Surface Active and Emulsifying Properties of Caseins/Caseinates as Influenced by State of Aggregation

Surface activities at the air/water interface and emulsifying properties of highly dispersed sodium, ammonium and low calcium caseinates, and highly aggregated high calcium caseinate and ethanol-precipitated and micellar caseins, were determined. The aggregated caseins/caseinates were less surface active than the dispersed caseinates and with the exception of high calcium caseinate, they emulsified lower oil volumes suggesting that aggregation state and the nature of interactions responsible for aggregation influenced oil emulsifying capacity. Fat surface area (FSA) formed on emulsification at different power inputs was higher for dispersed caseinates, while total protein adsorbed from the bulk phase at any FSA was higher for the aggregated caseins/caseinates. Protein loads were higher for the aggregated caseins/caseinates and corresponded to a coverage of submicelles or distorted (spread) micelles, while for the dispersed caseinates, protein loads corresponded to thin multilayer coverage. Emulsions formed with the aggregated caseins/caseinates were more stable at low FSAs than those formed with the dispersed caseinates, while, after storage for 30 days at 4 degrees C larger decreases in FSA occurred for emulsions stabilized by the dispersed caseinates.