Encapsulation of three different types of polyphenols in casein using a customized pH-driven method: Preparation and characterization

Phenolic compounds represent natural compounds endowed with diverse biological functionalities. However, their inherent limitations, characterized by poor water solubility and low oral bioavailability, limit their broader applications. Encapsulation delivery systems are emerging as a remedy, able to ameliorate these limitations by enhancing the stability and solubility of phenolic compounds. In this study, a novel, customized pH-driven approach was developed by determining the optimal deprotonation and protonation points of three different types of polyphenols: ferulic acid, resveratrol, and rhein. The polyphenols were successfully encapsulated in a casein carrier. The solubility, stability, LogD, and LogS curves of the three polyphenols at different pH values were analyzed to identify the optimal deprotonation points for ferulic acid (pH 9), resveratrol (pH 11), and rhein (pH 10). Based on these findings, three different nanoparticles were prepared. The encapsulation efficiencies of the three phenolic compounds were 95.86%, 94.62%, and 94.18%, respectively, and the casein nanoparticles remained stable at room temperature for seven days. FTIR spectroscopy, fluorescence spectroscopy, and molecular docking study substantiated the encapsulation of phenolic compounds within the hydrophobic core of casein-based complexes, facilitated by hydrogen bonding interactions and hydrophobic interactions. Furthermore, the analysis of antioxidant activity elucidated that casein nanoparticles heightened both the water solubility and antioxidant efficacy of the phenolic compounds. This customized encapsulation technique, by establishing a transitional pH value, resolves the challenges of chemical instability and facile degradation of polyphenols under alkaline conditions in the application process of pH-driven methods. It presents novel insights for the application of polyphenols in the domains of food and biomedical fields.