Detection of the effect of the sulphide-reducing pathogenic bacteria by using the analysis of the acoustic signals response

Abstract The sterilisation of tinned foods aims to improve the wholesomeness and the bacteriological stability of foods. The Clostridium botulinum, which is a sulphite-reducing anaerobic bacterium is often the choice of a reference bacterium because of its strong resistance to heat treatments typically used for sterilisation. The analysis of tinned foods by a microbiologic method entails the use of sterilised materials and very strict working conditions. Moreover, these analyses are relatively slow and expensive. Negative results obtained on samples subjected to a microbiologic analysis do not imply that the whole sample is relatively free of bacteria to a safe level. In this work, we utilise ultrasonic testing to detect the effects of the sulphite-reducing anaerobic bacteria on the ultrasonic properties of foods. The experiments on the samples take place in a parallelepipedic tank, and the samples are insonified by a short ultrasonic pulse of frequency 10 MHz which is generated and detected by the same transducer in a send–receive geometry. The signal detected by the transducer is amplified, captured on an oscilloscope and is then transmitted to a computer by an IEEE 488 interface. These ultrasonic data is processed in the computer to determine the viscoelastic properties of the samples, which are phase velocity and attenuation. The measured change in these properties as function of time allows us to determine the different phases of the development of C. botulinum bacteria within the sample. The results show also the effect of the bacterial charge on the evolution of different phases. Keywords: UltrasoundPulse echoPhase velocityCulture mediumSulphide-reducingAnaerobic pathogenic bacteria