Interpretation of small angle X-ray scattering from starch on the basis of fractals

Using small-angle X-ray scattering, the behaviour of corn and potato starches during gelatinization, swelling, and retrogradation was investigated. The scattering patterns were analysed on the basis of the fractal concept. The main scattering source from low moisture starches could be interpreted as a 'surface fractal' obeying a power law with an exponent of ca-4. When the starch swelled, the surface fractal characteristic was recognised only at very low angles, and on heating it disappeared at ca 80 degrees C. For gelatinised starches, the whole scattering pattern obeyed the power law with the power around -2.0. This result suggests that the physical arrangement of gelatinised starch molecules is a 'mass fractal', i.e. a self-similar structure, in nature. Further, it was found that the scattering of the retrograded starch showed a shoulder like peak superimposed the background scattering representing the mass fractal. The corresponding Bragg spacing was estimated to be 31 similar to 15 nm. (C) 1998 Elsevier Science Ltd. All rights reserved.