Non-destructive on-line sterility testing of long-shelf-life aseptically packaged food products by impedance measurements

This paper presents the results obtained in the application of the impedance measurement technique for the needs of non-invasive sterility tests. Two pilot food containers have been chosen: (1) Tetra Brik Aseptic (TBA) cartons and (2) Stork Food & Dairy Systems (NL) plastic bodies. The main characteristics of the TBA cartons are-unstable shape, tolerances in size, packaging laminate comprising paper layer, plastic layers and aluminum foil. The characteristics of the Stork bottles are relatively stable shape and relatively thick walls. An electric model has been developed for the measured impedance. A relation is derived between the resistive component of the measured impedance and the conductivity of the food in TBA cartons. It has been also demonstrated that with the impedance technique it is possible to acquire information about some important properties of the food container during the sterility testing procedure. The microbiological tests with a number of bacterial species proved the potential of this new non-invasive sterility testing technique.