Preparation of nanoparticles from denatured whey protein by pH-cycling treatment

Low temperature cross-linking of denatured whey protein through pH-cycling is proposed to develop nanoparticles with controlled size and properties. Soluble polymers were produced by heating whey protein dispersions at low ionic strength and neutral pH. Nanoparticulation was induced by acidification of diluted polymer dispersions followed by pH neutralization. The effect of aggregation conditions on the physicochemical characteristics and stability of nanoparticles was studied. Nanoparticles with a diameter ranging from 100 to 300 nm were produced depending on the pH of aggregation (5.0, 5.5, 6.0), the added calcium concentration (0, 2.5, 5 mM) and the ageing time at the aggregation pH (0–75 h). The size and the turbidity of nanoparticle dispersions increased with increasing ageing time and calcium concentration. Nanoparticle voluminosity decreased with increasing calcium concentration during pH-cycling, suggesting a more compact and less porous internal structure. The stability of nanoparticles in the presence of different dissociating buffers (EDTA, urea, SDS and DTT) was evaluated and the results showed that whey protein nanoparticles were covalently cross-linked by disulphide bonds.