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Ultrasonication Enhanced Low Concentration Electrolyzed Water Efficacy on Bacteria Inactivation and Shelf Life Extension on Lettuce

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Ultrasonication Enhanced Low Concentration Electrolyzed Water Efficacy on Bacteria Inactivation and Shelf Life Extension on Lettuce

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Abstract Effect of ultrasonication (40 kHz) to enhance low concentration electrolyzed water (LcEW) efficacy for microbial decontamination on lettuce leaves was investigated. Lettuce was separately treated with LcEW, ultrasonication, LcEW combined with ultrasonication, LcEW followed by ultrasonication, and ultrasonication followed by LcEW for 1, 3, and 5 min for each step at room temperature. The highest reduction (2.3 log CFU/g) in total bacteria count (TBC) was resulted from ultrasonication followed by LcEW. Subsequently, the effect of temperature was studied resulting in 2.6 and 3.18 log CFU/g reduction of TBC and Escherichia coli O157:H7 respectively, in 3 min ultrasonication followed by 3 min LcEW treatment at 40ºC. This optimum treatment also prevented lettuce from reaching 7.0 log CFU/g in TBC until the end of the 6 day storage at 10ºC. Therefore, this newly developed approach may result in improved microbiological safety and enhanced shelf life of produce.
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Food Sci. Biotechnol. 22(1): 131-136 (2013)
DOI 10.1007/s10068-013-0018-8
Ultrasonication Enhanced Low Concentration Electrolyzed Water
Efficacy on Bacteria Inactivation and Shelf Life Extension on Lettuce
Fereidoun Forghani, S. M. E. Rahman, Myoung-Su Park, Joong-Hyun Park, Jiyong Park, Kyung-Bin Song, and
Deog-Hwan Oh
Received: 20 June 2012 / Revised: 24 August 2012 / Accepted: 11 September 2012 / Published Online: 28 February 2013
© KoSFoST and Springer 2013
Abstract Effect of ultrasonication (40 kHz) to enhance
low concentration electrolyzed water (LcEW) efficacy for
microbial decontamination on lettuce leaves was investigated.
Lettuce was separately treated with LcEW, ultrasonication,
LcEW combined with ultrasonication, LcEW followed by
ultrasonication, and ultrasonication followed by LcEW for
1, 3, and 5 min for each step at room temperature. The
highest reduction (2.3 log CFU/g) in total bacteria count
(TBC) was resulted from ultrasonication followed by
LcEW. Subsequently, the effect of temperature was studied
resulting in 2.6 and 3.18 log CFU/g reduction of TBC and
Escherichia coli O157:H7 respectively, in 3 min ultra-
sonication followed by 3 min LcEW treatment at 40ºC.
This optimum treatment also prevented lettuce from reaching
7.0 log CFU/g in TBC until the end of the 6 day storage at
10ºC. Therefore, this newly developed approach may result
in improved microbiological safety and enhanced shelf life
of produce.
Keywords: ultrasonication, low concentration electrolyzed
water, bacterial population, shelf life, lettuce
Introduction
Fresh produce has continued to become more popular as a
convenient source of food in the last two decades (1).
Minimally processed vegetables (MPV) as a major group
of fresh produce have also gained consumer preference due
to the changes in lifestyle (2). This interest has substantially
risen over the last decade (3), resulting in the necessity to
develop new pretreatment technologies in food industry to
improve safety and extend shelf life. Foodborne illness
outbreaks linked to lettuce, radish sprout (4), watermelon
and cantaloupe (5), spinach (6), cucumber (7), and other
produce have been reported in the recent years. These
outbreaks showed that commercial operations relying on
wash treatments with antimicrobials as the main step to
reduce microbial populations on fresh produce may not be
enough to assure produce safety.
Recently, many sanitizing methods have been introduced
or studied for the purpose of food safety. Examples of
some prominent sanitizers include chlorine dioxide (8),
acidified sodium chlorite (ASC) (9), electrolyzed water
(EW) (10,11), warm water (12), and irradiation (13). Also
combination of these sanitizers with each other or other
methods to develop more efficient hurdles has always been
of great interest. The sanitizing effect of low concentration
(LcEW) is mainly based on the effective chlorine
compounds usually in the form of hypochlorous acid (HOCl),
having strong antimicrobial activity (14). Furthermore,
application of LcEW may reduce corrosion of equipment
surfaces and minimize human health and safety issues
from Cl2 off-gassing (15).
Although application of ultrasonication as an antimicrobial
agent has a long history (16) and it has been used in
industrial and medical fields (17-19) for decades, its use as
a sanitizing agent in food industry is more recent (20-22).
Fereidoun Forghani, S. M. E. Rahman, Myoung-Su Park, Joong-Hyun
Park, Deog-Hwan Oh ()
Department of Food Science and Biotechnology and Institute of
Bioscience and Biotechnology, Kangwon National University, Chuncheon,
Gangwon 200-701, Korea
Tel: +82-33-250-6457; Fax: +82-33-250-6457
E-mail: deoghwa@kangwon.ac.kr
Jiyong Park
Department of Biotechnology, Yonsei University, Seoul 120-749, Korea
Kyung-Bin Song
Department of Food Science and Technology, Chungnam National
University, Daejeon 305-764, Korea
RESEARCH ARTICLE
132 Forghani et al.
Ultrasonication has a bactericidal effect, caused by
intracellular cavitations that disrupt cellular structure and
function (23). Also it may enhance bacterial detachment
from surfaces due to micromechanical shocks to the bacterial
cells (8,24). It is broadly accepted that ultrasonication
alone, usually does not effectively inactivate bacteria on
food (25). However combined with other treatments it may
result in higher lethality (26,27).
