Abstract 047
Computer Simulation of Microbiological Sampling of Liquid Foods
J. Food Protection 56: 518-524, 1993
K. J. Siebert
A computer program that simulates the process of randomly selecting sample packages [of liquid foods] from a large lot and examining a portion of the package contents for microorganisms was developed. The program can be used to evaluate theoretical effects on results (mean, s.d. and detection or nondetection) of various choices for number of sample packages selected, sample vol. withdrawn for examination, package size and behaviour of organisms at different microorganism concn. Results can be used to compare theoretical effectiveness of and risk inherent in various sampling schemes. The simulation program was used to systematically study effects of varying the number of sample packages selected, distribution of samples between packages and sample vol. examined. Results indicate that, e.g. finding no counts when 5-ml vol. are drawn from each of 16 sample packages is no assurance of sterility, but only indicates an approx. 50% chance that the average microbial concn. is less than 1 cell/100 ml. Increasing the number of packages examined from 16 to 32 should decrease the likelihood of finding a nonzero result to approx. 25%. For 16 samples of 100 ml and the same organism concn., a zero result at this organism loading is very unlikely. The total vol. examined is the most important factor for most practical sampling situations. This finding implies that taking fewer samples of larger vol. is the more cost effective strategy to reduce risk.
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