Impedance measurement as a rapid method for the determination of the microbial contamination of meat surfaces, testing two different instruments

Abstract The suitability of the impedance measurement method was considered as a rapid method for use in the routine estimation of the microbial contamination of meat surfaces. Two instruments which have been developed recently were available, namely the Bactometer 32 and the 8-Channel Malthus-Meter. A total of 256 destructive and 82 rinsed samples were taken from beef carcasses and examined chilling temperatures for 3–7 days. Preliminary experiments using both instruments with 49 destructive samples yielded the correlation of r = −0.912 with s y · x = 0.39 (Malthus-Meter) and of r = −0.906 with s y · x = 0.42 (Bactometer) compared with cfu-values obtained by the drop plating method. 22 rinsed samples produced values of r = −0.812 with s y · x = 0.57 (Malthus-Meter) and r = −0.714 with s y · x = 0.83 (Bactometer). The Bactometer was manually more convenient. The interpretation of the results was easier with the Malthus-Meter. Some technical difficulties occuring with the Malthus-Meter may have been caused by the prototype nature of the instrument available. Further investigations with the Bactometer 32 yielded faster and better results using a Stomacher instead of an Ultra Turrax for homogenisation and brain heart infusion broth enriched with 0.1% yeast extract instead of tryptone soya broth with yeast extract. Correlation of r = −0.928 with s y · x = 0.17 could be achieved with destructive samples and of r = −0.896 with s y · x = 0.3 with rinsed samples. Microbial combination of 10 7 cells and above, per cm 2 meat surface, could be accurately detected within 2 h ( α = 0.05) including the preparation procedure. The impedance reactions were influenced to a large degree by the Enterobacteriaceae. This group correlates very well with the total count of meat surface flora. Impedance measurement can therefore be recommended as a routine method for the determination of the microbial load of this biotope of food microflora.