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The interfacial properties of homogenised mixtures of monoglycerides and milk proteins (casein) have been examined using dynamic surface rheology. Using applied oscillation it was shown that the adsorption and surface properties of these mixtures varied considerably in comparison with the individual components. Homogenised dispersions made with casein and saturated monoglycerides (C16) at 40 °C displayed controlled deposition of monoglyceride at the air–water interface. Cooling of the solution to 5 °C resulted in crystallisation of the monoglyceride at the air–water interface. This was characterised by increasing surface elasticity and viscosity. Both surface elasticity and viscosity reached steady state, implying that there was no adsorption from bulk phase to the interface. Similar adsorption behaviour was observed when an unsaturated monoglyceride (C18:1) was used, although the steady-state values for surface elasticity on cooling were consistently lower in comparison with the saturated monoglycerides. The shorter chain length monoglyceride, monolaurin, was found not to produce a metastable dispersion on homogenisation, and consequently controlled deposition at the air–water interface was not observed. The results have some important implications for foam stabilisation using monoglycerides and other food grade surfactants. |
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