Journal of Applied Crystallography

Volume 41, Part 3 (June 2008)

research papers

J. Appl. Cryst. (2008). 41, 628-633 [ doi:10.1107/S0021889808012648 ]

Application of small-angle scattering to study the effects of moisture content on a native soy protein

C. S. Kealley, M. M. Elcombe, R. Wuhrer and E. P. Gilbert

Abstract: The nano- and microstructure of glycinin, a soybean protein, has been investigated as a function of moisture for moisture contents between 4 and 21 wt%. Glycinin exhibits peaks in the small-angle region whose positions show minimal change with X-rays for samples up to 13% moisture. However, the use of neutron scattering, and the associated enhancement in contrast, results in the Bragg peaks being well resolved up to higher moisture contents; the associated shift in peak positions between 4 and 21% moisture are consistent with the expansion of a hexagonal unit cell as a function of moisture content. A Porod slope of -4 indicates that the interface between the `dry' protein powder and the surrounding medium at a length-scale of at least 3 µm down to 20 nm is smooth and sharp. Scanning electron microscopy indicates that the powders, with low moisture content, have a porous appearance, with the porosity decreasing and microstructure expanding as the moisture content increases.

Keywords: glycinin; proteins; moisture content; small-angle scattering; microstructures; nanostructures.