The influence of ionic and neutral hydrocolloid gums (pectin, guar gum, iota-carrageenan) on phase separation, emulsion activity and emulsion stability of whey protein isolate (WPI) was investigated. Mixtures of WPI/pectin and WPI/guar gum exhibited phase separation. Analysis of each phase after centrifugation revealed the formation of two polymer-rich phases, a protein-rich phase at the top and a polysaccharide-rich phase at the bottom, indicating the thermodynamic incompatibility. A visual phase separation was not observed in WPI/iota-carrageenan mixtures in either concentration. This was attributed to the high gelling ability of iota-carrageenan, which prevented the phase separation. Whey protein isolate-stabilized emulsions in the presence of hydrocolloid gums (pectin or guar gum) were prepared below the phase separation threshold and the emulsifying activity and emulsion stability were determined spectrophotometrically by measuring time-dependent changes in turbidity. The stability was observed to be changing with the concentration of hydrocolloids. Thus, stable emulsions were obtained as the concentration of gums increased. Also, an increase in the gum concentration decreased the creaming and a slow creaming was detected in the emulsions of WPI/guar gum as compared with WPI/pectin. (c) 2006 Elsevier Ltd. All rights reserved.