JFS
M: Food Microbiology and Safety
Utilizing Acidic Sprays for Eliminating
Salmonella enterica on Raw Almonds
STE
VEN PAO, AREF KAL
ANT
ARI, AND GUANGWEI HUANG
TEVEN
ALANT
ANTARI
ABSTRA
CT
n-shell or shelled almonds inoculated with Salmonella w
er
e spr
ay
ed with water
ic
ABSTRACT
CT:: IIn-shell
wer
ere
spray
ayed
water,, acetic acid, citr
citric
acid, acidified sodium chlorite, peroxyacetic acid, or a mixture of citric, hydrochloric, and phosphoric acids
befor
e testing for Salmonella on xylose-lysine-deo
xy
cholate (XLD) agar and tr
yptic so
y agar ((T
TSA). S
pr
aying
before
xylose-lysine-deoxy
xycholate
tryptic
soy
Spr
praying
acids on in-shell almonds reduced about 0.48 to 1.88 and 0.22 to 0.67 log colony-forming units (CFU)/g of
Salmonella on XLD agar and TSA counts
espectiv
ely
counts,, rrespectiv
espectively
ely,, on the in-shell almonds but had no effect on the edible
por
tion of the almonds (shelled almonds). When spr
aying acids on shelled almonds
ay application
portion
spraying
almonds,, a single spr
spray
(1.6 mL acid solution/25 g of shelled almonds) with 1 min holding caused 0.72 to 1.93 and 0.38 to 1.35 log CFU/
g rreductions
eductions of Salmonella counts on XLD agar and TSA, rrespectiv
espectiv
ely
ncr
easing the holding time to 5 min did
espectively
ely.. IIncr
ncreasing
not enhance the rreductions
eductions
aying shelled almonds
easing the number of application (1 to 3 times)
eductions.. When spr
spraying
almonds,, incr
increasing
enhanced S
almonella reduction. Except for the peroxyacetic acids, increasing total holding time (5 to 120 min)
Salmonella
improved the efficacies. Furthermore, increasing acid concentrations improved the efficacies of acetic, citric,
and peroxyacetic acid treatments. Estimated 5-log reductions on both TSA and XLD counts can be achieved under
laboratory conditions using 10% citric acid by (1) the combination of shelling, 1 spraying, and 3 d of storage, (2)
the combination of shelling, 2 sprayings, and 1 d of storage, or (3) the combination of shelling and 3 sprayings.
Acidic sprays may be utilized for enhancing the microbiological safety of raw nuts.
Keywords: salmonella, nuts, shelling, sanitizing, organic
Introduction
C
M: Food Microbiology & Safety
ontacts between nuts and natural contaminants from soil and
insects are unavoidable during nuts’ growing and harvesting
in the field. Consequently, the surfaces of nuts are not free of microbial contamination. The findings of various types of microorganisms on nuts were documented in the literature (Ostrolenk and
Hunter 1939; Hyndman 1963; Kokal 1969; Kokal and Thorpe 1969;
King and others 1970). Although most of the natural microorganisms are not harmful to humans, these findings stress the importance of good agricultural and manufacturing practices. Furthermore, the need to develop an effective decontamination process for
preparing raw nuts for direct consumption is enlightened by recent
Salmonella outbreaks associated with eating raw almonds (Chan
and others 2002; Isaacs and others 2004, 2005).
Edible sweet almonds (Prunus amygdalus) consist of 3 distinct
parts: an outer hull, a middle shell, and an inner kernel or meat
(King and others 1970). The harvesting process starts when the nuts
are partly dried on the trees. They are shaken down onto the
ground and picked up after further dehydration. A hulling process
then removes the outer hulls to produce in-shell almonds for the
market or further subjecting to a shelling process before the inner
kernels (meats) are processed into graded almond products (King
and others 1970; Isaacs and others 2005).
