Article

Efficacy of chlorine, acidic electrolyzed water and aqueous chlorine dioxide solutions to decontaminate Escherichia coli O157:H7 from lettuce leaves

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Abstract

This study compared the efficacy of chlorine (20-200 ppm), acidic electrolyzed water (50 ppm chlorine, pH 2.6), acidified sodium chlorite (20-200 ppm chlorite ion concentration, Sanova), and aqueous chlorine dioxide (20-200 ppm chlorite ion concentration, TriNova) washes in reducing populations of Escherichia coli O157:H7 on artificially inoculated lettuce. Fresh-cut leaves of Romaine or Iceberg lettuce were inoculated by immersion in water containing E. coli O157:H7 (8 log CFU/ml) for 5 min and dried in a salad spinner. Leaves (25 g) were then washed for 2 min, immediately or following 24 h of storage at 4 degrees C. The washing treatments containing chlorite ion concentrations of 100 and 200 ppm were the most effective against E. coli O157:H7 populations on Iceberg lettuce, with log reductions as high as 1.25 log CFU/g and 1.05 log CFU/g for TriNova and Sanova wash treatments, respectively. All other wash treatments resulted in population reductions of less than 1 log CFU/g. Chlorine (200 ppm), TriNova, Sanova, and acidic electrolyzed water were all equally effective against E. coli O157:H7 on Romaine, with log reductions of approximately 1 log CFU/g. The 20 ppm chlorine wash was as effective as the deionized water wash in reducing populations of E. coli O157:H7 on Romaine and Iceberg lettuce. Scanning electron microscopy indicated that E. coli O157:H7 that was incorporated into biofilms or located in damage lettuce tissue remained on the lettuce leaf, while individual cells on undamaged leaf surfaces were more likely to be washed away.

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... To date, the most used sanitizer in fresh produce washing is chlorine [2,8]. Chlorine application offers a number of advantages including a good oxidizing effect, affordable cost, relatively simple operation and widely commercial availability [8][9][10]. Despite the popularity of chlorine as a sanitizer, chlorine has shown a range of negative effects. ...
... Several innovative disinfection agents have been applied in fresh cut industry including chlorine dioxide (ClO 2 ), peroxyacetic acid (PAA), electrolyte water (EW) [10,[14][15][16][17]. The treatments with these sanitizers are expected to prolong the shelf-life without compromising the quality of the produce [9,18,19]. ...
... The antimicrobial activity of ClO 2 has been shown in many studies . For examples, the significant reductions in Escherichia coli, Listeria monocytogenes, Salmonella spp., Bacillus subtilis, rotavirus populations in fresh-cut fruits and vegetables by applying this sanitizer were reported [9,[22][23][24][25][26]. Thus, this agent could be considered as a promising replacement for controversy chemical sanitizing agents like sodium hypochlorite using in processing of fresh fruits and vegetables [27,28]. ...
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The aims of this project were to: 1) compare the antimicrobial efficacy and feasibility of three sanitizers including chlorine dioxide (ClO 2 ), neutral electrolysed water (EW) and peroxyacetic acid (PAA) for the treatment of fresh baby spinach leaves, and 2) to investigate the shelf life and quality attributes of spinach treated with these sanitizers. In the experiment for food safety, spinach leaves were inoculated with Salmonella Typhimurium and then treated by immerging in cold solutions of PAA, ClO 2, EW at different concentrations. Salmonella Typhimurium and total viable count (TVC) were determined immediately before and after the treatment. The treatment with 20 mg/L ClO 2 solution resulted in the highest reductions of S. Typhimurium and TVC (by 1.6 ± 0.1 log CFU/g) compared to other treatments. In the experiment for the shelf life of spinach, the samples were stored at 4 ℃ for 13 days after being treated with 75 mg/L PAA, 60 mg/L free chlorine (FCh) EW and 20 mg/L ClO 2 solutions. The results showed that TVC was significantly influenced by the treatments and storage time. At day 0, TVC of all treated samples was significantly lower than this of the control and the TVC of sample treated with ClO 2 was the lowest. However, by day 10, the TVC was not significantly different among the treated samples and the control. For the sensory qualities and physio-chemical properties of the spinach leaves, the treatment with ClO 2 showed significant reduction in quality of the treated sample since day 7 of the storage while other treatments did not show any significant effect on those parameters during the storage. In summary, although the treatment with 20 mg/L ClO 2 solution resulted in the highest antimicrobial efficacy against S. Typhimurium and TVC of spinach leaves, it also caused negative effects to the quality of spinach during the storage.
... Variation in the establishment and survival of E. coli O157:H7 on young vs. old leaves or abaxial vs. adaxial leaf surfaces may be explained by differences in nutrient availability (Brandl and Amundson, 2008;Van Der Linden et al., 2013) and other environmental (Brandl and Mandrell, 2002;Hora et al., 2005;Aruscavage et al., 2008;Lopez-Velasco et al., 2012;Moyne et al., 2013;Van Der Linden et al., 2013;Williams et al., 2013), biological (Tydings et al., 2011;Williams et al., 2013), and physical factors such as leaf roughness or venation Macarisin et al., 2013;Hunter et al., 2015). Variation in leaf surface topography, for example between different plant species and cultivars (Tydings et al., 2011;Macarisin et al., 2013), in combination with other conditions such as temperature, relative humidity, and free surface water (Brandl and Mandrell, 2002;Hora et al., 2005;Aruscavage et al., 2008;Tydings et al., 2011) may also underlie the observed variability in effectiveness of chlorine treatments to inactivate E. coli (Seo and Frank, 1999;Behrsing et al., 2000;Keskinen et al., 2009). ...
... The United States Food and Drug Administration recommends 50-200 ppm of available chlorine at pH 6.0-7.5 and contact times of 1-2 min (U.S. Food Drug Administration, 1998). Many studies have revealed a broad range of chlorine efficacy in inactivation of E. coli on leafy greens (Seo and Frank, 1999;Behrsing et al., 2000;Keskinen et al., 2009). Variation in efficacy may be attributed to differences in a number of factors, including leaf damage, internalization of E. coli cells, and the inactivation of chlorine by organic material associated with lettuce leaves (Seo and Frank, 1999;Behrsing et al., 2000;Keskinen et al., 2009). ...
... Many studies have revealed a broad range of chlorine efficacy in inactivation of E. coli on leafy greens (Seo and Frank, 1999;Behrsing et al., 2000;Keskinen et al., 2009). Variation in efficacy may be attributed to differences in a number of factors, including leaf damage, internalization of E. coli cells, and the inactivation of chlorine by organic material associated with lettuce leaves (Seo and Frank, 1999;Behrsing et al., 2000;Keskinen et al., 2009). The results we show here suggest that variation in leaf surface topography is another explanatory factor for differences in survival of E. coli on chlorine-treated leafy greens (Figures 5, 6). ...
Article
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The attachment of foodborne pathogens to leaf surfaces is a complex process that involves multiple physical, chemical, and biological factors. Here, we report the results from a study designed to specifically determine the contribution of spinach leaf surface topography as it relates to leaf axis (abaxial and adaxial) and leaf age (15, 45, and 75 days old) to the ability of Escherichia coli to resist removal by surface wash, to avoid inactivation by chlorine, and to disperse through splash impact. We used fresh spinach leaves, as well as so-called “replicasts” of spinach leaf surfaces in the elastomer polydimethylsiloxane to show that leaf vein density correlated positively with the failure to recover E. coli from surfaces, not only using a simple water wash and rinse, but also a more stringent wash protocol involving a detergent. Such failure was more pronounced when E. coli was surface-incubated at 24°C compared to 4°C, and in the presence, rather than absence, of nutrients. Leaf venation also contributed to the ability of E. coli to survive a 50 ppm available chlorine wash and to laterally disperse by splash impact. Our findings suggest that the topographical properties of the leafy green surface, which vary by leaf age and axis, may need to be taken into consideration when developing prevention or intervention strategies to enhance the microbial safety of leafy greens.
... Various EW-producing systems are summarized in Table 1. The factors determining the physicochemical properties of EW include current values, electrolysis time, water flow during electrolysis, and sodium chloride concentration [74]. Currently, systems for the production of SAEW are developed that provide the basis for the development of domestic and commercial SAEW generators for household and industrial utilization [75]. ...
... (iii) Some generators, when operated below pH 5, release a pungent chlorine odour, which makes it uncomfortable for the operator; therefore, appropriate on-site ventilation is required during operation. (iv) If EW is not supplied continuously with the oxidants Cl 2 , HOCl, and H + through electrolysis, the EW may start to lose its bactericidal potential at a much faster rate [74]. (v) EW may start losing its antimicrobial activity if it is stored inappropriately or in case of the presence of organic matter in the EW [73]. ...
Article
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Electrolyzed water is a novel disinfectant and cleaner that has been widely utilized in the food sector for several years to ensure that surfaces are sterilized, and that food is safe. It is produced by the electrolysis of a dilute salt solution, and the reaction products include sodium hydroxide (NaOH) and hypochlorous acid. In comparison to conventional cleaning agents, electrolyzed water is economical and eco-friendly, easy to use, and strongly effective. Electrolyzed water is also used in its acidic form, but it is non-corrosive to the human epithelium and other organic matter. The electrolyzed water can be utilized in a diverse range of foods; thus, it is an appropriate choice for synergistic microbial control in the food industry to ensure food safety and quality without damaging the organoleptic parameters of the food. The present review article highlights the latest information on the factors responsible for food spoilage and the antimicrobial potential of electrolyzed water in fresh or processed plant and animal products.
... However, the increased consumption results in illnesses and outbreaks when the products are contaminated with pathogenic microorganisms (Mahmoud and Linton 2008). Fresh horticultural produce has known to be a major vehicle of pathogens (Keskinen and Annous 2009). Postharvest decay of fruits and vegetables is a major challenge throughout the world (Abano and Buah 2014). ...
... For example, in addition to harvesting fruits and vegetables at optimal maturity stage, applying proper decontamination treatment and storage of fruits and vegetables in a modified atmosphere (MA) will further reduce quality loss and increase safety of horticultural products (Kader 1999). Furthermore, washing with plain water is a common practice to reduce the initial microbial load of fresh produce (Keskinen and Annous 2009). However, this approach alone is often not sufficient to achieve microbial reduction below the safe level. ...
... Chlorine-based sanitizers have been tested on leafy greens, and the reduction of E. coli O157:H7 was typically ,1.5 log CFU/g (45,67,68,73). To better understand the effects of washing, some studies have looked at the locations of E. coli O157:H7 on lettuce after being washed with chlorine solutions (66,75). E. coli O157:H7 was mostly located in stomata, in bacterial biofilms, or in small clusters on romaine and iceberg lettuce leaves (66,75). ...
... To better understand the effects of washing, some studies have looked at the locations of E. coli O157:H7 on lettuce after being washed with chlorine solutions (66,75). E. coli O157:H7 was mostly located in stomata, in bacterial biofilms, or in small clusters on romaine and iceberg lettuce leaves (66,75). Other treatments can also reduce E. coli O157:H7 levels on leafy greens such as the use of ozonated water, acids (acetic acid, citric acid, and lactic acid), irradiation (gamma ray), ultrasound, and UV radiation (45). ...
Article
Foodborne diseases are a major cause of illness in Canada. One of the main pathogens causing cases and outbreaks of foodborne illness in Canada is Escherichia coli O157:H7. From 2008 to 2018, 11 outbreaks of E. coli O157:H7 infection in Canada were linked to leafy greens, including 7 (63.6%) linked to romaine lettuce, 2 (18.2%) linked to iceberg lettuce, and 2 (18.2%) linked to other or unspecified types of leafy greens. The consumption of lettuce in Canada, the behavior of E. coli O157:H7 on lettuce leaves, and the production practices used for romaine and iceberg lettuce do not seem to explain why a higher number of outbreaks of E. coli O157:H7 infection were linked to romaine than to iceberg lettuce. However, the difference in the shape of iceberg and romaine lettuce heads could be an important factor. Among the seven outbreaks linked to romaine lettuce in Canada between 2008 and 2018, an eastern distribution of cases was observed. Cases from western provinces were reported only twice. The consumption of romaine and iceberg lettuce by the Canadian population does not seem to explain the eastern distribution of cases observed, but the commercial distribution, travel distances, and the storage practices used for lettuce may be important factors. In the past 10 years, the majority of the outbreaks of E. coli O157:H7 infection linked to romaine lettuce occurred during the spring (March to June) and fall (September to December). The timing of these outbreaks may be explained by the availability of lettuce in Canada, the growing region transition periods in the United States, and the seasonality in the prevalence of E. coli O157:H7. The consumption of romaine lettuce by the Canadian population does not explain the timing of the outbreaks observed. Highlights:
... Free chlorine reacts with all the organic matter in a solution, decreasing its action against bacteria. 25,26 Bactericidal efficacy of free chlorine is also diminished by pH variations regardless if generated via EW or NaClO. These two factors alone may explain why chlorine at 200 ppm was bacteriostatic in our assays. ...
... Both EW and free chlorine are volatile compounds that lose their antimicrobial action after a certain time. 30 Also, the loss of antimicrobial efficacy is related to the reaction with the organic matter, 25,26,28 and even light can accelerate the loss of chlorine efficacy. However, NaClO at 280 ppm was established as an effective X. citri suppressor (curve is also overlapped with the 'EW 9 min at 400 μL mL −1 ' dataset in Fig. 3). ...
