Stabilization of emulsions by OSA starches

In continuous mechanical emulsification, droplets of a coarse premix are first deformed and disrupted. Secondly, the newly formed interface has to be stabilized. Emulsions are thermodynamically unstable, as droplets tend to coalesce. To avoid coalescence of droplets, different effects have to be taken into account. The objective of this paper is to investigate the possibility of producing finely dispersed emulsions by using OSA starches as additive. Experiments were carried out using two commercially available OSA starches that differ mainly in viscosity of their aqueous solutions. In the experiments, the dispersed phase content, starch concentration as well as pH value and the influence of dissolved salts of different ion strength have been investigated. By droplet size analysis directly after production of oil-in-water emulsions the emulsifying properties of such starches were determined. Measurements of interfacial tension prove that OSA starches are surface active substances. It was shown by emulsification experiments that the stabilization of droplets by OSA starches is very efficient. The emulsification results achieved with OSA starches have been found to be independent from the type of starch and the starch concentration above the lower limit of starch needed for stabilization. The emulsification results are independent of pH value and ion valence. Therefore it can be concluded that steric hindrance is the main stabilizing mechanism of OSA starches. As proteins stabilize emulsion droplets mainly by electrostatic repulsive forces, the emulsification result depends strongly on pH, which leads to poor emulsification at pH values near the iso-electric point. The results of the work presented here suggest that whey proteins can be substituted by OSA starches with a specific advantage at low pH values near the iso-electric point of the protein.