Food Protection Trends - July/August 2021 - 413

populations on day 10 the same as those on day 0. These trends
are similar to findings for the main effect of day (Fig. 2).
DISCUSSION
The SP blend was evaluated in comparison to water,
chlorine, and an inoculated control to determine efficacy as
a novel postharvest wash intervention to reduce Salmonella
on fresh-cut spinach. SP was significantly the most effective
treatment, reducing Salmonella populations by 1.8 log
CFU/g compared with the control. Salmonella populations
varied within ±1 log CFU/g of day 0 populations throughout
the shelf life.
The interventions used in this study could have resulted
in cell injury rather than cell death for a portion of the
Salmonella population, which can lead to challenges
when enumerating populations on selective media that
contain chemicals, inhibitory ingredients, and other
substances that may be too harsh for injured cells to grow
(47). The resultant enumeration may not be an accurate
representation of the surviving Salmonella population. XLT4
+ TSA was used for enumeration in this study to account
for injured Salmonella populations.
Neal et al. (32) subjected Salmonella-inoculated spinach
to 2% L-lactic acid at 55°C and achieved a 2.7-log reduction.
However, application of calcium hypochlorite (200 mg/L),
PAA (80 mg/L), and chlorine dioxide gas resulted in
reductions of <1.0 log CFU/g, and a water wash achieved
a 0.7-log reduction. In the present study, the water wash
achieved a similar 0.8-log reduction, and SP surpassed
the efficacy of 80 mg/L PAA, significantly reducing
Salmonella populations by 1.8 CFU/g. Puerta-Gomez et
al. (36) inoculated spinach with Salmonella at 105
CFU/g
then washed it in water or 200 ppm of chlorine for 5 min,
achieving 0.54- and 1.17-log reductions, respectively. In
the present study, larger reductions were observed with a
shorter contact time (2 min); water reducing Salmonella
by 0.8 log CFU/g, and only 150 ppm of chlorine achieving
a 1.4-log reduction. By washing with water and chlorine,
Puerta-Gomez et al. achieved a 1.71-log reduction. Unlike
that double washing technique, the SP wash was applied as
a single washing step that produced similar results, reducing
Salmonella by 1.8 log CFU/g on XLT-4 + TSA. From a
feasibility perspective, it may be more advantageous to use
a single SP wash that achieves similar reductions rather than
multiple washes used in sequence.
Although internalization was not a specific focus of
this study, the submersion inoculation approach may
have facilitated Salmonella internalization or adherence
to protective sites within the leaves that prevent access to
sanitizers. Salmonella is capable of growing to moderately
high populations on or within plants (7-9, 20, 38, 46)
probably due to utilization of plant nutrients (8, 48).
Sampling day was a significant main effect, and Salmonella
populations varied during the shelf life (Fig. 2). Salmonella
remained viable and varied within ±1 log CFU/g of day 0
populations during storage (Figs. 2 and 3). Observed growth
may have been due to access to plant nutrients and storage at
7°C. These data indicate that internal and external pathogen
contamination remains on fresh-cut spinach after washing,
which emphasizes the importance of pathogen control in the
preharvest setting and effective postharvest interventions to
prevent cross-contamination and internalization in fresh-cut
spinach wash water.
The use of natural extracts to eliminate Salmonella on
spinach has also been investigated. A Sporan and acetic acid
combination and a cinnamaldehyde solution each achieved
larger reductions (1.29 and 1.06 log CFU/g, respectively)
of Salmonella on spinach than did water and chlorine
treatments (49). In comparison, the novel SP wash described
in the present study reduced Salmonella on spinach by up
to 1.8 log CFU/g. Orue et al. (35) found that Salmonella
populations on spinach were reduced by 1.3 log CFU/g
with chlorine, 1.7 log CFU/g with Citrol (a disinfectant
made from grapefruit), 2.0 log CFU/g with lime extract, and
1.2 log CFU/g with oregano extract. These reductions are
similar to those obtained in the present study. Olive extract,
hibiscus concentrate, and apple extract have also been used
to eliminate Salmonella on spinach, often with efficacy
increasing during storage time (up to 3 days) (30). Rada et
al. (37) reported Salmonella reductions of 2.91 and 2.21 log
CFU/g when mature spinach was treated with combinations
of 0.1% cinnamon leaf oil with 3.0% olive extract and 0.1%
oregano with 3.0% olive extract, respectively. Although some
natural extracts have efficacy that is similar or superior to
that of SP, organoleptic properties may be altered by the use
of natural extracts, and these alterations should be evaluated
in future comparison studies with SP. Although the impact
of SP on organoleptic properties was not the focus of the
present study, off-odors were not detected from SP spinach
throughout the shelf life.
Consumer studies have shown that purchasers of fresh
produce are willing to pay a premium when the likelihood
of foodborne illness is reduced by 50% (50). Thus, research
into effective chemical washes such as the SP blend evaluated
here is warranted. Chlorine, a chemical effective for reducing
microbial populations in plant systems (2), is frequently used
in the produce industry for water washes; however, increasing
numbers of foodborne illness outbreaks have challenged
assumptions about the efficacy of these chlorine washes (34).
Chlorine interacts with organic material, which reduces the
antimicrobial activity (1, 3, 6, 14, 31) and may lead to crosscontamination
between batches of produce in wash tanks
(29, 31, 40) and subsequent outbreaks of foodborne illness
(31, 45). The questionable efficacy and environmental and
health risks of chlorine have prompted producers to look
elsewhere for antimicrobial interventions (12, 34), especially
when considering the generation of disinfection by-products,
which can cause health problems (26). The SP wash of GRAS
July/August Food Protection Trends 413
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