Food Protection Trends - March/April 2023 - 132

Two surface conditions frequently evaluated in investigations
of bacterial attachment to food-contact surfaces are surface
topography and surface roughness. Surface topography
generally refers to the material's local deviations from a flat
plane and includes defects such as crevices and pits. Roughness
of a surface is quantifiable as the measure of total spaced
irregularities (41, 74, 75). Surface topography and roughness
affect the ability of microorganisms to adhere or attach to
a surface, and current research findings suggest that these
features are more relevant to biofilm formation than is the
specific material used to construct the surface (88). Surfaces
with rough or worn topography are more difficult to clean
than smooth or unworn surfaces, creating opportunity for
pathogen contamination (18, 173). For stainless steel, both
the average surface roughness in the vertical direction and
the shape of any defect (e.g., sharp narrow or deep scratches)
affected bacterial retention and cleanability; wider surface
defects were easier to clean than sharp scratches (18). Verran
et al. (173) reported that a greater force was required to
remove bacterial cells on surfaces that had been damaged
from use than on unused surfaces, even for defects with
dimensions smaller than the average size of the bacterial cell.
Addition of detergent to the water spray reduced the amount
of force required to remove the bacteria (173).
Despite evidence that surface topography and roughness
affect cleanability, numerous studies of how roughness and
topography influence bacterial adhesion often have produced
conflicting findings. A more complete understanding
of how the surface topography of materials commonly used
in the manufacture of harvesting equipment affects bacterial
adhesion would be useful for developing surfaces engineered
to reduce bacterial attachment. Stainless steel is one
of the most researched materials, often studied in relation
to Listeria attachment. Studies of L. monocytogenes adhesion
to stainless steel have produced inconsistent findings; some
researchers have reported a strong correlation between
adhesion and surface roughness (29, 43), whereas others
did not (69, 136). Crawford et al. (41) credited the discrepancies
of findings among studies to the lack of a consistent,
comprehensive topographical characterization of surfaces
at the nanoscale. They noted that most studies of surfaces
have included analysis of only one aspect of the surface
topography (i.e., average or root mean roughness measured
as the typical height variation of the surface) instead of a
collection of measurements that would better describe the
many aspects of surface roughness.
CONTAMINATION PREVENTION AND
CONTROL MEASURES
Cleaning and sanitation practices overview
Best practices for harvesting equipment, from the FDA
(168) Produce Safety Rule and the Codex Alimentarius (36)
Code of Hygienic Practice for Fresh Fruits and Vegetables to
commodity-specific food safety guidelines, include routine
132 Food Protection Trends March/April
cleaning and sanitizing of food-contact surfaces. Cleaning
and sanitizing of harvesting equipment are the primary
means of preventing bacterial transfer from equipment to
harvested crops during daily operations. When equipment
is not cleaned and sanitized appropriately and/or in a timely
manner, human pathogens may remain on the equipment and
may transfer to produce crops during harvesting operations
(103). Determination of where and when harvesting
equipment should be cleaned and sanitized (e.g., before
use, after use, or between fields) is also crucial to ensuring
that this equipment is not a source of contamination in the
field. Because chemicals used in cleaning and sanitation
may pose a hazard to harvested and unharvested crops, the
location in which these activities occur must be chosen to
prevent inadvertent contamination. Decisions about cleaning
and sanitation timing should be based on sound standards
of care for the microbial safety of the crop and must not
be compromised by expediency. Decisions on cleaning
and sanitation frequency and preoperational recleaning
and sanitizing must take into consideration factors such as
weather, rain events, adjacent land hazards, vector activity,
and other issues that enhance the risk of pathogen presence
and the risk of equipment contamination.
Sanitation standard operating procedures (SSOPs) should
be clearly written and easy to follow with a clearly defined
scope that addresses the range of applications, the equipment
and products to be used, the people responsible for the
cleaning procedures, and detailed cleaning instructions
(84). The SSOPs for any given piece of equipment should
be customized for each component (e.g., conveyor belt)
with consideration of the materials used in its construction,
accessibility for cleaning (such as conveyor lifts), type and
complexities of joints and product transfer points, and
frequency of breakdown or dissembling. Cleaning procedures
for harvesting equipment depend on the properties of the
component being cleaned such as the material with which
it was constructed, its structure, and where it is located
on the equipment, including its height from ground level.
Cleaning and sanitizing compounds and solutions may react
with equipment materials and coatings, causing corrosion
and degradation (47). Aside from the equipment itself,
other considerations in establishing SSOPs for cleaning
and sanitizing harvesting equipment include the chemicals
used in these activities (e.g., appropriate use, disposal, and
storage of these agents to prevent crop contamination), the
type and condition of soil fouling the equipment (e.g., dry
or wet soil), and the hardness (i.e., calcium and magnesium
concentrations) of the water used for cleaning.
Unlike the food processing and manufacturing industry
where periodic deep cleaning of equipment is essential to
prevent product contamination from established persistent
bacterial strains, the fresh produce industry does not typically
perform periodic deep cleaning of harvesting equipment
(57). Although equipment surfaces require cleaning and
Food Protection Trends - March/April 2023

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