Kinetic and Oxidative Stability of Oil-in-Water Pickering Emulsions Stabilized by Lysozyme-Ferulic Acid Conjugates

Abstract

The demand for ingredients with natural appeal has driven the development of multifunctional natural emulsifiers. This study aimed to synthesize covalent conjugates of lysozyme (LYS) and ferulic acid (FA) via a free radical reaction and investigate their application in stabilizing soybean oil Pickering emulsions. Conjugate formation was confirmed by SDS-PAGE and FTIR and UV-Vis spectroscopy, indicating alterations in the protein’s tertiary structure. The LYS-FA conjugate exhibited techno-functional properties superior to native lysozyme, including higher emulsifying capacity and antioxidant activity, with inhibition values above 74% for both DPPH and ABTS. Furthermore, in vitro digestion studies demonstrated that conjugation protected FA from degradation in the gastric phase. Oil-in-water Pickering emulsions were prepared with different conjugate concentrations from 2 to 4% w/w in the aqueous phase. The formulation with 4% LYS-FA resulted in an excellent kinetic stability, showing no creaming for 8 days. Rheology revealed pseudoplastic behavior with a predominantly elastic character, where G’ was higher than G’’, suggesting the formation of a robust network at the interface. In addition to physical stability, the Pickering emulsions significantly retarded the primary and secondary lipid oxidation of the encapsulated soybean oil compared to the control, attributed to the interfacial barrier and antioxidant action formed by the conjugate. These results suggest that LYS-FA conjugates are promising candidates as emulsifiers with good techno-functional properties and antioxidant capacity for applications in the food industry.