The Effects of Polysorbate 80 on the Fat Emulsion in Ice Cream Mix: Evidence from Transmission Electron Microscopy Studies

Emulsifiers are used in ice cream to produce a dry, smooth textured product with desireable melting properties. They function by promoting a partial destabilization of the fat emulsion. Polyoxythylene sorbitan monooleate is used very commonly in the ice cream industry for this purpose. The objective of this research was to examine by transmission electron microscopy the differences in the fat globules in typical ice cream mix emulsions prepared with and without 0.08% polyoxyethylene sorbitan monooleate.Ice cream mix was combined 3:1 with a 2% solultion of ultralow gelling temperature agarose at 20 degrees C, fixed with 4% glutaraldehyde, postfixed with 1% OsO4 in imidazole/phosphate buffer, embedded in Spurr resin and thin-sectioned for viewing. The emulsifier reduced the number of casein micelles adsorbed to the fat globules as determined by both TEM and quantification of membrane protein with Kjeldahl analyses. The fat/Serum interfacial tension was also significantly reduced by the presence of emulsifier in the mix. The data suggest that emulsifiers promote fat destabilization through reduction of membrane protein, based on their ability to reduce the fat serum interfacial tension. In the presence of crystallized fat, the emulsion then becomes less stable to shear forces during the whipping and freezing of ice cream.