Scientific Publications - Work Done by Microbiology Reader Bioscreen C

M.W. Griffiths, Rapid assessement of the quality of poultry carcasses, University orf Guelph, Ontario Food Processing Research, Ministry of Agriculture, Food and Rural Affairs, Ontario, Canada

SUMMARY

An assay has been developed whereby it is possible to assess microbial concentrations in poultry carcass rinses within 10 minutes. The test is a modification of one previously developed for determining raw milk quality. In the latter test, milk samples were treated with a detergent to lyse non-microbial cells present in the milk. Microbial cells were removed by filtration and the ATP present in the cells extracted and assayed using the luciferase-luciferin reaction. A number of problems were encountered when this protocol was applied to chicken carcass rinses. The primary problem was a quenching effect on the light emission by the luciferase reaction caused by the presence of particulate and lipid material in the rinse water. The quenching effect was substantially reduced by incorporating a pre-filtration step and an enzyme treatment prior to filtration through the bacteria-retaining filter. Using the modified assay, an excellent correlation (r=0.9) was obtained when the ATP count obtained on 150 chicken rinse samples was compared with plate counts carried out on the same rinse washes. The test can be used to make a rapid assessment of poultry carcass quality, based on selective cut-offs predetermined by the processor. If this level of count is exceeded, the carcass can be subjected to a heat treatment before sale. The accuracy of the prediction was high. Work was undertaken to compare methods used to enumerate bacteria in chicken carcass rinses. The methods studied included plate count (by the Spiral plater), ATP bioluminescence, impediometry (using the Bactometer), HGMF, and turbidiometry (Bioscreen and Vitek Junior). This enabled comparison of the repeatability and accuracy of the various methods. Only the ATP bioluminescence assay and HGMF correlated well with plate counts for chicken carcass rinses and the repeatability of these test methods was excellent. The ATP method was used to monitor critical control points in the poultry processing plant. The CCP's studied included the scald, the prechill and the chill tank waters. It was shown that the ATP test could be used to give a reliable indication of the microbial content of process waters during production and results could be obtained within 10 minutes. The microbial load in the scald tank water was shown to increase throughout the working day and this was shown to be due to accumulation of microorganisms washed from the carcass rather than growth. Levels of microbial contamination of the pre-chill and chill tanks were low in the plant studied on several sampling days. The microbial load in the tanks was dependent on flow rate of water through the tanks and it was concluded that, based on microbial load in the chill tank, water consumption at the plant could be reduced substantially. This will enable plant personnel to more efficiently respond to high microbial loads that may develop during chilling and result in more economical management of the water supply.

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Last modified: May 25, 2005