Abstract
An apparatus which can facilely and sanitarily be installed in food processing equipment because of electrodeless detection has been developed. It comprises a radio-frequency LC resonant circuit, a solenoid coil as a detection cell and a personal computer for control and measurement on the circuit. Resonance magnitude (Ir) of the circuit, which reflects electromagnetic loss of conductive materials put into the cell, was measured by NCM and used as an index of specific conductance (k) of samples. Twelve detection cells having different configuration, dimension and resonance frequency were made. Their Ir-k curves in the resonance frequency ranging from 8.1 MHz to 44.1 MHZ were investigated by measuring NaCl solutions with various concentrations. It was found that location and magnitude of the minimum peak in Ir-k curves were influenced by resonance frequency, passage diameter, coil diameter and turns of coils. Based on this result, cell configuration for high-resolution detection of conductance had been determined, and was applied for a detector of cultivation process of Bacillus subtilis AR42 in liquid culture medium. Amount of the bacteria was monitored on the medium extracted by Ir measured with the optimized detection cell and by absorbance. From this experiment, it was shown that changes in Ir were in good agreement with those of the absorbance.
