Design of control charts to monitor the microbiological contamination of pork meat cuts

The microbiological contamination of pork meat cuts was characterized from Enterobacteriaceae and Pseudomonas counts obtained by 9 French cutting plants on 14 different meat cuts from 1999 to 2003. Contaminations were lognormally distributed with Enterobacteriaceae mean log counts ranging from 0.6 to 2.2 log10 cfu cm−2 and Pseudomonas log counts ranging from 1.1 to 4.4 log10 cfu cm−2 depending on the year of processing, the type of meat cut and mainly on the cutting plant. The variability of log counts was also characterized with a standard deviation approximately equal to 0.6 log10 cfu cm−2 whatever the microorganism under consideration. These results were used to propose control charts to detect more or less large increases of the microbiological contamination (i.e., 0.3–1.0 log10 cfu cm−2). The performances of non-cumulative and cumulative attributes control charts, Shewhart (X and X-bar) and moving average control charts were compared and a moving average control chart calculated on five consecutive samples of one unit with a sampling rate of two samples per week was chosen as a process hygiene criterion to help operators to detect a breaking in their hygiene procedures.