Untitled

the logarithm ofmused in the three-class attributes plan. If a lot were to
fail a GMP criterion it would not lead to rejection of the lot but would
alert the manufacturer to an apparent failure of GMP.
If we take a practical example, let us assume that the critical safety/
quality limit is 10^7 cfu g
^1 (V¼7), but that under conditions of GMP a
level below 10^6 is usually attainable (v¼6). We are testing five samples
from the lot and wish to be 95% certain to reject lots where more than
10% of samples exceed a count of 10^7. From Table 11.4,k 1 ¼3.4 and our
specification becomes:

ifxþ 3 : 4 s 4 7 then reject:

If we also wish to be 95% sure of accepting lots with less than 20%
greater than our GMP limit then from Table 11.4,k 2 is 0.11 and our
GMP criterion becomes:

ifxþ 0 : 11 so6 then accept:

Three batches of product give the following log counts:

ABC

5.48 5.55 5.95

5.23 5.30 6.12

5.81 6.10 6.20

5.97 5.75 5.65

5.46 6.01 6.21

x 5.59 5.74 6.03
s 0.30 0.33 0.23

Applying the safety/quality limit and GMP formulae, batches A and B
are acceptable according to both criteria. Batch C, though acceptable
with respect to the safety/quality limit, is not acceptable according to the
GMP criterion and this may warrant further investigation.

11.3 Quality Control 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. 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

410 Controlling the Microbiological Quality of Foods