Structure and binding ability of self-assembled alpha-lactalbumin protein nanotubular gels

Partial hydrolysis of whey-based alpha-lactalbumin (alpha-La) with Bacillus licheniformis protease (BLP) induces the formation of nanotubular structures in the presence of calcium ions by a self-assembly process. alpha-La nanotubes (alpha-LaNTs) exist in the form of regular hollow strands with well-defined average dimensions. The growth of nanotubes induces the formation of stiff transparent protein gels due to the well-arranged networks that the strands can form; these gels can be used for entrapment, transportation, and target delivery of bioactive agents in the industry. High purity of alpha-La (free of other whey protein fractions) is desirable for nanotube formation; however, pure proteins are very expensive and not practically obtained for industrial applications. Thus, the purpose of this research was to construct alpha-LaNTs from an alpha-La preparation with lower purity and to study the gelation phenomena triggered by the self-assembled nanotubes. Some structural features of nanotube gels and their active agent-binding abilities were also investigated. A lower amount of alpha-LaNTs was observed when low purity alpha-La was used for nanotube formation. Nanotube growth induced gel formation and higher gel stiffness was obtained when compared to alpha-La hydrolysates. alpha-La was denatured after hydrolysis and self-assembly, and remarkable changes were observed in the alpha-helix and beta-sheet domains of alpha-La structure. Increased intensity in Amide I and II regions indicated potential locations for binding of active agents to alpha-LaNTs. Whey-based alpha-La without much purification can be used to produce nanotubular gels and these gels can be considered carrying matrices for active agents in various industrial applications.