Escherichia coli O157:H7 is a food-borne pathogen of
major public concern that has caused many outbreaks
especially related to the fresh produce (7,28). This pathogen
can be easily transferred to fresh produce form the environment
or organic fertilizers. Therefore, developing effective methods
for reducing or eliminating this pathogen is important for
the hazard analysis and critical control points (HACCP)
systems in the food industry.
There is a need to further examine the effectiveness of
ultrasonication, combined with other sanitizers for
decontamination of fresh produce. This study was therefore
undertaken to determine the effect of LcEW with or
without ultrasonication and also in 2 different orders of a 2-
step treatment on the reduction of total bacteria count
(TBC) and enhancement of the lettuce leaves shelf life.
Furthermore, to pre-evaluate the sanitization efficacy of the
novel 2-step procedure against pathogens, artificially E.
coli O157:H7 inoculated lettuce leaves were treated under
the optimal condition and reductions in bacterial population
were studied.
Materials and Methods
Fresh produce Fresh lettuce (Lactuca sativa var. capita)
samples were purchased from a local wholesale market in
Chuncheon, South Korea and transported to the laboratory.
Outer leaves, core, and leaves with visible damage were
discarded. Remaining fresh leaves were aseptically shredded
into 3× 3 cm pieces (10.0±0.3 g). These trimmed leaves
were used for subsequent analyses.
Preparation of low concentration electrolyzed water
(LcEW) The LcEW used in this study had a pH of 6.8-
7.4, an oxidation reduction potential (ORP) of 660-700 mV
and an available chlorine concentration (ACC) of 5-10 mg/
L. It was produced by electrolysis of a dilute NaCl solution
(0.9%) in a chamber without membrane using an electrolysis
device (model D-7; Dolki Co., Ltd., Wonju, Korea) at a
setting of 1.45 A and 3 V. The pH, ORP, and ACC of the
LcEW were measured immediately before sample treatment
with a dual-scale pH meter (Accumet model 15; Fisher
Scientific Co., Fair Lawn, NJ, USA) bearing pH and ORP
electrodes. The ACC was determined by a colorimetric
method using a digital chlorine test kit (RC-3F; Kasahara
Chemical Instruments Corp., Saitama, Japan). The detection
range was 0-300 mg/L.
Ultrasonication of fresh produce Ultrasonication was
performed using a bench-top ultrasonic cleaner (model
JAC-4020; Kodo Technical Research Co., Ltd., Hwaseong,
Korea) for 1 min at a fixed frequency of 40 kHz and
acoustic energy density (AED) of 100, 200, and 400 W/L
at room temperature (24 ± 2ºC) in distilled water (DW).
This step was necessary to choose the best AED based on
decontamination efficiency for the subsequent analyses in
combined experiments.
Inoculation of lettuce leaves To reduce the background
interference, before E. coli O157:H7 inoculation, trimmed
lettuce leaves (each of 3×3 cm and 10.0±0.3 g weight)
were placed on a sterile perforated tray and treated with
UV light (TUV 15W; Philips, Amsterdam, Netherlands) in
a UV cabinet (Entkeimungsschrank, 220 V; Ernst Schuttjun
Laborgerotebau, Gottingen, Germany) for 50 min (25 min
for each side). After UV treatment, the naturally existing
bacterial population was reduced to an undetectable level
(with 10 CFU/g detection limit) (29).
The E. coli O157:H7 strain B0259 (isolated from bovine
feces) was obtained from the Department of Food Science,
University of Georgia (Griffin, GA, USA). The stock
culture (100 µL) was transferred into 10 mL of tryptic soy
broth (TSB; BD, Sparks, MD, USA) and incubated at 35oC
for 24 h. Following incubation, the bacterial culture was
sedimented by centrifugation (3,000 ×g for 10 min at 4°C),
washed twice and resuspended in 10 mL of 0.1% buffered
peptone water (BPW, pH 7.3, BD) to obtain a final
concentration of 9 log CFU/mL. For inoculation, 100 µL of
bacterial suspension was inoculated on the surface of each
trimmed leaf in 20 locations by pipetting, resulting in
initial pathogen inoculum levels of approximately 7.0 log
CFU/g on lettuce leaves. The inoculated leaves were dried
in a laminar flow hood for 30 min at room temperature
(24±2oC) to allow for bacterial attachment. Finally, actual
starting concentrations were confirmed by plating serial
dilutions on the E. coli selective media, sorbitol MacConkey
(SMAC) agar (BD).
