Stabilizing zein nanoparticle dispersions with ι-carrageenan

Abstract

Zein nanoparticles (ZNPs) suspended in water were produced by the antisolvent precipitation method and combined with ι-carrageenan (ι-CGN) suspended in sodium phosphate buffer in order to evaluate the ability of the negatively-charged ι-CGN to stabilize ZNPs against flocculation and gravitational separation. Physical stability of 0.01% ZNP (w/v) dispersions with 0%–0.02% ι-CGN (w/v) was observed during storage at 4 °C and during centrifugation. Colloidal properties of the particles during storage, such as hydrodynamic radius, turbidity, and ζ-potential were characterized at pH values above pH 5. At pH 5, ZNPs were present as small aggregates with an average hydrodynamic radius of approximately 500 nm, and at higher pH values these aggregated further so that the average size was greater than 1000 nm. Addition of sufficient ι-CGN to achieve a ZNP:ι-CGN weight ratio less than or equal to 10:1 prevented aggregation in the pH range of 5.25–6.75 and limited aggregation at pH 7.0 (average particle radius of 200–400 nm). Enhanced stability was attributed to the adhesion of ι-CGN to the nanoparticle surface, as the ZNPs surface charge became significantly negative with introduction of ι-CGN. These particles remained stable for up to 30 days with significantly lower turbidity and greater resistance to gravitational separation when compared to ZNPs alone. Characterization of ZNPs with an atomic force microscope showed that the particles possessed a nearly spherical geometry with a Young's modulus of ∼100 MPa, neither of which was significantly altered after addition of interactive ι-CGN.