evaluation of ozone efficacy on the reduction of microbial population of fresh cut lettuce (lactuca...

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Evaluation of ozone efcacy on the reduction of microbial population of fresh cutlettuce (Lactuca sativa) and green bell pepper (Capsicum annuum)

A. Alexopoulos a,*, S. Plessas a, S. Ceciu b, V. Lazar c, I. Mantzourani a, C. Voidarou a, E. Stavropoulou a,E. Bezirtzoglou a

a Democritus University of Thrace, Faculty of Agricultural Development, Laboratory of Microbiology, Biotechnology & Hygiene, Pandazidou 193, GR68200 Orestiada, Greeceb NIRDMI Cantacuzino, Splaiul Independentei 103, Sector 5, Bucuresti 050096, Romaniac Faculty of Biology, University of Bucharest, Aleea Portocalilor 1-3, Sect. 6, Bucharest 060101, Romania

a r t i c l e i n f o

Article history:

Received 2 December 2011Received in revised form9 September 2012Accepted 16 September 2012

Keywords:

Ozone sanitationLettuceBell pepperColiformYeasts/moldsWeibull model

a b s t r a c t

Raw vegetables are usually contaminated by a variety of microorganisms. Post-harvest microora differsconsiderably, reecting environmental and handling conditions and might compromise the safety of theproduct and the consumers health.

Dipping or rinsing of vegetables in bleach solution is a common practice employed by the retailers andcatering companies in order to minimize the initial bacterial load on the surface of vegetables. Rinsing ordipping vegetables in water saturated with ozone could be an alternative environmental friendly andsafer process since no harmful by-products or residues are formed.

Lettuce (Lactuca sativa) and bell peppers (Capsicum annuum) dipped in chlorinated water (20 ppm)resulted in 1 log decrease of the total microbial count in the rst 15 min. Immersing of vegetables inwater pre-saturated with ozone (0.5 mg/L) did not make any difference because the total microbial countdecreased approximately 0.5 log for the same time. Sanitation treatments were most effective whenvegetables were dipped in continuously ozonated (0.5 mg/L) water, leading at about 2 log of microbialload decrease in the rst 15 min and 3.5 log after 30 min of exposure. The best results were achieved in

the case of bell pepper, as its smooth uniform surface allows higher ozone effectiveness. Bacteriareduction kinetics in continuous ozonation trials were tted satisfactorily by a Weibull-based modelallowing a better optimization of the process.

2012 Elsevier Ltd. All rights reserved.

1. Introduction

Fresh-cut vegetables are important components of the humandiet and there has been an increasing demand for their consump-tion in recent years. However, products such as fresh-cut or mini-mally processed vegetables, have been associated with severe food-borne disease outbreaks caused by bacteria contamination during

the various farming or post-harvest stages (Aytac, Ben, Cengiz, &Mercanoglu Taban, 2010; McEvoy, Luo, Conway, Zhou, & Feng,2009). Despite the technological progress and the establishing ofgood agricultural and manufacturing practices, it seems that theincidence of these outbreaks has increased, according to someinvestigators, even beyond what can be explained by the demandalone (Mercanoglu Taban & Halkman, 2011). Causing agentsare often highly virulent bacterial strains with a cross-border

geographical dispersion as shown in the case of the last year sEuropean outbreak of Shiga toxin producing Escherichia coliO104:H4 borne by sprouted seeds (Bilinski et al., 2012). In order toprovide safe vegetables of high quality and to face consumersdemands, food processors always seek for sustainable, yet efcientsanitation techniques (Arts, Gmez, Aguayo, Escalona, & Arts-Hernndez, 2008; Selma, Allende, Lpez-Glvez, Conesa, & Gil,

2008).Ozone disinfection technology gains more and more the atten-

tion of food industry during the last years ( Sopher, Battles, &Johnson, 2009) due to its distinct antimicrobial properties activeagainst bacteria, fungi, viruses and bacterial and fungal spores (Xu,1999). Ozone has been recognized as a Generally Safe (GRAS)substance (Khadre, Yousef, & Kim, 2001; Kim, Yousef, & Chism,1999) and was also approved as a direct food additive for thetreatment, storage and processing in foods (Rice, 1999). Suchapplications are the depuration of shellsh (Schneider, Steslow,Sierra, Rodrick, & Noss, 1991), the disinfection of poultry carcassesin the poultry industry (Chang & Sheldon, 1989), the sanitation of

* Corresponding author. Tel./fax: 30 2552041169.E-mail addresses:[email protected],[email protected](A. Alexopoulos).

