A method to determine free fat in emulsions

Small amounts of free (non-emulsified) fat in food emulsions can lead to an unacceptable appearance and product rejection. Most methods of analysis available for emulsions neglect this bulk scale heterogeneity and there is no generally accepted protocol to determine the amount of oiling-off. A new technique to determine free fat in emulsions was developed based on the principle that a lipid dye solution added to an oil-in-water emulsion will be diluted by the free fat but not by the emulsified fat present. The change in dye concentration (as measured from the decrease in absorbance) could then be used to calculate the amount of non-emulsified fat originally present. Oil Red O, a lipid soluble dye, diluted in corn oil was selected for this study. First it was shown the dye does not partition into typical aqueous food surfactant systems (2 wt% whey protein isolate, sodium caseinate, and polyoxyethylene sorbitan monolaurate) or emulsions (20 wt% corn oil) stabilized with the same surfactants. Corn oil spikes added to each of these emulsions, to represent different amounts of free fat, was quantitatively determined by this method. Finally the destabilization of the butter oil emulsion in ice cream mix during freezing was measured by dye dilution and compared to other methods (solvent extraction and turbidiometry).