CONSISTENCY DEVELOPMENT AND DESTABILIZATION OF A MODEL CREAM

Emulsions are thermodynamically unstable and with time show progressiv e signs of this instability with eventual phase separation. It is also an established fact that creams based on nonionic emulsifier systems exhibit an initial period of delayed consistency development prior to the destabilization process. To illustrate these phenomena, a cream ha ving a nonionic emulsifier system is destabilized by a surface-active ingredient that also exaggerates the period of retarded consistency de velopment. Using theologic and microscopic techniques, this study pres ents a systematic approach by which consistency development and destab ilization can be monitored. Characteristic patterns in the rheograms u pon aging are correlated with changes seen microscopically, and specif ic changes signaling the beginning of the destabilization process are identified. Rheologically, destabilization becomes apparent through fo rmation of additional spurs and inflections at low shear rates, a decr ease in hysteresis, and a shift to lower maximum shear stress values. Microscopically, polarized light shows formation of diffuse, weakly bi refringent structures while ordinary light shows an increase in drople t site. Thermal optical videomicroscopy and trace substance analysis h ave identified the structures as segments of agglomerated oil phase an d verify the photomicroscopy observation that the oil and wax componen ts phase separate as distinct entities.