Determination of the fractal dimension using turbidimetric techniques. Application to aggregating protein systems

Abstract

Scattering techniques are a powerful way of studying fractal structures. Depending on the characteristic length scale to be observed and the nature of the aggregate, it is possible to use the scattering of light, X-rays or neutrons, the fractal exhibiting power-law scaling of scattered intensity with wavevector, q, when 1/R≪q≪ 1/a. Normally for long-length scales (small q) angular dependence of laser light scattering is employed. It is shown here that the value of the fractal dimension of an aggregate is also accessible through measurement of the wavelength dependence of the turbidity of the solution, provided large enough aggregates are created. The remainder of the paper deals with specific applications of this technique to the study of aggregates of casein proteins both as individual proteins where aggregation is induced by the addition of calcium ions and as casein micelles where destabilization is brought about following enzyme (rennet) action or the addition of ethanol.