Article
BACKGROUND The largest and most profitable market for citrus is the production of fresh fruit. Xanthomonas citri subsp. citri is a Gram‐negative plant pathogen and the etiological agent of citrus canker, one of the major threats to citrus production worldwide. In the early stages of infection, X. citri can attach to plant surfaces by means of biofilms. Biofilm is considered an essential virulence factor, which helps tissue colonization in plants. Thus, sanitization of citrus fruit is mandatory in packinghouses before any logistic operation as packing and shipment to the market. The aim of this study was to evaluate electrolysed water (EW) as a sanitizer for the disinfection of citrus fruit in packinghouses. RESULTS Using a protocol to monitor cell respiration we show that EW, obtained after 8 and 9 min of electrolysis, sufficed to kill X. citri when applied at a concentration of 500 μL mL⁻¹. Furthermore, microscopy analysis, combined with time‐response growth curves, confirmed that EW affects the bacterial cytoplasmatic membrane and it leads to cell death in the first few minutes of contact. Pathogenicity tests using limes to simulate packinghouse treatment showed that EW, produced with 9 min of electrolysis, was a very effective sanitizer capable of eliminating X. citri from contaminated fruit. CONCLUSION It was possible to conclude that EW is significantly effective as sodium hypochlorite (NaClO) at 200 ppm. Therefore, EW could be an alternative for citrus sanitization in packinghouses. © 2020 Society of Chemical Industry
... The persistent antiseptic effects of the hot NaClO, O 3 and UV-C pre-treatments were not significant in E. coli. The NaClO, hot NaClO and ClO 2 pre-treatments showed similar sterilisation efficiencies immediately after sterilisation pre-treatments, considering harmful by-products and residual moisture; ClO 2 could be used as an alternative to aqueous sanitisers such as chlorine and NaClO solutions (Keskinen et al., 2009). Different sensitivities of microorganisms to the different kinds of chemical and physical sterilisation methods were exhibited. ...
... Chlorine is a widely used, economical and effective method of decontamination; however, the commodities washed in these solutions have been known to acquire an odor that is rejected by most consumers and most importantly, it is potentially carcinogenic (Keskinen, Burke, & Annous, 2009). Therefore, several Decontamination of fruit and vegetable . . . ...
Article
Fresh fruits and vegetables are a rich source of micronutrients. However, many foodborne illnesses have been linked to the consumption of fresh fruits and vegetables as they are reported to harbor contaminants such as microorganisms and pesticides. Recently reported foodborne outbreaks have been linked to a diverse group of fruits and vegetables due to the presence of various pathogens including Salmonella, Escherichia coli, and Listeria monocytogenes. Also, the increased use of pesticides has resulted in the deposition of chemical residues on the surface of fruits and vegetables, which has led to the adverse health conditions such as cancer, birth defects, and neurodevelopmental disorders. Fresh commodities are subjected to various treatments to prevent or minimize these outbreaks, and the main targets of such treatments have been the elimination of pathogens and degradation of toxic chemical residues. Here, we have discussed various decontamination methods including simple household washing, chemical treatments, and modern technologies with their mode of action for microbial and pesticide removal. The simple household processes are not very effective in the removal of pathogenic organisms and pesticides. The use of modern techniques like cold plasma, ozone, high hydrostatic pressure, and so on, showed better efficacy in the removal of microorganisms and pesticides. However, their industrial use is limited considering high installation and maintenance cost. In this review, we suggest combined methods based on their mode of decontamination and suitability for a selected fruit or vegetable for effective decontamination of microbes and pesticide together to reduce the treatment cost and enhance food safety.
... Sanitisers for fresh produce include chlorine dioxide, hydrogen peroxide, PAA, ozone, electrolysed oxidizing water, and organic acids [3,19,20]. PAA is a nonfoaming strong oxidant composed of hydrogen peroxide and acetic acid in an equilibrium mixture and decomposes into benign products that include water, acetic acid, carbon dioxide, and oxygen [21,22]. e PAA sanitiser is preferred over chlorine, as chlorine reacts with organic matter to form trihalomethanes which are potentially harmful to human health [23]. ...
Article
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Grit composed of dirt, sand, and small stones adheres to baby leafy salad vegetables during the growing period and can sometimes be difficult to remove with sanitiser only or tap water. For the first time, the effect of a surfactant, sodium dodecyl sulphate (SDS), alone (0.025, 0.05, and 0.1% SDS) and in combination (0.05% SDS) with peroxyacetic acid (40 mg·L ⁻¹ , PAA), on grit removal, quality, shelf-life, and taste of baby spinach was investigated. Increasing SDS from 0.025 to 0.1% resulted in a 21–50% increase in grit removal from spinach and coral lettuce. Overall, SDS treatments had no effect on microbial growth, colour, and electrolyte leakage during shelf-life. An increase in bruising, sliming, and yellowing scores was also observed regardless of the treatment, reaching an unacceptable score (<3) by d12 for all samples; however, yellowing scores were still within the acceptable range (>3) on d14. There were no differences in sensorial attributes, namely, flavour, aroma, and texture, between baby spinach samples treated with PAA alone or in combination with SDS. These results demonstrate that SDS treatment can be used to increase grit removal from baby leafy salad vegetables without compromising quality.
... The usage of chemical antimicrobial technologies is always accompanied by increased health risks due to the carcinogenic and teratogenic effects they can induce. 28,29 For instance, when hypochlorous acid, a substance present in NaOCl solution, comes into contact with an organic tissue, it acts as a solvent and releases chlorine, which interacts with protein amino groups and forms chloramines that interfere in the cell metabolism. 30 Hypochlorous acid (HOCl − ) and hypochlorite ions (OCl − ) lead to amino acid degradation and hydrolysis. ...
Article
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Sprouted seeds are gaining popularity across the world due to the high nutritional value. In parallel, they are among the highest contaminated fresh produce and have been recognized as the primary source of food-borne pathogen such as E. coli O157 and plenty of harmful microfungi. Antifungal and antibacterial properties of chlorophyllin-based photosensitization in vitro together with successful application of this treatment for microbial control of wheat sprouts have been investigated. First, we examined the antimicrobial efficiency of chlorophyllin (1.5×10-5-5×10-3 M) activated by visible light (405 nm, radiant exposure:18 J/cm2) against food-borne pathogen Escherichia coli and plant pathogen Fusarium oxysporum in vitro. Results revealed that this treatment (1.5×10-5 M Chl, incubation time 1 h, 405 nm, radiant exposure:18 J/cm2) can reduce E. coli population by 95 %. Moreover, at higher chlorophyllin concentration (5×10-4-5×10-3 M Chl) it is possible to achieve the delay of F. oxysporum growth by 51-74 %. The decontamination of wheat seeds by chlorophyllin-based photosensitization (5×10-4 M Chl, 405 nm, radiant exposure:18 J/cm2) remarkably reduced the viability of surface-attached mesophilic bacteria (~2.5 log CFU/g), E. coli (~1.5 log CFU/g) and yeasts/fungi (~1.5 log CFU/g). Moreover, SEM images confirmed that this treatment did not damage grain surface microstructure. Most important is the fact that Chl-based photosensitization did not reduce the seed germination rate, seedling growth and had no impact on visual quality of sprouts. In conclusion, chlorophyllin-based photosensitization being nonthermal, environmentally friendly and cost-effective treatment has huge potential for microbial control of highly contaminated germinated wheat sprouts and seeds used to produce sprouts, especially in organic farming.
... Chlorine is a widely used sanitizer in fresh produce wash water, and its efficacy at inactivating enteric pathogens on fresh produce as well as in wash water has been evaluated in a number of studies [22,[35][36][37]. We evaluated the efficacy of chlorine to inactivate EHEC when the pathogen had been associated with pre-harvest lettuce over time by comparing the number of cells remaining on lettuce after washing with buffered water and with 50 ppm chlorine. ...
Article
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In the field, foodborne pathogens such as enterohemorrhagic Escherichia coli (EHEC) are capable of surviving on produce over time, yet little is known about how these pathogens adapt to this environment. To assess the impact of pre-harvest environmental conditions on EHEC survival, we quantified survival on romaine lettuce under two relative humidity (75% and 45%) and seasonal conditions (March and June). Greenhouse-grown lettuce was spray-inoculated with EHEC and placed in a growth chamber, mimicking conditions typical for June and March in Salinas Valley, California. Bacteria were enumerated on days 0, 1, 3, and 5 post-inoculation. Overall, we found that the effect of relative humidity on EHEC survival depended on the seasonal conditions. Under June seasonal conditions, higher relative humidity led to lower survival, and lower relative humidity led to greater survival, five days post-inoculation. Under March seasonal conditions, the impact of relative humidity on EHEC survival was minimal over the five days. The bacteria were also tested for their ability to survive a chlorine decontamination wash. Inoculated lettuce was incubated under the June 75% relative humidity conditions and then washed with a 50 ppm sodium hypochlorite solution (40 ppm free chlorine). When incubated under June seasonal conditions for three to five days, EHEC strains showed increased tolerance to chlorine (adj. p < 0.05) compared to chlorine tolerance upon inoculation onto lettuce. This indicated that longer incubation on lettuce led to greater EHEC survival upon exposure to chlorine. Subsequent transcriptome analysis identified the upregulation of osmotic and oxidative stress response genes by EHEC after three and five days of incubation on pre-harvest lettuce. Assessing the physiological changes in EHEC that occur during association with pre-harvest lettuce is important for understanding how changing tolerance to post-harvest control measures may occur.
... In other studies, EGHA was used successfully as decontamination strategy to control foodborne pathogens and spoilage organisms on different fresh foodstuffs (Cao et al., 2009;Ding et al., 2011;Grac¸a et al., 2011;Issa-Zacharia et al., 2010;Keskinen et al., 2009;Park et al., 2008;Thorn et al., 2017). According to Kalchayanand et al. (2008), EGHA had intermediate effects on cheek meat experimentally contaminated with E. coli O157:H7, as compared with hot water and lactic acid. ...
Article
Antimicrobial treatments could help to decrease the transmission of microorganisms to beef carcasses and abattoir environments. The aim of this study was to evaluate the effectiveness of interventions in reducing Shiga toxin genes ( stx1 and stx2) presence in a commercial abattoir. Intervention measures included the application of electrolytically generated hypochlorous acid to steer pens (experiment 1), chlorinated water, electrolytically generated hypochlorous acid, and isoclor to steer pens (experiment 2), electrolytically generated hypochlorous acid to knocking pens (experiment 3), and aqueous ozone and electrolytically generated hypochlorous acid onto beef carcasses (experiment 4). Detection of stx in samples was performed with BAX® System Real-Time PCR Assay. Our results showed that treatment with pressurized electrolytically generated hypochlorous acid and isoclor were effective to reduce stx presence from hides on steer pens. Although there is no single strategy to ensure the reduction of stx presence in a commercial abattoir, the combined application of several antimicrobial interventions would be ideal.
... These three reasons can also explain why the single antimicrobial agents (except 1% H 2 O 2 ), such as 4 mg/L EW and 0.6% CA nearly had no reduction of microbial populations compared with control. For EW water, our result is consistent with previous reports (Keskinen, Burke, & Annous, 2009;Tan et al., 2015), that, the disinfected concentration of chlorine based sanitisers is 50e200 mg/L. In our study the FAC was only 4 mg/L. ...
Article
Potential organic compatible sanitisers including electrolysed water (EW, 4 mg/L free available chlorine (FAC)), citric acid (0.6%), H 2 O 2 (1%), and their combinations were applied on organic and conventional fresh-cut lettuce (Lactuca sativa Var crispa L.) to evaluate their effects on microbiological safety, physi-cochemical parameters and sensory analysis (including raw sample and boiled sample). The combination of 1% H 2 O 2 with 0.6% citric acid led to the highest reductions of microbial loads (2.26 log CFU/g for aerobic mesophilic count (AMC) and 1.28 log CFU/g for yeasts and moulds); however, it also caused the highest electrolyte leakage rate (3.11% vs. 0.91% for control). The combination of EW with 1% H 2 O 2 achieved 1.69 and 0.96 log CFU/g reductions for AMC and yeasts and moulds, respectively with elec-trolyte leakage rate of 1.41%. In terms of the content of polyphenolic compounds, firmness, colour and raw material sensory analysis, there were no significant differences among different treatments, and between organic and conventional counterparts. The results suggest that 1% H 2 O 2 combined with 4 mg/L EW is a promising approach for treating organic fresh-cut lettuce.
... Nevertheless, the treatment of iceberg lettuce leaves with 20-200ppm of aqueous chlorine dioxide displayed less than 1 log inactivation (Keskinen et al., 2009). Therefore the use of bacteriophages to eliminate bacterial pathogens that contaminate fresh food is one of the most environmentally friendly and safe solutions to reducing the incidence of foodborne diseases. ...
... It has been reported that high pH resulted in rapid disintegrated of GI VLPs (da Silva et al., 2011) and destruction of Gram-negative food-borne pathogens (Mendonca et al., 1994). It has been reported that acidic electrolyzed water had a stronger bactericidal effect on most known pathogenic bacteria (Cao et al., 2009;Keskinen et al., 2009;Ongeng et al., 2006;Park et al., 2008;Venkitanarayanan et al., 1999). It might be a practical approach to use low pH solution to remove BPCs from contaminated Romaine lettuce and other produce. ...