A broad spectrum of chemical solutions and their usages has
been developed by the food industry for minimizing microbial contamination on surfaces of raw agricultural commodities. For examples, calcium hypochlorite has been recommended for disinfecting
sprouting seeds (USFDA 1998), quaternary ammonium comMS 20050454 Submitted 7/28/05, Revised 9/7/05, Accepted 10/14/05. Authors Pao
and Kalantari are with Virginia State Univ., Agricultural Research Station, P.O.
Box 9061, Petersburg VA 23806. Author Huang is with the Almond Board of California, Modesto, Calif. Direct inquiries to author Pao (Email: [email protected]).
M14 JOURNAL OF FOOD SCIENCE—Vol. 71, Nr. 1, 2006
Published on Web 1/11/2006
pounds have been approved for sanitizing shell eggs (USEPA 1999),
alkaline cleaners have been used for washing oranges (Pao and
others 2000), and acidified sodium chlorite has been developed as
an antimicrobial agent on meats (Kim and Mustapha 2004). However, information on the potential application of antimicrobial
chemicals on nuts is largely lacking. The purpose of this research is
to evaluate the efficacy of acidic sprays along with common shelling and storage processes for eliminating Salmonella on almonds.
Materials and Methods
Inoculum preparation
Four Salmonella cultures (S. Enteritidis ATCC 13076, S. Montevideo ATCC 8387, S. Newport ATCC 6962, and S. Typhimurium ATCC
14028) were maintained at 4 °C on tryptic soy agar (TSA) (unless
otherwise stated, all media were from BioPro, Bothell, Wash.,
U.S.A.). Each of the cultures was transferred to tryptic soy broth
(TSB) at 36 °C for 20 h followed by spreading onto tryptic soy agar
(0.2 mL/plate) to produce a bacterial lawn at 36 °C for 24 h. To prepare the inoculum for immediate almond inoculation, the bacterial
lawns were pooled with sterile swabs and blended by a laboratory
blender (IUL Instruments, Barcelona, Spain) with 0.1% peptone
water, similar to methods described previously (Pao and others
2004), to obtain a Salmonella slurry with cell level at about 1010/mL
as later confirmed by plate counts.
Almond inoculation
All raw almonds (Nonpareil, in-shell or shelled almonds) were
obtained from the Almond Board of California (Modesto, Calif.,
U.S.A.) and refrigerated upon receipt at 4 °C for experiments within
2 mo. Before inoculation, almonds were warmed to room temperature (24 °C) and placed in sterile bags (400 g/bag). The almonds
were then sprayed with the Salmonella slurry (25 mL/bag) followed
© 2006 Institute of Food Technologists
Further reproduction without permission is prohibited
Acidic sprays for almond safety . . .
Table 1—Effect of spraying inoculated in-shell almonds on the reduction of Salmonella on in-shell and shelled almondsa
Salmonella reduction (log colony-forming units (CFU)/g)
Spraying
Chemical
solutions b
Control (without spraying)
Deionized water
Acetic acid (10%)
Citric acid (10%)
Acidified sodium chlorite
Peroxyacetic acid (500 ppm)
Hydrochloric-phosphoric-citric acids
Spraying + shelling
TSA
XLD
0.00 ± 0.19
–0.15 ± 0.07
0.63 ± 0.04*
0.22 ± 0.10
0.17 ± 0.07
0.65 ± 0.17*
0.51 ± 0.14*
0.00 ± 0.28
0.19 ± 0.08
1.88 ± 0.15*
1.27 ± 0.22*
0.48 ± 0.15
1.27 ± 0.13*
1.43 ± 0.19*
TSA
1.75
1.60
1.65
1.65
1.68
1.89
1.56
±
±
±
±
±
±
±
0.06
0.25
0.11
0.05
0.04
0.06
0.14
XLD
1.75
1.73
1.71
1.59
1.53
1.90
1.48
±
±
±
±
±
±
±
0.11
0.40
0.18
0.12
0.11
0.04
0.21
a Means (n = 3; ±S.E.) of log values in the same column followed by a (*) symbol are significantly higher than control (P < 0.05).
b In-shell almonds (inoculated with Salmonella at 7.95 ± 0.19 log CFU/g on tryptic soy agar (TSA) and 7.52 ± 0.28 log CFU/g on xylose-lysine-deoxycholate
[XLD] agar) were sprayed once with an acid solution (1.6 mL/25 g) and held for 20 min at 24 °C before microbial testing with or without shelling.
