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This study shows that the aggregation and creamingstability of whey-protein stabilized emulsions is stronglydependent on pH and calcium chloride concentration.Emulsion droplets were highly unstable to aggregationnear the isolectric point of the whey proteins because ofthe relatively low electrostatic repulsion between thedroplets. The emulsion stability was relatively insensitive to CaCl2 (< 20 mM) when the pH was below theisoelectric point. On the other hand, fairly low CaCl2concentrations were capable of promoting droplet ¯occulation and creaming instability when the pH wasabove the isoelectric point. The pH dependence of the¯occulation stability can be accounted for by the factthat the counter-ions are monovalent (Clÿ) below theisoelectric point and divalent (Ca2+ ) above it. Multivalent ions are much more eective at screening electrostatic interactions and at binding to oppositelycharged surfaces than monovalent ions. Our resultshave important consequences for the application ofwhey proteins in food products. To produce an emulsion that is stable to ¯occulation, it is important toensure that the pH is suciently far from the isoelectricpoint of the proteins and that the calcium ion concentration is less than that required to promote ¯occulation. Higher calcium concentrations could be used ifsome other compound could be added to the aqueousphase of the emulsions to complex the calcium ions or if
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