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Food Control

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0956-7135/$ e see front matter 2012 Elsevier Ltd. All rights reserved.

http://dx.doi.org/10.1016/j.foodcont.2012.09.018

Food Control 30 (2013) 491e496
mailto:[email protected]:[email protected]:[email protected]://www.sciencedirect.com/science/journal/09567135http://www.elsevier.com/locate/foodconthttp://dx.doi.org/10.1016/j.foodcont.2012.09.018http://dx.doi.org/10.1016/j.foodcont.2012.09.018http://dx.doi.org/10.1016/j.foodcont.2012.09.018http://dx.doi.org/10.1016/j.foodcont.2012.09.018http://dx.doi.org/10.1016/j.foodcont.2012.09.018http://dx.doi.org/10.1016/j.foodcont.2012.09.018http://www.elsevier.com/locate/foodconthttp://www.sciencedirect.com/science/journal/09567135mailto:[email protected]:[email protected]


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food plant equipment and reuse of waste water (Rice, Farquhar, &Bollyky, 1982;Seydim, Bever, & Greene, 2004). Particular applica-tions of ozone on the sanitation of fruits and fresh-cut or minimallyprocessed vegetables have also reported (Arts et al., 2008;lmez& Kretzschmar, 2009;Selma et al., 2008;Seydim et al., 2004). Aneffective inactivation of microorganisms in shredded lettuce andpeppers exposed to various forms of ozone was reported byKimet al. (1999)and Han, Floros, Linton, Nielsen, and Nelson (2002).Besides sanitation, ozone has been used in the shelf lifeextension ofpacked vegetables as broccoli and seedless cucumbers (Skog & Chu,2001) and mushrooms (Esciche, Serra, Gomez, & Galotto, 2001).Some arguments on the use of ozone in working places and itseffects on the equipment and on the plant tissue have beenreviewed bylmez and Kretzschmar (2009).

Fresh vegetables in chain fast-food premises and cateringcompanies are commonly treated with tap water before theirconsumption (Bott,1991) and in many occasions with disinfectants,such as chlorine in the form of sodium hypochlorite (Graham,1997). However ozonation is considered a safer method becausein contrast to chlorination, it does not cause the formation ofcarcinogenic trihalomethanes (Fawell, 2000) and may not alterconsiderably the sensorial properties of the commodity (lmez &

Akbas, 2009). Another signicant advantage of ozone againstchlorine is the fact that ozone does not leave any chemical residuesand thus it has a minor environmental impact after the treatmentor disposal of washing wastes (lmez & Kretzschmar, 2009).

In terms of bacteria inactivation, ozone acts through oxidationand destruction of cell walls and cytoplasmic membranes andnally on their genetic material. If the bacterial DNA is the naltarget of ozone then bacteria will be unable to develop ozoneresistance which is also another advantage (Cullen et al., 2010;Naito & Takahara, 2006). Additionally, ozone has elevated diffusioncapabilities that enables its rapid and readily diffuse through bio-logical cell membranes. Therefore, differences in the membranestructure of various microorganisms could explain their inherentsensitivity since bacteria are more sensitive than yeasts and fungi

and Gram-positive bacteria are more sensitive than Gram-negative(Cullen et al., 2010).

Besides the several studies on the ozone efciency at microbes,scarce information is available on modeling the kinetic behavior offood contaminants. It is desirable to design and optimize the ozonesanitation of fresh-cut vegetables by using kinetic models that canbe evaluated quantitatively in order to improve the process design(Alexandre, Brandao, & Silva, 2011). In ozone bacterial inactivationkinetics the rapid reactivity between ozone and microorganismsalong with other environmental factors, as the presence of organicmaterial shouldbe considered.Therefore in most of the cases,thosekinetic models exhibiting non-linear behavior and could includeshoulder and tailing characteristics (Cullen et al., 2010) addingdifculties in the procedure. Taking into account those particular-

ities a Weibull-based model has been proposed byMafart, Couvert,Gaillard, and Leguerinel (2002)andAlbert and Mafart (2005).This study is focused on the determination of the efcacy of

ozone in the treatment of fresh-cut lettuce (Lactuca sativa) and bellpeppers (Capsicum annuum) as sanitizing agent. Additionally,a Weibull-based model was assumed for microbial load reductionover time, in order to modeling the kinetic behavior of microbialcontaminants.

