Designing covalent sodium caseinate-quercetin complexes to improve emulsifying properties and oxidative stability.

The complexation of proteins with phenolic compounds has been considered a promising route to improve the oxidative stability of oil-in-water (O/W) emulsions. In this context, physicochemical and techno-functional properties of sodium caseinate (SC) chemically modified by the interaction with quercetin (Q) under alkaline conditions were evaluated using different molar ratios of the components (SC:Q). The formation of covalent complexes was analysed by the changes in SC structure and properties.. The results showed that the surface hydrophobicity of SC gradually decreased with increasing Q concentration. Whereas an increase in phenolic content and antioxidant activity by DPPH and FRAP was observed. The techno-functionality of the complexes was evaluated by their capacity of stabilizing oil-in-water emulsions. The emulsion stabilized by complexes and non-modified SC showed an average droplet size (D) between 1,632 ± 0,068 and 1,945 ± 0,431 µm. After 21d of storage, no coalescence was observed, evidencing the formation of stable emulsions. Furthermore, the highest oxidative stability of the emulsion was observed at the highest concentration of Q, while the formation of hydroperoxides and aldehydes was greater in the emulsions stabilized with non-modified SC. The formation of primary lipid oxidation compounds was approximately 3x higher in emulsions stabilized only with SC compared to those stabilized with the SC:Q complex in a 1:1 ratio. These results suggest that modification of SC with Q is a potential approach tuning both chemical and techno-functional properties of SC.