Treatment procedures Fresh and E. coli O157:H7
inoculated samples (each of 10±0.3 g) were divided into 5
different groups and control (no treatment) for treatment
procedures. All treatments were performed in 200 mL of
the appropriate solution. Samples in group 1 were only
dipped in LcEW. Group 2 samples were treated by
ultrasonication (using distilled water). For the 3rd group,
ultrasonication was performed in LcEW (Sonication+
LcEW). Samples of the 4th group were first dipped in
LcEW and then ultrasonication was undertaken immediately
LcEW and Ultrasonication Synergism 133
(LcEW-Sonication). Finally for group 5, ultrasonication
and LcEW dipping were performed respectively (Sonication-
LcEW). All treatments were performed at room temperature
(24± 2oC) for 1, 3, and 5 min for each step. The temperature
effect was studied by treatment of all groups in 40oC using
the best dipping time. A metal net was used to hold the
leaves in the solutions to make sure that all samples were
dipped completely during ultrasonication or treatments.
Shelf life study For the shelf life study, uninoculated
fresh samples from all 5 treatment groups and control
(without treatment) were packaged using Ziploc® vegetable
bags (about 2.5 microholes/cm2, density 1.75 with vapor
transmission 1.3) and stored at 10oC. Sampling was
conducted on day 0, 3, and 6 during storage followed by
bacterial enumeration procedure.
Bacterial enumeration All samples from treatment
procedures (fresh and E. coli O157:H7 inoculated) and
shelf life study were aseptically and immediately placed in
a stomacher bag (Nasco Whirl-Pak, Janesville, WI, USA)
containing 90 mL of BPW and homogenized for 2 min
using a Seward stomacher (400 Circulator; Seward,
London, UK). Following homogenization, 1 mL aliquots
of the samples were serially diluted in 9 mL of sterile BPW
and 100 µL of the appropriate dilutions were spread-plated
onto tryptic soy agar (TSA; BD) and SMAC agar for
enumeration of TBC and E. coli O157:H7 respectively. All
plates were incubated at 37oC for 24 h. Results were
expressed as log CFU/g.
Statistical analysis All analyses were conducted in
duplicates with 3 replicates of each experiment. Data were
expressed as the means±standard errors (SE). An analysis
of variance (ANOVA) was performed using SPSS 17.0
statistical package (SPSS Inc., Chicago, IL, USA). Tukey’s
multiple range tests were used to determine the significant
difference of mean values (p0.05).
Results and Discussion
Ultrasonication wave effect The changes in TBC by
ultrasonication wave effect are shown in Fig. 1. Using
ultrasonication with a frequency of 40 kHz and AED of
100, 200, and 400 W/L, our results showed the highest
reduction in the initial count (0.35 log CFU/g) compared to
the control (no treatment) in case of 400 W/L AED while
100 and 200 W/L AED did not make sensible changes.
Therefore, AED of 400 W/L was selected for the subsequent
analyses. This result was in comparison with the work of
Zhou et al. (17) suggesting that 400 and 500 W/L were
more efficient than 200 and 300 W/L AEDs. This might be
due to ultrasonication mechanism of action producing
micromechanical energy fields resulting in cell cavitation
and/or surface removal of bacterial cells (23). Therefore,
higher AED or longer treatment time might be necessary to
maximize the inactivation effect of ultrasonication (30).
The bacterial reduction values resulted from ultrasonication
were in agreement with other reports suggesting that
ultrasonication alone, usually does not effectively inactivate
bacteria on food (25) and different from the work of
Ajlouni et al. (2) who reported a 0.98 log CFU/g reduction
following ultrasonication with a frequency of 40 kHz.
Effect of treatments and dipping time on the TBC of
lettuce Effects of different treatments and dipping times
(1, 3, and 5 min) on the reduction of TBC are shown in
Fig. 2. The bacterial reductions resulting from different
Fig. 1. Effect of different ultrasound acoustic energy densities
on the reduction of total bacteria counts. Data are shown as
means of bacterial population±SD.
Fig. 2. Effect of different treatments and dipping times (1, 3,
and 5 min) on the reduction of TBC. Data are shown as means
of log reduction±SD; Bars labeled with different lower case letters
in the same treatment and upper case letters in the betwee
n
treatment groups indicate a significant difference (p0.05);
LcEW+Sonication (LcEW combined with sonication), LcEW-
Sonication (LcEW followed by sonication), Sonication-LcE
W
(sonication followed by LcEW)
134 Forghani et al.
treatments at room temperature (24± 2oC) ranged from 0.3
(ultrasonication alone for 1 min) to 2.25 log CFU/g in case
of 3 min ultrasonication followed by 3 min LcEW treatment.
Although, ultrasonication alone did not effectively inactivate
bacteria, it promoted bacterial reduction in all treatments
and all time periods. Huang et al. (8) and Seymour et al.
(31) also reported that application of ultrasonication as an
extra hurdle step would result in the enhanced bactericidal
effect of the sanitizers in foods. This might be due to the
ultrasound mechanism of action, creating local regions of
high pressure and temperature, damaging the bacterial cell
wall, resulting in higher uptake of LcEW (25) which would
consequently result in maximum cellular damage (32). Also
the micromechanical shocks created in the local regions of
high pressure and temperature may physically remove a
number of cells and make the surface attachment of some
other cells weaker (24). Consequently, these cells can be
more accessible to free chlorine. As a result, the 2-step
procedure Sonication-LcEW would have stronger bactericidal
effect compared to Sonication+LcEW and LcEW-Sonication.