2. Materials and methods

2.1. Sample preparation

Twenty ve samples of fresh green leaf lettuce (L. sativa) and

twenty

ve samples of green bell peppers (C. annuum) were

purchased from local markets at the day of harvest. In lettuce, thecore and the wrapper leaves were discharged and the remainingleaves were separated and grouped in portions of 200 g each. Greenpeppers were also grouped in portions of 200 g. All vegetablesamples remained unwashed and uncut prior to sanitation in orderto simulate the practice most often used by caterers and vegetableprocessors.

2.2. Chlorine and ozone sanitation trials

Sanitation experiments were conducted in glass beakers con-taining 5 L of sterile distilled water (w15 C) either chlorinatedwith sodium hypochlorite (20 ppm of total chlorine) or ozonated. Inthe latter trials, water was either pre-saturated with ozone (0.5 mg/L) or continuously fed with air containing 5% ozone froma commercial ozone gas generator (Air & Water System PC1325,USA) in order to retain a relatively constant concentration of0.5 mg/L O3.

Ozone and free chlorine concentration was estimated photo-metrically with the indigo method by using a commercially avail-able kit (Hach Co., Loveland Co., USA). Nephelometric turbidityunits (NTU) in washing water was estimated photometrically (Hach

Co., Loveland Co., USA) and pH by means of a portable digital pH-meter (Cyberscan pH11, Eutech Instruments).

2.3. Microbiological analysis

Vegetables were analyzed for their surface microora before(0 min) and after portions of 200 g were immersed in washingsolutions. Every 5 min and until the end of the experiment (i.e. 5,10,15, 20, 25 and 30 min) three subsamples of 10 g each were asep-tically removed from the solution, analyzed and the average countof bacteria was estimated. The microbiological tests were per-formed with the surface overlay technique after 3 min homogeni-zation of 10 g of each sample with 90 mL of sterilized peptone waterin a Stomacher apparatus (BagMixer-Interscience, France). One

hundred microliters from a series of 1/10 dilutions in peptone waterwere plated onto different selective and non-selective growthmedia as follows: Violet Red Bile Lactose Agar (Oxoid Ltd., Basing-stoke, Hampshire, UK) for the enumeration of coliforms afterincubation at 37 C for 24 h. Aerobic mesophilic counts wereenumerated by using Plate Count Agar (Oxoid Ltd., Basingstoke,Hampshire, UK) after incubation at 30 C for 24e48 h. SabouraudDextrose Agar (Oxoid Ltd., Basingstoke, Hampshire, UK) was usedfor cultivation of yeasts and molds. Incubation of the plates wasperformed accordingly to the medium aerobically for 48e96 h at22 C.

2.4. Statistical analysis

Prior to the statistical analysis microbial counts were logarith-mically transformed. The data were statistically analyzed by anal-ysis of variance (ANOVA) using SPSS 17.0. Duncans multiple range(DMR) test was used at a signicance level of 0.05 (Steel & Torrie,1994). A Weibull-based model (1) was assumed for microbial loadreduction throughout time (Albert & Mafart, 2005;Mafart et al.,2002), able to describe concave, convex or linear curves followedbya tailing effect. In this model Nis the bacterial population, N0 andNres represents the initial bacterial population at t 0 and theresidual bacterial population at the end of the observation. Thed parameter represents the time of therst decimal reduction andpis related to the shape of the curve. The experimental data wereanalyzed and model tted to the equation below by using GinaFIT

v1.5 (Geeraerd and Van Impe Inactivation model Fitting Tool)

a Microsoft Excel

Add-inn which is available online via the

A. Alexopoulos et al. / Food Control 30 (2013) 491e496492


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KULeuven/BioTeC-homepage http://cit.kuleuven.be/biotec/ by thedevelopers (Geeraerd, Valdramidis, & Van Impet, 2005).

Log10N Log10h

N0 Nres$10

t

d

p Nres

i (1)

3. Results and discussion

In our study, microbiological analyses (aerobic mesophiles,coliforms and yeasts) of fresh lettuce and green bell pepper wereapplied in order to evaluate ozone efcacy as an alternative sani-tizing agent. For comparison, sodium hypochlorite was usedbecause it is considered as the most common treatment on fruitsand minimally processed vegetables (McEvoy et al., 2009). Duringour experiments, ozone was supplied either continuously or at thebeginning of the experiment and in all instances concentration waskept constant at 0.5 ppm. This was chosen because it is reportedthat concentrations of ozone in water solution higher than 2 ppmmay lead to symptomatic, irritant, toxic, and irreversible health

effects in humans if excess of undissolved gas appears (Khadreet al., 2001;Pascual, Llorca, & Canut, 2007). Concerning the phys-icochemical parameters of washing water, the temperature rangedfrom 15 to 17 C, pH varied from 6.5 to 7.3 and turbidity was below2.7 NTU.