Article
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Norovirus is a very contagious virus that causes acute gastroenteritis. Contaminated produce is a main vehicle for dissemination of human noroviruses (HuNoVs). As HuNoVs could bind to bacteria effectively, it is highly possible that produce could be contaminated by bacteria-HuNoVs complex. In this study, we used a bacterialsurface- display system to express genogroup I (GI) or genogroup II (GII) HuNoV capsid protein (P protein) on the surface of bacteria. The bacteria-P protein complex (BPC) was used to characterize the conditions for binding to Romaine lettuce extract and removal of the bound BPCs. We demonstrated both GI and GII BPCs could bind to extract from leaf (LE) and vein (VE) effectively. Carbohydrates in LE and VE were involved in GI BPCs binding, and both carbohydrates and proteins were involved in GII BPCs binding. Saliva from both type A and O secretors could completely block binding of both BPCs to LE and VE. Saliva from type B secretors only partially blocked binding of GII but not GI BPCs to LE and VE. However, LE- and VE-bound BPCs could not be reversely removed by washing solution containing free HBGAs from saliva. The binding of GI BPCs to LE and VE was enhanced when pH was below pI (6.1) of GI and reduced when pH was above pI of GI (p < 0.05). The optimal binding for GII BPCs to LE and VE occurred at pI (6.4) of GII. All LE- or VE-bound BPCs could be reversely removed by washing with low (3.0–5.0) or high (9.0–10.0) pH buffer. The effect of ionic strength (NaCl and MgCl2, from zero to 100 g/L) on binding of BPCs to LE and VE was tested. The optimal ionic strength for binding of BPCs to LE and VE was 10.0 g/L (GI) and 5.0 g/L (GII) for NaCl, and 5.0 g/L for MgCl2. LE- and VE-bound BPCs could be reversely removed by washing with high ionic solutions. All LE- or VE- bound BPCs could be released when washed with NaCl concentrations of above 75.0 g/L (GI) and 25.0 g/L (GII), or with MgCl2 concentrations of above 75.0 g/L (GI) and 50.0 g/L (GII). Binding of BPCs to LE and VE was inhibited in the presence of Tween-80 (nonionic surfactant) as low as 0.05% (v/v). All LE- and VE-bound BPCs could be reversed by Tween-80 concentrations over 0.1% (v/v). The study provided important parameters for BPCs binding to and removal from lettuce extract.
... Microscopy-based techniques, such as scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) have been used to visualize plant-microbe interactions. Bacterial invasion into stomata or damaged tissue has been studied with SEM (Keskinen et al., 2009;López-Gálvez et al., 2010;Wang et al., 2010). Although SEM micrographs reveal presence of bacteria on leaf surface, with this approach it is not possible to distinguish between artificially introduced and residential bacteria. ...
Article
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This study examined the biological and food safety relevance of leaf lesions for potential invasion of food pathogens into the plant tissue (internalization). This was done by determining the role of artificial leaf damage in terms of damaged leaf area on proliferation of E. coli O157:H7 gfp+. In a two-factorial experiment, unwashed fresh baby leaf spinach (Spinacia oleracea L.) was subjected to four damage levels (undamaged, low, moderate, high damage; factor 1) and three incubation intervals (0, 1, 2 days post-inoculation; factor 2). Individual leaves were immersed for 15 s in a suspension loaded with E. coli O157:H7 gfp+ (106 CFU × mL–1). The leaves were analyzed individually using image analysis tools to quantify leaf area and number and size of lesions, and using confocal laser scanning and scanning electron microscopy to visualize leaf lesions and presence of the introduced E. coli strain on and within the leaf tissue. Prevalence of E. coli O157:H7 gfp+ was assessed using a culture-dependent technique. The results showed that size of individual lesions and damaged leaf area affected depth of invasion into plant tissue, dispersal to adjacent areas, and number of culturable E. coli O157:H7 gfp+ directly after inoculation. Differences in numbers of the inoculant retrieved from leaf macerate evened out from 2 days post-inoculation, indicating rapid proliferation during the first day post-inoculation. Leaf weight was a crucial factor, as lighter spinach leaves (most likely younger leaves) were more prone to harbor E. coli O157:H7 gfp+, irrespective of damage level. At the high inoculum density used, the risk of consumers’ infection was almost 100%, irrespective of incubation duration or damage level. Even macroscopically intact leaves showed a high risk for infection. These results suggest that the risk to consumers is correlated with how early in the food chain the leaves are contaminated, and the degree of leaf damage. These findings should be taken into account in different steps of leafy green processing. Further attention should be paid to the fate of viable, but non-culturable, shiga-toxigenic E. coli on and in ready-to-eat leafy vegetables.
... However, for food system, this sanitizing efficacy might be limited. Keskinen, Burke and Annous (2009) reported the efficacy of acidic EW (50 mg/L FAC, pH 2.6) at reducing populations of E. coli O157:H7 on artificially inoculated iceberg lettuce, and only 0.68 log CFU/g reduction was observed after 2 min treatment at 22°C. ...
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.
... However, several non-thermal interventions exist that have potential to reduce carriage of ARB and ARGs on vegetables surfaces interest. Common post-harvest practices include washing in water containing sanitizers, modified atmosphere packaging (MAP), and refrigerated storage are used to reduce bacterial numbers on produce surfaces, and increase the product shelf life in part due to reduced growth rates of spoilage (Beuchat et al., 1998;Parish et al., 2003;Keskinen et al., 2009). However, the ability of pathogens, such as E. coli O157:H7, to internalize into cut lettuce tissues, consequently reducing the efficacy of sanitizer washing (Takeuchi and Frank, 2000;Solomon et al., 2002), has warranted the approval of ionizing radiation (irradiation) for treatment of fresh lettuce and spinach for control of pathogens and shelf-life extension (US Food and Drug Administration [US FDA], 2008). ...
Article
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Contamination of romaine lettuce with human pathogens, antibiotic-resistant bacteria (ARB), and antibiotic resistance genes (ARGs) occurs during production. Post-harvest interventions are emplaced to mitigate pathogens, but could also mitigate ARB and ARGs on vegetables. The objective of this research was to determine changes to lettuce phyllosphere microbiota, inoculated ARB, and the resistome (profile of ARGs) following washing with a sanitizer, gamma irradiation, and cold storage. To simulate potential sources of pre-harvest contamination, romaine lettuce leaves were inoculated with compost slurry containing antibiotic-resistant strains of pathogenic (Escherichia coli O157:H7) and representative of spoilage bacteria (Pseudomonas aeruginosa). Various combinations of washing with sodium hypochlorite (50 ppm free chlorine), packaging under modified atmosphere (98% nitrogen), irradiating (1.0 kGy) and storing at 4°C for 1 day versus 14 days were compared. Effects of post-harvest treatments on the resistome were profiled by shotgun metagenomic sequencing. Bacterial 16S rRNA gene amplicon sequencing was performed to determine changes to the phyllosphere microbiota. Survival and regrowth of inoculated ARB were evaluated by enumeration on selective media. Washing lettuce in water containing sanitizer was associated with reduced abundance of ARG classes that confer resistance to glycopeptides, β-lactams, phenicols, and sulfonamides (Wilcoxon, p < 0.05). Washing followed by irradiation resulted in a different resistome chiefly due to reductions in multidrug, triclosan, polymyxin, β-lactam, and quinolone ARG classes (Wilcoxon, p < 0.05). Irradiation followed by storage at 4°C for 14 days led to distinct changes to the β-diversity of the host bacteria of ARGs compared to 1 day after treatment (ANOSIM, R = 0.331; p = 0.003). Storage of washed and irradiated lettuce at 4°C for 14 days increased the relative abundance of Pseudomonadaceae and Carnobacteriaceae (Wilcoxon, p < 0.05), two groups whose presence correlated with detection of 10 ARG classes on the lettuce phyllosphere (p < 0.05). Irradiation resulted in a significant reduction (∼3.5 log CFU/g) of inoculated strains of E. coli O157:H7 and P. aeruginosa (ANOVA, p < 0.05). Results indicate that washing, irradiation and storage of modified atmosphere packaged lettuce at 4°C are effective strategies to reduce antibiotic-resistant E. coli O157:H7 and P. aeruginosa and relative abundance of various ARG classes.
... The efficacy of ClO 2 against artificially inoculated pathogens, such as E. coli, Salmonella spp., and L. monocytogenes, has been extensively investigated in lettuce. A 2 min-long treatment with 100 or 200 ppm aqueous ClO 2 in iceberg lettuce resulted in >1 log reduction in E. coli O157:H7 load (Keskinen et al., 2009). Similar results were obtained for S. typhimurium and L. monocytogenes inoculated on iceberg lettuce with lower ClO 2 concentrations but longer exposure (10 min) (Kim et al., 2008). ...
Article
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Maintaining microbial safety and quality of fresh fruits and vegetables are a global concern. Harmful microbes can contaminate fresh produce at any stage from farm to fork. Microbial contamination can affect the quality and shelf-life of fresh produce, and the consumption of contaminated food can cause foodborne illnesses. Additionally, there has been an increased emphasis on the freshness and appearance of fresh produce by modern consumers. Hence, disinfection methods that not only reduce microbial load but also preserve the quality of fresh produce are required. Chlorine dioxide (ClO2) has emerged as a better alternative to chlorine-based disinfectants. In this review, we discuss the efficacy of gaseous and aqueous ClO2 in inhibiting microbial growth immediately after treatment (short-term effect) versus regulating microbial growth during storage of fresh produce (long-term effect). We further elaborate upon the effects of ClO2 application on retaining or enhancing the quality of fresh produce and discuss the current understanding of the mode of action of ClO2 against microbes affecting fresh produce.
... To minimize cross-contamination between the water and the product, commercial flume washing of fresh produce almost invariably involves the use chlorine-based sanitizers, most commonly at concentrations of 50 to 200 ppm and exposure times of 1 to 2 min (5,11,18,21,39,42). Although microbial reductions of 4 to 5 log are common in produce wash water during processing, populations on the product have generally decreased by only 1 to 2 log after washing (12,27,38,50,52). Chlorine-based sanitizers are particularly sensitive to changes in water pH, organic load, and temperature; therefore, common industry practices involve continual monitoring of the wash water and adjustment of the pH to about 6.5 (5) to maintain efficacy (18,24). ...
Article
Several outbreaks of foodborne illness traced to leafy greens and culinary herbs have been hypothesized to involve cross-contamination during washing and processing. This study aimed to assess the redistribution of Salmonella Typhimurium LT2 during pilot-scale production of baby spinach and cilantro and redistribution of Escherichia coli O157:H7 during pilot-scale production of romaine lettuce. Four inoculated surrogate:uninoculated product weight ratios (10:100, 5:100, 1:100, and 0.5:100) and three inoculation levels (103, 101, and 10-1 CFU/g) were used for the three commodities. For each of three trials per condition, 5-kg batches containing uninoculated product and spot-inoculated surrogate products at each ratio and inoculation level were washed for 90 s in a 3.6-m-long flume tank through which 890 L of sanitizer-free, filtered tap water was circulated. After washing and removing the inoculated surrogate products, washed product (∼23, 225-g samples per trial) was analyzed for presence or absence of Salmonella Typhimurium or E. coli O157:H7 by using the GeneQuence Assay. For baby spinach, cilantro, and romaine lettuce, no significant differences ( P > 0.05) in the percentage of positive samples were observed at the same inoculation level and inoculated:uninoculated weight ratio. For each pathogen product evaluated (triplicate trials), inoculation level had a significant impact on the percentage of positive samples after processing, with the percentage of positive samples decreasing, as the initial surrogate inoculation level decreased. The weight ratio of contaminated:noncontaminated product plays an important role: positive samples ranged from 0% to 11.6% ± 2.05% and from 68.1% ± 33.6% to 100% among the four ratios at inoculation of 10-1 and 101 CFU/g, respectively. To our knowledge, this study is the first to assess the redistribution of low levels of pathogens from incoming product to leafy greens during processing and should provide important data for microbial risk assessments and other types of food safety analyses related to fresh-cut leafy greens.
... In general, the inoculation procedures of Danyluk et al. (2005) and Keskinen et al. (2009) were followed with minor modifications. The inoculum was prepared by transferring a loopful of the working stock to 9 ml TSB and incubated at 37 C for 18-24 h. ...
Article
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This study investigated the efficacy of integrated electron beam (e‐beam) irradiation and hydrogen peroxide (H2O2) aqueous solution treatments to inactivate mixed strains of Salmonella inoculated in grape tomatoes. Whole grape tomatoes were inoculated with a mixed bacterial cocktail composed of five strains of Salmonella enterica corresponding to serotypes Rissen (SAL1449), Montevideo (SAL4599), Saintpaul (476398), and Typhimurium (ATCC 13311 and ATCC 700720), dried in a biological safety cabinet for 2 h at room temperature and then stored at 4°C for 24 h to facilitate bacterial attachment before treatment. Tomatoes in H2O2 (60 mg/L) aqueous solution were irradiated at 0.45, 0.60, 0.75, 1.0, and 1.25 kGy dose. The combined treatment of 1.0 kGy radiation dose and 60 mg/L H2O2 achieved 4‐log reductions in Salmonella. The D10−average value of Salmonella in the present study was 0.25 ± 0.01 kGy. Regarding the effect of the treatment on tomato quality, the combined application of e‐beam up to 1.25 kGy and H2O2 (60 mg/L) did not affect (p > .05) the color and texture of grape tomatoes compared to non‐irradiated samples. Furthermore, the combined treatments of e‐beam and H2O2 aqueous solution reduced the dose uniformity ratio (DUR) by 7%, a relevant finding regarding commercial applications of electron beam accelerators. Exposure of the tomatoes to e‐beam and water wash with added H2O2 is a promising decontamination system for use in tomatoes and other produce processing. Further studies on the optimization of this integrated treatment are needed. Practical Applications Electron beam irradiation of tomatoes immersed in hydrogen peroxide (H2O2) solution reduces the dose required to eliminate pathogens in the fresh produce. The integrated treatment ensures minimal changes to produce quality and increased treatment efficiency in terms of dose uniformity.
