Comparison of Surfactants Typically Used for Stabilizing Oil-in-Water Emulsions in Terms of Their Surface, Emulsifying, and <i>in Vitro</i> Digestion Properties

Emulsifiers play key roles in a number of industries including those concerned with the production of food, medicines and cosmetics. In the present study, the surface effects, interfacial properties and emulsification characteristics of nine types of commonly deployed O/W emulsifiers, namely soy lecithin (SL), sodium stearyl lactate (SSL), sodium lauryl sulfonate (SLS), sucrose esters L1695, P1670 and S1670, Tween 80, polyglyceryl-10 laurate (PL) as well as sodium caseinate (SC), have been evaluated in a comprehensive and systematic manner. S1670, P1670, and L1695 exhibited the lowest critical micelle concentration (CMC) values among the eight emulsifiers tested (SLS could not be evaluated because of solubility issues) while L1695, Tween 80, and P1670 were found to significantly modify the wettability of a glass substrate. In terms of foaming performance, L1695 and SLS were best. O/W emulsions stabilized by these nine emulsifiers could all be stored for at least 15 days over the temperature range 2 to 8 °C in neutral and alkaline environments but, with the exception of those derived from Tween 80, not below pH 7. Emulsions stabilized by S1670, P1670, and L1695 were found to be sensitive to higher salt concentrations. In their evaluation under simulated digestion conditions, the emulsions remained intact under the oral and stomach phases but collapsed in the corresponding small intestine stage. This resulted in free fatty acid (FFA) release of between 70 and 80% (the equivalent release arising from emulsions prepared using L1695 and PL was below 40%). Such profiles should be capable of exploitation in the development of encapsulated (controlled release) delivery systems that protect delicate active components.