The rst set of experiments were organized in order to evaluatethe impact of ozonation in fresh green lettuce (L. sativa) and bellpeppers (C. annuum) regarding reduction of aerobic mesophilescompared to sodium hypochlorite. Afterward, continuous ozona-tion was compared to ozonation conducted at the beginning of thetreatment regarding seduction of coliforms and yeast/molds. Asshown by the results inTable 1and Fig. 1,continuous ozonationprevailed in efciency, since the reduction of the microbial load was1.7 log higher than the one achieved by sodium hypochlorite (1 log

decrease) and pre-ozonation (0.46 log) after the

rst 15 min (DMR,

p < 0.05). These differences were even higher after 30 min ofexposure reaching 3.04 log and3.27 log for continuous ozonation inlettuce and bell peppers respectively in contrast to 0.67 log and0.85 of pre-ozonation or even 2.03 log and 2.64 log of chlorination(DMR,p < 0.05). The last set of experiments concerned the exam-ination of coliforms and yeasts/molds reduction for both the lettuce

and green pepper (Table 1, Fig. 2). More satisfying results wereobserved in the case of green bell peppers (C. annuum) wherecoliform counts were reduced by 3 log units after the rst 7 min ofcontinuous ozonation. On the other hand, in the case of lettuce,a 2.2 log reduction was observed for coliforms but only after 15 minof treatment. The overall reduction of coliforms for lettuce

Table 1

Effect of exposure time and sanitation method on microorganism reduction (Log10CFU/g) on fresh lettuce and bell peppers.

Time (min) Lettuce Bell peppers

Continuous ozonationa Pre-ozonationb Chlorinated waterc Continuous ozonationa Pre-ozonationb Chlorinated waterc

Aerobic mesophiles 0 3.75 0.06A 3.74 0.02A 3.26 0.01B 3.47 0.02C 3.42 0.06C 3.26 0.03B

5 3.51 0.01A 3.62 0.03B 2.89 0.04C 3.09 0.02D 3.11 0.07D 2.91 0.06C

10 2.99 0.12A 3.50 0.02B 2.83 0.03C 2.76 0.02C 3.05 0.06A 2.78 0.04C

15 2.04 0.06A 3.28 0.03B 2.26 0.01C 2.07 0.02A 2.92 0.03D 2.26 0.02C

20 1.20 0.05A 3.15 0.03B 2.06 0.02C 0.45 0.11D 2.65 0.03E 1.48 0.10F25 1.05 0.06A 3.08 0.04B 1.81 0.08C 0.25 0.06D 2.58 0.04E 1.16 0.08F

30 0.66 0.02A 3.07 0.05B 1.17 0.03C 0.20 0.12D 2.57 0.05E 0.62 0.14A

Coliforms 0 3.25 0.04A 4.53 0.05B

5 2.79 0.03A 2.27 0.10B

10 2.45 0.03A 1.42 0.04B

15 1.09 0.04A 1.50 0.07B

20 0.87 0.15A 1.19 0.09B

25 0.77 0.15A 1.10 0.04B

30 0.78 0.07A 0.87 0.08A

Yeasts/molds 0 4.48 0.03A 4.06 0.04B

5 3.45 0.06A 3.66 0.11B

10 2.77 0.04A 3.54 0.05B

15 2.50 0.04A 2.90 0.06B

20 2.15 0.05A 2.35 0.07B

25 2.20 0.11A 2.14 0.03A30 2.34 0.04A 2.04 0.04B

Data represent average value of three counts with theirstandard deviation. Means of the same row with different superscriptletters differ signicantly (p < 0.05) according toDuncans multiple range test (DMR).

a Ozone concentration was kept constant to 0.5 mg/L.b Initial ozone concentration: 0.5 mg/L.c Initial free chlorine concentration: 20 ppm.

Fig. 1. Effect of pre-ozonated, continuous ozonated and chlorinated water (20 ppm

free chlorine) on Log10 CFU/g reduction of aerobic mesophiles in lettuce and bell

pepper. Fitted model (lines) in the case of continuous ozonated water is also shown.

