High internal phase Pickering emulsions stabilized by walnut protein–galactooligosaccharide nanoparticles: effect of cinnamon oil entrapment

Abstract Walnut protein–galactooligosaccharide (WalPI–GOS) nanoparticles were used to prepare high internal phase Pickering emulsions (HIPPEs). The entrapment properties of HIPPEs for cinnamon oil were investigated by varying the ratios of camellia and cinnamon oils (cinnamon oil contents: 0%, 2.5%, 5.0%, 10%, 15%, and 20%), and the droplet size, rheological properties, Raman spectroscopy results, microstructure, thermal stability, storage stability, and antioxidant activity of HIPPEs were determined. Results showed that the droplet size of HIPPEs increased with increasing cinnamon oil content. Among samples, HIPPEs with the cinnamon oil content of 10% had the highest storage and loss moduli and apparent viscosity (13.64 Pa·s). However, the thixotropic recovery ability of HIPPEs decreased with the increase in cinnamon oil content. Raman spectroscopy and microstructural analysis revealed that proteins covalently cross-linked with cinnamaldehyde to form a three-dimensional network structure, which showed the highest stability when the cinnamon oil content was 10%. HIPPEs exhibited high thermal stability without delamination after heating, as well as good storage stability without delamination or discoloration after 15 days of storage at 25 °C and 50 °C. Among samples, HIPPEs with 10% cinnamon oil content had the lowest POV and MDA values during storage. The addition of cinnamon oil significantly enhanced the antioxidant activity of HIPPEs. In summary, the best overall performance of HIPPEs was achieved at a cinnamon oil content of 10%. This result provides a theoretical foundation for the development of WalPI and the application of cinnamon oil in food, as well as a theoretical basis for the development of novel food delivery systems.