Fabrication and Morphological Characterization of Biopolymer Particles Formed by Electrostatic Complexation of Heat Treated Lactoferrin and Anionic Polysaccharides

Biopolymer particles fabricated from proteins and/or polysaccharides can be used to encapsulate functional components or to modify various functional properties of materials. In this study, sub-micrometer biopolymer particles were fabricated by electrostatic complexation of heat-denatured protein (lactoferrin, LF) particles with anionic polysaccharides (alginate, carrageenan, or pectin). The aim of the study was to exploit macromolecular electrostatic interactions to form sub-micrometer sized particles and study their stability and morphological characteristics. Initially, protein particles were formed by heat treatment (91 °C, 20 min) of a lactoferrin solution (0.2% LF, pH 7), which led to a suspension of protein particles with mean diameter of 200−400 nm and isoelectric point of pI ≈ 8.5. Biopolymer particles were then formed by mixing the protein particles with anionic polysaccharides at pH 8 and then lowering the pH to promote electrostatic deposition of polysaccharides onto the protein particle surfaces. The influence of pH (2−11) and ionic strength (0−200 mM NaCl) on the properties and stability of the complexes was studied using turbidity, dynamic light scattering, and electrophoresis measurements. Relatively stable particles could be formed from pH 5 to 8, but appreciable aggregation occurred at lower pH which was attributed to charge neutralization and bridging effects. LF−pectin complexes were relatively stable to salt addition, but LF−carrageenan and LF−alginate complexes exhibited aggregation at higher salt concentrations. These results have important implications for the application of lactoferrin−polysaccharide complexes as functional components in commercial products, such as pharmaceuticals, personal care products, and foods.