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(2.47 log) was lower and differed signicantly (DMR,p < 0.05) fromthe reduction observed in peppers (3.66 log). Accordingly, signi-

cant differences (although of lower magnitude) were also recordedfor yeasts/molds since the overall reduction of yeasts/molds in bothvegetables after 30 min of treatment was in the range of 2.02e2.14 log units. According to the Weibull-based model, thedparameter which represents the time of the rst decimal reduc-tion was 3.32 min for coliform and 13.88 min for yeasts/molds inpeppers. As observed, bacteria in general were more prone to ozoneaction than yeasts/molds since their counts were reduced consid-erably after shorter times of exposure. In a similar study where theinvestigators applied different ozone concentrations, a 6 logreduction of total mesophilic bacteria in escarole, carrot andspinach was reported after 20 min of ozone treatment while thereduction of molds and yeasts ranged between 2 and 3 logrespectively (Selma et al., 2008). Such ndings have been attributed

on each microorganisms inherent sensitivity which is one of themajor parameters governing the ozone efcacy (Cullen et al., 2010).As a result, yeasts molds and especially spore forming bacteria,require increasing ozone concentrations and longer exposure timesfor their inactivation. Akbas and Ozdemir (2008) examined theozone action in aked red peppers and observed that ozoneconcentrations above 5.0 ppm for 360 min must be used in order toreduce Bacillus cereusspores by 1.0e2.0 log units.

Concerning the reduction kinetics of different sanitizing agentsour results are also in accordance with those obtained by otherinvestigators.Kim, Kwon, Kwon, Cha, and Jeong (2006) reportedreductions about 2.5 log units in the natural microora of lettuce bythe application of 1.5e3.0 ppm ozonated water and these valueswere comparable with the reductions obtained by 100 ppm chlo-

rine treatment which is ve times the concentration we used. Ina study ofHorvitz and Cantalejo (2008), fresh-cut red peppers weretreated with 0.7 ppm gaseous ozone for 1, 3 and 5 min beforepacking. It was observed that ozone treatment reduced the countsof yeasts, molds, aerobic mesophilic and psychrotrophic bacteriawhile chlorinated water (200 ppm) used in parallel was not equallyeffective. In accordance, the superior sanitizing action of ozone incomparison to other sanitizing methods as the ultraviolet radiationtreatment of washing water has been also reported (Selma et al.,2008).

In our study, peppers showed a dynamic direct effect upon themicroora with a constant decrease in bacterial population (Fig. 2).In contrast,the ozone effecton lettuces showed several uctuationson the populationsdynamic prole. Green peppers have a smooth

quite uniform surface whereas leafy vegetables as lettuce have

extremely irregular and rugged surfaces with many hides whichcould be a niche for bacteria contaminants. It is expected that

microbes should be detached from plant tissue and released inows in order to get exposed in the ozone action ( Cullen et al.,2010); this fact could explain the observed uctuations in ourreduction kinetics regarding lettuce. Therefore, getting a betterozone dispersion in the sanitizing solution is critical as ndingspublished by various authors showed that sanitization treatmentswere more effective when ozone was bubbled, for example duringapple surface washing, than by simply dipping the fruits in pre-ozonated water (Achen & Yousef, 2001; Sapers, Miller, &Mattrazzo, 1999). Our results are in agreement with the above; aswe observed that continuous ozonation of washing waterwas moreeffective than the immersion of vegetables in pre-saturated water.Additionally, in the study ofAchen and Yousef (2001), an increasedreduction ofE. coli counts was observed, reaching the levels of 3.7

and 2.6 log CFU on apple surface, compared to 1 log CFU decrease inthe stem-calyx region. The stem-calyx region is an irregular regionwith hides detaining microbes compared to the smooth applesurface region. Probably variables related with vegetablemorphology (porous surface, waxy cuticle) inuenced ozonediffusion and sanitation efciency leading to relatively poor Wei-bull model tting into our non-continuous ozone experiments. Onthe opposite, this model satisfactorily tted to the data from ourcontinuous ozonation trials exhibiting R-square values ranged from0.973 to 0.989. Mathematical models as the one applied here havebeen adequately used in experiments of microbial inactivation bythermal preservation methods (Albert & Mafart, 2005;Mafart et al.,2002), and contribute to determine the extend to which the processshould be applied improving safe standards and process design.

