A novel mechanism of dynamic interfacial tension reduction in triglyceride-alkaline aqueous solution system

Emulsification of edible oils in aqueous solutions is of interest in diverse applications. The energy required for emulsification of oil in water is dependent on properties like the viscosity ratio, the local shear rates and the Interfacial Tension (IFT) of the oil–water interface, at the expansion rates prevailing during the process. This paper shows that dynamic IFT and emulsification in edible oil/water systems is dependent on the aqueous phase pH. Experiments aimed at identifying the causes of this are discussed. This study, of the pH dependence of dynamic IFT, reveals a novel mechanism for IFT lowering which is more effective than surfactant adsorption. The results of this study clearly show that the dynamic IFT of an edible-oil–aqueous solution interface, has marked pH dependence, at room temperature. However, when the commercial edible oil is purified, using known techniques for triglyceride purification, the sensitivity of its dynamic IFT to pH of the aqueous phase is significantly reduced. This study shows that the observed pH dependence of dynamic IFT and ease of emulsification at high aqueous phase pHs, is due to in-situ surfactant generation, which occurs during edible oil–alkaline aqueous solution contact. Surprisingly, in-situ surfactant generation is much more effective in reducing oil–water dynamic IFT compared with adsorption of its pre-formed equivalent. This study probes this observation. Not only is in-situ generation more effective in tension reduction, experiments discussed in this paper show that the presence of pre-formed surfactants is actually detrimental to the tension reduction that is achievable by in-situ generation.