Routine microbiological sampling and analysis of ground meat for quality control purposes - practical experience and statistical conclusions

The microbiological status of ground beef was routinely assessed at two production facilities over a period of at least one year. Five re-plicate samples were tested per day in accordance with European meat hygiene directives. In light of the high workload it was of great interest to decide whether the sample number could be reduced by combining the 5 single samples per lot to a pool sample without causing a significance loss of information. Concerning the "aerobic total plate count" as the main criterion the findings showed that: Analysing a pool sample and using 3m reads in 129 of 131 lots of producer A to the same decision (acceptance/rejection) as 5 random samples in connection with the official 3-class-sampling plan (3(m)/c(m) = 2; M/c(M) = 0). In the case of producer B there have been 3 opposite decisions in 319 lots despite of a very heterogeneous structure of the microbiological counts. More defective lots were observed on Mondays. No other trends could be observed. Obviously the microbiological results of 5 samples/day are only used for documentation and not for corrective actions or improvement of the hygienic status, ii there are no severe objections against the bacteriological quality. Because the relatively poor information does not justify the analytical workload a modification of the official sampling plan is proposed: Following the principles of moving sum procedure the 5 random samples of minced meat per lot are combined to a pool sample and tested against the limit 3m as long as no more than 2 plate counts exceed the limit 3m in the last 11 days of production.