Treatment of almonds
A 500-mL spray bottle was filled with 200 mL of deionized water
or 1 of the following chemical solutions: (1) acetic acid (Fisher Scientific, Fair Lawn, N.J., U.S.A.) at 5%, 10%, or 15% (w/w); (2) citric acid
(Fisher Scientific) at 5%, 10%, or 15%; (3) acidified sodium chlorite
(SANOVA®, a mixture of 1.1% citric acid and 0.2% sodium chlorite to
generate ⱕ400 ppm chlorous acid; Alcide Co. Redmond, Wash.,
U.S.A.); (4) peroxyacetic acid (a mixture of acetic acid and hydrogen
peroxide; 80 ppm from Tsunami® 100, Ecolab, St. Paul, Minn.,
U.S.A. or 500 ppm from VigorOX® XA-15, FMC Co., Philadelphia,
Pa., U.S.A.); and (5) a mixture of hydrochloric, phosphoric, and citric
acids (FreshFxTM, 83 mL/L; SteriFx, Inc., Shreveport, La., U.S.A.). All
solutions were prepared using sterile deionized water at 24 °C.
About 25 g of almonds (either shelled or in-shell almonds) were
placed in a single layer on a hexagonal polystyrene weighing dish
(Fisher Scientific) and misted with one of the chemical solutions (to
reach 1.6 mL/25 g on an electronic balance) followed by gentle
shaking to allow thorough wetting of almond surfaces. For shelled
almonds, the almonds were sprayed up to 3 times and held for 1, 5,
10, 20, or 40 min after each spray before the samples were analyzed
for Salmonella. For in-shell almonds, the almonds were sprayed 1
time with 1 of the chemical solutions and were held for 20 min. Each
almond sample was then analyzed directly or after manual shelling
wearing sterile gloves. To evaluate the effect of storage following
acid treatment, shelled almonds were sprayed with 10% citric acid
(1.6 mL/25 g) before holding at 24 °C for 20 min, rinsing twice with
deionized water (50 mL /25 g), air-drying for 2 h at 25 °C, and storing at 24 °C for 1, 3, and 7 d.
Microbial enumeration
Each sample (about 25 g) was macerated with 99 mL of Butterfield’s phosphate buffer by a laboratory blender (IUL Instruments)
at high speed for 4 min. Appropriate dilutions of the sample slurry
were prepared and spread-plated on xylose-lysine-desoxycholate
(XLD) and TSA plates for counting non-injured and overall survived
Salmonella, respectively. The plates were incubated at 36 °C, and
typical colonies (pink colonies with or without black centers on XLD
URLs and E-mail addresses are active links at www.ift.org
and shiny, convex colonies with entire margins on TSA) were counted after 24 and 48 h of incubation. Non-inoculated samples had
XLD and TSA counts less than 10 and 100 colony-forming units
(CFU)/g (the minimum detection levels used by this study), respectively, indicating that the potential interference from the
growth of natural background microflora on colony enumerations
was not significant. In addition, representative colonies on the highest dilution plates (both XLD and TSA) were picked for confirmation
(Pao and others 1998). The colonies were inoculated into triple sugar iron and lysine iron agar slants from each plate and incubated for
24 h at 36 °C. Isolates with positive slant reactions were then tested for agglutination with Salmonella O poly A-I & Vi antiserum (Becton, Dickinson and Co., Sparks, Md., U.S.A.).
Statistical analysis
Microbial populations were analyzed by t test, 2-way analysis of
variance (ANOVA), or multiple linear regressions using SigmaStat
(Version 3.0, SPSS Inc., Chicago, Ill., U.S.A.) software. Significance
of difference was defined at P ⱕ 0.05.
