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tation proceeds. Many vegetable ferments are optimally
stored between 18.3 and 22.2°C (65 and 72°F), allowing for
efficient metabolic activity from the LAB, with subsequent
rapid lactic acid biosynthesis and enhancement of complex
flavor development throughout the stages of microbial
succession. For example, optimum conditions for cabbage
fermentation are 2% NaCl and 18°C (46). However, temperatures ranging from 10 to 24°C (50 to 75°F) have been
used to successfully produce fermented vegetable products
(46, 51). Fermentation at > 30°C can negatively impact
product quality, resulting in undesirable changes in texture
and the development of off-odors (44). Changes in quality
attributes are the consequence of both biotic and abiotic
changes in the ferment; temperature influences the selective
growth of spoilage biota relative to fermentative LAB, as
well as the enzymatic activity occurring within the vegetable substrates. In general, vegetable fermentation below
10°C will proceed normally, but at a slower pace, increasing
the time required to reach the final pH. Partly for this reason, there is no universally specified time for a fermentation
to achieve a pH below 4.6. However, because acid accumulation and the accompanying pH decrease are essential
to the control of biological hazards, e.g., pathogenic E. coli
and C. botulinum, active managerial control over endpoint
pH monitoring is usually necessary. As a result, while pH
rather than temperature is the critical factor addressed in
many fermented-vegetable HACCP plans, when deviations
in monitoring pH occur, addressing fluctuations in storage
temperature may be a part of the root-cause analysis and
corrective action. The food safety risks must also be carefully considered in the manufacture of incompletely acidified
'half-sour' products, as refrigerated storage significantly
slows fermentation and accompanying pH drop. At room
temperature these 'half-sour' products will rapidly ferment
to 'full-sour' pickles, typical of a normal cucumber fermentation, with concomitant reduction in bacterial pathogens
as described (2). Overall, vegetable ferments are dynamic
systems, and an interplay of factors influences microbial
metabolism with the resultant target pH achieved over time.
Control principles
Regardless of which food safety system governs manufacturing activities - Preventive Controls or HACCP - the
identification of key hazard reduction steps is critical. Critical control points (CCPs) are key processing steps under
active management, in contrast to various other prerequisite
programs and activities that, while also supporting food
safety, do not provide an equal degree of control over the
relevant microbial hazards. The U.S. FDA has issued guidance on differentiation of CCPs from prerequisite activities
(37). While numerous intrinsic and extrinsic production
factors contribute to microbial proliferation or lethality,
process control requires differentiation between those
factors for which active management and record keeping as

CCPs are crucial for ensuring safety and those factors that
play supporting roles, here termed Control Points, or CPs.
Given the importance of this distinction in the development of food safety programs by small food processors, a
sample process flow diagram and hazard analysis for the
manufacture of kimchi has been provided to illustrate these
points (Table 1).
We advocate for one CCP in the manufacture of traditionally fermented vegetable products, and that is pH
reduction accompanying fermentation. Based on published
research and extensive experience in the field, we further
advocate for additional Control Points (CPs) that are necessary to support the manufacture of a safe product but that
are not managed in the same way as a CCP. Post-fermentation, we note that there are additional CPs for refrigerated
storage and/or packaging and labeling as a shelf-stable
product.
CCP1: Fermentation
The fermentation step is a key food safety control because
of acid production and corresponding 5-log inactivation of
the target pathogen, enterohemorrhagic E. coli. Control is
verified via pH monitoring during fermentation. Decreasing pH to below 4.6 makes the outgrowth of C. botulinum
spores a hazard not reasonably likely to occur in traditionally fermented vegetable products. A steady decrease in pH
over time is necessary for the fermentation process to be
under control. Because the vegetables used for fermentation typically exhibit little buffering capacity, pH may be
monitored in the brine. The brine pH should be monitored
in each fermentation vessel with sufficient frequency during
active fermentation so that a continued decline in pH to
< 4.6 is recorded. The brine pH should also be monitored
after evident microbial activity has ceased to demonstrate
that pH is not increasing. Incompletely fermented vegetables, referred to as lightly fermented or half-sours, may
represent an increased risk to food safety (9) (Fig. 3).
Additionally, vegetable ferments that fail to reach a pH of
< 4.6, or products in which a continued pH decline is not
recorded, should be discarded. Effectively managed vegetable fermentation systems typically expect to reach a pH of
< 4.6 within a week after the start of fermentation, although
it may take longer depending on the vegetable matrix and
temperature at which fermentation occurs (Fig. 1). While
many factors such as NaCl concentration and storage temperature contribute to the rate and extent of acidification,
these are most effectively applied as CPs.
Processors should consider the development of an SOP
that specifies appropriate methods for brine sampling in
each fermentation vessel, and the method and frequency of
brine pH determination. pH can be measured directly on
brine samples taken from each fermentation vessel; samples
must be representative of the whole, and generally two or
three distinct measurements are taken at each time point

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Food Protection Trends - July/August 2020

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