DETERMINATION OF INTERFACIAL-AREAS IN EMULSIONS USING TURBIDIMETRIC AND DROPLET SIZE DATA - CORRECTION OF THE FORMULA FOR EMULSIFYING ACTIVITY INDEX

Derivation of the emulsifying activity index (EAI) (Pearce, K. N.; Kinsella, J. E. J. Agric. Food Chem. 1978, 26, 716-723) from first principles demonstrates that a simple correction must be made. The original EAI does not provide units of interfacial area per gram of emulsifier as claimed: its value varies with the oil volume fraction. The correction provides the index with the desired units of square meters of interfacial area per gram of emulsifier. The interfacial areas of three suspensions of monodisperse latex beads were determined in four different ways: by turbidimetry using the original and corrected formulas for EAI; by calculation from the droplet size distribution measured by laser diffraction; and by calculation using bead diameters supplied by the manufacturer. For three bead sizes covering the range of droplet sizes in typical emulsions the interfacial area value based on the distribution of particle sizes was closest to the actual value. The interfacial area calculated by original formula for EAI was least accurate. The correction to the EAI formula improved correspondence of interfacial area measured turbidimetrically to the actual value and eliminated its dependence on the oil volume fraction in the emulsion.