Production and characterization of oil-in-water emulsions containing droplets stabilized by β-lactoglobulin-pectin membranes

Oil-in-water emulsions containing droplets stabilized by beta-lactoglobulin (beta-Lg)-pectin membranes were produced using a two-stage process. A primary emulsion containing small droplets (d(32) approximate to 0.3 mum) was prepared by homogenizing 10 wt % corn oil with 90 wt % aqueous solution (1 wt % beta-Lg, 5 mM imidazole/acetate buffer, pH 3.0) using a high-pressure valve homogenizer. The primary emulsion was then diluted with pectin solutions to produce secondary emulsions with a range of pectin concentrations (5 wt % corn oil, 0.45 wt % beta-Lg, 5 mM imidazole/acetate buffer, 0-0.22 wt % pectin, pH 3.0). The electrical charge on the droplets in the secondary emulsions decreased from +33 +/- 3 to -19 +/- 1 mV as the pectin concentration was increased from 0 to 0.22 wt %, which indicated that pectin adsorbed to the droplet surfaces. The mean particle diameter of the secondary emulsions was small (d(32) < 1 mum) at relatively low pectin concentrations (<0.04 wt %), but increased dramatically at higher pectin concentrations (e.g., d(32) approximate to 13 mum at 0.1 wt % pectin), which was attributed to charge neutralization and bridging flocculation effects. Emulsions with relatively small mean particle diameters (d(32) approximate to 1.2 mum at 0.1 wt % pectin) could be produced by disrupting flocs formed in secondary emulsions containing highly negatively charged droplets, for example, by sonication, blending, or homogenization. The particles in these emulsions probably consisted of small flocs containing a number of protein-coated droplets bound together by pectin molecules. These emulsions had good stability to further particle aggregation up to relatively high ionic strengths (less than or equal to 500 mM NaCl) and low pH (pH 3). The interfacial engineering technology used in this study could lead to the creation of food emulsions with improved physicochemical properties or stability.