Impact of pea protein-inulin conjugates prepared via the Maillard reaction using a combination of ultrasound and pH-shift treatments on physical and oxidative stability of algae oil emulsions

Algal oil is an aquatic plant source of polyunsaturated fatty acids, especially docosahexaenoic acid (DHA), which may exhibit health benefits when consumed in sufficiently high quantities. But its application as a healthy lipid in functional foods is often limited by its tendency to rapidly oxidize and produce rancid off-flavors. In this study, algal oil-in-water emulsions were prepared using pea protein isolate (PPI)-inulin conjugates as emulsifiers. These conjugates were prepared via the Maillard reaction using a combination of ultrasound and pH-shift treatments. The algal oil phase was mixed with lemon oil (0 to 1.2 wt%) prior to homogenization to improve its sensory characteristics. The addition of 0.6 wt% of lemon oil did not significantly affect the formation and physical stability of the emulsions but it did mask the unpleasant odor of algae oil. The conjugate-stabilized emulsions exhibited shear thinning behavior and had a higher viscosity than PPI-stabilized emulsions. They also had a higher surface load and formed thicker interfacial layers. The conjugates, especially the conjugates prepared by the combined treatments, also significantly improved the physical and oxidative stability of the emulsions. These effects were attributed to an increase in the steric repulsion between the oil droplets due to the hydrophilic inulin chains, as well as to an increase in the antioxidant activity of the interfacial layers due to the presence of more antioxidant proteins. Overall, our results show that the quality attributes and shelf life of DHA-fortified algae oil emulsions can be significantly improved using a plant-based protein-inulin conjugate.