Influence of protein emulsifier interfacial properties on oil-in-water emulsion stability

The purpose of this study was to determine whether the interfacial properties of emulsifier films could be related to emulsion stability and therefore be used as stability predictors using Bovine serum albumin (BSA) as a model oil-in water (o/w) emulsifier. Soybean o/w emulsions were prepared by ultrasonication, emulsion droplet interfacial charge was determined by microelectrophoresis, droplet size distribution was measured using an Accusizer, and centrifugal stress was studied using an ultracentrifuge. Real time, thermal kinetic, and centrifugal stress accelerated stability tests were performed. Stability data obtained from centrifugal stress tests followed the same trends as real time stability data and these data were in general agreement with stability predictions made based on interfacial properties. The thermal kinetic accelerated tests were not predictive of stability, because emulsion breakdown was rapid and did not allow differentiation between the emulsions. Emulsion stability increased with an increase in emulsifier concentration (emulsions prepared at 2% w/v BSA had not cracked at 60 days, whereas those prepared at 0.1% w/v had cracked-by 30 days), increase in ionic strength (emulsions prepared at an ionic strength of 1 mM had cracked by 60 days, whereas those prepared at an ionic strength of 10 mM had cracked by 90 days), and decrease in temperature (emulsions prepared at 37 and 60 degrees C had cracked by 5 days, whereas those prepared at 5 and 25 degrees C had not cracked at 60 days). There was no significant change in stability for emulsions prepared at pH 5.3 and pH 7.4. The addition of dextran sulfate improved emulsion stability, whereas the addition of acacia decreased stability. Emulsions prepared with BSA alone cracked by 90 days, those prepared with BSA and acacia cracked by 30 days, and those prepared with BSA and dextran sulfate had not cracked at 90 days. Interfacial properties were useful in predicting emulsion stability.