Bacterial reduction counts showed significant difference
(p0.05) compared to the control (5.8 log CFU/g, without
treatment) regardless of dipping time. The results showed
significant difference (p0.05) between 3 and 5 min dipping
time with 1 min in all treatment groups. There was either
no significant difference (p0.05) between 3 and 5 min
dipping time or 3 min showed dominance. Ding et al. (33)
also reported 3 min as the best dipping time while using
LcEW alone as sanitizer resulting in a reduction of 1.08 log
CFU/g at room temperature (23 ± 2oC). Therefore 3 min
dipping time was applied for the subsequent analyses. This
might be due to the loosening but not completely removing
some remaining cells on the produce surface with longer
exposure time (5 min), resulting in reattachment of colony
forming units in more locations and higher cell counts.
Effect of dipping temperature on the reduction of TBC
To determine the effect of dipping temperature on the
reduction of TBC, all treatments were repeated with 3 min
dipping time at 40oC. This mild heat temperature was
selected according to the work of Ajlouni et al. (2)
suggesting that washing in 50oC water might have negative
effects on the leaves tissue while lower temperatures might
not result in a significant decontamination.
Effect of dipping temperature on the reduction of TBC
is shown in Fig. 3. The highest TBC reduction value (2.6
log CFU/g) was resulted from ultrasonication followed by
LcEW (Sonication-LcEW) at 40oC showing a significant
(p0.05) difference compared to the control (initial count
of 5.81 log CFU/g) and the same treatment at 25oC. These
results were in comparison with the works of Ding et al.
(33) and Rahman et al. (34) reporting that LcEW antimicrobial
activity was enhanced as temperature increased. This might
be due to the increased physical removal of sediments and
facilitated bacterial detachment as the temperature increases
(35).
Effect of different treatments on the removal of E. coli
O157:H7 from lettuce leaves The mean reduction of E.
coli O157:H7 population (log CFU/g) by different treatment
groups under optimal condition is shown in Fig. 4. Initial
bacterial count for E. coli O157:H7 inoculated samples
was 7.03 log CFU/g in control (without treatment).
Different treatments with LcEW, ultrasonication, LcEW+
Sonication, LcEW-Sonication, and Sonication-LcEW at
40ºC for 3 min showed 4.71, 6.01, 4.59, 4.48, and 3.85 log
Fig. 3. Effect of temperature on the reduction of TBC. Data are
shown as means of log reduction±SD. Bars labeled with differen
t
lower case letters in the same treatment and different upper case
letters between treatment groups indicate a significant difference
(p0.05) between different temperatures. LcEW+Sonicatio
n
(LcEW combined with sonication), LcEW-Sonication (LcE
W
followed by sonication), Sonication-LcEW (sonication followe
d
by LcEW)
Fig. 4. Effect of different treatments on removal of E. col
i
O157:H7. Data are shown as means of log reduction±SD. Bars
labeled with different letters indicate a significant difference
(p0.05). LcEW+Sonication (LcEW combined with sonication),
LcEW-Sonication (LcEW followed by sonication), Sonication-
LcEW (sonication followed by LcEW)
LcEW and Ultrasonication Synergism 135
CFU/g of bacterial population, respectively. These results
were all significantly different from the control (p0.05).
However, ultrasonication, resulting in a 1.02 log CFU/g
reduction was significantly less effective than the other
treatment groups. LcEW, LcEW+Sonication, and LcEW-
Sonication showing 2.32, 2.47, and 2.55 log CFU/g
reduction, respectively, were not significantly different from
each other while Sonication-LcEW with a reduction of
3.18 log CFU/g was significantly more effective than the
other 3 combined treatment groups (p0.05). This might
be due to the synergistic effect of ultrasonication combined
with temperature prior to LcEW treatment.
Effect of treatment temperature on enhancement of
lettuce shelf life during storage at 10oCThe changes in
microbial population during the 6 day storage are shown in
Table 1. The end of shelf life was considered to occur when
TBC reached 7-8 log CFU/g, known as the maximum
acceptable level for TBC on fresh produce (36,37). Results
of the present study revealed that except for 3 min
ultrasonication followed by 3 min LcEW (Sonication-
LcEW) at 40oC other treatment groups were unable to
prevent microbial counts to reach unacceptable levels ( 7-
8 log CFU/g) until the end of the 6 day storage at 10oC. In
case of Sonication-LcEW (3 min for each step) at 40oC as
the optimum treatment, a final reduction of 2.59 log CFU/
g was obtained compared to the control. This reduction
value was significantly different (p0.05) from the other 2-
step treatment (LcEW-Sonication) and also the combined
treatment (Sonication+LcEW) both in 25 and 40oC. Thus
3 min ultrasonication followed by 3 min LcEW dipping at
40oC was determined as the optimum treatment among all.
Although there have been previous studies on the combined
application of sanitizers and ultrasonication (2,8,17,27) and
2-step sanitizing procedures (38), no study has been
undertaken to investigate the sanitizing effect of either
combined or 2-step treatment of fresh produce with LcEW
and ultrasonication to the best of authors knowledge.
