Determination of protein surface concentration for emulsions containing a partially crystalline dispersed phase

This study was undertaken to determine the effect of dispersed phase crystallinity on the determination of protein surface concentration. Butteroil (25%) or soya oil (25%) was emulsified with whey protein isolate (1%) or sodium caseinate (1%). The emulsions were centrifuged at several temperatures (5, 20, 40 degrees C) and speeds (5000, 10 000, 15 000g) for a variety of times (20, 40, 60 min) and the protein surface concentration determined for the isolated fat droplets. The isolated fat phase was also resuspended and the particle size distribution determined by light scattering. For the soya oil emulsions no difference was seen in the protein surface concentration or particle size distribution for any of the centrifugation conditions. For the butteroil emulsions the speed and time of centrifugation had little effect but the temperature appeared critical. When centrifuged at 5 degrees C the butteroil emulsions underwent pronounced destabilization in the centrifuge and the resulting protein surface concentrations determined were very low. Centrifugation of an emulsion for protein surface concentration determination should be conducted at a temperature which eliminates the solid fat content of the dispersed droplets. (C) 1999 Elsevier Science Ltd. All rights reserved.