A NOVEL-APPROACH TO TURBIDIMETRY OF DENSE SYSTEMS - AN INVESTIGATION OF THE ENZYMATIC GELATION OF CASEIN MICELLES

A novel approach to turbidimetry enabling the er,traction of structura l information about highly turbid systems has been developed, Turbidim etric spectra have been obtained in the wavelength region 500-1100 mn using an acceptance angle of 1 degrees for detecting the transmitted l ight. It is demonstrated that the influence of multiple scattering can be eliminated by measurement of turbidimetric spectra at several samp le thicknesses and subsequent extrapolation to zero thickness. The val idity of this method is demonstrated by Monte Carlo simulations of mul tiple scattering of light using simple Rayleigh-Debye-Gans theory. The simulations demonstrate that turbidimetric spectra are very insensiti ve to multiple scattering measured with an acceptance angle of 1 degre es when the particles are smaller than about 1 mu m. It was further sh own that no shape information can be derived from turbidimetric spectr a under our condition for objects having diameters up to 6 mu m. The t urbidimetric spectra of casein aggregation/gelation have been fitted b y modeling the aggregates either as homogeneous spheres or as fractals . The turbidimetric averaged mean radii found using the sphere model a re at all stages of the process consistently smaller than radii found by either static or dynamic light scattering. This is found to be a co nsequence of the angular integration involved in turbidimetry which we ights larger radii less than in the case of light scattering. (C) 1998 Academic Press.