In conclusion, Sonication-LcEW at 40oC can effectively
remove bacteria from lettuce leaves resulting in improved
safety and extended shelf life. Considering the irregular
surface of lettuce leaves providing some protection to the
bacterial cells, it is very likely that the application of this 2-
step procedure on fruits and vegetables with smoother surfaces
can result in similar or higher levels of decontamination.
Furthermore, LcEW is cheap and environmentally-friendly
due to the lack of Cl2 off-gassing resulting in human health
hazard. Thus, Sonication-LcEW at 40oC can be a useful
method for the disinfection of fresh produce.
It is recommended that effectiveness of LcEW
combined with ultrasonication at higher frequencies and
other treatments should be further investigated. Our results
revealed that thus performing ultrasonication alone, does
not effectively reduce the bacterial population on lettuce, it
can significantly enhance the sanitizing effect of LcEW, if
performed as a pre-step to LcEW dipping. Therefore,
future investigations can further study this 2-step procedure
using LcEW with different properties (ORP, ACC) or
combined with different sanitizers. Also, further studies
should be carried out to simulate typical commercial and
applied conditions in others types of fruits, vegetables, and
microbial pathogens.
Acknowledgments This work was supported by a grant
from The Korea Institute of Planning and Evaluation for
Technology of Food, Agriculture, Forestry and Fisheries
IPET project (310013-03-1-WT121), Korea.
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... However, potatoes washed at 60 • C with US treatment have shown color changes [29]. Other studies have reported that dipping in electrolyzed water for 3 min has the best sanitizing effect [31][32][33]. The present study also showed that washing for 3 min with SAEW + US at 10 times the sample volume at 25 • C was the most effective treatment condition to reduce the population of EPEC in fresh-cut carrot. ...
... These results showed that UV-C is an effective non-chemical treatment to maintain the qualities of fruits and vegetables. Previous studies have reported the survival of foodborne pathogens in vegetables after different treatments [19,32]. Total bacterium counts on lettuce and button mushroom applied combined treatment with SAEW and US are lower than those without treatments after 6-8 days of storage at 4 and 10 • C [19,32]. ...
... Previous studies have reported the survival of foodborne pathogens in vegetables after different treatments [19,32]. Total bacterium counts on lettuce and button mushroom applied combined treatment with SAEW and US are lower than those without treatments after 6-8 days of storage at 4 and 10 • C [19,32]. Jiang et al. [28] have also studied the reduction effect of combined treatment with SAEW and UV-LED on Salmonella Typhimurium and E. coli O157:H7 in coriander after 6 days of storage at 4 • C. ...
Article
Full-text available
We investigated the combined effect of using slightly acidic electrolyzed water (SAEW), ultrasounds (US), and ultraviolet-C light-emitting diodes (UV-C LED; 275 nm) for decreasing pathogenic Escherichia coli and Staphylococcus aureus (SEA) in fresh-cut vegetables, including carrots, celery, paprika, and cabbage. Survival of pathogenic E. coli and SEA and quality properties of fresh-cut vegetables at 5 and 15 °C for 7 days were also investigated. When combined treatment (SAEW + US + UV-C LED) was applied to fresh-cut vegetables for 3 min, its microbial reduction effect was significantly higher (0.97~2.17 log CFU/g) than a single treatment (p < 0.05). Overall, the reduction effect was more significant for SEA than for pathogenic E. coli. At 5 °C, SAEW + US and SAEW + US + UV-C LED treatments reduced populations of pathogenic E. coli and SEA in all vegetables. At 15 °C, SAEW + US + UV-C LED treatment inhibited the growth of both pathogens in carrot and celery and extended the shelf life of fresh-cut vegetables by preventing color changes in all vegetables. Although the effects of treatments varied depending on the characteristics of the vegetables and pathogens, UV-C LED can be suggested as a new hurdle technology in fresh-cut vegetable industry.
... PAW can be combined with other treatments to increase antimicrobial efficacy, taking a hurdle technology approach. The antimicrobial properties of ultrasound, alone or in combination with other treatments, have been investigated in foods previously (Turantas et al., 2015), including on fresh produce and seeds (Chiu and Sung, 2014;do Rosário et al., 2017;Forghani et al., 2013;Kim et al., 2006;Sango et al., 2014;São José et al., 2014). Most of the effects of ultrasound are directly related to cavitation occurring in the liquid, that is the growth of vapour bubbles which violently collapse, generating locally high pressures and temperatures (Tiwari and Mason, 2012). ...
... Ultrasound treatments have been applied, either as single treatments or in combination with other approaches for the disinfection of fresh produce crops and sprouted seeds (Chiu and Sung, 2014;do Rosário et al., 2017;Forghani et al., 2013;Kim et al., 2006;Sango et al., 2014;São José et al., 2014). In this work, the combined activity of PAW and US treatments for the disinfection of mung beans inoculated with S. Montevideo was investigated. ...