Results and Discussion
Effects of treating in-shell
almonds with acidic sprays
Data in Table 1 show that a single spray (with 20 min holding at
24 °C) of 10% acetic acid, 10% citric acid, acidified sodium chlorite
(SANOVA®), 500 ppm peroxyacetic acid (VigorOX®), or a mixture of
hydrochloric, phosphoric, and citric acids (FreshFXTM) to the inoculated in-shell almonds reduced 0.22 to 0.65 and 0.48 to 1.88 log
CFU/g of Salmonella on TSA and XLD, respectively, on the in-shell
almonds. The differences between TSA and XLD reductions observed in individual treatments were 0.31 to 1.25 log CFU/g, showing that the treatments may cause significant injury to Salmonella
besides killing. The phenomena of acid injury and lowered XLD
counts on Salmonella were also observed in previous studies without almonds (Blankenship 1981; Wu and others 2001).
Shelling alone (without spraying) removed the highly contaminated shells from the inoculated almonds (with Salmonella at 7.95
and 7.52 log CFU/g on TSA and XLD counts, respectively) producing
shelled almonds with 1.75 log CFU/g less Salmonella than the inshell almonds. Data in Table 1 also show that acidic spray applications did not significantly change the levels of Salmonella on the
subsequently shelled almonds compared with the non-sprayed
controls in either TSA or XLD counts. These results indicate that the
impact of spraying acids on in-shell almonds is restricted on the
shells, thus rendering the applications ineffective for minimizing
microbial contamination of the edible portion of the nuts. On the
Vol. 71, Nr. 1, 2006—JOURNAL OF FOOD SCIENCE
M15
M: Food Microbiology & Safety
by gentle shaking and mixing for about 1 min to allow thorough
wetting of almond surfaces (Danyluk and others 2005). The shells
of Nonpareil almonds are porous and have natural openings that
allow in-shell kernels to be contaminated with the inoculum. To simulate natural drying and cell desiccation in the field, the wetted almonds were then placed in single layer on a sterile surface for 2 h at
25 °C in a forced-air chamber (Model 680A, Lab-line, Dubuque,
Iowa, U.S.A.) before left at room temperature for another 22 h before testing.
Acidic sprays for almond safety . . .
Table 2—Effect of spraying shelled almonds on the reduction of inoculated Salmonellaa
Salmonella
reduction (log CFU)/g)
Chemical solutionsb
Deionized water
Acetic acid (5%)
Acetic acid (10%)
Acetic acid (15%)
Citric acid (5%)
Citric acid (10%)
Citric acid (15%)
Acidified sodium chlorite
Peroxyacetic acid (80 ppm)
Peroxyacetic acid (500 ppm)
Hydrochloric-phosphoric-citric acids
TSA
XLD
–0.13 ± 0.07
0.65 ± 0.03*
1.32 ± 0.39*
1.42 ± 0.04*
0.85 ± 0.13*
1.12 ± 0.22*
1.35 ± 0.17*
0.45 ± 0.15*
0.38 ± 0.09*
0.89 ± 0.14*
0.99 ± 0.04*
0.09 ± 0.07
1.45 ± 0.15*
1.86 ± 0.23*
1.93 ± 0.16*
1.50 ± 0.36*
1.87 ± 0.20*
1.75 ± 0.09*
0.72 ± 0.15*
0.77 ± 0.24*
0.94 ± 0.21*
1.24 ± 0.04*
a Means (n = 3; ±S.E.) of log values in the same column followed by a (*)
symbol are significantly higher than control (P < 0.05).
b Shelled (inoculated with Salmonella at 8.04 ± 0.03 log CFU/g on tryptic soy
agar (TSA) and 7.67 ± 0.03 log CFU/g on xylose-lysine-deoxycholate [XLD]
agar) were sprayed once with an acid solution (1.6 mL/25 g) and held for 1
min at 24 °C before microbial testing.
other hand, the shell of almonds may prevent some direct contamination from the surface to the inner kernel. The process of shelling that physically removes the highly contaminated almond shells
may significantly increase the overall pathogen reduction. Current
commercial hulling-shelling operations involve a series of rollers
and screens that progressively remove the hull and shell. Because
the process creates enormous amounts of dust and contact opportunities between the nutmeats and debris, the transfer of surface
contaminants from the hull and shell to the edible meat at production environment should be evaluated on-site under normal operation conditions.
