Pickering emulsion stabilized by conjugated sodium caseinate-ascorbic acid nanoparticles: Synthesis and physicochemical characterization

Abstract

This study investigated the effect of sodium caseinate (SC)-ascorbic acid (AA) interaction under thermal (as a Maillard reaction) treatment on the physicochemical properties of the SC-AA colloidal particles, as well as, the physical and oxidative stability of the prepared Pickering emulsion (PE) using colloidal particles as an aqueous phase with the volumetric ratio of 50:50 water and oil. The stable colloidal suspensions were obtained when the concentration of SC-AA solution was set at 10 and 1 mg/mL for SC and AA, respectively. The fluorescence and FT-IR results showed strong hydrophobic interaction in SC-AA complex, but after heat treatment of SC and AA (HSC-AA), the covalent Schiff base type bond formed. In the HSC-AA sample, the percentage of free amino group reduction (∼32%) confirmed the Maillard reaction occurrence, and the results of SDS-PAGE showed cross-linking between SC particles. A significant decrease in interfacial tension was observed in samples containing AA, which reached the lowest value in HSC-AA (6.5 mN/m). Also, the wettability of HSC-AA increased based on a three-phase contact angle analysis to θ ∼82°. In the case of physical stability, while SC, SC-AA, and HSC samples could not stabilize the PE, the HSC-AA showed the best physical stability for more than 90 days at 4 °C and 7 days at 37 °C. CLSM images showed HSC-AA particles were located around the oil droplet. Based on TBARS results, the value of advanced oxidation product was the lowest for HSC-AA stabilized PE, indicating the protective effect of HSC-AA solid particles against lipid oxidation. This research confirmed the HSC-AA effectiveness as a solid particle stabilizer for PE, especially in reduced fat formulations. These results are valuable due to the common use of SC and AA as food-grade additives.