Food Protection Trends - January/February 2021 - 154

TABLE 1. Chemical and physical food attributes (intrinsic factors) considered in
grouping matrices
Intrinsic factor
pH
Water activity
Natural occurring inhibitors - cocoa polyphenols, enzymes
% Fat
% Protein
% Fiber
% Carbohydrate
Added organic acids
Microbial load - active cultures, raw agricultural product, meat

Food matrix grouping approach: Commonality in
enrichment procedures
When a matrix has not previously been evaluated, we are
concerned with two primary risks to method performance: (i)
the alternative method selected may not allow propagation of
the target organism to detectable levels, and (ii) matrix effects
may interfere with the assay's chemistry or technology.
Enrichment procedures are the foundation for detection
of pathogens, requiring growth of the pathogen to sufficient
numbers for detection by either traditional or rapid methods.
Within a particular test method, there is often a significant
common core in validated enrichment procedures between
matrices (Tables 2 and 3), demonstrating substantial
robustness of the method, even when exceptions are noted.
This common core of enrichment conditions increases
our confidence that a method can recover the pathogen of
concern, even from an unevaluated matrix, and suggests that
a limited demonstration of efficacy may often be sufficient.
This point is discussed further and explored using the Matrix
Evaluation Level Assessment Tool available online.
Rapid test methods increasingly use proprietary enrichments, usually for some claimed reduction in the required
incubation period or simplification from a two-stage to a single-stage enrichment. Newer methods may have more limited
validations, and if faced with evaluating a new matrix it is best
to consult the manufacturer for enrichment recommendations.
When conducting a matrix addition with an established
and validated method, choosing the enrichment used by that
method for a matrix from a similar validated category is a
good starting point. If further method development is needed
following evaluation, using validated enrichments for
fdifferent matrix categories within the same method or a

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Food Protection Trends January/February

Surface structure
Salt
Sugar
Added humectants - polysaccharides, dietary fiber,
hydrocolloid, pectin
Emulsifiers
Fermentation products and by-products
Microbial inhibitors and preservatives used in formulation
Type of processing - roasted, high-pressure processing, irradiated
Physical form - dried, intermediate-moisture food, high moisture

similar matrix with a different method may increase the
chances of success. Validated enrichment schemes mitigate a
portion of the risk for detection failure due to failure to grow
the organism to a detectable level and move the risk element
to matrix interference with the detection system. However,
method modifications such as additional dilutions, modified
enrichment media, or other significant method changes may
require a " full " validation. Interference by matrix effects is
addressed further in the fit-for-purpose approach described
below.
Public health risk versus detection risk approach
Less rigorous evaluation approaches might be acceptable
for use with food matrices that are rarely associated with
foodborne illness, recalls, or pathogens due to intrinsic
properties and evidence (as assessed through surveillance
programs and reported isolations).
Figure 1 diagrams the interaction of public health issues
and detection failure along a continuum in relation to
the need for more rigorous matrix evaluation studies.
As consumer risk increases, so does the level of matrix
evaluation that may be required. In making this assessment,
it is important to be current on the hazards associated
with different matrices. For example, recently discovered
associations include those between Salmonella and soy
lecithin (1) or hydrolyzed vegetable protein (18, 21).
The inherent risk to the consumer presented by these
matrices was previously considered to be low. Similarly, the
association between Shiga toxin-producing Escherichia coli
and flour came to prominence in the United States with some
high-profile recalls in 2016 and again in 2019 (2, 16).
Food Protection Trends - January/February 2021

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