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The influence of pH, protein concentration and calcium ratio on the formation and structure of nanotubes from partially hydrolyzed bovine α-lactalbumin

Abstract

Formation of nanotubes from partially hydrolysed α-lactalbumin (α-La) was investigated at five pH values, two concentrations of α-La and two calcium levels. Nanotubes were formed under almost all combinations of the investigated factors, and for the first time formation of nanotubes at low pH (4.0) and low protein concentration (10 g l-1) was observed. Only one sample (10 g l-1), calcium ratio 2.4, pH 7.5) formed mainly fibrils instead of nanotubes. By altering the three investigated factors, fibrils and/or aggregates sometimes formed together with nanotubes resulting in transparent, semi-transparent, or non-transparent gels, or in sedimentation. However, structural modelling based on small-angle X-ray scattering data indicated that the formed nanotubes were only to a minor degree affected by the investigated factors. The majority of nanotubes were found to have an outer diameter around 19 nm, an inner diameter of 6.6 nm and a wall thickness of 6.0 nm, except for three samples at low α-La concentration and high calcium level which exhibited slightly smaller dimensions. These three factors affected the hydrolysis as well as the self-assembly rate, resulting in the observed differences. However, these factors did not influence the architecture of the self-assembled nanotubes, and the lateral spacing of the individual parallel β-sheet motifs was found to be 1.05 ± 0. 03 nm for all nanotubes. This study provides novel fundamental knowledge of the formation and structure of α-La nanotubes at different conditions, which will facilitate future application of these nanotubes in food and pharmaceutical areas.

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Publication details

The article was received on 18 Jan 2019, accepted on 10 Apr 2019 and first published on 11 Apr 2019


Article type: Paper
DOI: 10.1039/C9SM00127A
Citation: Soft Matter, 2019, Accepted Manuscript

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    The influence of pH, protein concentration and calcium ratio on the formation and structure of nanotubes from partially hydrolyzed bovine α-lactalbumin

    X. L. Geng, J. J. K. Kirkensgaard, L. Arleth, J. Otte and R. Ipsen, Soft Matter, 2019, Accepted Manuscript , DOI: 10.1039/C9SM00127A

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