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SSOP should be validated or drawn from scientifically valid
studies subject to peer review to ensure these procedures
accomplish what they are intended to accomplish, meaning
these cleaning and sanitizing procedures should have
predictable outcomes when repeatedly implemented. The
FDA did not include equipment SSOP validation requirements
in the Produce Safety Rule (168), however harvesting
companies must validate their SSOPs or identify established
studies as specifically suitable validations as part of their food
safety program and risk management strategies. In addition
to equipment-specific SSOP validation, companies supplying
or manufacturing cleaning technologies, equipment, and
chemicals may provide validation of their products. These
documents are useful as supplementary validation resources
but, as noted by Fagerlund et al. (54), may not be adequate
for effective cleaning of a specific piece of equipment.
Because specific aspects of the equipment and the environment
in which it is used may differ from a chemical manufacturer's
validation procedure, the manufacturer's product
validation should not be solely relied upon without some
form of verification of the SSOPs by a harvesting company or
a qualified third-party agent.
In the produce industry, it is a fairly common practice
to visually inspect equipment to ensure it is in a condition
appropriate for entering the field and contacting crops. Visual
inspections of harvesting equipment are typically performed
prior to harvesting to verify that the equipment is clean and
field ready. When equipment is visually inspected, personnel
doing the inspection typically follow a written standard
procedure and record their findings. Inspection records can
be shared with cleaning crews to provide essential feedback
on the quality of their work. However, although essential,
visual inspection is subjective (i.e., dependent on human
senses and worked-related experience) and should not be
solely relied on as evidence that the equipment has been
thoroughly and appropriately cleaned and sanitized and is
ready to harvest crops in the field (115). Best practices for
ensuring harvesting equipment is field ready include making
quantitative or qualitative measurements demonstrating the
hygienic state of the equipment.
Numerous quantitative and qualitative methods are
available to assess cleaning and sanitation efficacy (i.e., by
measuring equipment surface hygiene), many of which are
already routinely used in produce packing and processing
facilities (86, 137). For harvesting equipment, frequent
movement and constant use during harvesting season necessitates
timely cleaning and sanitation verification. This timing
is generally before movement to the next location or the next
day of harvesting; retrospective microbiological testing may
be problematic for linking multiple crops or locations when
an out-of-compliance result is obtained. The time constraints
associated with harvesting equipment generally rule out the
use of swab and plate microbial techniques, which require
≥ 24 h to get results. Thus, hygienic assessment options may
be limited to rapid methods that produce results in minutes
or, at the most, a few hours. For decades, the food industry
at large has commonly used ATP-based assays for rapid
assessment of equipment cleaning. These assays produce light
(bioluminescence) when ATP (an energy-bearing molecule
found in living organisms) is detected (115). The ATP
detected on equipment surfaces could be from soil or plant
residues or from microorganisms, and the intensity of the
light emitted is used to estimate the ATP concentration
(115). In a tofu manufacturing facility, Sogin et al. (150)
compared ATP bioluminescence monitoring of food-contact
surface cleanliness with microbiological enumeration and
reported that the two methods agreed on site cleanliness
status only 75.1% of the time. Although these data support
the value of ATP testing, they should not be misinterpreted
as suggesting that ATP testing can verify sanitation; ATP
testing can be used to only verify cleaning. Multiple experiences
in practice have indicated that ATP testing works well
on many food-contact surfaces but very poorly in general on
surfaces such as brushes and rollers.
Although ATP testing is widely used in produce
packinghouses and processing facilities, little published
information is available that describes the performance
of these tests in those settings. Ruiz-Llacsahuanga et al.
(137) examined the accuracy of ATP-based assays for
assessing the hygiene of equipment used in apple packing
facilities and reported no significant association between
ATP-based rapid test results and plate counts of aerobic
bacteria, Enterobacteriaceae, coliforms, and E. coli. In a
laboratory study, Corbitt et al. (39) evaluated the ability
of ATP bioluminescence alone or in combination with the
cellular marker adenylate kinase (an enzyme involved in
ATP production) to detect broccoli and potato residues
on stainless steel surfaces. ATP plus adenylate kinase
performed better for detecting either vegetable than did
ATP bioluminescence alone. Lane et al. (97) concluded,
based on their laboratory study, that ATP bioluminescence
measurement is an appropriate tool for measuring leafy green
residues and bacterial contamination on stainless steel or
high-density polyethylene plastic surfaces; however, ATP
testing does not detect low levels of bacteria and therefore
is never appropriate as a tool to verify sanitation. Recently
published cleaning and sanitation verification assays include
a more sensitive version of the ATP assay that detects total
adenylates: ATP, ADP, and AMP (7). Other innovations
include paper biosensors combined with a smartphone for
detecting and measuring ATP (24). Although ATP-based
testing is an appropriate tool for verifying the cleanliness of
harvesting equipment, it should be supplemented by periodic
evaluation of total bacterial counts to verify sanitation
practices. Recently adopted industry recommended practice
is to start with weekly microbiological swabs or agar contactpress
plates to build a history of performance for cleaning and
to reduce this testing frequency based on use, environment,
season, and data-informed experience.
March/April Food Protection Trends 135
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