Food Protection Trends - May/June 2021 - 320

inoculum on these dried products (Fig. 1B). Salmonella levels
averaged between 2.10 (quinoa) and 3.61 (hemp) log CFU/g
on the raw products prior to soaking. Salmonella inoculum
levels were significantly higher on hemp, walnuts, and pili
nuts and significantly lower on almonds, pecans, and quinoa.
Initial pH (positively correlated; P-value < 0.0001) and
moisture content (negatively correlated; P-value = 0.0022)
were statistically significant parameters associated with the
stability of the Salmonella inoculum on the grains, nuts, and
seeds. The small reduction of the Salmonella inoculum during
the drying phase was expected and has been reported in
numerous previous studies of low-moisture foods (e.g., 2, 13,
15, 22).
The primary purpose of this study was to quantify the
potential for Salmonella to grow on grains, nuts, and seeds
during the soaking process (ambient temperature, 24 h) used
for creating " sprouted " products. The growth of Salmonella
on various commodities commonly " sprouted " is shown in
Fig. 1B and 1C. All 15 of these commodities supported
significant growth of Salmonella (>3.00 log CFU/g) within
the 24-h soaking period. Salmonella populations increased by
>5.00 log CFU/g during the soaking of almonds, cashews,
hazelnuts, peanut, and buckwheat. Significantly less growth
(3- to 4-log CFU/g increase) was measured in hemp, brown
rice, and flax. The growth of Salmonella during soaking of
pumpkin seeds (3.95 log CFU/g) and sunflower seeds (3.84
log CFU/g) is very similar to that seen in the previous study
by Keller et al. (14). For the seeds, population increases
in the natural microbiota and Salmonella were similar.
Interestingly, Salmonella had significantly more growth
during the soaking period than did the natural microbiota
in two nuts (almond and pili) and significantly less growth
in three of the grains (brown rice, buckwheat, millet) and
two nuts (hazelnut and peanut). Salmonella cell density after
the 24-h soaking is likely influenced by the rate of hydration
and the release of nutrients into solution. These, along with
many other factors (temperature, pH, macronutrient profile,
mineral content, competing natural microbiota, etc.), will
influence the lag time and the growth rate of Salmonella.
Keller et al. (14) reported average lag times of 3.45 h
(sunflower) to 6.68 h (chia) during soaking at 25°C; however,
these times were highly variable between replicates (standard
deviations averaging 2 h). Shortening the soaking time to
< 3 h to mitigate the potential growth of Salmonella is not a
viable option because many of these commodities would not
be fully hydrated in this time frame.
The overall goal of the soaking step is to hydrate the grains,
nuts, and seeds; however, this hydration also stimulates
previously dormant bacterial cells into rapid proliferation.
Due to the market demand for " sprouted " ingredients,
it is important to identify and verify practical measures
that would prevent the growth of pathogens during the
soaking step. The potential for grains, nuts, and seeds to
be contaminated with low levels of Salmonella or other

320

Food Protection Trends May/June

foodborne pathogens is a significant risk; however, the risk
for foodborne illness increases significantly if processing
steps would support the proliferation of these pathogens.
Almonds were selected as the target matrix due to their
ability to support the most growth of Salmonella during
soaking as well as for their high utilization in commercially
available " sprouted " products. Through conversations
with industry partners, the inclusion of salt in the soaking
process and refrigeration were determined to be the
most cost-effective and easily implementable options for
modifying current procedures. High salt concentrations
(>10%) prevented the growth of Salmonella throughout
the 24-h soaking of almonds under ambient conditions
(Fig. 2). At higher salt concentrations (20%), there was
a significant inactivation (1.44-log CFU/g reduction) of
Salmonella during soaking. Low-salt concentration (1.5%)
had no impact on the growth of Salmonella during soaking.
Refrigeration (< 7°C) was also effective at preventing the
growth of Salmonella on almonds within the 24-h soaking
period. Whereas Salmonella is capable of growth at 7°C,
the growth rate is substantially slower and did not result
in a measurable increase in cell density within the 24-h
soaking period. Processors relying on refrigeration must
take care to confirm that refrigeration conditions are < 4°C
and/or limit the soaking time at lower temperatures to
prevent Salmonella growth. Investigations surrounding the
2015 Salmonella Paratyphi B outbreak linked to " sprouted "
nut butters reported that the company conducted their
soaking process under refrigeration but they did not apply
a validated kill step (12). This situation demonstrates that
refrigerated soaking may be an important control to prevent
the growth of Salmonella; however, this approach was
insufficient to eliminate risk associated with contaminated
starting ingredients. Had their " sprouting " process occurred
at ambient temperature without a subsequent kill step, the
outbreak would likely have led to significantly more illnesses.
CONCLUSIONS/RECOMMENDATIONS
The use of typical soaking processes in the production of
" sprouted " grains, nuts, and seeds at ambient temperature
poses a significant risk due to the ability of Salmonella to
grow rapidly in all 15 of the commodities tested. Although
many companies further process " sprouted " ingredients, most
use low-temperature dehydration to maintain a " raw " label.
Dehydration, or other processing steps, could be optimized
and validated to achieve a significant pathogen reduction;
however, the current study demonstrates that the soaking
stage of the " sprouting " process could lead to an increase
in Salmonella of > 5 log CFU/g. Therefore, the standard
5-log reduction typically targeted in process validation
studies would be inadequate to achieve food safety goals
in these processing systems. Potential growth of pathogens
in a processing facility also creates a number of challenges
for sanitation and other prerequisite programs that provide
Food Protection Trends - May/June 2021

Table of Contents for the Digital Edition of Food Protection Trends - May/June 2021
