Effect of surface-active stabilizers on the surface properties of coconut milk emulsions

Recently we have shown how surface-active stabilizers (<= 1 wt% sodium dodecyl sulfate, polyoxyethylene sorbitan monolaurate, whey protein isolate, and sodium caseinate) added either before or after homogenization affect the stability and properties of coconut milk emulsions [Tangsuphoom, N., & Coupland, J.N. (2008). Effect of surface-active stabilizers on the microstructure and stability of coconut milk emulsions. Food Hydrocolloids, 22(7),1233-1242]. In this work, we propose a mechanism to explain these observations based on changes in surface composition and properties. Coconut milk has a high Surface protein load similar to 7 mg m(-2)), of which the major component is cocosin. Small-molecule surfactants (>0.25%) added to the homogenized coconut milk displaced the coconut proteins from the surface resulting in a change in zeta-potential. Dairy proteins added to the coconut milk after homogenization did not accumulate at the droplet surface. Addition of small-molecule surfactants to the coconut milk prior to homogenization completely displaced coconut proteins from the oil-water interface. Homogenization of coconut milk with proteins resulted in a decrease in total protein surface concentration (to about 2 mg m-2) and a significant replacement of coconut proteins by the dairy proteins. The change in zeta-potential also reflected the change in protein and surface composition as the values moved close to the value of coconut oil emulsions stabilized solely with the corresponding added stabilizer. (C) 2008 Elsevier Ltd. All rights reserved.