An Evaluation of the Role of Microbiological Criteria for Foods and Food Ingredients (1985) / Chapter Skim
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6 Consideration of Sampling Associated With a Criterion
6 Consideration of Sampling Associated With a Criterion
Pages 132-144
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From page 132... ...
The ICMSF publication is especially useful because it deals with statistically based sampling plans as applied to microorganisms in foods. It is important to establish a sampling plan that can effectively discriminate between good and bad lots.
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From page 133... ...
Difficulties in the application of acceptance sampling plans that test for microbial levels in foods have been outlined by a number of sources (Clark, 1978; Cowell and Morisetti, 1969; Ingram and Kitchell, 1970; Kilsby et al., 1979; Wodicka, 19734. The first difficulty arises in sampling because the microorganisms in many foods are often unevenly distributed within a lot, e.g., Salmonella in dried milk powder.
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From page 134... ...
. These sampling plans are valid regardless of the statistical distributions of the microbiological counts provided that an appropriate probability sampling scheme has been used to select the units to be tested.
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From page 135... ...
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From page 136... ...
VARIABLES SAMPLING PLANS As stated previously, for the 2-class attributes sampling plan, no assumption is necessary regarding the distribution of counts in the population of sample units from which the sample is taken. When the distribution of counts is known, this additional information can be used to increase the chance of making a correct decision or equivalently to reduce the sample size while maintaining the same probability of a correct decision.
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From page 137... ...
The acceptance quality level is defined as the maximum proportion of unacceptable sample units that a lot can possess and still be acceptable. Some larger proportion of defective units, judged to be the minimum proportion of defective units for which the lot is entirely unacceptable might be termed the defective quality level.
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From page 138... ...
It is apparent from these examples that as the sample size increases, the difference between producers' and consumers' risks can be made smaller. In fact, one can calculate the minimum sample size required to satisfy prescribed producers' and consumers' risks.
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From page 139... ...
When the sample size exceeds 10% of the lot size, the binomial distribution should be replaced by the hypergeometric distribution for computing probabilities of acceptance (Purl and Mullen, 1980~. In the 3-class plans the OC curve is replaced by an OC surface.
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From page 140... ...
Sampling plans for use in the microbiological examination of foods are usually by necessity single sampling plans based on one sample size with a number of sample units, because the analytical procedures are frequently destructive and time-consuming. Such conditions generally make double or sequential sampling plans uneconomical for frequent application in microbiological criteria.
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From page 141... ...
The establishment of limits for variables sampling plans for commodities such as meat has been described by Kilsby (1982) and Brown and Baird-Parker (19821.
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From page 142... ...
Thus, the acceptance criteria for a lot are based on a 2-stage sampling plan with determined probabilities. Two-stage sampling plans, when properly used, can reduce the average sample size necessary to achieve adequate protection because, with badly contaminated lots, a small first-stage sample may be sufficient to reject the lot.
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From page 143... ...
Charbonneau 1978 Sampling plans and guidelines for domestic and imported cocoa from a Canadian national microbiological survey.
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From page 144... ...
H Lewis 1971 Microbiology of frozen cream type pies, frozen cooked peeled shrimp and dry food grade gelatin.
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