A Novel Approach to Turbidimetry of Dense Systems: An Investigation of the Enzymatic Gelation of Casein Micelles.
A novel approach to turbidimetry enabling the extraction of structural information about highly turbid systems has been developed. Turbidimetric spectra have been obtained in the wavelength region 500-1100 nm using an acceptance angle of 1 degrees for detecting the transmitted light. It is demonstrated that the influence of multiple scattering can be eliminated by measurement of turbidimetric spectra at several sample thicknesses and subsequent extrapolation to zero thickness. The validity of this method is demonstrated by Monte Carlo simulations of multiple scattering of light using simple Rayleigh-Debye-Gans theory. The simulations demonstrate that turbidimetric spectra are very insensitive to multiple scattering measured with an acceptance angle of 1 degrees when the particles are smaller than about 1 µm. It was further shown that no shape information can be derived from turbidimetric spectra under our condition for objects having diameters up to 6 µm. The turbidimetric spectra of casein aggregation/gelation have been fitted by modeling the aggregates either as homogeneous spheres or as fractals. The turbidimetric averaged mean radii found using the sphere model are at all stages of the process consistently smaller than radii found by either static or dynamic light scattering. This is found to be a consequence of the angular integration involved in turbidimetry which weights larger radii less than in the case of light scattering. Copyright 1998 Academic Press.
Department of Mathematics and Physics, The Royal Veterinary and Agricultural University, Copenhagen, Denmark
P
Worning
R
Bauer
L
Øgendal
S
Lomholt