STUDIES ON THE OIL-IN-WATER EMULSIONS STABILIZED WITH GUM-ARABIC BY USING THE TURBIDITY RATIO METHOD

Emulsion stability is often expressed in terms of the turbidity ratio, the ratio of the turbidities, tau, of a diluted emulsion estimated at two wavelengths lambda1 and lambda2. In this paper, it is shown that the theoretical values of the turbidity ratio, f, can be calculated by f = tau(lambda1)/tau(lambda2) = (lambda1/lambda2)-n, since the values of the wavelength exponent n for spherical particles are known to be a function of m and D, where m is the relative refractive index of the particle to the medium and D is the diameter of the particle. The relation between the experimentally determined turbidity ratio, f, at lambda1 = 800 and lambda2 = 555, and the average particle diameter determined by optical microscopy agreed well with the theoretical curves with m = 1.10 for vegetable oil and m = 1.20 for polystyrene latex. Therefore, the oil-in-water emulsions stabilized with gum arabic were studied by use of the turbidity ratio method. For the emulsions of vegetable oils, the turbidity ratio decreased and the particle diameter decreased with the concentration of gum arabic. Addition of beta-carotene in the oil phase, up to the ordinary dose, resulted in a very little change in the diameter. The effect of the kind of vegetable oil on the particle diameter was not large, but the emulsion of rice oil had a little smaller diameter than that of olive oil or soybean oil. The results obtained with triglycerides as an oil phase were dependent on their molecular weight rather than their iodine value.