Air Bubble Dispersion Imaging of Whipping Cream by Electrical Tomography

Abstract

This special feature presents an application of electrical tomography (ET) for imaging air bubble dispersion in whipping cream during the agitation process. ET, a non-destructive and non-contact technique, reconstructs the conductivity or permittivity distribution by measuring impedance or capacitance, which is categorized into electrical impedance tomography (EIT) and electrical capacitance tomography (ECT). The ET system includes an impedance analyzer, capacitance meter, multiplexer, sensor, and control software, which together provide real-time insights into the internal structure of whipping cream. In this study, a fuzzy phase classification-implemented EIT is applied to image the air bubble dispersion. This EIT consists of non-linear conductivity σ reconstruction and fuzzy phase classification, which categorizes σ into probabilistic clusters uj (j=1: oil-in-water phase, j=2: air bubble). In the experiments, both σ and probabilistic air bubble cluster u₂ are reconstructed for whipping cream samples with three different fat contents to image air bubble dispersion. As a result, σ exhibited two distinct distribution patterns corresponding to changes in overrun (OR): a slight decrease due to initial air bubble formation and a sharp decline caused by significant changes in homogeneity and shrinkage. Through fuzzy phase classification, air bubble dispersion is imaged at the yield point of each whipping cream sample, during which the continuous liquid phase transitioned to the air bubble phase induced by agitation. The images also reveal that whipping cream with higher fat content reaches the maximum air bubble content at an earlier stage, which is consistent with OR. Local electrochemical impedance spectroscopy (EIS) is applied to validate the EIT results. For all whipping cream samples, the conductivity reduction rates obtained from both EIT and local EIS show a consistent trend, as both increased with agitation.