Factors influencing the production of o/w emulsions stabilized by β-lactoglobulin-pectin membranes

A primary emulsion was prepared by homogenizing 10 wt%com oil with 90 wt% aqueous beta-lactoglobulin solution (0.5 wt%beta-lg,pH3 or 7) using a two-stage high-pressure valve homogenizer. This emulsion was mixed with aqueous pectin (citrus, 59% DE) stock solution (2 wt%, pH 3 or 7) and NaCl solution to yield secondary emulsions with 5 wt% corn oil, 0.225 wt% beta-lactoglobulin, 0.2 wt% pectin and 0 or 100 mM NaCl. The final pH of the emulsions was then adjusted (3-8). Primary and secondary emulsions were ultrasonically treated (30 s, 20 kHz. 40% amplitude) to disrupt any flocculated droplets. Secondary emulsions were more stable than primary emulsions at intermediate pHs. Secondary emulsions prepared at pH 7 had smaller particle diameters (0.35 to similar to 6 mum) than those prepared at pH 3 (0.42 to similar to 18 mum) across the whole pH range studied, and also had smaller diameters than the primary emulsions (0.35 to similar to 14 mum). Ultrasound treatment reduced the particle diameter of both primary and secondary emulsions and towered the rate of creaming. The presence of NaCl screened the charges and thus the electrostatic interaction between biopolymer molecules and primary emulsion droplets. Secondary emulsions were more stable to the presence of 100 mM NaCl at low pHs (3-4) than primary emulsions. This study shows that stable emulsions can be prepared by engineering their interfacial membranes using the electrostatic interaction of natural biopolymers, especially at intermediate pHs where proteins normally fail to function. (C) 2004 Elsevier Ltd. All rights reserved.