The activation energy of a reasonable order of magnitude was estimated for the coalescence of oil droplets in an O/W emulsion by formulating the balance of forces acting on a droplet that crosses over the potential barrier to coalesce with another droplet by the DLVO theory and Stokes’ law. An emulsion with smaller oil droplets was shown to be more stable.

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A theoretical method to calculate the evolution of the size distribution of oil-droplets in O/W emulsions over time was proposed based on the model where the coalescence rate of two oil-droplets was expressed by second-order kinetics using the rate constant evaluated from the activation energy for coalescence. The force between two oil-droplets of different diameters was appropriated by the force between two oil-droplets of equivalent diameter, and the increase in the rate of the number density of oil-droplets was estimated by solving the mass balance equation. The evolution of the size distribution of oil-droplets in several conditions agreed well with well-known features of coalescence of oil-droplets in O/W emulsion such as instability with larger oil-droplet size.

In this study, we obtained the liquid-solid phase diagrams of a ternary solution of sodium chloride, acetic acid, and water, and a diagram of the frozen ratio of this ternary mixture. Based on the data from differential scanning calorimetry (DSC) measurement, the phase equilibria of this ternary system were successfully visualized. The formation of the ternary eutectic phase occurred between −34°C and −35°C, and the formation of the binary eutectic phase was suggested around −22°C to −34°C. Higher concentrations of a component had a significant effect on the phase equilibrium. A diagram of the frozen ratio of the ternary solution of sodium chloride at −20°C was also obtained by a simple temperature measurement method. This diagram is useful for estimating the ice fraction at the phase equilibrium of a frozen food system containing sodium chloride and acetic acid.

Freezing and thawing of oil-in-water (O/W) emulsion-type foods bring about oil-water separation and deterioration; hence, the effects of freezing and thawing conditions on the destabilization of O/W emulsions were examined. The freezing rate and thawing temperature hardly affected the stability of the O/W emulsion. O/W emulsions having different oil fractions were stored at temperatures ranging from -30 to -20 °C and then thawed. The stability after thawing depended on the storage temperature, irrespective of the oil fraction of the emulsion. A good correlation was found between the time at which the stability began to decrease and the time taken for the oil to crystalize. These results indicated that the dominant cause for the destabilization of the O/W emulsion during freezing and thawing is the crystallization of the oil phase and that the effects of the freezing and thawing rates on the stability are insignificant.