Effects of treating shelled almonds with acidic sprays
M: Food Microbiology & Safety
In a subsequent experiment, we evaluated the effects of acid
treatments (with 1 to 3 spray applications, and 1 to 40 min holding
time per spray) on shelled almonds that were inoculated with Salmonella at 8.04 and 7.67 log CFU/g on TSA and XLD counts, respectively. Data in Table 2 show that a single-spray application of 1 of the
tested acids with 1-min holding caused 0.38 to 1.35 log and 0.72 to
1.93 reductions of Salmonella on TSA and XLD counts, respectively.
Again, the reductions in XLD counts were consistently higher than
the reductions observed with the related TSA counts as the result
of Salmonella injury.
For all single-spray applications, increasing the holding time
from 1 to 5 min did not significantly reduce the counts of Salmonella. Figure 1 to 5 show the results of multiple spraying with extended
holding time on the reduction of Salmonella on shelled almonds.
Increasing the number of spray application (1 to 3 times) enhanced
Salmonella reduction, regardless of which chemical solution was
used for spraying. In addition, increasing acid concentrations significantly improved the efficacies of acetic, citric, and peroxyacetic
acid treatments. Except for the peroxyacetic acids, increasing the
total holding time (5 to 120 min) improved the efficacies of all acids.
Furthermore, acid injuries (greater reductions in XLD counts) were
observed with all but the peroxyacetic acid treatment.
The goal of 5-log reduction has been discussed in recent communication for surface decontamination of almonds (ABC 2005). Our
results indicate that acidic sprays may be utilized to contribute at
least a portion of the desired pathogen reduction. For example,
spraying almonds (inoculated with Salmonella at 8.04 and 7.67 log
CFU/g on TSA and XLD counts, respectively) once with 10% citric
M16
JOURNAL OF FOOD SCIENCE—Vol. 71, Nr. 1, 2006
Figure 1—Effects of acetic acid sprays (5%, 10%, and 15%)
on the recovery of inoculated Salmonella from shelled almonds (bars represent the means of 3 replications)
acid achieved 2.12 ± 0.14 and 1.78 ± 0.16 CFU/g reduction of Salmonella after 20 min holding (Figure 2). Furthermore, about 5.01 ± 0.66
and 3.96 ± 0.91 log CFU/g reductions of Salmonella on XLD and TSA,
respectively, were observed when using 3 applications of 15% acetic
URLs and E-mail addresses are active links at www.ift.org
Acidic sprays for almond safety . . .
acid with 40 min of holding time per each application (Figure 1). The
effect of multiple spray may in part be due to acid concentration;
future study may use dip treatments or increasing the volume of
spray to validate this issue. Although mechanical washing and rins-
ing processes are widely adapted and proven effective in produce
industry for cleaning fruits and vegetables, they are not used in current almond-packing operation. With the increased interest in enhancing nut safety, the potential benefit of adding similar washing
or rinsing steps to almond packing should not be overlooked.
Cumulative effects of spraying and storage
To understand the effect of storage after spraying, inoculated
shelled almonds were sprayed up to 3 times with a 10% citric acid
solution and tested for Salmonella after rinsing, drying, and storage
at 24 °C. Data in Table 3 show that sprayings of 10% citric acid
(along with rinsing and drying) 1 to 3 times caused 1.62 to 2.22 and
1.73 to 2.41 log CFU/g reduction on the TSA and XLD counts, respectively, off the inoculation levels (about 8.16 CFU/g on TSA and
7.56 log CFU/g on XLD). Rinsing alone (without acid spraying and
storage) produced near half a log reduction (Table 3).
