Formation of nanotubes and gels at a broad pH range upon partial hydrolysis of bovine α-lactalbumin

The influence of pH (from 7.5 to 4.0) on the hydrolysis and self-assembly process of nanotubes formed from partially hydrolysed bovine α-lactalbumin was studied. The results showed that the pH had no influence on the products resulting from hydrolysis, but a decrease in pH dramatically reduced the hydrolysis rate. In contrast, the self-assembly process was favoured by decreased pH due to the reduced electrostatic repulsion between the fragments making up the nanotubes. Initially, upon adding a protease, a rapid change in conformation was indicated by circular dichroism spectroscopy. Subsequently no further change was observed. Due to slower hydrolysis and faster self-assembly at pH 6.5 and 4.0, the main building fragments were integrated quickly into nanotubes, and hence avoided further hydrolysis. Self-assembly of protease-induced α-lactalbumin nanotubes can thus be extended over a broad range of pH values. These findings might be useful for future applications in both food and pharmaceutical industries.