Food Protection Trends - September/October 2022 - 388

Figure 3. Schematic of product and environmental Listeria transfer vectors.
with a map of the processing area showing the layout of food
processing equipment and services. Overlying this map can
be specific diagrams of, e.g., alternative production equipment
set-ups, air flows, personnel flows, transport flows, and waste
flows. At a simplistic level, this plan can be achieved by the use
of colored acetates, which can be overlaid to build up a " 3-D "
picture of the processing environment; or it can be undertaken
more structurally in, e.g., CAD software packages (Fig. 2). The
diagrams' prime purpose is to be used in step 8 to help in the
identification of potential cross-contamination vectors.
Step 7. On-site confirmation of flow diagrams. The
PEP team should audit the processing area at all processing,
sanitation, maintenance, and down times to ensure that the
flow diagrams produced are accurate and representative. The
flow diagrams can then be signed off as a true record of the
processing area.
Step 8. List all potential hazards, conduct a hazard analysis,
and consider any measures to control the identified
hazards. Within this step, the PEP team conducts a thorough
investigation, via physical examinations and microbiological
sampling, to identify any Listeria sources and any mechanisms
or vectors via which Listeria could enter the food product
directly or indirectly.
Sources may be harborage sites or growth niches. Harborage
sites are physical areas in which Listeria can lodge and be protected
from external forces, such as cleaning and disinfection actions,
e.g., poor hygienic design features of processing equipment or
damaged areas of the factory's building structure. Growth niches
are also harborage sites, but they also provide an environment for
growth, e.g., nutrients, temperature, oxygen, water or humidity,
and lack of competition from other microbial flora.
The processing environment and equipment are sampled
following a hygienic design risk assessment that may indicate
388 Food Protection Trends September/October
areas of the building fabric and equipment that could be
difficult to effectively clean. Areas to sample could include the
following:
* Around thermal movement joints, usually associated
with oven installation
* Damaged floors and coving
* Damaged building fabric, particularly areas that could
allow the ingress of cleaning and rinsing fluids
* Poorly adhered structures to surfaces, e.g., panels or
checker plating that are not effectively sealed
* Poorly adhered structures to floors, e.g., equipment legs,
platform legs, access equipment legs, posts, and crash bars
* Drainage systems
* Areas subject to condensation build-up
* Poorly designed processing equipment that cannot be
effectively dismantled
* Poorly designed equipment framework that is not sealed or
whose integrity has been penetrated by, e.g., fixing holes
* Equipment producing condensate, e.g., evaporative
condensers
Potential environmental sources should be sampled toward
the end of production periods, when the chance for Listeria
movement out of such sources may be greatest. Additionally,
and particularly for equipment, samples can be taken either
after the rinsing stage of the cleaning program, when Listeria
may be flushed out of the equipment, or on initial start-up of
production, when Listeria may be driven out of equipment by
its return to operation.
Listeria may transfer from sources directly to the food
product, on product vectors, or indirectly to other parts of
the processing environment via environmental vectors, from
which they could then contaminate the product (Fig. 3).
Product contamination occurs through three main vectors:
Food Protection Trends - September/October 2022

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