-water interface. It is expected that the physical, as well as the oxidative stability of emulsions are affected by the interfacial composition. Controlling the interfacial composition can therefore be a means to improve emulsion stability, and in particular lipid oxidation. In this work, we varied the ratio of pea protein and sunflower phosphatidylcholine and investigated the resulting interfacial composition and oxidative stability of oil-in-water (O/W) emulsions prepared at fixed pea protein concentration. Increasing the phospholipid concentration led to a monotonic decrease in the adsorbed proteins and to an increase in the adsorbed phospholipids. Cryo-transmission electron microscopy revealed a slight decrease in interfacial thickness, measuring 2.8 nm for pea protein alone, compared to 2.3 nm at the highest phosphatidylcholine-to-pea protein ratio (PC/sPPI) of 0.8 (w/w), and a slight decrease in interfacial roughness, albeit that the differences are small. The oxidative stability of the emulsions globally increased with increasing the PC/sPPI ratio, with the exception of the system with a PC/sPPI ratio of 0.6, which was more sensitive to oxidation than all the other PC-containing emulsions. This peculiar behavior is discussed in the context of model interfacial films of comparable mixed compositions, which exhibit discrete spherical structures and strands. Our results suggest that the PC/sPPI ratio determines the specific interfacial structure that is formed (i.e., packing and patchiness), and it can be expected that thereby the oxidative stability of O/W emulsions stabilized by proteins and phospholipids is modulated.