Suppressive effects of salts on droplet coalescence in a commercially available fat emulsion during freezing for storage.

To assess possible improvements in the practical use of long-term freezing storage for commercially available fat emulsions, the effects of salts on coalescence (fusion) of emulsions during freeze-thawing cycles were studied. For this purpose, apparent size changes were measured by dynamic light scattering, and the dispersed droplets were directly observed by freeze-fracture electron microscopy before and after the freeze-thawing processes. Intravenous high-calorie nutrient fluid, based on soybean oil in water (2.2 wt% glycerin) and emulsified by egg phosphatides, was selected as a representative commercially available fat emulsion. Possible mechanisms of the suppressive effects of various salts (Li, Na, K, Rb, and Cs chlorides) on coalescence during repeated freezing with liquid nitrogen and subsequent thawing were examined in terms of the zeta-potential of the emulsion droplets and differential scanning calorimetry heating curves of the water-salt-glycerin ternary solution. The suppressive effects of salts on the coalescence of the emulsion droplets during freeze-thaw cycles could be ascribed to the suppression of ice crystal formation and the condensation of the droplets in unfrozen aqueous channels between the ice crystals during the freezing cycle.