Comparison of protein–polysaccharide nanoparticle fabrication methods: Impact of biopolymer complexation before or after particle formation

Biopolymer nanoparticles can be formed using two methods: Type 1 particles are formed by creating β-lactoglobulin nanoparticles by heating, and then coating them with pectin; Type 2 particles are formed by heating β-lactoglobulin and pectin complexes together. The nature of protein–polysaccharide nanoparticles prepared using two fabrication methods was compared: Type 1 particles were formed by creating β-lactoglobulin nanoparticles, and then coating them with pectin; Type 2 particles were formed by heating β-lactoglobulin and pectin complexes together. Protein nanoparticles ( d = 180 nm) were created by heating β-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 β-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.