... As with other fresh produce, chlorine (50-200 ppm) is the most frequently used chemical disinfectant in the mango industry (Beuchat, 1999;Li et al., 2001;Shen et al., 2013;NMB, 2014). Although an effective antimicrobial agent, the efficacy of chlorine is quickly compromised in the presence of organic matter, as is commonly the case with routine produce washing (Keskinen et al., 2009;Shen et al., 2013;NMB, 2014). In fact, inadequately chlorinated wash water is thought to be a contributing factor to the Salmonella outbreaks associated with the consumption of whole mangoes (Beatty et al., 2004). ...
... Adhered microorganisms, microorganisms in biofilms or microorganisms in crevices may escape cleaning and disinfecting procedures and become sources of contaminating food products during processing, thus, a major part of the requirement of a good manufacturing plant is to ensure that microbial biofilms are removed effectively (Marriott and Givanni, 2006). It is recommended that disinfectants should be used in order to avoid cross contamination from contaminated produce to clean produce (Keskinen et al., 2009).Dairy products are susceptible to biofilm contamination due to their perishability and limitations in cleaning procedure (Jessen and Lammert, 2003). In 2011, about 20 pounds of raw milk distributed in Washington were recalled due to contamination with Listeria monocytogenes (Srey et al., 2013). ...
Article
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Biofilms are structured communities of microorganisms attached to a surface. Microorganisms such as bacteria,algae, fungi, protozoa may be found in a biofilm consortium attached to biological or non-biological surfaces. Their formation starts from initial attachment to their dispersal to other surfaces where they colonize and sometime cause infections especially on biological surfaces like living tissues and medical devices, which is of great importance to public health. Cells in the biofilm assemblage communicate through quorum sensing, affecting biofilm processes like cell detachment and exchange of genetic materials. Biofilms cause slow and persistent infections which interfere with antibiotic therapy. They are also a major concern in food industries, oil industries and aquaculture. To assay biofilms, methods like Tissue culture plate method, tube method and Congo red agar method can be used. Chemical, physical and biological methods are being used to control biofilms. A greater understanding of biofilm processes will lead to novel and effective strategies for biofilm control and a resulting improvement in patient management, enhancing the clinical decision-making process.
... As an alternative of the traditional chlorine sanitizer, the strong antibacterial effect of electrolyzed oxidizing water (EOW), which include strong acidic electrolyzed water (AEW) with pH of 2.2-2.7 approximately , slightly acidic electrolyzed water (SAEW) with pH of 5.0-6.5 approximately and neutral electrolyzed water pH of 7.0-8.0, showed a promising prospect in food industry (Huang, Hung, Hsu, Huang, & Hwang, 2008;Keskinen, Burke, & Annous, 2009;Rahman, Wang, & Oh, 2013). Apart from the disinfection efficacy on the planktonic strains, the removal effects of AEW on the bacterial biofilm were also demonstrated (Arevalos-Sánchez, et al., 2012;Cheng, et al., 2016;Okanda, et al., 2019). ...
Article
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In the present study, the bactericidal efficacy of slightly acidic electrolyzed water (SAEW) against L. monocytogenes planktonic cells and biofilm on food-contact surfaces including stainless steel and glass was systematically evaluated. The results showed that SAEW (pH of 5.09 and available chlorine concentration (ACC) of 60.33 mg/L) could kill L. monocytogenes on food-contact surfaces completely in 30 s, whose disinfection efficacy is equal to that of NaClO solutions (pH of 9.23 and ACC of 253.53 mg/L). The results showed that long exposure time and high ACC contributed to the enhancement of the disinfection efficacy of SAEW on L. monocytogenes on food-contact surfaces. Moreover, the log reduction of SAEW treatment presented an increasing tendency within the prolonging of treatment time when SAEW was used to remove the L. monocytogenes biofilm formed on stainless steel and glass surfaces, which suggested that SAEW could remove L. monocytogenes biofilm effectively and its disinfection efficacy is equal to (in case of stainless steel) or higher than (in case of glass) that of high ACC of NaClO solutions. In addition, the results of the crystal violet staining and scanning electron microscopy (SEM) also demonstrated that SAEW treatment could remove the L. monocytogenes biofilm on food-contact surfaces.
... Pathogenic bacteria such as Escherichia coli, Salmonella, Listeria monocytogenes, and Yersinia spp. can adhere to plant tissues and form biofilms (Keskinen et al. 2009;L opez-G alvez et al. 2010;Sadekuzzaman et al. 2018). Due to the structure of vegetables, the effect of sanitizers on these microorganisms is decreased. ...
Article
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Microbial biofilms are difficult to control due to the limited accessibility that antimicrobial drugs and chemicals have to the entrapped inner cells. The extracellular matrix, binds water, contributes to altered cell physiology within biofilms and act as a barrier for most antiproliferative molecules. Thus, new strategies need to be developed to overcome biofilm vitality. In this review, based on 223 documents, the advantages, recommendations, and limitations of using bacteriophages as ‘biofilm predators’ are presented. The plausibility of using phages (bacteriophages and mycoviruses) to control biofilms grown in different environments is also discussed. The topics covered here include recent historical experiences in biofilm control/eradication using phages in medicine, dentistry, veterinary, and food industries, the pros and cons of their use, and the development of microbial resistance/immunity to such viruses.
... Besides surface decontamination, biocontrol agents have been reported to control the internalization of foodborne pathogens into fresh produce. Internalization can happen at both preharvest and postharvest stages through natural apertures (e.g., stomata, stem; Chen et al., 2016), damaged tissues (Keskinen et al., 2009), and germination of seeds (Shen et al., 2017). Internalization of pathogens has been reported on various produce, such as cabbage (Erickson et al., 2019), leafy greens (Vonasek & Nitin, 2016), sprouts (Ge et al., 2014), tomato (Zhou et al., 2018), mango (Mathew et al., 2018), cantaloupe (Macarisin et al., 2017), and avocado (Chen et al., 2016). ...
Article
Although tremendous efforts have been made to ensure fresh produce safety, various foodborne outbreaks and recalls occur annually. Most of the current intervention strategies are evaluated within a short timeframe (less than 1 h), leaving the behavior of the remaining pathogens unknown during subsequent storages. This review summarized outbreak and recall surveillance data from 2009 to 2018 obtained from government agencies in the United States to identify major safety concerns associated with fresh produce, discussed the postharvest handling of fresh produce and the limitations of current antimicrobial interventions, and reviewed the intervention strategies that have the potential to be applied in each storage stage at the commercial scale. One long-term (up to 12 months) prepacking storage (apples, pears, citrus among others) and three short-term (up to 3 months) postpacking storages were identified. During the prepacking storage, continuous application of gaseous ozone at low doses (≤1 ppm) is a feasible option. Proper concentration, adequate circulation, as well as excess gas destruction and ventilation systems are essential to commercial application. At the postpacking storage stages, continuous inhibition can be achieved through controlled release of gaseous chlorine dioxide in packaging, antimicrobial edible coatings, and biocontrol agents. During commercialization, factors that need to be taken into consideration include physicochemical properties of antimicrobials, impacts on fresh produce quality and sensory attributes, recontamination and cross-contamination, cost, and feasibility of large-scale production. To improve fresh produce safety and quality during storage, the collaboration between researchers and the fresh produce industry needs to be improved.
... Los múltiples usos del dióxido de cloro (ClO2) son de desinfectante de alimentos, potabilizador de agua, desinfectante industrial, hasta blanqueador industrial. (8,9) Se ha promovido en redes sociales y por medidas gubernamentales el uso de esta sustancia como medida preventiva y curativa de la COVID-19, siendo esto falso y propagado por diversos medios de comunicación. ...
Article
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Introducción: el creciente número de casos de COVID-19 a nivel mundial han dado paso al deterioro de la de salud mental y la investigación de nuevos tratamientos; esto ha dado lugar a una explosión de búsquedas en internet de palabras clave. Objetivo: en esta investigación se ha descrito el uso de Google Trends para medir las búsquedas en internet de términos asociados a la pandemia por COVID-19 en distintas regiones de Perú y su potencial para realizar investigaciones en salud. Método: se midió la tendencia de búsquedas en internet del término “dioxido de cloro” en el período entre el 3 de junio al 3 de septiembre de 2020. Se utilizaron los datos de Google Trends sobre una fracción de las búsquedas de las palabras clave, y se analizaron los resultados de acuerdo con una ubicación geográfica dada y un período definido. Resultados: se encontró que los países que presentaron mayor nivel de búsqueda para dicho término fueron Bolivia, Perú, Ecuador, Argentina y México. Se encontró correlación positiva alta entre el nivel de búsqueda en Argentina y el número de casos en este país, a comparación de Perú, Ecuador y México, donde la correlación fue positiva muy baja. En el caso de Bolivia, se presentó una correlación negativa muy baja. Google Trends podría, además, definir potencialmente el momento y la ubicación adecuada para practicar estrategias de comunicación de riesgos a las poblaciones afectadas. Conclusiones: existe correlación entre en número de casos y las búsquedas de dióxido de cloro como medida médica contra la COVID-19. Palabras clave: dióxido de cloro; Google Trends; COVID-19; tendencia; Internet
Article
This study was conducted to investigate the Salmonella inactivation effects of washing in combination with pulsed light (PL), ultrasound, and chlorine on lettuce shreds. First, the effect of washing combined with PL and chlorine on the inactivation of Salmonella on lettuce and in wash water was evaluated in a small-scale study with clear tap water and turbid tap water containing lettuce extract and silicon dioxide. In general, water wash combined with PL (PL wash) and chlorine wash combined with PL (PL-Cl) were significantly more effective on killing Salmonella on lettuce than the chlorine wash and water wash regardless the wash water quality and inoculation method. We then tested washing combined with PL, ultrasound and chlorine using a large-scale UV setup with turbid wash water. Increasing the sample size decreased the decontamination efficacy of all the treatments. All the treatments resulted in <2 log reductions of Salmonella on lettuce shreds. For both small- and large-scale studies, treatments involving chlorine could keep the Salmonella population in wash water under the detection limit of 2 CFU/mL for almost all the replicates. Taking everything into consideration, we concluded that the combined PL-Cl treatment could be a better alternative to the chlorine wash for lettuce decontamination since it was in general more effective on inactivating Salmonella on lettuce than chlorine wash and could maintain the Salmonella level in wash water under the detection limit of 2 CFU/mL regardless the inoculation method, water quality and sample size, preventing the potential cross contamination through wash water.
Chapter
Reducing postharvest losses will not only add a sizable quantity to the global food supply, but also reduce the need to intensify food production, as well as minimizing the environmental impacts of food production. Optimal packaging solutions should reduce the risks of both microbiological spoilage and physiological disorder. Successful implementation of modified atmosphere (MA) packaging depends on the correct choice of appropriate package parameters from virtually countless options. The materials typically used for MA packaging of fresh produce, such as polyethylene and polypropylene films, have functional limitations. MA and modified humidity (MH) packaging have the potential to extend the shelf‐life of fresh and minimally processed fruits and vegetables by limiting oxidative processes, controlling decay, and reducing water loss. Researchers have developed various forms of sensors for the detection of spoilage volatiles to determine the quality of products in real time.
Chapter
As food industry flourished, the use of EW as a novel sanitizing agent has gained interest worldwide. The chapter reviews recent progress in the application of EW in fruits and vegetables industry, summarizing its efficacy on disinfection and pesticide removal during their processing, and disease control along with inhibiting moth infestation throughout storage as well as the effect on physiochemical properties, chemical components, and postharvest physiology. Furthermore, it specially generalized the application of EW in the field of sprouts vegetables (our researching focus) to open up a new way for the development of functional food. It indicated that EW has sufficient obliterating efficacy on spoilage or pathogenic microorganisms, pesticide residues, and some insect pests existing on fruits and vegetables without compromising sensory and nutritional quality of them in most occasions. Besides, the employment of EW to sprouts vegetables makes those healthful components such as CABA and flavonoids accumulated. However, optimal processing parameters such as washing time along with physiochemical properties of EW need further selection. And, hurdle technology should not be tolerated to maximize treatment efficacy and prolong the shelf life of fresh produce. In brief, EW has a promising prospect in future utilization of fruits and vegetables.
Article
Consumption of fresh‐cut vegetables has rapidly increased over the past decades. Among salads, escarole is one of the most popular varieties. Specific packaging limits gas exchange and consequently water loss and bacterial respiration, increasing the shelf life of salads. Although the major cause of quality loss for minimally processed salads is the leaf textural changes, this aspect has rarely been investigated. Therefore investigating structural changes of leaves during storage is important in order to understand and minimize quality loss of salads. In this study, we focused on the impact of storage duration and temperature on the escarole leaf structure. The complex leaf structure was investigated by relaxation NMR, via transverse relaxation times, which allows the specific description of vacuolar water compartment of the cell. The storage duration (maximum 12 days) and temperatures (4, 7, 10, and 12°C) have been chosen in order to represent the conditions registered in factory. The results showed that the temperature did not have significant impact on the salad structure during the first week. During the second week, changes in the water distribution and changes in the relaxation time T2 have been observed. The changes in transverse relaxation times associated with vacuolar water are related to lost of cell membrane and wall integrity. The NMR results confirmed the effect of storage temperature on the degradation process of the cell before visual detection of the salad leaf degradation. The present study confirmed the sensibility of NMR relaxometry for monitoring water changes in the leaf.
