The effect of different water temperatures on knife decontamination

Summary

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In Australia, and internationally, knives used during the slaughter and dressing of carcases are required to be sanitized in water at 82ºC.
Regulations allow science-based equivalent alternative procedures to 82ºC dipping to be used.
Recent studies have established the potential for alternative practices to achieve the same or better reduction in bacterial numbers than the typical 82ºC immersion.
There is, however, limited sufficiently replicated time-temperature combination data available on the response of bacteria to hot water treatment on knives.The current study was undertaken to determine the effect of time:temperature combinations ranging from 1 to 60 seconds and 60 to 82ºC on the disinfection of knives artificially contaminated with Escherichia coli and Listeria monocytogenes. In addition the effect of a pre-rinse at 40ºC on the disinfection of artificially contaminated knives treated under the same controlled conditions as above was established.
Triplicate experiments on one strain of each of the above bacterial species on knives in a meat matrix at each of 42 time:temperature combinations, with and without the pre-rinse, were performed in a laboratory water bath. Bacterial reductions were established by plate counts from the knife blade before and after emersion.
Data was converted to mean log reductions, subjected to statistical analysis and basic models generated from the results.
The results of the study demonstrated that dipping knives in water for shorter times at higher temperatures or longer times at lower temperatures can produce equivalent reductions of bacteria.
Pre-rinsing knives at 40ºC increases the performance of the subsequent dipping step. The reductions in bacterial numbers reported here are consistent with those in previous laboratory and processing plant-based studies. Models produced from the data in this study can be used to predict suitable time:temperature combinations to achieve a desired bacterial reduction. To achieve a reliable >3log reduction performance criteria with current industry practice or small variations of these is not easily achievable.
It is recommended that models developed in this study should be used to establish alternative time:temperature combinations which will result in equivalent reductions to current industry practice where appropriate. The feasibility of a >3 log reduction criteria needs to be revaluated in the light of the findings of this study. Work validating models and assessing the role of microbial transference from knives to caresses in the hygiene of meat production would be useful additions to this study.