This paper presents a theoretical approach. of scattering by fractal a
ggregates based on a model with four parameters. It assumes that the a
ggregates are fractal and polydisperse with a number distribution whic
h has a power law dependence on the molar mass. In addition the extern
al cut-offs for the number distribution and the fractal structure are
supposed to be stretched exponential functions. beta-lactoglobulin agg
regates formed after heat-induced denaturation were studied by light a
nd neutron scattering techniques over a range of wave vectors covering
more than 4 decades. The results demonstrate clearly that the aggrega
tes have a fractal structure at larger length scales and their number
distribution is self similar. Their local structures depend on the pH
and the ionic strength of the solutions and can be either globular at
pH 7 or rigid rodlike at pH2 with a persistent length which increases
with decreasing ionic strength. The explicit analysis of the dynamic l
ight scattering data allows one to characterise precisely the mass dis
tribution. The calculated structure factors are in good agreement with
the experimental data.