Insight into natural biopolymer-emulsified solid lipid nanoparticles for encapsulation of curcumin: Effect of loading methods

Abstract

Encapsulation of lipophilic bioactives into solid lipid nanoparticles (SLNs) has been a promising approach to incorporate them into functional foods with attempt to improve bioavailability. Nevertheless, how these bioactives should be loaded into the lipid core have never been systematically studied before. Thus, in the present study, biopolymer-emulsified SLNs were prepared using a recently developed synthetic surfactant-free technique, and four different loading methods were tested for their efficacy to encapsulate curcumin into SLNs. Sodium caseinate (NaCas) and pectin were used as natural emulsifier and stabilizer, respectively, to prepare food-grade SLNs using stearic acid. Four loading methods varied in the use of organic solvent, and the order of critical steps including addition of curcumin and solid lipids, deprotonation of NaCas at pH 12, as well as pectin adsorption at pH 4. The resulting four types of curcumin-loaded SLNs were subject to comprehensive characterization, such as measurement of particle size, polydispersibility, zeta potential, stability test in simulated gastrointestinal (GI) fluids, antioxidant activities of encapsulated curcumin, as well as morphological observation under transmission electron microscopy. Nano spray drying technology was then exploited to obtain ultrafine powders from colloidal SLNs and their redispersibility in water was also evaluated. Our results suggested that solubilization of curcumin in deprotonated NaCas was a better approach than using organic solvent which resulted in large and aggregated SLNs. Furthermore, mixing curcumin with deprotonated NaCas and then adding melted lipid and pectin at pH 12 before emulsification were the two critical steps in fabricating uniform and small SLNs that were GI-stable and re-dispersible in water after spray drying. This study provides insight into the preparation of natural biopolymer-emulsified SLNs as a potential food-grade oral delivery system for lipophilic bioactives.