The nature of protein-polysaccharide nanoparticles prepared using two fabrication methods was compared: Type 1 particles were formed by creating beta-lactoglobulin nanoparticles, and then coating them with pectin; Type 2 particles were formed by heating beta-lactoglobulin and pectin complexes together. Protein nanoparticles (d=180 nm) were created by heating beta-lactoglobulin above its thermal denaturation temperature (T(m)) at pH 5.8. Type 1 particles were then formed by mixing these particles with high methoxy (HM) pectin under conditions where pectin adsorbed to the protein (pH<6). Type 2 particles were created by heating beta-lactoglobulin-HM pectin electrostatic complexes above T(m) at pH 4.75. At pH 4.5, Types 1 and 2 particulates had similar charge (-33 mV), protein content, and shapes (spheroid), however, Type 1 particulates were larger (d=430 nm) than Type 2 particulates (d=300 nm). The influence of pH, ionic strength and protein:pectin mass ratio (r) on the physical stability of the two types of particles was tested. A weight ratio of 2:1 (protein:pectin) gave good pH stability of the particles against aggregation by imparting more surface charge. Type 2 particles had a higher electrical charge, better stability to aggregation at lower pH values (pH<4), and better stability to aggregation at high salt concentrations (200 mM NaCl) than Type 1 particles. These differences suggested that Type 2 particulates had a higher surface coverage with pectin, thereby reducing their tendency to aggregate. These results have important consequences for the design of biopolymer nanoparticles based on thermal treatment of proteins and polysaccharides.
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