Influence of protein concentration on the stability of oil-in-water emulsions formed with aggregated milk proteins during spray drying

Abstract

The ability of aggregated milk proteins to stabilize oil-in-water emulsions during the spray drying process is not well understood and has been highlighted in this study. We investigated the behavior of oil droplets in emulsions (12.0%, w/w, maltodextrin; 20.0%, w/w, soya oil) stabilized with either milk protein concentrate (MPC) or calcium caseinate (CaCas) (0.5–5.0%, w/w) before and after spray drying. In comparison with the respective parent emulsions, spray drying and redispersion caused a shift in the droplet size distribution toward larger values for emulsions made using low concentrations (0.5–2.0%) of MPC or CaCas. However, the droplet size distribution was affected very slightly by spray drying when the protein concentration was between 3.0 and 5.0%. The average droplet diameters of redispersed CaCas emulsions were noticeably larger than those of redispersed MPC emulsions. The unadsorbed protein concentrations in the parent emulsions were comparable for emulsions containing CaCas and MPC, except at 5.0% (w/w) when emulsions containing MPC had a higher concentration of unadsorbed protein in the bulk phase. The amount of extractable oil in MPC-containing powders decreased with an increase in the protein concentration in the emulsions prior to spray drying. However, the amount of extractable oil in CaCas emulsion powders was nearly twice that in MPC emulsion powders even at 5.0% protein in the emulsion. The results obtained from this study clearly show that aggregated milk proteins are able to provide stability to oil droplets during the spray drying process, albeit a higher concentration of protein is required as compared to non-aggregated protein products.