Food Protection Trends - March/April 2023 - 134

available sanitizer performance on conveyor belt material
and reported that when sanitizer concentration, the number
of follow-up treatments, exposure time, and temperatures
were increased over the typical standard daily cleaning and
sanitizing process recommended by the manufacturers,
L. monocytogenes biofilm removal improved from a maximum
1.8-log reduction to a >5.5-log reduction.
Because chemical sanitizers are most commonly used
to reduce microbes on produce harvesting and packing
equipment, the correct selection and use of sanitizing agents
is vital for preventing cross-contamination of product during
harvesting and field-packing operations. Chemical sanitizing
agents approved for use on food-contact surfaces include
halogens (e.g., chlorine- and iodine-based products), ozone,
peroxides (e.g., peracetic acid [PAA]), and quaternary
ammonium compounds (QACs) (15, 141). Although
some researchers have reported that for QACs, higher
minimum inhibitory concentration are needed to kill some
L. monocytogenes strains (51, 160), these strains appear to
be killed at equal efficacy as those killed by lower MICs
(16). Although these findings support the need for use of
appropriate sanitizer concentrations, current evidence is not
sufficient to advise against the use of QAC-based sanitizers.
In numerous studies of sanitizer efficacy against foodborne
pathogens under various conditions (frequently in the
presence of food residues), sanitizer efficacy depended on
the target microorganisms (73, 89, 90, 93, 140, 183). Many
researchers have investigated sanitizer efficacy against
L. monocytogenes, which is a key environmental pathogen due
to its ability to readily attach to surfaces and the frequency at
which it has been identified as both a transient and resident
contaminant in food pro-cessing facilities (26, 112, 152,
156). The efficacy of sanitizers (e.g., PAA, QACs, chlorine, or
chlorine dioxide) commonly used against L. monocytogenes
biofilms has been variable, depending on the materials being
investigated, the specific L. monocytogenes strain, and the
degree of biofilm develop-ment (34, 73, 79, 90). However,
researchers have consistently emphasized the importance of
timely and thorough cleaning of food-contact surfaces before
sanitation to further optimize sanitizer efficacy and reduce
biofilm formation.
Biofilm control
A finding common to many studies is that pathogens
attached to equipment, especially in the form of biofilms,
are much more difficult to eliminate than those present as
individual cells (60, 90, 140, 183). As they mature, biofilms
become more difficult to remove (54, 90, 183). L. monocytogenes
may not form true biofilms but often co-occurs with
biofilm producers such as Pseudomonas and Burkholderia
(159). Korany et al. (90) reported that the efficacies of
QACs, chlorine, chlorine dioxide, and PAA were much lower
against L. monocytogenes cells that have been attached for
7 days than against cells attached for only 2 days.
134 Food Protection Trends March/April
Driven largely by the food manufacturing, meat, dairy, and
medical industries, research into new sanitizing technologies
and/or chemicals with enhanced efficacy against biofilms
has increased over the past decade. Several publications
have provided comprehensive reviews of these innovative
and promising approaches to sanitation, which include use
of visible and UV light, proteins, cold plasma and plasmagenerated
compounds, electric currents, natural products,
nanoparticles, nanomaterials, nanobubbles, peptides,
bacteriophages, and low-frequency high-intensity ultrasound
(5, 6, 42, 67, 114, 121, 138, 144, 175). The mechanisms of
action behind these novel approaches to sanitation are based
on increasing the bacterial cell membrane permeability,
disrupting bacterial communication via quorum sensing
(quorum quenching), promoting bacterial cell lysis,
degrading components of the biofilm matrix, and/or
inhibiting enzyme activity or protein synthesis-all of these
mechanisms may facilitate the disruption and dismantling
of biofilms or bacterial cell death (114, 138, 144).
A hurdle approach to biofilm control or elimination by use
of a combination of sanitizing treatments or technologies
has frequently been more effective against biofilms than a
single antimicrobial intervention alone (114, 132, 138, 174).
For example, ultrasound treatment plus 30 s in 1 ppm of
chlorinated water reduced E. coli O157:H7 counts below the
limit of detection (1.10 CFU/cm2
) on the coring ring blade
and welding joint of lettuce coring knives (188). Rafeeq and
Ovissipour (132) reported a synergistic effect of ultrasound
and nanobubbles against E. coli O157:H7 and Listeria innocua
on spinach leaves that surpassed the efficacy of either
treatment alone. In other cases, bacteriophage addition or
treatments that dismantle or dissolve the biofilm matrix (e.g.,
quorum quenching) in combination with sanitizing agents
have effectively reduced pathogens in biofilms on food-contact
surfaces (42, 138). However, in the " real world " the
persistence of pathogen communities and biofilms is often
due to contamination in equipment locations that are not
reached by chemicals in niches or harborage sites (112). Use
of specific chemicals targeting biofilms is often ineffective
because the liquid or gaseous chemicals cannot reach the
target organisms in hollow areas. In these cases, removal
of persistent pathogen communities and/or biofilms will
require equipment disassembly and enhanced mechanical
cleaning rather than use of specialized chemicals (23).
Validation and verification of cleaning and sanitizing
processes
In the Validation of Cleaning Processes guide for inspectors
of the pharmaceutical industry, the FDA (168) states " the
test of any validation process is whether scientific data shows
that the system consistently does as expected and produces a
result that consistently meets predetermined specifications. "
In a similar way, for the produce industry, cleaning and
sanitizing procedures as outlined in a harvesting company's
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