Article
To evaluate the feasibility of acidified sodium benzoate (NaB) as alternative washing solutions of fresh produce, the survival of inoculated pathogens, the background molds and yeasts counts, and quality parameters were compared during 4 and 21 °C storage of cherry tomatoes washed with 3000 ppm NaB at pH 2.0, 200 ppm free chlorine at pH 6.5, water adjusted to pH 2.0, and distilled water. The acidified NaB solution was the most effective in reducing the population of Escherichia coli O157:H7, Salmonella enterica and Listeria monocytogenes cocktails on tomatoes (>4 log CFU/g). NaB was more effective than free chlorine (P < 0.05) in reducing the two Gram-negative bacteria on tomatoes, while the reduction of Gram-positive L. monocytogenes by NaB (5.49 log CFU/g) and chlorine (4.98 log CFU/g) was similar (P > 0.05). No recovery of bacteria was found in all treatments during storage for 15 days. The acidified NaB effectively controlled yeasts and molds on cherry tomatoes to <1 log CFU/g or below the detection limit at both temperatures during 15-d storage, while free chlorine did not. Compared to unwashed controls, NaB had no effect on color, weight loss, firmness, and total soluble solids content of tomatoes during storage. The effect of NaB reducing pathogenic and spoilage microorganisms on tomatoes and maintaining quality during storage suggests its potential as an alternative wash solution in postharvest processing of fresh produce.
Chapter
Temperate crops cover a wide range of delicious fruits which are popular all over the world, and their safety assurance related to supply chain management is very crucial. The fruit industry has the responsibility to implement safety management systems in order to control the potential contamination of possible hazards. The safety management in temperate fruits can be maintained through the use of guidelines and standards of hazard analysis of critical control points, good agriculture practice, and standard operating procedures. Safety management in temperate fruits is important to track down the deficiencies and loopholes in sanitation, hygiene, and improper practices related to production.
Chapter
Electrolyzed water (EW) considered as a novel broad-spectrum and high-performance bactericide has gained immense popularity over the last few decades. It offers several advantages over other sanitizers for sanitation of both food contact and noncontact surfaces, such as safety, effective disinfection, easy operation, relatively inexpensive, and environmentally friendly. EW can be produced by electrolyzing soft tap water with sodium chloride as the chemical additive. Different producing equipment and parameters greatly influence the types and properties of EW. During production period, preparation settings are vital factors on the basic properties of EW (available chlorine concentration (ACC), pH, and oxidization reduction potential (ORP)) and then influence its inactivation efficiency, including current, water flow rate, salt/acid concentration, electrolyte and electrode, water temperature and hardness, storage environments, and so on. This chapter provides an overview of the production, properties, types of EW, as well as a section on its advantages and disadvantages.
Article
This study was performed to examine the inhibitory effect of combined treatments with a positively charged cinnamon leaf oil (P-CL) emulsion and various organic acids against Listeria monocytogenes inoculated on fresh-cut Treviso leaves. Combined treatments with a P-CL emulsion and an organic acid exhibited a higher inhibitory effect than treatment with each alone or NaOCl. The highest inhibitory effect was achieved by combined treatment with the P-CL emulsion and lactic acid (LA), which showed a 2.85-log reduction compared to distilled water washing. In addition, the inhibitory effect of the combined treatment was maintained during 6 days of subsequent storage, and showed a 3.24–3.39-log reduction compared to unwashed samples. Treviso leaves treated with the P-CL emulsion and LA also maintained their sensorial properties, including appearance, odor, hardness, freshness, and overall acceptability, during subsequent storage. Therefore, combined treatment with a P-CL emulsion and LA can be used to effectively ensure the microbial safety and organoleptic quality of fresh-cut Treviso leaves.
Article
This study carried out a systematic quantitative analysis of published literature on the efficacy of essential oils (EOs) as sanitizers in fresh leafy vegetables (FLVs). Efficacy of EO was measured by determining if their application could cause a reduction of microbial population in FLV, as well as by identifying experimental factors that might affect the achieved reduction levels. Data on efficacy of EO to reduce the microbial population and experimental conditions were collected from selected studies and compiled for a distribution and relational analysis. Reduction of an artificial inoculum and/or natural microbiota of FLV caused by 14 different EO were measured in 404 (73.8%) and 143 (26.2%) experiments, respectively. Results of quantitative analysis showed that EO are consistently effective to reduce microbial population in FLV either when the target microorganisms are forming an artificial inoculum or the natural microbiota, being overall similarly effective to or more effective than substances used ordinarily as sanitizers. EO were more effective to reduce the population of microorganisms forming an artificial inoculum than the natural microbiota. EO concentration and inoculum size had no significant effect on achieved reductions. Duration of sanitization treatment with EO had significant effect on achieved reductions and highest reductions were found when the sanitization time was >3 min. Although with the inherent variability in experimental designs found in available literature, the results of this quantitative analysis provide strong evidence that EO are promising candidates for use in strategies to sanitize FLV.
Article
This study synthesized and characterized ZIF‐8 nanoparticles encapsulated with trans‐cinnamaldehyde oil (TC) and evaluated their antimicrobial effectiveness against Escherichia coli O157:H7 on fresh spinach leaves. The antimicrobial activity of different mass ratios of TC‐encapsulated ZIF‐8 against E. coli O157:H7 (ATCC 43895) strain was assessed and the best mass ratio of 1:2 TC to ZIF‐8 identified. Spinach leaves were treated with (1) 0.5TC@ZIF‐8_PL nanoparticle complexes solution, (2) 200 ppm chlorine, (3) free TC, and (4) sterilized distilled water (control). All sample groups were rinsed for 1 min, dried in a biosafety cabinet, weighted, and packed in sterilized Whirl‐pkTM Stand‐Up sampling bags, and stored at 4°C for 15 days for shelf life studies. Samples were dipped into a solution of nanoparticles and another group was sprayed. The quality of spinach samples was assessed by monitoring changes in moisture content (MC), water activity (Aw), color, pH, texture (firmness and work), vitamin C content, total carotenoid, and chlorophyll content. Spinach leaves treated with 0.5TC@ZIF‐8_PL had less (p < 0.05) water, total chlorophyll, and total carotenoid losses, with minimal changes in pH. However, treatment did not prevent the color degradation (p > 0.05) and adversely affected spinach firmness. The spinach samples treated with 200 ppm chlorine and free TC had higher (p < 0.05) total chlorophyll degradation than the samples treated with the nanoparticles. The mass ratio of TC‐encapsulated ZIF‐8 must be readjusted to reduce potential toxicity issues while maintaining the antimicrobial properties. Zeolitic imidazolate framework‐8 (ZIF‐8) nanoparticle complex can be used to encapsulate natural antimicrobials to inhibit growth of pathogens on fresh produce. A 2‐log reduction in populations of Escherichia coli O157:H7 on fresh spinach leaves was achieved using trans‐cinnamaldehyde at low concentrations. The results can be used to embed the compounds into polymeric films for antimicrobial packaging applications.
Article
The application of chemical disinfectants in postharvest food processing facilities is important for the control of foodborne pathogen outbreaks. Similar to drinking water disinfection, food processors will need to optimize disinfectant exposures to balance pathogen inactivation against exposure to potentially toxic disinfection byproducts (DBPs). Since most disinfection research has focused on drinking water, this review summarizes research related to disinfection in food washing facilities, particularly by chlorination and ozonation. Although these disinfectants are also used for drinking water, the conditions are significantly different at food processing facilities. After a brief summary of foodborne pathogen outbreaks, this review describes food processing treatment trains, particularly the critical differences in conditions encountered relative to drinking water disinfection (e.g., short disinfectant contact times and high and variable disinfectant demands). The review discusses research related to pathogen inactivation and DBP formation by chlorine and ozone during washing of produce, meat and seafood. In particular, the research highlights the difficulty of inactivating pathogens on food, but the efficacy of these disinfectants for controlling pathogen cross-contamination through the washwater. While most research on food-associated DBPs has focused on the same, low molecular weight DBPs of interest in drinking water, these DBPs partition to the washwater. This review highlights the need for research on the initial transformation products of disinfectant reactions with biomolecules, since these products may present a risk for consumer exposure by remaining within the food.
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The focus of this study was to develop technologies using chlorine dioxide (ClO2) gas to control postharvest stem-end rot of citrus caused by Lasiodiplodia theobromae. Mycelial growth of L. theobromae on potato dextrose agar (PDA) plugs was completely inhibited by a 24-h ClO2 exposure provided by 0.5 g of solid ClO2 generating granular mixture in a 7.7-liter sealed container. In vivo experiments were conducted on artificially inoculated 'Tango' and naturally infected 'US Early Pride' mandarins. When ClO2 treatments were initiated 0 to 6 h after inoculation, decay development was significantly reduced as compared with the control and higher ClO2 doses were more effective. A ClO2 treatment (using 3 g of generating mixture/7.7-liter sealed container) administered 0 h after inoculation resulted in 17.6% Diplodia stem-end rot incidence compared to 95.6% in the control, while the same treatment administered 24 h after inoculation was much less effective, resulting in 63.0% incidence compared to 85.4% in the control. Diplodia stem-end rot incidence of naturally infected fruit after using 6 or 9 g generating mixture/24-liter sealed box was 23.8 or 25.7%, respectively, compared to 47.9% for control fruit. The ClO2 treatments had no negative effects on fruit quality characteristics including weight loss, firmness, puncture resistance, titratable acids (TA), total soluble solids (TSS), and rind color. Albedo pH at wounds was significantly reduced from 6.0 to 4.8 by the ClO2 treatments while undamaged albedo remained at 5.8. In addition, no visible physiological defects, such as peel browning and bleaching, were observed on ClO2 treated fruit. These results indicate that ClO2 gas has the potential to be developed as a component of an integrated citrus postharvest decay control system to minimize fruit losses.
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This study evaluated the effect of sterilizing harvesting knives with sodium hypochlorite (NaOCl) on soft rot in Kimchi cabbage. Knives were infected with Pectobacterium carotovorum subsp. carotovorum (Pcc), sterilized with NaOCl (100, 200, and 300 mg/L), and used to cut Kimchi cabbage slices, which were incubated for 70 h in a 28 °C incubator. In Kimchi cabbage slices cut with a Pcc-inoculated knife without NaOCl sterilization, symptoms began to appear after 20 h, and approximately 60% of the cabbage slices were infected after 70 h of incubation. In contrast, in cabbage cut with a sterilized knife, soft rot symptoms were delayed, and they began to appear after 40 h of incubation in the 200 mg/L-treated. The expression levels of PG10, PG12-1, PG12-3, WRKY 33, MPK3, ACO1, and ACO2 were increased in infected plants, and NaOCl treatment decreased these expression levels. Transmission of soft rot can be minimized by disinfecting harvesting knives with 200 mg/L NaOCl.
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In this study the applicability of cold plasma, produced by surface dielectric barrier discharge (SDBD), to inactivate Pseudomonas tolaasii (P.tolaasii), polyphenol oxidase (PPO) and peroxidase (POD) enzymes, as well as its impact on quality parameters such as, color, texture, pH and weight loss were evaluated. The study evidently shows that treating with combination of 30% hydrogen peroxide vapor)with flow rate of 0.47 mL min⁻¹) and argon (H2O2 + Ar) for 180 s is capable of reducing the activity of PPO (0.17 U min⁻¹ g⁻¹ FW) and POD (0.21 U min⁻¹ g⁻¹ FW) and increasing the SOD enzyme (16.29 U g⁻¹ FW) in a 21-day storage period compared to control samples. This is while the quality characteristics of button mushroom are preserved during storage after such treatment. Industrial relevance This study provides information of A. bisporus storage during 21-day period after SDBD plasma treatment, which is rarely. Greater inactivation of P. tolaasii after 180 s treatment with combination of hydrogen peroxide vapor and air (H2O2 + air) was shown compared to control samples, but this treatment caused also slightly degradation of button mushroom color. A better reduction of PPO and POD enzyme activity as well as further increase of SOD enzyme activity was observed following treatment with 180 s of H2O2 + Ar gas in a 21-day storage period. This research work contributes to the understanding SDBD plasma induced effects on the shelf-life of button mushroom and could be a basis for a possible industrial implementation.
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Chlorine dioxide (ClO2) is commonly generated by mixing sodium chlorite and acid. This study aimed to evaluate how acid affects the release kinetics and antimicrobial property of ClO2. Solutions made with weak acids released ClO2 more slowly and had higher stability than those made with hydrochloric acid. Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes were treated with 1, 2.5, and 5 ppm ClO2 for 3 or 5 min. Lettuce inoculated with the pathogenic bacteria were treated with 2.5 and 5 ppm ClO2 for 5 min. The effects of peptone load at 0.01% and 0.02% on the antimicrobial efficacy of ClO2 were investigated in S. Typhimurium cell suspensions. The contribution of acids alone at the pH of the ClO2 solutions to bacterial reduction was also evaluated. The 2.5 ppm ClO2 solutions made with citric acid, lactic acid, and malic acid showed higher reductions in all three bacteria than ClO2 made with hydrochloric acid and sodium bisulfate. The 5 ppm ClO2 solutions produced with organic acids reduced populations of all bacterial strains from 7 log CFU/mL to undetectable level in 3 min, except S. Typhimurium treated by ClO2 produced with lactic acid. On inoculated Romaine lettuce model, 5 ppm ClO2 produced with lactic acid and malic acid resulted in the highest reduction of E. coli O157:H7, S. Typhimurium, and L. monocytogenes of approximately 1.4, 1.7, and 2.4 log CFU/g, respectively. The antimicrobial efficacy of ClO2 made with HCl and NaHSO4 were affected by 0.01% and 0.02% peptone load, respectively. Food-grade organic acids produced aqueous ClO2 solutions with stronger antimicrobial properties than inorganic acids. The acids alone at the pH of ClO2 did not show significant bacterial reductions.