M: Food Microbiology & Safety
Figure 3—Effect of acidified sodium chlorite sprays on the
recovery of inoculated Salmonella from shelled almonds
(bars represent the means of 3 replications)
Figure 2—Effects of citric acid sprays (5%, 10%, and 15%)
on the recovery of inoculated Salmonella from shelled almonds (bars represent the means of 3 replications)
URLs and E-mail addresses are active links at www.ift.org
Figure 4—Effect of peroxyacetic acid (80 and 500 ppm)
sprays on recovery of inoculated Salmonella from shelled
almonds (bars represent the means of 3 replications)
Vol. 71, Nr. 1, 2006—JOURNAL OF FOOD SCIENCE
M17
Acidic sprays for almond safety . . .
Table 3—Effect of spraying shelled almonds with 10% citric acid followed by rinsing, and storage on the reduction of
inoculated Salmonella on shelled almondsa
Salmonella reduction (log colony-forming units [CFU]/g) after storage
Number of sprayingb
0
1
2
3
TSA
XLD
TSA
XLD
TSA
XLD
TSA
XLD
0.45
0.38
1.62
1.73
1.99
1.99
2.22
2.41
0d
1d
3d
±
±
±
±
±
±
±
±
0.87 ± 0.03ab
0.94 ± 0.21ab
2.21 ± 0.05b
2.44 ± 0.15ab
2.51 ± 0.22ab
2.51 ± 0.11ab
2.61 ± 0.14a
2.99 ± 0.27ab
1.29 ± 0.01b
1.44 ± 0.05b
2.44 ± 0.01b
2.75 ± 0.09b
2.42 ± 0.10ab
2.87 ± 0.15bc
3.27 ± 0.36b
3.66 ± 0.28bc
0.03a
0.13a
0.04a
0.06a
0.08a
0.07a
0.01a
0.15a
7d
1.27
1.21
2.32
2.55
2.87
3.43
3.68
3.85
±
±
±
±
±
±
±
±
0.22b
0.04b
0.21b
0.51b
0.11b
0.15c
0.17b
0.31c
a Means (n = 3; ±S.E.) of log CFU/g values in the same row followed by a same letter are not significantly different (P > 0.05).
b Shelled almonds (with inoculated Salmonella at 8.16 ± 0.01 log CFU/g on tryptic soy agar (TSA) and 7.56 ± 0.06 log CFU/g on xylose-lysine-deoxycholate
[XLD] agar) were sprayed up to 3 times with 10% citric acid before rinsed by water, air dried, and stored for microbial testing. A 20-min holding was applied
after each spraying.
Data in Table 3 also show that storing treated almonds for ⱖ3 d
generated additional Salmonella reduction in both XLD and TSA
counts with or without 10% citric acid spraying. During storage, the
almonds that were treated with higher numbers of spraying had
greater Salmonella reduction. The greatest reduction was observed
in treatment with 3 spray applications followed by storage for 7 d,
which lowered Salmonella counts from 8.16 to 4.48 log CFU/g on
TSA and 7.56 to 3.71 log CFU/g on XLD. In general, reductions were
maximized at day 3 of storage; increasing storage time from 3 to 7 d
did not significantly improve the reductions. Moreover, the reductions occurred with or without acid spraying and did not change the
differences between TSA and XLD counts. These results suggest
that the observed storage effect can be (1) independent from, (2)
cumulative to, and (3) synergistic with acid pre-exposure. The reductions observed during almond storage are likely caused by the
stressful process of cell desiccation that was reported as a significant contributing factor to pathogen reduction on the surfaces of
other plant materials (Beuchat and others 2001).
Cumulative effects of shelling, spraying, and storage
Figure 6 illustrates the reductions of Salmonella on almonds samples during the preparation of shelled almonds from artificially
contaminated in-shell almonds. The initial inoculation level was
about 8.16 or 7.58 log CFU/g on TSA or XLD counts, respectively.
