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In this article we will discuss about how can we control quality by using microbiological criteria.
In the 1970s in Oregon in the United States standards were introduced governing the microbiological quality of ground meat in retail stores. After they had been in force for a few years an enquiry was conducted into their effect. The principal conclusion was that, although there was felt to have been a general improvement in sanitation and handling, the standards had produced no significant change in quality.
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There was no evidence that the bacterial load on ground meat or the risk of foodborne illness had been reduced and, on the debit side, significant costs had been incurred as a result of rejection of material not meeting the standard and through the expense of microbiological testing.
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It was also felt that consumers had been misled, since their expectation had been that the introduction of standards would lead to an improvement in quality. As a result of this enquiry, the standards were revoked.
An interesting comparison is provided by the Milk Marketing Board’s scheme of paying English and Welsh farmers on the basis of the bacterial count of the milk they supply. In this case, feedback of the results to fanners resulted in a dramatic decrease in the recorded count of milk over a period of just four months.
The difference in these two experiences can be ascribed to a number of reasons. Firstly, microbiological testing of milk is more likely to give an accurate reflection of microbiological quality in the batch as a whole since it is easier to obtain truly representative samples of a liquid.
Also, much is known on how to produce raw milk hygienically so that bacterial contamination is minimized, farmers had simply not been assiduous in the application of these procedures until financial penalties acted as an incentive. Another crucial difference is that the standards in Oregon had applied later in the supply chain, at the point of sale.
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Earlier stages in meat production such as conditions of slaughter, dressing and storage make a major contribution to the microbiological quality of meat and the standards had done nothing to improve these. The enquiry had noted that there had been an improvement of hygiene at the retail level but since this produced no significant reduction in count it clearly indicates that the problem lay elsewhere.
These two cases indicate two important features of microbiological quality control. Namely the ineffectiveness of retrospective systems of quality control and the importance of control at source.
A system of retrospective quality control based on testing samples of a product and accepting or rejecting a lot on the basis of test results suffers from a number of limitations. We have already discussed the inhomogeneous distribution of micro-organisms in food, the problems of representative sampling and the producer’s and purchaser’s risks associated with any sampling plan.
To minimize these risks requires plans entailing the testing of large numbers of samples and these entail high costs as a result of both the amount of product required to be tested and the costs of laboratory resources.
Even with representative samples there is the problem of the relative inaccuracy of traditional microbiological methods and their long elapsed times. If results of laboratory tests are required before a product can be released for sale (a positive release system), then the product’s useful shelf-life is reduced.
Finally, a major weakness of retrospective systems of quality control is that they provide little in the way of remedial information. They help identify that there is a problem but often give little information as to where it has arisen and what is required for its solution.
If a product has high counts, is this due to poor quality raw materials, poor hygiene in the production process, poor conditions of storage, or some combination of all three?
The most effective way of controlling quality is through intervention at source, during the production process. On its own, any amount of testing will not improve product quality one jot, to do this requires action where the factors which determine quality operate, namely in the processing and supply chain itself.