Chapter
The pathogenic microbial biofilm is gaining increasing concern in the food safety field. Biofilms may exist in food raw materials, food processing equipment as well as food products and packages during transportation and storage. Since the microbial biofilms have strong survivability in various pressure conditions (pH, temperature, ultraviolet, antibiotics, disinfectants, etc.) in food processing, they become a nonnegligible source of foodborne diseases, thus have potential threat to human health. Here, we focus on discussing the general phenomenon of food-associated pathogen biofilms, the survival mechanism of biofilms under various stimuli in food processing, commonly used detection methods, and the characteristic of virulence of biofilm.
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L. monocytogenes has been linked to fresh produce and detected in the retail environment. This study simulated the retail practices (crisping, misting, and storage) of unbagged whole heads of romaine lettuce to determine the growth of L. monocytogenes and natural psychrotrophic microflora. Three nalidixic acid-resistant strains of L. monocytogenes strains were inoculated to each head of lettuce (≈5 log 10 CFU/g). For crisping, 24 heads of romaine lettuce were immersed in tap water or electrolyzed water (EW; free chlorine: 55 ppm) for 5 min, followed by holding at 5 ○ C for 2 h. The water-crisped (WC), EW crisped (EWC), or non-crisped (NC) lettuces were placed in a commercial refrigerated cabinet for misting at 5 ○ C. After 24-h misting, heads of lettuce were placed in perforated drain boxes with cover at 5 ○ C or 15 ○ C. The tap water and EW crisping achieved 1.3 and 2.9 log 10 CFU/g reduction of L. monocytogenes, respectively. Approximately 1 log additional reduction of L. monocytogenes in the non-crisped lettuce was shown after misting ( p < 0.05), but no significant effect of misting on the population of L. monocytogenes was observed on WC or EWC lettuces ( p > 0.05). Regardless of the storage temperature or misting, L. monocytogenes populations remained significantly ( p < 0.05) lower on EWC lettuce than NC and WC lettuce. On days 4 and 7 of storage, the natural psychrotrophic bacteria on lettuce stored at 5°C was significantly lower than stored at 15°C, and its population was not affected by crisping and misting. These provide insight into the influence of retail lettuce handling practices on the risk of L. monocytogenes.
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Chapter
This chapter reviews nutritional composition, harvesting, storage, packing, processing of spinach and lettuce. Spinach is a rich source of calcium, magnesium, phosphorus, potassium, and zinc. Flavonoids found in spinach act as antioxidants that may provide protection against oxidative stress. Spinach consumption is associated with decreased risk of age-related macular degeneration (AMD). Spinach is consumed as fresh or processed into different forms, including frozen, canned, or dried. Lettuce is the most popular salad vegetable and is usually eaten raw. Lettuce contains bioactive compounds, including vitamins, carotenoids, flavonoids, and phenolic acids that can improve nutritional status and benefit health. Lettuce is a good source of dietary fiber. A high fiber diet may reduce the risk of cardiovascular diseases by decreasing low-density lipoprotein (LDL) cholesterol and blood pressure. Consuming lettuce may play a role in blood sugar control for people with diabetes.
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The Institute of Food Technologists has issued this Scientific Status Summary to provide readers with a tutorial on biofilms, their purposeful mechanism of interaction (quorum sensing), and recent findings on how to inhibit their formation.
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The efficacy of electrolyzed oxidizing water for inactivating Escherichia coli O157:H7, Salmonella enteritidis, and Listeria monocytogenes was evaluated. A five-strain mixture of E. coli O157:H7, S. enteritidis, or L. monocytogenes of approximately 10(8) CFU/ml was inoculated in 9 ml of electrolyzed oxidizing water (treatment) or 9 ml of sterile, deionized water (control) and incubated at 4 or 23 degrees C for 0, 5, 10, and 15 min; at 35 degrees C for 0, 2, 4, and 6 min; or at 45 degrees C for 0, 1, 3, and 5 min. The surviving population of each pathogen at each sampling time was determined on tryptic soy agar. At 4 or 23 degrees C, an exposure time of 5 min reduced the populations of all three pathogens in the treatment samples by approximately 7 log CFU/ml, with complete inactivation by 10 min of exposure. A reduction of >/=7 log CFU/ml in the levels of the three pathogens occurred in the treatment samples incubated for 1 min at 45 degrees C or for 2 min at 35 degrees C. The bacterial counts of all three pathogens in control samples remained the same throughout the incubation at all four temperatures. Results indicate that electrolyzed oxidizing water may be a useful disinfectant, but appropriate applications need to be validated.
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Ozone (3 ppm), chlorine dioxide (3 and 5 ppm), chlorinated trisodium phosphate (100- and 200-ppm chlorine), and peroxyacetic acid (80 ppm) were assessed for reduction of Escherichia coli O157:H7 and Listeria monocytogenes in an aqueous model system and on inoculated produce. Initially, sanitizer solutions were inoculated to contain approximately 10(6) CFU/ml of either pathogen, after which aliquots were removed at 15-s intervals over a period of 5 min and approximately plated to determine log reduction times. Produce was dip inoculated to contain approximately 10(6) E. coli O157:H7 or L. monocytogenes CFU/g, held overnight, submerged in each sanitizer solution for up to 5 min, and then examined for survivors. In the model system study, both pathogens decreased > 5 log following 2 to 5 min of exposure, with ozone being most effective (15 s), followed by chlorine dioxide (19 to 21 s), chlorinated trisodium phosphate (25 to 27 s), and peroxyacetic acid (70 to 75 s). On produce, ozone and chlorine dioxide (5 ppm) were most effective, reducing populations approximately 5.6 log, with chlorine dioxide (3 ppm) and chlorinated trisodium phosphate (200 ppm chlorine) resulting in maximum reductions of approximately 4.9 log. Peroxyacetic acid was the least effective sanitizer (approximately 4.4-log reductions). After treatment, produce samples were stored at 4 degrees C for 9 days and quantitatively examined for E. coli O157:H7, L. monocytogenes, mesophilic aerobic bacteria, yeasts, and molds. Populations of both pathogens remained relatively unchanged, whereas numbers of mesophilic bacteria increased 2 to 3 log during storage. Final mold and yeast populations were significantly higher than initial counts for chlorine dioxide- and ozone-treated produce. Using the nonextended triangle test, whole apples exposed to chlorinated trisodium phosphate (200 ppm chlorine) and shredded lettuce exposed to peroxyacetic acid were statistically different from the other treated samples.
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Chlorine is widely used as a sanitizer to maintain the microbial quality and safety of fresh-cut produce; however, chlorine treatment lacks efficacy on pathogen reduction, especially when the fresh-cut processing water contains heavy organic loads. A more efficacious sanitizer that can tolerate the commercial processing conditions is needed to maintain microbial safety of fresh-cut produce. This study evaluated the efficacy of Escherichia coli O157:H7 reduction on fresh-cut carrots using new and traditional sanitizers with tap water and fresh-cut processing water scenarios. Fresh-cut carrot shreds inoculated with E. coli O157:H7 were washed in sanitizer solutions including 200 ppm chlorine, citric acid-based sanitizer (Pro-San), 80 ppm peroxyacetic acid-based sanitizer (Tsunami 100), and 1,000 ppm acidified sodium chlorite (SANOVA) prepared in fresh tap water or simulated processing water with a chemical oxygen demand level of approximately 3,500 mg/liter. Samples were packaged and stored at 5 degrees C. Microbial analyses performed at days 0, 7, and 14 indicate that the organic load in the process water significantly affected the efficacy of chlorine on pathogen removal and was especially evident on samples tested during storage. Acidified sodium chlorite provided a strong pathogen reduction even under process water conditions with up to a 5.25-log reduction when compared with the no-wash control. E. coli O157:H7 was not recovered on acidified sodium chlorite-treated samples during the entire 14 days of storage, even following an enrichment step. These results suggest that acidified sodium chlorite holds considerable promise as an alternative sanitizer of fresh-cut produce.
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The Institute of Food Technologists has issued this Scientific Status Summary to provide readers with a tutorial on biofilms, their purposeful mechanism of interaction (quorum sensing), and recent findings on how to inhibit their formation.
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The primary method to eliminate, or significantly reduce, pathogens on produce is strict adherence to Good Agricultural Practices (GAPs), Good Manufacturing Practices (GMPs), Hazard Analysis Critical Control Points (HACCP), and other relevant strategies that prevent contamination from occurring. This includes the concept of "good management practices" as described in the Guide to Minimize Microbial Food Safety Hazards for Fresh Fruits and Vegetables (FDA 1998). Although the frequency of produce contamination by pathogens is thought to be very small, there are no known mitigation strategies that will completely remove pathogens after contamination has occurred while maintaining produce freshness. A variety of mitigation regimens and sanitizers are available to reduce microbial populations depending upon the type of produce involved. Washing and sanitizing efficiencies depend on several factors, including characteristics of the produce surface, water quality, cleaner/sanitizer used, contact time, and presence and type of scrubbing action. Based on reported data, it is likely that different sanitation mitigation strategies are needed for different produce items.
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Leafy salad species are increasingly consumed in the human diet and there is increased concern about the levels of microbial organisms in these raw foods, and especially bacteria such as Salmonella that cause food poisoning. Various chemical sanitizers therefore are used to control microorganisms and fungi, but there is very little information on the effects of these chemicals on food composition. Wild rocket (Diplotaxis tenuifolia L. DC) leaves were washed using tap water, chlorine (100 mg L−1), ozonated water (10 mg L−1), lactic acid (Purac® 20 mL L−1), acidified sodium chlorite (Sanova® 250 mg L−1) and peroxyacetic acid (Tsunami® 300 mg L−1). The effects of sanitizers on the contents of Vitamin C, polyphenols and glucosinolates of rocket leaves were studied under air and low O2 (1–3 kPa) + high CO2 (11–13 kPa) for 15 days at 4 °C. All the sanitizers effectively reduced microbial growth on the day of processing, but only Purac, Tsunami and Sanova inhibited the microbial growth throughout the shelf life. The visual quality was acceptable for all treatments in air while it was poor under low O2 + high CO2. In addition, Purac was particularly detrimental for sensory quality. Both chlorophyll a and chlorophyll b contents were reduced throughout storage but were independent of washing treatments and storage conditions. The content of vitamin C was maintained for up to 8 days of storage under air and low O2 + high CO2, but Purac washes markedly reduced the vitamin C content. A clear decrease in ascorbic acid followed by an increase in dehydroascorbic acid was observed when samples were stored under low O2 + high CO2. The content of flavonoids was not affected by the washing solutions on the processing day and remained almost constant throughout the storage in air. However, marked reductions were observed when samples were stored under low O2 + high CO2. The glucosinolates were the most affected constituents of rocket leaves as the content was reduced from 4 to 33% when samples were stored in air while the decrease was between 60 and 100% in low O2 + high CO2. These data revealed that Sanova and Tsunami could be alternative sanitizers to chlorine for rocket leaf washes due to good retention of sensory quality with no detrimental reduction of the antioxidant constituents.
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Demand for fresh, healthier convenience-type foods has stimulated sales of fresh-cut vegetables in North America. As part of an overall program to better define the microbiological safety of these products, studies were done to examine the effects of various disinfectants againstListeria monocytogeneson fresh-cut vegetables. Some of the more established disinfectants such as chlorine and chlorine dioxide, as well as some of the newer ones including SalmideRand trisodium phosphate were tested againstL. monocytogeneson lettuce and cabbage. Different exposure times, as well as concentrations of the disinfectants were evaluated. In addition, organic acids such as lactic and acetic were examined for their ability to inactivateL. monocytogenespresent on the surface of vegetables. Chlorine was also tested in combination with the organic acids and various surfactants. For chlorine (200ppm, 10min), the maximum observed log10reduction ofL. monocytogenesat 4 and 22°C, respectively, was 1.3 and 1.7 for lettuce and 0.9 and 1.2 for cabbage. Chlorine dioxide treatment (5ppm, 10min) of lettuce and cabbage at 4 and 22°C, respectively, resulted in a maximum observed log10reduction ofL. monocytogenesof 1.1 and 0.8 for lettuce and 0.4 and 0.8 for cabbage. In comparison, the highest levels of SalmideRused on cabbage and lettuce (200ppm) at 22°C led to maximum reductions of 1.8 and 0.6 logs, respectively. None of the surfactants tested improved the disinfectant efficiency of chlorine, and actually proved to be antagonistic. Trisodium phosphate had almost no effect on reducing numbers ofL. monocytogenes, at levels that did not affect the organoleptic quality of lettuce. Lactic acid proved to be more effective than acetic acid in reducing numbers ofL. monocytogenes, although maximum reductions of only 0.5 and 0.2 logs were observed after a 10min exposure to 1% solutions of each organic acid. In general, therefore, one can expect approximately a 1log reduction in numbers ofL. monocytogenes, regardless of the disinfectant used.