The antimicrobial efcacy of ozone also depends on factorsassociated with its solubility, stability and decomposition(Bezirtzoglou & Alexopoulos, 2008). In our study the role of suchparameters was not examined but it is known that increasedtemperatures could lower the solubility of ozone (Rice, 1999).Ozone activity could also be inuenced by the presence of organiccompounds and extreme pH variations (lmez & Akbas, 2009).However, it has also been demonstrated that under usual sanitizingconditions i.e. ambient temperatures between 15 and 20 C, pHvalues of 6.5e7.5 and turbidity of washing waters below 5Nephelometric Turbidity Units (NTU) has no pronounced effect oninactivation with ozone (Khadre et al., 2001; Kinman, 1975;Rennecker, Kim, Corona-Vasquez, & Marias, 2001;Walsh, Sproul,& Buck, 1980). In any case, the kinetics of C T concept (product of

disinfectant concentration and contact time) looks applicable as

Fig. 2. Effect of continuously ozonated water Log10CFU/g reduction of coliforms and yeasts/molds in lettuce and bell pepper. Fitted model (lines) in the case of coliform reduction is

also shown.



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with chlorine inactivation, when the limitations in extrapolationare taken in account (Gyurek, Finch, & Belosevic, 1997; Khadreet al.,2001).

A possible effect in the sensorial properties of sanitized vege-tables is another issue of concern. In our experiments, such alter-ations was not evaluated as our intention was to study theefciency of ozone treatment on vegetables intended for imme-diate consuming and not forlong-term storage or packaging, wheresome effects could be appear. Akbas and Ozdemir (2008) foundslight, but signicant changes in avor, appearance and overallpalatabilityofaked redpepper ozonated between 5.0 and 9.0 ppmbut not in the case of lower concentrations of ozone as for examplethe 0.5 mg/L we used.Martnez-Snchez et al. (2006)reported nodifferences in color, texture and freshness in rocket leaves in thestday after ozone treatment while the same results were previouslyfound for fresh-cut iceberg lettuce washed with ozone-treatedwater at different concentrations (Beltrn, Selma, Marn, & Gil,2005). Also, in the same study the authors reported no signicantchanges in vitamin C or in the phenolic contents of lettuces washedwith different sanitizing solutions. These ndings suggest thatozone treatment do not deteriorate the quality of the product morethan any other method do.

Raw vegetables are usually contaminated by different microor-ganisms. Increasing attention has been paid on the safety of vege-tables and fruits, and in particular on the interventionaltechnologies focused to reduce and eliminate microbial pathogeniccharges from these fresh produces. Traditionally, water is used towash fruits and vegetables surfaces. However, chlorine is the mostknown sanitizing agent for these fresh products. As mentioned,chlorination causes the formation of carcinogenic trihalomethanesin food (Fawell, 2000;Kim et al., 1999) and seems to have a limitedeffect in killing bacteria on fruit and vegetable surfaces up to 1- or2-log reduction (Sapers et al., 1999). Ozone is a strong antimicrobialagent in both gaseous and aqueous phases. The oxidizing mecha-nisms of ozone mayinvolve directreactions of molecular ozone andfree radical e mediated destruction (Bezirtzoglou & Alexopoulos,

2008). The main advantage of ozone use consists of its superi-ority compared to chlorine for a few capital reasons; Ozone is re-ported to have 1.5 times the oxidizing potential of chlorine and 3.0times the potential of hypochlorous acid (Hernandez, Zappi,Colucci, & Jones, 2002), acting 3000 times faster than chlorine(Hoign & Bader, 1985) and without producing harmful decompo-sition products (Troyan & Hansen, 1989). Additionally, occurringefuents are environmental safer and require fewer treatment anddisposal efforts.

As a conclusion, it seem that regarding to the sanitation method,the continuous ozonation of washing water with relatively lowconcentration of ozone (0.5 mg/L) gave better results on bacteriareduction, and was efciently tted by a Weibull-based model thanchlorination or even washing the vegetables in pre-ozonated water.

Total mesophiles and coliforms were more prone to ozone action incomparison to yeast/molds. A nal observation concerns ozoneefciency on the type of vegetable, indicating that maybe thismethod of sanitation cannot be widelyadopted for all kinds of freshvegetables and different approaches should be considered by thefood industry.

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evaluation of ozone efficacy on the reduction of microbial population of fresh cut lettuce (lactuca...

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