Design of an impedance measurement system for measuring the degree of disintegration of cells

The application of pulsed electric fields (PEF) to plant cells enables energy efficient and gentle disintegration in the course of food processing. The on-line measurement of the degree of disintegration of the tissue based on the measurement of the complex impedance enables a control of the applied energy according to specific requirements of the plant material. As the degree of disintegration governs a subsequent extraction process, the extraction result can be controlled by the energy applied during PEF-treatment. Experiments on the extraction of pigments and tannins from grape mash into the must showed a clear dependence of the complex impedance measured after treatment and the chemical analysis after the extraction process. An on-line measurement system tailored to the needs of the online impedance measurements of gape mash has been designed. The measurement system needs to operate reliably in an industrial environment next to a pulse generator. Hence, some measures against interference, like shielding of the measurement chamber or filtering of measurement signals have been implemented. The paper describes the design concept and presents a first measurement result.