The stability of aerated milk protein emulsions in the presence of small molecule surfactants

The effects of milk proteins and small molecular surfactants on oil droplet surface coverage and emulsion stability were studied in model emulsions, and the results were related to the microstructure and physical properties of ice creams. Emulsions became increasingly more stable during partial coalescence at increased surface coverage as the protein concentration was increased. Model emulsions of 20% (wt/wt) 50:50 palm kernel oil and coconut oil, stabilized by skim milk powder emulsions, were more stable than sodium caseinate or whey protein emulsions, respectively. In ice cream premixes containing 12% butter oil and 13% skimmed milk powder, the water-soluble surfactant Tween 60 was much more effective in displacing protein from the interface than were oil-soluble surfactants, such as monoglycerides. Tween 60 destabilized the emulsions more than did unsaturated monoglyceride. Although saturated monoglyceride also displaced protein from the oil droplet interface, these emulsions were relatively stable at high surfactant concentrations under the shear conditions used in this study. The melting resistance of ice creams containing 12% butter oil was related not only to the amount of extractable fat, but also to the air cell stability, both of which were dependent on the type of surfactant. A better understanding of the functionality of surfactants in ice cream enables optimal ingredient selection, which should improve product properties.