Food Protection Trends - September/October 2022 - 390

It is then possible to undertake a risk assessment of the
sources and vectors, both before and after controls have been
applied, to understand the severity of the risk of Listeria contamination
from these sources or vectors and the adequacy of
the controls. A risk assessment for a source is the risk of Listeria
being present at the potential source and the ability of the
Listeria to be transferred from this source via an environmental
and/or product vector. A risk assessment for a contamination
transfer vector is the potential for Listeria to be present on the
product vector and the frequency of the vector. At its simplest,
a risk assessment can be undertaken using, e.g., a 3-point
scale of low (1), medium (2), or high (3); and the presence
or spread, or presence or frequency, scores can be multiplied
together to obtain an overall risk score (15).
Step 9. Determine operational prerequisites. Control of
food product contamination with Listeria is a combination of
eliminating or controlling the number of possible harborage
sites and niches and removing all unnecessary contamination
vectors and controlling those that remain or are intrinsic to the
food production process.
However, the control of some sources or vectors (prerequisites)
may be more critical to the safety of the food product than
others, dependent on the precontrol risk score, particularly if
controls failed. For sources or vectors that cannot be eliminated
and have high precontrol risk scores, but effective controls,
the control of these prerequisites can be elevated to the level of
OPs. OPs may also be established on a temporary basis until a
source or vector is eliminated. For example, a broken floor that is
known to be a source of Listeria and that is currently controlled
by spraying it with disinfectant every 8 h may be elevated to an
OP until it is replaced or repaired. As noted previously, OPs can
be managed to the same level as CCPs.
Step 10. Establish control or operating limits. Wherever
possible, control or operating limits should be identified for
each OP. These may be defined in legislation, codes of practice,
and other guidance documents, though the majority are likely
to be determined from collection of experimental data during
trials, e.g., cleaning validation data. The specific control limit
for each OP must be a measurable (e.g., ATP or protein level
after cleaning, disinfectant concentration, flow rate, pH, temperature,
pressure, contact time) or an observable parameter
related to the control option. Measurements are preferred; but,
where control limits are based on subjective data (e.g., visual
observations), clear guidance should be provided (e.g., photographs
to define clean surfaces or appropriate wearing of protective
clothing). The PEP team should record details of how
the control limit was determined, including relevant sources of
information or experimental and validation trial data.
Step 11. Establish a monitoring system. Monitoring systems
describe the methods by which the food processor ensures that
the OPs are operating within their defined control or operating
limits and are, thus, " in control " and, as a corollary of this,
produce an accurate performance record that can be used for
process verification (step 13). The monitoring system must be
390 Food Protection Trends September/October
able to detect loss of control at the OP in a time frame sufficient
to provide corrective actions that will regain control.
Monitoring systems should ideally be on-line and could
include air and gas pressure, humidity, temperature, chemical
concentration, redox, conductivity or pH probes; UV intensity,
flow rate, and rapid hygiene checks such as ATP and protein
tests. Some on-line monitoring systems have a direct feedback
system with the ability to directly control (and record) any drift
in the control limit, and these are preferred. Other monitoring
checks may be visible and could include an assessment of
cleanliness, an assessment of a personnel clothing changing
procedure, or whether a procedure is correctly being followed.
Step 12. Establish a corrective action plan. Practical and
achievable corrective actions should be undertaken when the
results of monitoring at an OP detect a situation in which a
control limit has not been met (deviation) or when a treatment
system is drifting out of control. Responsibilities for corrective
actions should be clearly defined, and any product that could
have been contaminated through any loss of control should be
placed on hold following company quarantine procedures to
allow authorized personnel to determine its fate.
Step 13. Verification. The verification stage is concerned
with three activities: validation, verification, and review. The
objective of the validation stage is to ensure that all sources and
contamination vectors for Listeria that could be present in the
processing environment have been considered and that the
controls put in place to reduce or eliminate them are technically
sound and effective. Identified control actions should then be
validated as appropriate, using best practice techniques.
Verification of the PEP gathers information from routine analytical
tests that are used to demonstrate the effectiveness of the
Listeria controls and OPs in a time frame beyond that of monitoring
(step 11). Verification can include microbiological sampling;
internal and external auditing; analysis of customer complaints;
trending of monitoring and verification results; and a review of any
deviations, corrective actions, and any resulting foodstuff disposal.
In accordance with the general practices of food-safety
management, the PEP should be reviewed at least annually
and following any significant change to the food production
process or the processing environment.
Step 14. Establish documentation and record keeping.
Accurate, timed, and dated records, including the actual as well
as any calculated results, should be retained for at least the shelf
life of any foodstuffs and be sufficient to enable records to be
available to support a defense of due diligence. In Europe, due
diligence applied to food safety refers to being able to prove (to
a court) that the food business operator has done everything
reasonably possible to prevent food safety breaches.
Environmental monitoring and microbiological
verification sampling program
Existing Listeria prerequisite controls, and those identified in
step 8 of the PEP, should be appropriately validated. To ensure their
subsequent control, they then should be monitored and verified.
Food Protection Trends - September/October 2022

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