Shelling, as expected, reduced the respective counts to 6.18 and
5.92 log CFU/g. Cumulative reductions on these shelled almonds
were obtained by spraying 10% citric acids (with rinsing and drying)
and storage at 24 °C. Estimated 5-log reductions on both TSA and
XLD counts were achieved by (1) the combination of shelling, 1
spraying, and 3 d of storage, (2) the combination of shelling, 2
sprayings, and 1 d of storage, or (3) the combination of shelling and
3 sprayings.
These results suggest that the goal of 5-log Salmonella reduction
can be achieved in fresh almond preparation by introducing a simple acidic spraying step (followed by rinsing and drying) to the existing fresh almond operation. The spraying could contribute a significant portion of the overall 5-log reduction that may be
cumulatively achieved over the entire (including shelling, spraying,
and storage) operation. Because treatments with simple procedures and low acid concentrations are favored in processing cost
and product quality considerations, future research should consider (1) maximizing and/or optimizing the effects of spraying, drying,
or storage using varied treatment volume, temperature, and time,
(2) further exploring the combination effects between acid and
desiccation stresses using milder acid sprays, and (3) evaluating the
combination effects between acid treatment, drying, and other
M: Food Microbiology & Safety
Figure 5—Effect of a mixed acid spray on the recovery of inoculated Salmonella from shelled almonds (bars represent
the means of 3 replications)
M18
JOURNAL OF FOOD SCIENCE—Vol. 71, Nr. 1, 2006
URLs and E-mail addresses are active links at www.ift.org
Acidic sprays for almond safety . . .
physical intervention techniques (such as ultraviolet light treatments). A processing validation study is also needed to test the
cumulative effect at industrial scale using surrogate microorganisms (Pao and Davis 2001) and with additional almond varieties.
Conclusions
T
his research report offers an initial view on the potential usage
of acid sprays for eliminating Salmonella on Nonpareil almonds.
We found that acid sprayings, when applied to either in-shell or
shelled almonds, can significantly reduce Salmonella contamination. An estimated 5-log reduction may be achieved using various
combinations of shelling, spraying with 10% citric acid, and storage
treatments such as (1) the combination of shelling, 1 spraying, and
3 d of storage, (2) the combination of shelling, 2 sprayings, and 1 d
of storage, or (3) the combination of shelling and 3 sprayings. Adding a surface-sanitizing step to the conventional nut packing operation may enhance the microbiological safety of fresh nuts.
Acknowledgments
The article is a contribution of Virginia State Univ. Research Station
(Journal Article Series nr 245). This study was funded in part by the
Almond Board of California (Modesto, Calif., U.S.A.). Technical
support from Mrs. W. Westbrook is acknowledged.
Figure 6—Levels of Salmonella on almonds sampled at 6
stages (after inoculation, shelling, spraying, and storage
for 1, 3, or 7 d). After shelling, almonds were sprayed 1 to
3 times (A, B, and C) with 10% citric acid before rinsing,
air-drying, and storage.
URLs and E-mail addresses are active links at www.ift.org
Vol. 71, Nr. 1, 2006—JOURNAL OF FOOD SCIENCE
M19
M: Food Microbiology & Safety
References
[ABC] Almond Board of California. 2004. Food quality and safety: action plan
and pasteurization; frequently asked questions. Available from:
www.almondboard.com/Programs/content.cfm?ItemNumber = 890&snItemNumber = 450. Accessed on 2005 July 28.
Beuchat LR, Harris LJ, Ward TE, Kajs TM. 2001. Development of a proposed standard method for assessing the efficacy of fresh produce sanitizers. J Food Prot
64:1103–15.
Blankenship LC. 1981. Some characteristics of acid injury and recovery of Salmonella bareilly in a model system. J Food Prot 44:73–7.
