Nonelectrochemical interfacial impedance

In the food industry, microbial tests are performed to screen the product for dangerous pathogens as well as to guarantee that the total microbial concentration is below the allowed threshold values. The sampling inspection can be conducted at the site and if the results are suspicious, therefore further analysis of contaminated sample can be done in the laboratory using expensive techniques [47]. The impedance method was approved by the Association of Ofiicial Analytical Chemists International (AOAC) as a first action method for screening Salmonella in food samples [48]. 

Several commercial analytical instruments are based on this principle. These systems include the Bactometer (BioMerieux, Nuertingen, Germany), the Malthus system (Malthus Instruments Ltd., Crawley, UK), the Rapid Automated Bacterial Impedance Technique (RABIT Don Whitley Scientific Ltd., Shipley, UK), and the Bac-Trac (Sy-Lab, Purk-ersdorf, Austria). However, these measurement systems are not suitable for on-the-spot applications, so many efforts have been made to minimize the instruments [3]. 

The use of impedance measurements to analyze the coagulation process provides a basis for the control of the soymilk coagulation process. Li et al. developed a method to characterize and analyze the soymilk coagulation process and to evaluate the influence of coagulation temperature on this process by monitoring the electrical impedance. 

An electrical equivalent circuit model, composed of a resistor and a capacitor which were connected in series, was adopted to represent the soymilk-electrode system. High frequency impedance measurements presented an increase in resistance and constant value in reactance for different coagulation times. This resistance is attributed to the bulk resistance of soymilk mixture and changed minimally when the coagulation process is finished [50]. 

A system to carry out a nondestructive punctual measurement of salt content in meat samples using impedance spectroscopy was designed by Masot et al. The choice of the electrodes and their configuration in EIS experiments is one of the most critical points. The designed system includes a concentric needle electrode that is introduced into the food sample. Collected impedance data were then statistically processed. Partial least squares (PLS) was applied to a set of samples in order to obtain a model. Studies were carried 

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