Article
Microbial contamination of fresh produce is a major public health concern, with the number of associated disease outbreaks increasing in recent years. The consumption of sprouted beans and seeds is of particular concern, as these foodstuffs are generally consumed raw, and are produced in conditions favourable for the growth of zoonotic pathogens, if present in seeds prior to sprouting or in irrigation water. This work aimed to evaluate the activity of plasma activated water (PAW) as a disinfecting agent for alfalfa (Medicago sativa) and mung bean (Vigna radiata) seeds, during seed soaking. Each seed type was inoculated with Escherichia coli O157, E. coli O104, Listeria monocytogenes or Salmonella Montevideo, and treated with PAW for different times. A combination of PAW and ultrasound treatment was also evaluated. The germination and growth rate of both seeds were assessed after PAW treatments. PAW was demonstrated to have disinfecting ability on sprouted seeds, with reductions of up to Log10 1.67 cfu/g in alfalfa seeds inoculated with E. coli O104, and a reduction of Log10 1.76 cfu/g for mung bean seeds inoculated with E. coli O157 observed. The germination and growth rate of alfalfa and mung bean sprouts were not affected by the PAW treatments. The combination of a PAW treatment and ultrasound resulted in increased antimicrobial activity, with a reduction of Log10 3.48 cfu/g of S. Montevideo in mung bean seeds observed. These results demonstrate the potential for PAW to be used for the inactivation of pathogenic microorganisms which may be present on sprouted seeds and beans, thereby providing greater assurance of produce safety.
... The US has an antimicrobial effect on Staphylococcus aureus [6], Pseudomonas fluorescens [7], Listeria monocytogenes and other pathogens [8], which was mainly due to the destruction of cell structure and integrity by ultrasonic cavitation leading to microbial apoptosis [9,10]. The recent researches showed that ultrasound in combination with SAEW and other physical processing methods could reduce the number of bacteria efficiently [11][12][13]. ...
Article
Full-text available
A novel technique for sea bass (Lateolabrax Japonicus) fillets by combining ultrasound (US) and slightly acidic electrolyzed water (SAEW) to inactivate bacteria and maintain quality was developed. Samples were treated with distilled water (DW), US, SAEW and ultrasound combined with slightly acidic electrolyzed water (US+SAEW) for 10 min, respectively. The results suggested that US+SAEW treatment could retard the increase of total viable counts (TVC), Pseudomonas bacteria counts and H2S-producing bacteria counts, which also inhibit the rise of total volatile basis nitrogen (TVB-N), thiobarbituric acid (TBA), pH and K value. In addition, compared with SAEW or US treatment alone, US+SAEW treatment had distinctly effects on inhibiting protein degradation and maintaining better sensory scores. Compared with DW group, the shelf life of sea bass treated with US+SAEW was increased for another 4 days. It indicated that the combined treatment of US and SAEW could be used to the preservation of sea bass.
... In addition, the ultrasound could make better dispersion of HClO in the aqueous media, which was probably caused by localised heating and pressure (Piyasena, Mohareb, & McKellar, 2003). In another report, when the ultrasound was followed by NEW (5e10 mg/L FAC), the microorganism reduction on the lettuce increased from 2.32 to 3.18 log CFU/g compared to NEW individually (Forghani et al., 2013). In this current research, when the combination method was applied for sanitising stainless steel coupons, it not only shortened the bactericidal reaction time but also improved the sanitising effect. ...
Article
The sanitising effect of low concentration neutralised electrolysed water (LCNEW, pH: 7.0, free available chlorine (FAC): 4 mg/L) combined with ultrasound (37 kHz, 80 W) on food contact surface was evaluated. Stainless steel coupon was chosen as attachment surface for Escherichia coli ATCC 25922, Pichia pastoris GS115 and Aureobasidium pullulans 2012, representing bacteria, yeast and mold, respectively. The results showed that although LCNEW itself could effectively reduce survival population of E. coli ATCC 25922, P. pastoris GS115 and low concentration A. pullulans 2012 in planktonic status, LCNEW combined with ultrasound showed more sanitising efficacy for air-dried cells on coupons, with swift drops: 2.2 and 3.1 log CFU/coupon reductions within 0.2 min for E. coli ATCC 25922 and P. pastoris GS115, respectively and 1.0 log CFU/coupon reductions within 0.1 min for A. pullulans 2012. Air-dried cells after treatment were studied by atomic force microscopy (AFM)/optical microscopy (OM) and protein leakage analyses further. All three strains showed visible cell damage after LCNEW and LCNEW combined with ultrasound treatment and 1.41 and 1.73 mg/mL of protein leakage were observed for E. coli ATCC 25922 and P. pastoris GS115, respectively after 3 min combination treatment, while 6.22 mg/mL of protein leakage for A. pullulans 2012 after 2 min combination treatment. For biofilms, LCNEW combined with ultrasound also significantly reduced the survival cells both on coupons and in suspension for all three strains. The results suggest that LCNEW combined with ultrasound is a promising approach to sanitise food equipment.
... The sanitising action of acidic EW has been attributed to the high oxidation-reduction potential and the oxidative action of hypochlorous acid (Ding et al., 2015;Zhao, Zhang, & Yang, 2017). For this reason, EW is used as an alternative means to improve the shelf life and safety of food (Forghani et al., 2013). ...
