Droplet Size and Coalescence Stability of n-Hexadecane Emulsions Homogenized in Aqueous Solution of Proteins before and after High-Energy Processes

Properties of protein-based O/W emulsions are influenced by various factors including species and concentration of the protein, oil content, and employed homogenization technique, which make it difficult to establish suitable conditions to prepare stable emulsions. To address this issue, two proteins, bovine serum albumin (BSA) and ovalbumin (OVA), were used as emulsifiers in a wide concentration range to disperse n-hexadecane, and necessary conditions to prepare reasonably stable, submicron-size emulsions were explored. A two-step homogenization process, premixing with a rotor-stator mixer followed by either sonication or high-pressure homogenization, was employed, and volume-weighted average droplet diameter (d43), adsorption density of proteins (Gamma), and coalescence stability of oil droplets were measured. For sonicated emulsions in the emulsifier-rich regime, d(43) was ca. 1 mu m for both BSA and OVA, and G was ca. 2-3 mg m(-2) (over 15 mg m(-2)) for BSA (OVA). The high-pressure homogenization could reduce d(43) down to 0.4 mu m provided BSA (OVA) concentration was 5g L-1 (15 g L-1) or higher. These submicron-size emulsions were stable for several days only for BSA emulsions with the concentration >= 15 g L-1, otherwise coalescence proceeded. These results suggested that the adsorbed OVA films are more easily broken than the BSA films.