Unique milk protein based nanotubes

(Nanowerk News) Researchers in the Netherlands investigated novel α-lactalbumin nanotubes with potentially interesting applications in the food and pharma industries.
Under certain conditions, partial hydrolysis of the milk protein α-lactalbumin by a protease from Bacillus licheniformis (a large, aerobic bacillus that produces endospores) leads to self-assembly of nanotubes several micrometers in length. One potential application of these long, stiff nanotubes is as controlled-release drug delivery agents.
Because α-lactalbumin is a milk protein, it will be fairly easy to apply the nanotubes in food applications as a novel ingredient with specific functionality. Furthermore, α-lactalbumin has significant nutritional properties and is associated with some positive health effects upon consumption.
Schematic presentation of the self-assembly of partially hydrolysed α-lactalbumin into nanotubes in presence of Ca²+. (Source: Graveland-Bikker)
Joanke Graveland-Bikker, who now is at the Center for Biomedical Engineering at MIT but co-authored this article while she was at NIZO food research, and Professor Cornelis de Kruif from the Van’t Hoff Laboratory for Physical and Colloid Chemistry at Utrecht University investigated these novel nanotubes.
Their recent paper (in press) titled "Unique milk protein based nanotubes: Food and nanotechnology meet", was published online in the Feb. 21, 2006 edition of Trends in Food Science & Technology.
"An important issue for example in food applications is the stability of the α-lactalbumin nanotubes under a variety of conditions" Graveland-Bikker explained to Nanowerk. "In our experiments it appeared that these nanotubes could withstand some important treatments, such as those, which might be encountered in industrial manufacturing processes and applications."
"They withstand conditions similar to a pasteurisation step (40 seconds at 72°C) and they withstood a freeze-drying treatment" she says.
TEM image of α-lactalbumin nanotubes. Scale 1µm. (Source: Graveland-Bikker)
"Another important feature for applications, controlled release in particular, is the controlled disassembly of the α-lactalbumin nanotubes" says Graveland-Bikker. Disassembly can be induced by decreasing the Ca²+ concentration. "Simply by varying the Ca²+ concentration in the solvent the disassembly rate can be controlled" she says.
What makes the α-lactalbumin nanotubes interesting for industrial food applications is their high aspect ratio, their relative stiffness, their nanometre-sized cavity and the ability of controlled degradation. This could make them useful as viscosifying agent (because of the high aspect ratio and their stiffness) and as gelation agent for strong, transparent gels where gel formation could be made reversible.
"Perhaps most importantly" Graveland-Bikker says "because of their cavity, the α-lactalbumin nanotubes could well serve as vehicles for drugs or other encapsulated molecules, such as vitamins and enzymes, or protect or mask encapsulated compounds."
Michael Berger By – Michael is author of three books by the Royal Society of Chemistry:
Nano-Society: Pushing the Boundaries of Technology,
Nanotechnology: The Future is Tiny, and
Nanoengineering: The Skills and Tools Making Technology Invisible
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