Particle size distribution of sodium caseinate in water-ethanol solutions

The particle size distribution of an industrially produced spray dried sodium caseinate dissolved in water or in 15-60% (v/v) ethanol at pH 7.0 was measured with a helium-neon laser (lambda = 633 nm). The size distribution seems to be of the gaussian type and monomodal with the modal number radius of similar to 90 nm and the modal volume radius of similar to 200 nm for water solutions. The logarithm of the modal radius and the width of the gaussian curves are linear functions of the ethanol concentration. The average caseinate particle dissociates into about 2 to 32 sub-units with the ethanol volume fraction increasing from 0.15 to 0.60, respectively. Half of the casein's aggregates volume has a radius between 118 and 303 nm for water solution, while for 60% ethanol it is between 45 and 77 nm. The casein particles dissociation is most probably driven by the rise of the electrostatic energy with the decreasing solvents dielectric constant.