Effect of bulk viscosity and surface tension kinetics on structure of foam generated at the pilot scale

The texture properties and the stability of foam are highly dependent on foam structure after processing. The Weber Number, widely used to predict mean bubble size, takes in account the shearing rate during process, the bulk viscosity, and the surface tension at equilibrium. The objective of this study was to illustrate the importance of surface tension kinetics on structure of food foam. Since surfactant adsorption is a complex process, it is essential to decide whether equilibrium or surface tensions at short times have to be considered for the size prediction of bubbles generated at pilot scale. To do so, we formulated model systems with controlled bulk viscosity and interfacial properties: Newtonian fluids at different viscosity levels and various surface tension kinetics. Characteristic parameters were obtained by adjusting the dynamic surface tension measurements to kinetic models found in the literature. Structure of processed foam was accessed by Sauter Diameter and bubble size distribution. Whipping conditions were the same for all solutions. The experimental design showed a clear effect of viscosity and surfactant concentration on adsorption kinetics. These had in turn an impact on foam structure: slow adsorption kinetic led to bigger bubbles with larger size distribution whereas fast adsorbing conditions produced smaller and more homogeneous bubbles.

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