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FIGURE 4. The survival of E. coli O157:H7, S. enterica, and L. monocytogenes strains in acidiﬁed pickle jars at 10°C. The data for E. coli O157:H7
(circles), S. enterica (triangles), and L. monocytogenes (squares) show the log of the viable cell count from seven or more replicate experiments,
each with a cocktail of five strains of a given species. The solid lines represent the predicted survival curves from the Weibull model (3).

and approved supplier programs in both manufacturing facilities and retail food establishments. Additionally, prudent
processors should consider potential chemical and physical
hazards. This review focuses on microbiological pathogens
and their control, i.e., mitigation of biological risks.
While a diverse array of microbial pathogens may potentially contaminate vegetables, identification of only the
most treatment-tolerant pathogen(s) reasonably likely to
be present is necessary in the hazard analysis. In vegetable
fermentation, the 5-log pathogen reduction target is generally achieved through acidification during fermentation.
Pathogenic E. coli, Salmonella spp. and L. monocytogenes
are reasonably likely to be found on raw produce and must
be controlled, especially early in the fermentation process
(2, 5). Breidt and colleagues investigated the holding time
needed to achieve a 5-log reduction in E. coli O157:H7,
Salmonella, and L. monocytogenes in vegetable products
acidified with acetic acid (pH 3.3) at 10 and 25°C (3).
Results indicated that E. coli O157:H7 was generally the
most acid-tolerant pathogen, especially in acidified-vegetable systems (Fig. 4). In other work, Inatsu et al. noted
that Salmonella survival was similar to E. coli O157:H7
survival in kimchi fermentations (20). Fermentation
management, therefore, requires identification of controls
validated for the inactivation of pathogenic E. coli; these
controls may include time, temperature, final pH, and/or
NaCl concentration.

In addition to control of vegetative bacterial pathogens
potentially present on the raw material, risk enhancement due to processing and packaging conditions must
also be considered in the hazard analysis. Specifically, the
creation of low oxygen environments that allow for spore
germination, growth, and toxin production by Clostridium
botulinum should be considered. Competitive growth of
LAB and the accompanying decrease in pH can mitigate
spore germination of C. botulinum during fermentation. Ito
and colleagues originally showed that the outgrowth of C.
botulinum was inhibited at pH as high as 4.8 in fresh-pack
pickles acidified with acetic acid. Inoculation experiments
with whole cucumbers showed that as little as 0.9% acetic
acid in the brine was sufficient to prevent outgrowth from
spore inocula as high as 106 per cucumber (22). The pH in
fermented vegetable products eventually decreases below
the minimum necessary for germination and growth of C.
botulinum, considered to be pH 4.6 for high-water-activity
shelf-stable food products (54).
Processing steps such as transfer or filling operations
can also introduce pathogens into the product and must be
considered in risk management. Depending on the extent to
which fermentation is allowed to progress, E. coli O157:H7
and related serotypes may survive in commercial fermentation brines for extended periods, e.g., up to 2 weeks at
20°C (2) and up to 1 month or longer in acidified brines at
4°C (30). An illness outbreak in 2012 that sickened 1,642

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Food Protection Trends - July/August 2020

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