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Increasing concerns about the possible formation of carcinogenic compounds and the emergence of new, more tolerant pathogens, have raised questions on the use of chlorine in fresh-cut produce. There is a growing need to investigate the efficacy of new commercial sanitizing and other alternative technologies. In the present study, the effectiveness of chlorine and other commercial sanitizer agents (Sanova, Sanoxol 20, Tsunami 100, Purac FCC 80, Citrox 14W and Catallix) was evaluated on epiphytic microorganisms and their influence on the sensory quality of fresh-cut escarole and lettuce. Different sanitizer concentrations (manufacturer's recommended dose and half of this dose) and application systems (submersion and spray) were also compared. The antimicrobial efficacy of the treatments was evaluated, initially after washing, and after 8 days of storage simulating a commercial shelf-life (3 days at 4 °C + 5 days at 8 °C). All the tested washing solutions were more effective in reducing the microbial load than water washes, particularly in fresh-cut escarole. However, the microbial load of fresh-cut escarole and lettuce after 8 days of storage was very similar for most of the treatments despite the different application systems and concentrations of the sanitizers. Clearly epiphytic microorganisms of fresh-cut escarole and lettuce were able to grow rapidly during storage under low temperature, reaching similar or higher values than the unwashed fresh-cut produce at the day of production. The overall visual quality of fresh-cut salad leaves was scored as good or very good (≥6) after 8 days of storage, except for the product washed with Purac. Thus, despite the high number of mesophilic bacteria present in the product, between 6 and 8 log cfu g−1, it was not associated with a detrimental quality. Therefore, the determination of the initial epiphytic reductions of fresh-cut products after washing with different sanitizing agents provides little information about the microbial or sensory quality of the product at the time of consumption.
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Several outbreaks of Escherichia coli O157:H7 infections have been associated with minimally processed leafy vegetables in the United States. Harvesting and processing cause plant tissue damage. In order to assess the role of plant tissue damage in the contamination of leafy greens with E. coli O157:H7, the effect of mechanical, physiological, and plant disease-induced lesions on the growth of this pathogen on postharvest romaine lettuce was investigated. Within only 4 h after inoculation, the population sizes of E. coli O157:H7 increased 4.0-, 4.5-, and 11.0-fold on lettuce leaves that were mechanically bruised, cut into large pieces, and shredded into multiple pieces, respectively. During the same time, E. coli O157:H7 population sizes increased only twofold on leaves that were left intact after harvest. Also, the population size of E. coli O157:H7 was 27 times greater on young leaves affected by soft rot due to infection by Erwinia chrysanthemi than on healthy middle-aged leaves. Confocal microscopy revealed that leaf tip burn lesions, which are caused by a common physiological disorder of lettuce, harbored dense populations of E. coli O157:H7 cells both internally and externally. Investigation of the colonization of cut lettuce stems by E. coli O157:H7 showed that the pathogen grew 11-fold over 4 h of incubation after its inoculation onto the stems, from which large amounts of latex were released. The results of this study indicate that plant tissue damage of various types can promote significant multiplication of E. coli O157:H7 over a short time and suggest that harvesting and processing are critical control points in the prevention or reduction of E. coli O157:H7 contamination of lettuce.
Article
The ability of electrolyzed water (EW) to inactivate foodborne pathogens on the surfaces of lettuce and spinach was investigated. Lettuce and spinach leaves were inoculated with a cocktail of 3 strains each of Escherichia col O157:H7, Salmnonella Typhimurium, and Listeria monocytogenes and treated with acidic electrolyzed water (AC-EW), alkaline electrolyzed water (AK-EW), alkaline electrolyzed water followed by acidic electrolyzed water (sequential treatment, AK-EW + AC-EW), deionized water followed by acidic electrolyzed water (sequential treatment, DW + AC-EW), and deionized water (control, DW) for 15, 30 s, and 1, 3, and 5 min at room temperature (22 +/- 2 degrees C). For all 3 pathogens, the same pattern of microbial reduction on lettuce and spinach were apparent. The relative efficacy of reduction was AC-EW > DW + AC-EW approximately = AK-EW + AC-EW > AK-EW > control. After a 3-min treatment of AC-EW, the 3 tested pathogens were reduced below the detection limit (0.7 log). DW + AC-EW and AK-EW + AC-EW produced the same levels of reduction after 5 min when compared to the control. AK-EW did not reduce levels of pathogens even after a 5-min treatment on lettuce and spinach. Results suggest that AC-EW treatment was able to significantly reduce populations of the 3 tested pathogens from the surfaces of lettuce and spinach with increasing time of exposure.
Article
In 2005 a large outbreak of verotoxin-producing Escherichia coli (VTEC) occurred in Sweden. Cases were interviewed and cohort and case-control studies were conducted. Microbiological investigations were performed using polymerase chain reaction (PCR) to detect the Shiga-like toxin (Stx) genes followed by cultivation and pulsed-field gel electrophoresis. A total of 135 cases were recorded, including 11 cases of hemolytic uremic syndrome. The epidemiological investigations implicated lettuce as the most likely source of the outbreak, with an OR of 13.0 (CI 2.94-57.5) in the case-control study. The lettuce was irrigated by water from a small stream, and water samples were positive for Stx 2 by PCR. The identical VTEC O157 Stx 2 positive strain was isolated from the cases and in cattle at a farm upstream from the irrigation point. An active surveillance and reporting system was crucial and cooperation between all involved parties was essential for quickly identifying the cause of this outbreak. Handling of fresh greens from farm to table must be improved to minimize the risk of contamination.
Article
Inspection of the available literature reveals that a detailed investigation of the aqueous organic chemistry of chlorine dioxide and systematic identification of products formed during water disinfection has not been considered. This must be done before an informed assessment can be made of the relative safety of using chlorine dioxide as a disinfectant alternative to chlorine. Although trihalomethanes are generally not formed by the action of chlorine dioxide, the products of chlorine dioxide treatment of organic materials are oxidized species, some of which also contain chlorine. The relative amounts of species types may depend on the amount of chlorine dioxide residual maintained and the concentration and nature of the organic material present in the source water. The trend toward lower concentrations of chlorinated by-products with increasing ClO2 concentration, which was observed with phenols, has not been observed with natural humic materials as measured by the organic halogen parameter. Organic halogen concentrations have been shown to increase with increasing chlorine dioxide dose, but are much lower than those observed when chlorine is applied. Aldehydes have been detected as apparent by-products of chlorine dioxide oxidation reactions in a surface water that is a drinking water source. Some other nonchlorinated products of chlorine dioxide treatment may be quinones and epoxides. The extent of formation of these moieties within the macromolecular humic structure is also still unknown.
Article
Confocal scanning laser microscopy was used to observe the location of Escherichia coli O157:H7 on and within lettuce leaves. Sections of leaves (ca. 0.5 by 0.5 cm) were inoculated by submersion in a suspension of E. coli O157:H7 (ca. 10(7) to 10(8) CFU/ml) overnight at 7 degrees C. Fluorescein isothiocyanate-labeled antibody was used to visualize the attached bacteria. E. coli O157:H7 was found attached to the surface, trichomes, stomata, and cut edges. Three-dimensional volume reconstruction of interior portions of leaves showed that E. coli O157:H7 was entrapped 20 to 100 microm below the surface in stomata and cut edges. Agar plate culturing and microscopic observation indicated that E. coli O157:H7 preferentially attached to cut edges, as opposed to the intact leaf surface. Dual staining with fluorescein isothiocyanate-labeled antibody and propidium iodide was used to determine viability of cells on artificially contaminated lettuce leaves after treatment with 20 mg/liter chlorine solution for 5 min. Many live cells were found in stomata and on cut edges following chlorine treatment. E. coli O157:H7 did not preferentially adhere to biofilm produced by Pseudomonas fluorescens on the leaf surface. In contrast to E. coli O157:H7, Pseudomonas adhered to and grew mainly on the intact leaf surface rather than on the cut edges.
Article
The effectiveness of various disinfectants against two potentially pathogenic Yersinia enterocolitica strains (Y. enterocolitica W1024 O:9 [strain A] and Y. enterocolitica B O:5 Lis Xz [strain B]) on shredded lettuce was examined. Dip-wash treatments using 25, 100, and 300 ppm of chlorine at 4 and 22 degrees C, 0.2% Orenco Peel 40, 0.1% Tergitol, 0.5% acetic acid, and 0.5% lactic acid at 22 degrees C were performed. Surfactants and organic acids were also tested in combination with 100 ppm of chlorine. Reductions of Y. enterocolitica counts with 100 ppm (2.68 log10 for strain A and 2.36 log10 for strain B at 22 degrees C) and 300 ppm of chlorine (3.15 log10 for strain A and 2.55 log10 for strain B at 4 degrees C) were observed after 10 min. Inhibitory effect of different chlorine solutions was not significantly (P < 0.05) influenced by temperature. Surfactants in combination with chlorine were more effective than surfactants alone. Treatment with 0.2% Orenco Peel 40 plus 100 ppm of chlorine resulted in reductions of 2.69 log10 CFU/g for strain A and 3.18 1og10 CFU/g for strain B at 10 min. Dip solutions containing 0.1% Tergitol plus 100 ppm of chlorine produced a significant reduction of 2.73 log10 CFU/g in strain A (P < 0.05). With the 0.5% lactic acid plus 100 ppm of chlorine combination, inactivation of Y. enterocolitica was >6 log10. The bactericidal effect of disinfectants was related to the concentration, exposure time, combination with chlorine (surfactants and organic acids), and susceptibility of each strain. Since the presence of pathogenic Y. enterocolitica on ready-to-use vegetables represents a health hazard, treatments as effective as 0.5% lactic acid plus 100 ppm of chlorine are recommended for washing of fresh lettuce.
Article
Bovine feces are a potential vehicle for transmitting enterohemorrhagic Escherichia coli O157:H7 to humans. A study was undertaken to determine survival characteristics of E. coli O157:H7 on iceberg lettuce using 0.1% peptone water and bovine feces as carriers for inocula. Four levels of inoculum, ranging from 10(0) to 10(5) CFU of E. coli O157:H7 per g of lettuce, were applied. Populations surviving on lettuce stored at 4 degrees C were monitored for up to 15 days. Regardless of the type of carrier, viable cells of E. coli O157:H7 were detected on lettuce after 15 days, even when the initial inoculum was 10(0) to 10(1) CFU/g. Spray treatments of lettuce with 200 ppm chlorine solution or deionized water were equally effective in killing or removing E. coli O157:H7 from lettuce. Holding lettuce for 5 min after spray treatment was not more effective in reducing populations than holding for 1 min before rinsing with water. Prevention of contamination of lettuce with bovine feces that may harbor E. coli O157:H7 as well as other infectious microorganisms is essential to minimizing the risk of illness. The development of sanitizers more efficacious than chlorine for the removal of pathogens from raw fruits and vegetable is needed.
Article
Penetration of Escherichia coli O157:H7 into iceberg lettuce tissues and the effect of chlorine treatment on cell viability were evaluated. Attachment of different inoculum levels (10(9), 10(8), and 10(7) CFU/ml) was examined by determining the number of cells at the surface and the cut edge of lettuce leaves (2 by 2 cm). E. coli O157:H7 attached preferentially to cut edges at all inoculum levels, with greater attachment per cm2 of lettuce at higher inoculum levels. A longer attachment time allowed more cells to attach at both sites. Immunostaining with a fluorescein isothiocyanate-labeled antibody revealed that cells penetrated into lettuce leaves from cut edges. Cells showed greater penetration when lettuce was held at 4 degrees C compared with 7, 25, or 37 degrees C and were detected at an average of 73.5 +/- 16.0 microm below the surfaces of cut tissues. Penetrating cells were mostly found at the junction of lettuce cells. The viability of attached cells after treatment with 200 mg/liter (200 ppm) of free chlorine for 5 min was examined by plating on tryptic soy agar and by a nalidixic acid elongation method. Although chlorine treatment caused significant reduction in attachment (0.7- and 1.0-log reduction at surfaces and cut edges, respectively), cells remained attached at high numbers (7.9 and 8.1 log CFU/cm2 at surfaces and cut edges, respectively). Elongated cells were observed in stomata and within the tissues of the lettuce, indicating they were protected from contact with chlorine.
Article
Studies have demonstrated that electrolyzed oxidizing (EO) water is effective in reducing foodborne pathogens on fresh produce. This study was undertaken to determine the efficacy of EO water and two different forms of chlorinated water (chlorine water from Cl2 and Ca(OCl)2 as sources of chlorine) in inactivating Salmonella on alfalfa seeds and sprouts. Tengram sets of alfalfa seeds inoculated with a five-strain cocktail of Salmonella (6.3 x 10(4) CFU/g) were subjected to 90 ml of deionized water (control), EO water (84 mg/liter of active chlorine), chlorine water (84 mg/liter of active chlorine), and Ca(OCl)2 solutions at 90 and 20,000 mg/liter of active chlorine for 10 min at 24 +/- 2 degrees C. The application of EO water, chlorinated water, and 90 mg/liter of Ca(OCl)2 to alfalfa seeds for 10 min reduced initial populations of Salmonella by at least 1.5 log10 CFU/g. For seed sprouting, alfalfa seeds were soaked in the different treatment solutions described above for 3 h. Ca(OCl)2 (20,000 mg/liter of active chlorine) was the most effective treatment in reducing the populations of Salmonella and non-Salmonella microflora (4.6 and 7.0 log10 CFU/g, respectively). However, the use of high concentrations of chlorine generates worker safety concerns. Also, the Ca(OCl)2 treatment significantly reduced seed germination rates (70% versus 90 to 96%). For alfalfa sprouts, higher bacterial populations were recovered from treated sprouts containing seed coats than from sprouts with seed coats removed. The effectiveness of EO water improved when soaking treatments were applied to sprouts in conjunction with sonication and seed coat removal. The combined treatment achieved 2.3- and 1.5-log10 CFU/g greater reductions than EO water alone in populations of Salmonella and non-Salmonella microflora, respectively. This combination treatment resulted in a 3.3-log10 CFU/g greater reduction in Salmonella populations than the control (deionized water) treatment.
