Competitive adsorption in O/W emulsions stabilized by the new Portulaca oleracea hydrocolloid and nonionic emulsifiers

A new water-soluble anionic, low-molecular weight polysaccharide (gum) with surface, interfacial and emulsification properties was extracted from leaves of the legume Portulaca oleracea (termed by us FOG). Vegetable oil-in-water emulsions with small droplets (2-5 mu m), stable to flocculation and coalescence (for a few months) can be formed in the presence of 0.1-0.8 wt% FOG. The gum adsorbs onto the oil-water interface. The nature of this adsorption was tested by evaluating the competitive adsorption of Tweens (ethoxylated sorbitan esters) and the FOG in oil-in-water emulsions. It was demonstrated that Tweens form weak associates with the FOG at the interface at certain emulsifier/gum binary mixtures, but any excess concentrations of the Tween will cause a gradual displacement of the gum from the interface. The FOG and/or the gum-Tween associates (complex) have weak anchoring capabilities at the interface. (C) 1999 Elsevier Science Ltd. All rights reserved.