protected. Finished product testing is useful if there is reason to
believe that the process is not well under control (e.g. CCP out of
control or recontamination can occur), and as explained above, for
verification of the whole food safety management system.
Testing of finished product samples can indicate whether microorganisms
occur in the food chain and whether control strategies
are effective, i.e. the efficiency of inactivation and
recontamination control. However, if the prevalence and concentrations
are expected to be low, the number of samples taken
should be high in order to be able to gain useful information from
the sampling. At the time the process and environmental pressure
to recontamination is under control, it is more efficient to monitor
the production process than to test finished products only.
Also it is important to have reliable suppliers consistently
providing the required quality of raw materials. This can be achieved
through audits which in particular are focused on the controls
the supplier has in place to reduce the hazard in incoming raw
materials. Records from supplier audits may be useful to document
and assure consistent quality of raw materials supplied to the
factory.
Analyses on incidents, recalls or consumer complaints should be
carried out regularly and can lead to actions aimed at avoiding
repetition of such events. When corrective actions are needed
because critical limits have been violated the reason why the process
went out of control must be established and measures to
prevent recurrence should be implemented and documented.
4. Statistics of sampling
For sampling plans in which detection of positives is not
accepted (c ¼ 0), which is often the case for pathogens, the equation
to determine the probability of detection is:
Pdetect
n; c ¼ 0; Pdefective
¼ 1
1 Pdefective
n
(1)
In words this equation can be explained as follows: The probability
that one sample is not defective is 1 minus the probability of a
defective. For all n samples to be not defective, the probability is
this term to the power n. So (1-Pdefective)n is the probability that all n
samples are not defective. One minus this value is the probability
that one or more of the samples are contaminated, so that the organism
is detected in one or more samples.
This equation shows that the performance of sampling is often
rather poor, definitely with a low rate of defective (i.e., contaminated)
products (Table 2) and even when large numbers of samples
Epidemiology
Level and prevalence in
the environment
Transfer
Growth: Final level
s
Validation
(data on initial levels in the environment and transfer and inactivation)
Verification
Survival
Recontamination
Finished product
testing
Reduction
(e. g. heating)
Raw materials:
Initial level and
prevalence
Fig. 1. Overview of the relevant phenomena in food safety control, indicating the position of validation and verification.
Table 1
Examples of measurements and records that can be useful to build the history of safe products in a food safety management system.
Where and what Activities and records
Suppliers Efficacy of their food safety management system Compliance to an agreed standard of food safety management certification
and efficiency of control measures, records
Factory/Process steps Raw materials (including packaging material) Monitoring or verification results on contamination of pathogens, spoilage
or indicator organisms based on a priori risk rating applied to supplier and
raw materials
Storage Temperature, atmosphere, storage time
CCP monitoring results (e.g. heat process) Holding time and temperature
Process parameters Time to acidification, pH drop, cooling time, etc.
Semi-finished product Occasionally microbial testing as verification: sampling plan and results
Prerequisite programs Factory environment Test results on hygiene or pathogens from swab samples, product residues
or air quality
Cleaning Results from verification of efficiency (visual inspections, microbiological
tests, ATP-test, etc.)
Verification of finished
products
Microbial tests Sampling plan and microbiology results
Intrinsic properties Verification results on pH, aW, preservative concentration, etc.
Extrinsic properties Verification results on modified atmosphere, storage temperature etc.
After factory release, during
product shelf-life
Extrinsic properties of finished products Verification results on modified atmosphere, storage temperature, in-market
supply-chain testing and product durability and stability testing