Article
The influence of bacterial inoculation methods on the efficacy of sanitizers against pathogens was examined. Dip and spot inoculation methods were employed in this study to evaluate the effectiveness of acidic electrolyzed water (AcEW) and chlorinated water (200 ppm free available chlorine) against Escherichia coli O157:H7 and Salmonella spp. Ten pieces of lettuce leaf (5 by 5 cm) were inoculated by each method then immersed in 1.5 liters of AcEW, chlorinated water, or sterile distilled water for 1 min with agitation (150 rpm) at room temperature. The outer (abaxial) and inner (adaxial) surfaces of the lettuce leaf were distinguished in the spot inoculation. Initial inoculated pathogen population was in the range 7.3 to 7.8 log CFU/g. Treatment with AcEW and chlorinated water resulted in a 1 log CFU/g or less reduction of E. coli O157:H7 and Salmonella populations inoculated with the dip method. Spot inoculation of the inner surface of the lettuce leaf with AcEW and chlorinated water reduced the number of E. coli O157:H7 and Salmonella by approximately 2.7 and 2.5 log CFU/g, respectively. Spot inoculation of the outer surface of the lettuce leaf with both sanitizers resulted in approximately 4.6 and 4.4 log CFU/g reductions of E. coli O157:H7 and Salmonella, respectively. The influence of inoculation population size was also examined. Each sanitizer could not completely eliminate the pathogens when E. coli O157:H7 and Salmonella cells inoculated on the lettuce were of low population size (10(3) to 10(4) CFU/g), regardless of the inoculation technique.
Article
The elimination of Listeria monocytogenes inoculated onto a piece of cut iceberg lettuce (3.8 by 3.8 cm) by treatment with chlorinated water (200 micrograms/ml free chlorine) and a 0.5% (wt/vol) solution of FIT Professional Line Antibacterial Cleaner (FIT) was investigated. The efficacy of the two sanitizers was not influenced by the composition of the medium used to culture the L. monocytogenes used in the inocula, the number of strains in the inoculum, or the recovery medium used to enumerate the pathogen on lettuce after treatment. Drying inoculum on lettuce for 45 min at 37 degrees C caused more cells to die or not be retrieved compared with drying inoculum for 30 min at 25 degrees C. However, the percentage of cells in the inoculum recovered from lettuce treated with chlorine or FIT was not significantly different, regardless of the drying method. Stomaching, homogenizing, or stomaching followed by homogenizing lettuce treated with sanitizers resulted in recovery of similar numbers of L. monocytogenes, indicating that stomaching and homogenizing are equivalent in extracting cells; the sequential use of both processing methods did not substantially increase the efficiency of recovery. Washing lettuce with water or treating lettuce with 200 micrograms/ml chlorine or FIT resulted in decreases in populations of 0.60, 1.76, and 1.51 log CFU per lettuce piece, respectively, regardless of variations in test parameters. Reductions caused by sanitizers were significantly greater (alpha = 0.05) than that observed for water but not significantly different from each other. It is concluded that evaluation of sanitizers for their efficacy in killing L. monocytogenes on lettuce can be determined by spot inoculating 50 microliters of a five-strain mixture of cells from 24-h cultures suspended in 5% horse serum albumen, followed by drying the inoculum for 45 min at 37 degrees C, treatment by submerging in 50 ml of sanitizer for 5 min, stomaching samples in 50 ml of Dey-Engley neutralizing broth for 2 min, and enumerating survivors on modified Oxford medium.
Article
The efficacy of chlorine (100 microg/ml) and a peroxyacetic acid sanitizer (80 microg/ml; Tsunami 100) in killing Listeria monocytogenes inoculated at populations of 1 to 2, 2 to 3, and 4 to 5 log CFU/g of iceberg lettuce pieces, shredded iceberg lettuce, and Romaine lettuce pieces was determined by treatment conditions simulating those used by a commercial fresh-cut lettuce processor. The lettuce/treatment solution ratio was 1:100 (wt/vol), treatment temperature was 4 degrees C, and total treatment time was 30 s. Compared with washing in water, treatment of iceberg lettuce pieces containing all levels of inoculum and shredded iceberg lettuce containing 2 to 3 or 4 to 5 log CFU/g with chlorine or Tsunami resulted in significant reductions (P < or = 0.05) of pathogen populations. Populations recovered from Romaine lettuce pieces treated with chlorine or Tsunami were not significantly different from populations recovered from pieces washed with water, regardless of the inoculum level. Within lettuce type and inoculum level, in no instance was the number of L. monocytogenes recovered from lettuce treated with chlorine or Tsunami significantly different. The rate of decrease in free chlorine concentration in treatment solution as affected by the weight/volume ratio (1:100, 1:10, 2:10, and 4:10) of lettuce and solution was determined. The rate of reduction increased as the ratio decreased. The overall order of magnitude of reduction was shredded iceberg lettuce > iceberg pieces > Romaine pieces. The highest reductions in free chlorine concentration in solutions used to treat shredded lettuce are attributed to the release of tissue juices, which increases the concentration of soluble organic materials available for reaction with chlorine.
Article
The effects of method for applying inoculum and of drying time after inoculation on survival and recovery of foodborne pathogens on iceberg lettuce and parsley were studied. Five-strain mixtures of Escherichia coli O157:H7, Salmonella, or Listeria monocytogenes were applied to lettuce and parsley by dip, spot, or spray inoculation methods. Inocula were dried for 2 h at 22 degrees C or for 2 h at 22 degrees C and then 22 h at 4 degrees C before being treated with water (control) or chlorine (200 microg/ml). Significantly higher populations (CFU per lettuce or parsley sample) of E. coli O157:H7 and Salmonella (alpha = 0.05) were recovered from dip-inoculated produce than from spot- or spray-inoculated produce. This difference was attributed to larger numbers of cells adhering to lettuce and parsley subjected to dip inoculation. Populations of E. coli O157:H7 and Salmonella recovered from lettuce inoculated by spot and spray methods were not significantly different, but populations recovered from spot-inoculated parsley were significantly higher than those recovered from spray-inoculated parsley, even though the number of cells applied was the same. Significantly different numbers of L. monocytogenes were recovered from inoculated lettuce (dip > spray > spot); populations recovered from dip-inoculated parsley were significantly higher than those recovered from spot- or spray-inoculated parsley, which were not significantly different from each other. Populations of pathogens recovered from lettuce and parsley after drying inoculum for 2 h at 22 degrees C were significantly higher than or equal to populations recovered after drying for 2 h at 22 degrees C and then for 22 h at 4 degrees C. Significant differences (water > chlorine) were observed in populations of all pathogens recovered from treated lettuce and parsley, regardless of inoculation method and drying time. It is recommended that spot inoculation with a drying time of 2 h at 22 degrees C followed by 22 h at 4 degrees C be used to determine the efficacy of chlorine and other sanitizers in killing foodborne pathogens on lettuce and parsley.
Article
Interaction of Escherichia coli O157:H7/pGFP with hydroponically grown lettuce plants was evaluated in this study. Lettuce seedlings were planted in contaminated Hoagland's nutrient solution and thereafter subjected to gamma radiation at 0.25, 0.5, and 0.75 kGy, and aqueous chlorine at 200 ppm. There was no trace of E. coli O157:H7/pGFP in lettuce leaves harvested from noncontaminated nutrient solution (control); however, for plants grown in contaminated nutrient solution, the pathogen was recovered from the leaves disinfected with 80% ethanol and 0.1% mercuric chloride. Most of the lettuce seedlings grown in contaminated nutrient solution tested negative for E. coli O157:H7/pGFP under controlled conditions. Gamma radiation at 0.25 and 0.5 kGy, and aqueous chlorine at 200 ppm failed to eliminate E. coli O157:H7/pGFP in lettuce tissue completely; however, the bacteria were not detected in 0.75-kGy treated plants. The presence of E. coli O157:H7/pGFP in lettuce leaves is an indication that the pathogen migrated from the contaminated hydroponic system through the roots to the internal locations of lettuce tissue. Due to inaccessibility and limited penetrating power, aqueous chlorine could not eliminate the bacteria localized in the internal tissue. Findings from this study suggest that gamma irradiation was more efficacious than was aqueous chlorine to control internal contamination in hydroponically grown lettuce. Gamma irradiation is a process that processors can use to inactivate E. coli O157:H7 and therefore, consumers benefit from a safer food product [corrected]
Article
To study and compare the efficacy of organic acids and chlorine dipping in inactivation of Escherichia coli and Listeria monocytogenes on fresh-cut iceberg lettuce. Fresh-cut iceberg lettuce leaves were inoculated with E. coli or L. monocytogenes. After inoculation, samples were stored at 4 degrees C for 24 h and dipped in organic acid or chlorine solutions for 2 and 5 min. E. coli and L. monocytogenes were enumerated on selective media. Treatment of fresh-cut iceberg lettuce with chlorine solution caused 1.0 and 2.0 log(10) CFU g(-1) reductions in the number of L. monocytogenes and E. coli, respectively. Maximum reduction for E. coli (about 2.0 log(10) CFU g(-1)) was obtained for samples dipped in lactic or citric acids while maximum reduction for L. monocytogenes (about 1.5 log(10) CFU g(-1)) was attained for samples dipped in lactic acid. Dipping of iceberg lettuce in 0.5% citric acid or 0.5% lactic acid solution for 2 min could be as effective as chlorine for reducing microbial populations on fresh-cut iceberg lettuce. Dipping in solutions containing organic acids is shown to be effective to reduce E. coli and L. monocytogenes on fresh-cut iceberg lettuce.
Article
Recent foodborne outbreaks implicating spinach and lettuce have increased consumer concerns regarding the safety of fresh produce. While the most common commercial antimicrobial intervention for fresh produce is wash water containing 50 to 200 ppm chlorine, this study compares the effectiveness of acidified sodium chlorite, chlorine, and acidic electrolyzed water for inactivating Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes inoculated onto leafy greens. Fresh mixed greens were left uninoculated or inoculated with approximately 6 log CFU/g of E. coli O157:H7, Salmonella, and L. monocytogenes and treated by immersion for 60 or 90 s in different wash solutions (1:150, wt/vol), including 50 ppm of chlorine solution acidified to pH 6.5, acidic electrolyzed water (pH 2.1 +/- 0.2, oxygen reduction potential of 1,100 mV, 30 to 35 ppm of free chlorine), and acidified sodium chlorite (1,200 ppm, pH 2.5). Samples were neutralized and homogenized. Bacterial survival was determined by standard spread plating on selective media. Each test case (organism x treatment x time) was replicated twice with five samples per replicate. There was no difference (P > or = 0.05) in the time of immersion on the antimicrobial effectiveness of the treatments. Furthermore, there was no difference (P > or = 0.05) in survival of the three organisms regardless of treatment or time. Acidified sodium chlorite, resulted in reductions in populations of 3 to 3.8 log CFU/g and was more effective than chlorinated water (2.1 to 2.8 log CFU/g reduction). These results provide the produce industry with important information to assist in selection of effective antimicrobial strategies.
Method for optimizing the efficacy of chlorous acid and other disinfecting sprays for poultry and other meats
  • R D Kross
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Kross, R.D., Kemp, G.K., 2000. Method for optimizing the efficacy of chlorous acid and other disinfecting sprays for poultry and other meats. United States Patent No. 6063425.
Biofilms on fresh produce and difficulties in decontamination
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Annous, B.A., Solomon, E.B., Niemira, B.A., 2006. Biofilms on fresh produce and difficulties in decontamination. Food Quality 13, 80-84.
Efficacy of electrolyzed oxidizing water in inactivating Salmonella on alfalfa seeds and sprouts
  • Co Ltd
Hoshizaki Electric Co., Ltd., 2003. ROX water electrolyzer. http://www.hoshizakiamerica. com/rox.asp. Accessed August 11, 2008. Kim, C., Hung, Y.-C., Brackett, R.E., Lin, C.-S., 2003. Efficacy of electrolyzed oxidizing water in inactivating Salmonella on alfalfa seeds and sprouts. Journal Food Protection 66, 208–214.
Ongoing multistate outbreak of Escherichia coli serotype O157:H7 infections associated with consumption of fresh spinach-United States
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ROX water electrolyzer
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Soderstrom, A., Osterberg, P., Lindqvist, A., Jonsson, B., Lindberg, A., Ulander, S.B., Welinder-Olsson, C., Lofdahl, S., Kaijser, B., De Jong, B., Kuhlmann-Berenzon, S., Boqvist, S., Eriksson, E., Szanto, E., Andersson, S., Allestam, G., Hedenstrom, I., Muller, L.L., Andersson, Y., 2008. A large Escherichia coli O157 outbreak in Sweden associated with locally produced lettuce. Foodborne Pathogens and Disease 5, 339–349.
Biofilms on fresh produce and difficulties in decontamination
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