Chan ES, Aramini J, Ciebin B, Middleton D, Ahmed R, Howes M, Brophy I, Mentis
I, Jamieson F, Rodgers F, Nazarowec-White M, Pichette SC, Farrar J, Gutierrez M,
Weis WJ, Lior L, Ellis A, Isaacs S. 2002. Natural or raw almonds and an outbreak
of a rare phage type of Salmonella enteritidis infection. Can Comm Dis Rep
28:97–9.
Danyluk MD, Uesugi AR, Harris LJ. 2005. Survival of Salmonella Enteritidis PT
30 on inoculated almonds after commercial fumigation with propylene oxide.
J Food Prot 68:1613-22.
Hyndman JB. 1963. Comparison of enterococci and coliform microorganisms in
commercially produced pecan nut meats. Appl Microbiol 11:268–72.
Isaacs S, Aramini J, Ciebin B, Farrar JA, Ahmed R, Middleton D, Chandran AU,
Harris LJ, Howes M, Chan E, Pichette AS, Campbell K, Gupta A, Lior LY, Pearce
M, Clarke C, Rodgers F, Jamieson F, Brophy I, Ellis A. 2005. An international
outbreak of salmonellosis associated with raw almonds contaminated with a
rare phage type of Salmonella Enteritidis. J Food Prot 68:191–8.
Isaacs S, Berisha V, Klein R, Johnson B, Hopkins J, Reporter R, Wilkin W, Bernazzani D, Fontana J, Gould E, Stobierski MG, Bonnema A, Jung MA, Madden J,
Vega R, Cook CR, Krouse DA, Tait JM, Lofy K. 2004. Outbreak of Salmonella
serotype Enteritidis infections associated with raw almonds—United States
and Canada, 2003-2004. Morbid Mortal Wkly Rep 53:484–7.
Kim K, Mustapha A. 2004. Effects of cetylpyridinium chloride, acidified sodium chlorite, and potassium sorbate on populations of Escherichia coli O157:H7, Listeria
monocytogenes, and Staphylococcus aureus on fresh beef. J Food Prot 67:310–5.
King AD, Miller MJ, Eldridge LC. 1970. Almond harvesting, processing, and microbial flora. Appl Microbiol 20:208–14.
Kokal D. 1969. Evaluation of a washing procedure in the examination of almonds
for Escherichia coli. Appl Microbiol 17:897–8.
Kokal D, Thorpe DW. 1969. Occurrence of Escherichia coli in almonds of nonpareil variety. Food Technol 23:227–32.
Ostrolenk M, Hunter AC. 1939. Bacteria of colon-aerogenes group on nut meats.
Food Res 4:453–60.
Pao S, Brown GE, Schneider KR. 1998. Challenge studies with selected pathogenic bacteria on freshly peeled Hamlin orange. J Food Sci 58:359–62.
Pao S, Davis CL. 2001. Comparing attachment, heat tolerance and alkali resistance of pathogenic and non-pathogenic bacterial cultures on orange surfaces. J Rapid Meth Automat Microbiol 9:271-278.
Pao S, Davis CL, Kelsey DF. 2000. Efficacy of alkaline washing for the decontamination of orange fruit surfaces inoculated with Escherichia coli. J Food Prot
63:961–4.
Pao S, Randolph SP, Westbrook EW, Shen H. 2004. Use of bacteriophages to control
Salmonella in experimentally contaminated sprout seeds. J Food Sci 69:M127–30.
[USFDA] U.S. Food and Drug Administration. 1998. Guidance for industry: reducing microbial food safety hazards for sprouting seeds. Rockville, Md. Available
from: www.foodsafety.gov/about dms/prodguid.html. Accessed on 2005 July 28.
[USEPA] U.S. Environmental Protection Agency. 1999. Guidance for use of foodgrade shell-egg sanitizers. Washington, D.C. Available from: www.epa.gov/
oppad001/gdnceggs.htm. Accessed on 2005 July 28.
Wu VCH, Fung DYC, Kang DH, Thompson LK. 2001. Evaluation of thin agar layer
method for recovery of acid-injured foodborne pathogens. J Food Prot 64:1067–
71.