Food Protection Trends - March/April 2023 - 131

When subjected to the same contamination and subsequent
sanitation as used for the commercially available knives,
the prototypes retained significantly less E. coli O157:H7
between the cutting blade and the coring ring than did the
commercially available knives with the rough welding joint.
These findings are consistent with studies in which enhanced
bacterial attachment to weld zones on food processing
equipment was found (29, 106).
Concerns about problematic construction such as roughness
and fractures of welding joints also apply to other
harvesting equipment such as mechanized harvesters and
field-packing platforms. The Produce Safety Rule requires
seams on food-contact surfaces of equipment to be either
" smoothly bonded or maintained to minimize accumulation
of dirt, filth, food particles, and organic material " (168).
Other design features such as right angles and hollow
structures (e.g., legs, conveyors, and framing) add difficulty
to cleaning and may harbor pathogens when water and debris
are collected in these structures (17, 167). In 2021, a study
on the deep cleaning of harvesting equipment was conducted
by a select group of produce processing and harvesting
companies in collaboration with industry organizations and
academic extension faculty and facilitated by an industry
vendor (37). The study findings included several areas on
a mechanical harvester (e.g., difficult-to-reach and hidden
locations beneath belts, cog wheels, framework, cutting
surfaces, bearings, support components, and tunnel flaps)
as " at-risk " for contamination that would benefit from
hygienic design improvements. The study authors called for
more testing and further coordination between harvesting
operations and equipment manufacturers " to enhance
hygienic design and sanitation processes. "
Materials used in construction
Equipment used in harvesting fresh produce may be
constructed with a variety of materials such as stainless steel,
aluminum, plastics, wood, textiles, silicone, and rubber.
Many of these materials have been the focus of research on
the ability of human pathogens to survive on surfaces (29,
31, 43, 58, 72, 94, 111, 136, 171, 181). The properties and
characteristics of materials impact pathogen survival on foodcontact
surfaces, especially the ability to form biofilms (89).
Wood has generally been considered more conducive
to pathogen survival, especially in moist and/or soiled
conditions, than other surfaces such as stainless steel (9,
181). Over the past several decades, the produce industry
has moved away from the use of wood to construct rigid,
solid food-contact surfaces in favor of other materials,
including metals and plastics. Collectively the research
related to the microbial safety of wood is inconclusive, as
revealed in an extensive review by Aviat et al. (2). These
authors cited numerous studies comparing wood and plastic
cutting boards that produced conflicting findings regarding
microbial counts over time under various conditions. In a
study of E. coli transfer from wood, corrugated fiberboard,
newly manufactured plastic, and reused plastic to apples,
wood performed better than did the other three materials for
limiting both pathogen survival on the material and transfer
to the apples (3). In a study comparing E. coli-contaminated
onions held in either wooden or plastic storage containers,
no detectable E. coli was found on onions after 6 weeks
of storage, leading the investigators to conclude that no
difference in inherent risk existed between the two types of
containers (134). In contrast, stainless steel is considered
one of the most hygienic materials for construction of foodcontact
surfaces and is frequently used in the construction
of harvesting equipment (8, 9, 18, 61, 171, 173). Foodcontact
surfaces such as conveyor belts and curtain tails on
harvesting equipment may be constructed with soft and
flexible materials such as textiles, rubber, or rubber-like
materials. Research findings related to pathogen persistence
on specific materials indicate pathogen growth and survival
may depend on environmental factors such as moisture,
ambient temperature, and relative humidity (31). Overall,
the most common finding among the majority of studies
was that consistent, properly administered cleaning methods
significantly reduced bacterial contamination on foodcontact
surfaces.
Surface cleanability
In addition to the design and the type of material used
to construct harvesting equipment, the condition of foodcontact
surfaces and of the overall equipment also affects
the ability to clean and sanitize effectively. Decades of food
industry research has indicated that microbial adhesion
to surfaces, when it occurs, requires only small amounts
of food sediment to provide nutrients and makes bacteria
more resistant to cleaning and sanitation (59, 75, 140).
Bacterial attachment to surfaces also is affected by properties
of both the material to which the bacteria adhere (145)
and the bacteria themselves (72, 180). Once they are
transferred to equipment, bacteria modify their physiology
and morphology to better adhere to a surface (72). As
part of the physiological changes that enhance attachment,
some pathogens can form biofilms, an extracellular
polymeric substance, as a means of protection from harsh
environmental conditions (27, 99, 114). It is not within
the scope of this review to cover the vast body of research
published on biofilm formation on food-contact surfaces
in the food industry; thorough reviews by Carrascosa et
al. (27), Li et al. (99), and Mevo et al. (114) have been
recently published. Recent approaches to address biofilm
contamination on equipment surfaces include novel methods
to prevent bacteria from attaching, to disperse (chemically
or enzymatically) and remove established biofilms, or to
kill resident bacteria in the biofilms (8, 49, 186). However,
physical forces applied during cleaning are very important for
biofilm removal prior to sanitation.
March/April Food Protection Trends 131
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