Article
Electrolysed water (EW) is an activated liquid with a high oxidation-reduction potential. EW causes oxidative damage to pathogenic microorganisms and as a result, may have utility in the food industry. The molecular mechanism of EW's action is not understood. In this study, we exposed Escherichia coli ATCC 25922 to a sub-lethal concentration of EW and examined structural and metabolic changes. Atomic force microscopy revealed that EW caused damage to E. coli membranes. To understand the metabolic responses to EW perturbations in of E. coli, multivariate data analysis of NMR spectroscopy demonstrated that EW significantly influenced the metabolic state. This included reducing nucleotide and amino acid biosynthesis, suppressing energy-associated metabolism, altering osmotic adjustment, and promoting fatty acid metabolism. The results enrich our understanding of E. coli metabolic changes caused by EW perturbation and support the effectiveness of the NMR metabolomics as a valuable tool to analyse and evaluate such a complex biological system.
... log CFU/g due to the LcEW treatment at 70°C. This is in agreement with a report (Forghani et al., 2013); LcEW demonstrates as a good potential sanitizer to improve microbiological safety. ...
Article
In the present study, the synergistic disinfection efficacy of low concentration electrolyzed water (LcEW) (free available chlorine, 4mg/L) combined with brief heat enhancement was evaluated and the bactericidal mechanism was investigated by atomic force microscopy (AFM). The inactivation kinetics of Escherichia coli O157:H7 and Salmonella Typhimurium on organic carrot were fitted with Weibull model to evaluate the synergistic effects. LcEW is effective at inactivating E. coli O157:H7 and S. Typhimurium on organic carrots, and the efficacy is dependent on the temperature. The combined treatment with LcEW at 80°C resulted in decimal reductiontime(TR)of7.42and3.27sforE.coliO157:H7andS.Typhimurium,respectively.Thereactiveoxygen species generated from LcEW were responsible for the microbial inactivation. In addition, AFM observation of E. coli O157:H7 and S. Typhimurium revealed morphological alterations in the bacterial cell structure, which illustrated the damage of cell membrane injury and intracellular component leakage. Quality attributes of carrot treated with LcEW and short-time heating (70°C, 1min) were not significantly different from controls. Compared to the control group, the combined treatment exhibited significantly (P < 0.05) greater inhibition of naturally occurring microbiota on organic carrots during storage at 4°C. Consequently, the application of LcEW combined with short-time heat improved safety of organic carrot, without negatively affecting the sensory properties, which can be explored by the organic industry.
Article
Fruits and vegetables deteriorate mostly due to microbial and enzymatic activity during postharvest storage. The objective of the work was to see if electrolyzed water and ultrasound can be applied combinedly in the industry to extend the shelf life of harvested fruits and vegetables. Ultrasound is a novel postharvest treatment method that has the potential to inactivate enzymes and microbes. Pectinmethylesterase, polygalacturonase, peroxidase, polyphenoloxidase, and lipoxygenase are the enzymes that are most commonly deactivated by ultrasound in fruits and vegetables. On the contrary, electrolyzed water is a potential antibacterial agent for fresh fruits and vegetables. Electrolyzed water treatment has some limitations in terms of microbial load reduction, which can be solved using sonication. This article deeply looked into the principles, advantages, disadvantages, and mechanism of action of both techniques. Novelty impact statement: Individual and synergistic effects on shelf life extension of fruits and vegetables were reviewed. In addition, the inactivation mechanisms of microorganisms and enzymes of fruits and vegetables have been explained.
Article
Full-text available
Fruits and vegetables deteriorate mostly due to microbial and enzymatic activity during postharvest storage. The objective of the work was to see if electrolyzed water and ultrasound can be applied combinedly in the industry to extend the shelf life of harvested fruits and vegetables. Ultrasound is a novel postharvest treatment method that has the potential to inactivate enzymes and microbes. Pectinmethylesterase, polygalacturonase, peroxidase, polyphenoloxidase, and lipoxygenase are the enzymes that are most commonly deactivated by ultrasound in fruits and vegetables. On the other hand, electrolyzed water is a potential antibacterial agent for fresh fruits and vegetables. Electrolyzed water treatment has some limitations in terms of microbial load reduction, which can be solved using sonication. This article deeply looked into the principles, advantages, disadvantages, and mechanism of action of both techniques.
Article
The aim of this study was to investigate the effect of slightly acidic electrolyzed water (SAEW) and ultrasound (US) combination on the inactivation of Vibrio parahaemolyticus in vitro and in fish samples. The bacterial log reductions caused by the US and SAEW treatment for 15 min were 0.99 and 2.63 log CFU/mL in vitro, respectively, while SAEW‐US combination achieved a 3.10 log reduction. MTT assay and protein leakage test showed that SAEW‐US combination impaired cell viability and damaged cell membrane. In addition, compared to the US or SAEW treatment, SAEW‐US combination induced higher reactive oxygen species (ROS) production, more apoptotic cells, and severer damage in bacterial cells. In spiked sliced tilapia samples, SAEW‐US combination caused about 2 log reduction of inoculated pathogen. In conclusion, these findings demonstrate that SAEW‐US combination could be potentially developed as an alternative strategy to control Vibrio parahaemolyticus contamination in aquatic foods.
