Sedimentation field-flow fractionation as a tool for the study of milk protein-stabilized model oil-in-water emulsions: effect of protein concentration and homogenization pressure

Milk protein-stabilized model emulsions were formed using high-pressure homogenization and the effect of protein concentration and homogenization pressure during emulsification on the particle size was studied. Various techniques are available for determining particle size distribution, each one of which has its own advantages and disadvantages. In this study, sedimentation field-flow fractionation was employed for the size characterization of oil-in water emulsion droplets. Increasing protein content results in significant reduction in emulsion particle size for the concentration range (0.5–3.0% w/w) employed in this study. Low protein content (<1%) may be correlated with bridging flocculation leading to increased particle size, as indicated by optical microscopy. Similarly, increasing pressure during the homogenization process results in decreasing significantly the particle size of the oil-in-water emulsions, for the pressure range (20–60 MPa) utilized in this study. Increased heating associated with high levels of pressure during the homogenization process, can result in changes in the oil or protein structure, which in turn may have an impact on the physicochemical properties of the oil-in-water emulsions on a long-term basis. The results of this study indicate that sedimentation field-flow fractionation can be employed to reliably monitor changes in particle size of model emulsions induced by protein concentration and homogenization pressure. The technique can be a valuable tool for understanding the properties of colloidal systems and therefore its implementation in emulsion/dispersion technology laboratories is certainly justified.