Food In Canada

Plant micro results are good, but bad in the field

Food in Canada   

Food Safety Processing food safety food testing

Reconciling good micro results in the plant with bad micro problems in the field

I don’t think that I am the only food scientist who has had the problem of trying to reconcile good micro results in the plant with bad micro problems in the field. An infinite number of things can lead to this. In some cases, the problem can be of our own making.


Setting the Stage



The objective of all activities in a food processing plant is to achieve a desirable outcome for the lowest cost. But in doing so, decisions made to cut time and cost can limit the effectiveness of microbiological programs and lead to problems.




Adequate sampling is critical to the success of any microbial program. Things to consider in any sampling plan are the frequency of sample collection, sample size (number and quantity) and the conditions under which the samples are stored prior to analysis. More is always better, but deciding on the right number and quantity is difficult. One needs to consider the microbiological risk factors of the product, quantity produced, package size, the nature of the production process (batch or continuous) and the microbial quality history of the product (recent and past). Be careful about getting overly confident about your great results if you are just taking one sample from the beginning, middle and end of a production. The odds are likely 50/50 that your data accurately reflects the entire production. Your luck may have just run out.


Store and transport your samples in their original condition prior to testing. Freezing and re-freezing can significantly reduce microbial counts. Minimize the time between sample collection and testing as the numbers of some bacteria can double every two hours.




Many people neglect to consider the limitations of the equipment and procedures used to test the collected samples. No analytical equipment and procedure, from the oldest to the newest, is without its limitations. None are 100 per cent reliable and all have their limits of detection. The capability of the equipment and the procedures employed do have an impact upon the results you see. You or someone in your company should know what these limitations are.


Unless required to test for a specific species, companies will frequently test for a surrogate species and/or for the total number of undifferentiated species for reasons of expediency and cost control. A surrogate is either a species that is related to the pathogen of concern or a totally different species known to be present when the pathogen of concern is present. The total aerobic plate count is a widely accepted procedure for monitoring overall microbial quality of both equipment and products. In each case, be sure to have your own in-plant data to justify the practices you are using. There is always a risk that pathogens will escape detection.




The competency of the numerous individuals carrying out the program also needs consideration. This includes those who prepare the sampling kits, take the samples, prepare the collected samples for analysis, carry out the testing, interpret and report the results and who, when necessary, ensure corrective measures are taken on a timely basis then follow up to ensure compliance. Even a small oversight can compromise the microbial results for a sample and possibly everything you have ever produced. Have a qualified outside lab come in and validate your entire program at least once a year.


Other considerations


In addition to considering the things mentioned above, it is a good practice to retain samples of finished products for a period not less than the shelf life of the product, and longer if possible. Retention samples of perishable products should be frozen, even though doing so reduces the original microbial level. If results start trending high or problems escalate in the field, double the number of samples taken and double the frequency of sampling. If the business risk is high, hold product until the micro results verify compliance. You can’t test quality of a product, but you can prevent bad product from leaving the plant.


Dr. R.J. (Ron) Wasik PhD, MBA, CFS, is president of RJW Consulting Canada Ltd. in Delta, B.C. Contact him at

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