Chapter
Food safety is a burning issue in the present world. Safe sanitizers are obligatory for maintaining quality of food and increasing the shelf life of fresh produce and other agricultural products. Food industries have been using electrolyzed water (EW) as a unique sanitizer for the past two decades which has excellent results to reduce the microbial count. Hurdle technology, e.g., combination of EW with ultrasonication, short-term heat treatment, organic acids, and salts, found to have more effective results in reducing microorganisms which overcame the little shortcomings with EW like corrosiveness and maintained organoleptic qualities. In this chapter, we are going to discuss the production of EW and its combination with ultrasonication, short-term heat treatment, organic acids, and salts to produce a novel sanitizer.
Article
Full-text available
Microbial control of postharvest diseases has been extensively studied and appears to be a viable technology. Food safety must be ensured at each postharvest processing step, including handling, washing of raw materials, cleaning of utensils and pipelines, and packaging. Several commercial products are available for this purpose. The time is ripe for developing new techniques and technologies. The use of electrolyzed water (EW) is the product of a new concept developed in Japan, which is now gaining popularity in other countries. Little is known about the principle behind its sterilizing e#ect, but it has been shown to have significant bactericidal and virucidal and moderate fungicidal properties. Some studies have been carried out in Japan, China, and the USA on the pre-and postharvest application of EW in the field of food processing. EW may be produced using common salt and an apparatus connected to a power source. As the size of the machine is quite small, the water can be manufactured on-site. Studies have been carried out on the use of EW as a sanitizer for fruits, utensils, and cutting boards. It can also be used as a fungicide during postharvest processing of fruits and vegetables, and as a sanitizer for washing the carcasses of meat and poultry. It is cost-e#ective and environment-friendly. The use of EW is an emerging technology with considerable potential.
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Preliminary studies indicate that ultrasonic excitation may allow nondestructive evaluation of the quality of selected fruits and vegetables. Ultrasonic surface wave velocity and attenuation in the peel of whole melon and avocado fruits were tested to determine the ripening process. Experimental setup for nondestructive, whole-fruit testing included an ultrasonic head with transmitter, receiver, and special arrangement to allow inclined transmission and reception of ultrasonic signals. A summary of previous experiments related to ultrasonic testing of fruit tissue and fruit halves is also presented.
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The potential use of ultrasonics to reduce bacteria on poultry carcasses is discussed. It is shown that ultrasound in combination with chlorine is more effective in reducing bacterial counts on poultry than either ultrasound of chlorine alone. Sonication of Salmonella-inoculated broiler skin with and without chlorination revealed a considerable difference in log10 count. A study showed that salmonellae attached to broiler skin were reduced by 1-1.5 log10 by sonication in peptone at 20 kHz for 30 min; by <1 log10 by chlorine alone; but by 2.5-4 log10 by sonicating skin in a chlorine solution with 0.5 ppm free residual.
Article
Cut lettuce dip-inoculated with Escherichia coli O157:H7 and Salmonella was treated with alkaline electrolyzed water (AlEW) at 20°C for 5min, and subsequently washed with acidic electrolyzed water (AcEW) at 20°C for 5min. Pre-treatment with AlEW resulted in an approximate 1.8log10cfu/g reduction of microbial populations, which was significantly (p⩽0.05) greater than microbial reductions resulting from other pre-treatment solutions, including distilled water and AcEW. Repeated AcEW treatment did not show a significant bacterial reduction. Mildly heated (50°C) sanitizers were compared with normal (20°C) or chilled (4°C) sanitizers for their bactericidal effect. Mildly heated AcEW and chlorinated water (200ppm free available chlorine) with a treatment period of 1 or 5min produced equal reductions of pathogenic bacteria of 3log10 and 4log10cfu/g, respectively. The procedure of treating with mildly heated AlEW for 5min, and subsequent washing with chilled (4°C) AcEW for period of 1 or 5min resulted in 3–4log10cfu/g reductions of both the pathogenic bacterial counts on lettuce. Extending the mild heat pre-treatment time increased the bactericidal effect more than that observed from the subsequent washing time with chilled AcEW. The appearance of the mildly heated lettuce was not deteriorated after the treatment. In this study, we have illustrated the efficacious application of AlEW as a pre-wash agent, and the effective combined use of AlEW and AcEW.
Article
The ability of Escherichia coli O157: H7 to survive and grow on cubes of cantaloupe and watermelon and on the external rind surface of these fruits was investigated. Populations of the pathogen increased on cubes stored at 25°C but remained constant at 5°C over a 34-h storage period. Growth was observed on the rind of melons stored under high relative humidity at 25°C for 14 to 22 days. The pathogen rapidly died on the rind surface of melons stored at 5°C. Copyright ©, International Association of Milk, Food and Environmental Sanitarians.
Article
Pre-chill broiler drumsticks were exposed to ultrasonic energy in water at 25 and 40°C for 15 and 30 min to study the effect on skin microbial counts. Aerobic plate counts (APC) after 0, 7, and 14 days at 4°C indicated no significant effects (p>0.05) due to ultrasonication. In another experiment, post-chill broiler drumsticks were treated with ultrasonic energy in 1% lactic acid at pH 2 and 4 for 0.5, 2, and 3.5 min. After 0 and 10 days at 4°C there was no significant effect (p>0.05) of ultrasonication on APC.