Influence of surface properties and bulk viscosity on bubble size prediction during foaming operation

The aim of the present studies was to follow in detail and understand how the surfaces properties, viscosity of the continuous phase according to-process conditions (whipping rotation speed, pressure, and flow rates) were related to the micro-structure of the foam (bubble size). Newtonian model foods containing glucose syrup and foaming agents (WPI or sucrose fatty ester) were prepared and characterized using rheometry and tensiometry. The effect of surfactant type, surfactant concentration and bulk viscosity on interface properties were evaluated using a drop tensiometer. Foams were generated by an instrumented industrial rotor-stator mixer. Bubble size distributions were determined by image analysis. A dimensional approach allowed us to determine the correlation between the Sauter diameter and some interfacial properties, bulk viscosity and process variables. The bubble size in the foams was found to decrease in line with increasing mixing speed, increasing viscosity and increasing concentration of surfactant. Dynamic surface properties appeared to be relevant and should be included in the prediction. (C) 2013 Elsevier B.V. All rights reserved.