SEARCH

SEARCH BY CITATION

Keywords:

  • chlorine;
  • coconut water;
  • fresh fruit;
  • green coconut;
  • Listeria monocytogenes;
  • peracetic acid;
  • sanitization

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. References

Aims:  To evaluate the efficacy of sanitizing green coconuts (Cocos nucifera L.) through the treatment applied by juice industries using sodium hypochlorite and peracetic acid.

Methods and Results:  The surface of the fruits was inoculated with a mixture of five Listeria monocytogenes strains. The treatments consisted in immersing the fruits for 2 min at room temperature in sodium hypochlorite solution containing 200 mg l−1 residual chlorine at pH 6·5, and 80 mg l−1 solution of peracetic acid or sterile water. Bacterial populations were quantified by culturing on trypticase soy agar supplemented with yeast extract and Oxford selective culture medium; however, recovery was higher on the nonselective medium. Immersion in water produced a reduction in the L. monocytogenes population of 1·7 log10 CFU per fruit, while immersion in sodium hypochlorite and peracetic acid solutions resulted in population reductions of 2·7 and 4·7  log10 CFU per fruit respectively.

Conclusions:  The treatments studied are efficient to green coconuts.

Significance and Impact of the Study:  Sanitation of green coconut is one of the most important control measures to prevent the contamination of coconut water. This article provides information that shows the adequacy of sanitizing treatments applied by the juice industries.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. References

Coconut water is a refreshing beverage much appreciated in tropical countries, especially in coastal areas. On the international market, coconut water has an all-natural appeal, in addition to a wide array of alleged functional benefits (Hollingsworth 2000). In Brazil, processed coconut water have been commercialized with the McDonald’s brand on the box (Kohler 2008). However, the sensory characteristics of fresh coconut water are considered much superior to the overall flavour profile of the processed beverage (Frassetti et al. 2003; Abreu et al. 2005).

Traditionally, coconut water is consumed directly from the fruit after sectioning out a centre hole to access the juice. However, because of difficulties to transport and cut the fruit open, unprocessed coconut water is often extracted, refrigerated and conveniently filled into retail containers. However, during this process, the juice is contaminated because of the direct contact with the epidermis of the coconuts and equipment surfaces (Walter et al. 2009).

The chemical composition of coconut water, with its high levels of sugars and mineral salts (Jayalekshmy et al. 1986), pH value above 4·5 and water activity close to 1·0, provides favourable conditions for microbial growth. Escherichia coli and Salmonella have been detected in cold-stored in natura (that is, fresh, unprocessed) coconut water (Melo et al. 2003), in addition to Staphylococcus aureus populations of up to 8·0 × 104 CFU ml−1 (Hoffmann et al. 2002) and Bacillus cereus counts of 1·6 × 105 CFU ml−1 (Leite et al. 2000). Fortes et al. (2006) analysed 20 samples of unprocessed coconut water in plastic bottles and found that none met the minimum microbiological requirements set forth in Brazilian legislation. Our previous work showed the development of Listeria monocytogenes in coconut water stored at 4, 10 and 35°C (Walter et al. 2009).

Listeria monocytogenes is a psychrotrophic and ubiquitous pathogen (Fenlon 1999; Gandhi and Chikindas 2007). This pathogen presents a high mortality rate among some high risk groups, including the newborn, the aged and people with compromised immune systems (Slutsker and Schuchat 1999). These people and pregnant women choose to consume coconut water because of its natural isotonic appeal and other claimed therapeutic properties. Despite no Listeriosis outbreaks associated with the consumption of coconut water have been found, vegetables have been recognized to harbour L. monocytogenes (Fröder et al. 2007; Little et al. 2007; Chen et al. 2009) or have been associated with listeriosis outbreaks (Schlech et al. 1983; Varma et al. 2007). The risk for coconut contamination by L. monocytogenes is increased because of the agricultural practices. During harvest the fruits are placed directly on the soil, the natural habitat of L. monocytogenes. In addition, during fresh coconut water processing, there is no lethal step between extraction and packaging that assures beverage microbial safety. Furthermore, L. monocytogenes has the ability to survive for longer periods under adverse environmental conditions when compared to nonsporeforming pathogenic bacteria relevant to public health (Fenlon 1999; Gandhi and Chikindas 2007), in addition to being more chlorine resistant than Salmonella and E. coli O157:H7 (Burnett and Beuchat 2000).

Chlorinated compounds, particularly hypochlorites, are widely used in microbial control and have along history of application in the food processing industry (Wei et al. 1985). In addition to their economic benefits, hypochlorites are effective in inactivating micro-organisms suspended in water and on nonporous surfaces (Brackett 1987). However, on the surface of fruits and green leafy vegetables, their efficacy is rather limited (Burnett and Beuchat 2000). Other negative side effects are associated with the formation of potentially toxic compounds that contaminate the environment (Wei et al. 1985; Richardson 2003). Peracetic acid appears as an alternative to chlorinated compounds because of its higher efficiency and lower pollution potential, in spite of its higher costs.

The objective of this study was to evaluate the efficacy of sodium hypochlorite and peracetic acid in eliminating L. monocytogenes artificially inoculated onto the surface of green coconuts.

Materials and methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. References

Preparation of the green coconuts

The experiments were conducted with 7-month-ripened green coconuts (Cocos nucifera L.) of the Dwarf variety, produced in the State of Espírito Santo (Brazil). The fruits were visually selected from bunches and washed by hand using a sponge and an alkaline detergent. This procedure reduced natural microbial load of the fruits, enabling reliable enumeration of L. monocytogenes on nonselective medium. After air-drying the green coconuts at room temperature, the outlines of a surface area 3·0 vs 2·0 cm in size were traced using a sterilized scalpel on one of the relatively flat side fruit surfaces without mechanical injuries. This area on the fruit surface, delineated as described, is the testing surface onto which L. monocytogenes was inoculated.

Test micro-organisms

The inoculum consisted of a mixture of five L. monocytogenes strains: IOC 1898 (serovar 1/2a, isolated from spinach), ATCC 19115 (serovar 4b, clinical isolate), IOC 1551 (serovar 1/2a, isolated from bacon), IOC 1324 (serovar 1/2b, isolated from fresh sausage), IOC 1527 (serovar 1/2a, isolated from frozen cooked meat). The first strain was obtained from the culture collection of the University of São Paulo (São Paulo, Brazil), while the other strains were provided by the Fundação Oswaldo Cruz (Rio de Janeiro, Brazil). The strains had their identity confirmed by biochemical tests (Pagotto et al. 2001) and were screened for mutual antagonism (Beuchat et al. 2001). No mutual antagonism was detected between the L. monocytogenes strains in this cross-inhibition test, in which the strains exhibited compatible development and growth on trypticase soy agar supplemented with 0·6% yeast extract (TSA-YE) (Difco). The cultures were grown on TSA-YE (Difco) at 4°C.

Inoculum preparation

The five L. monocytogenes strains were cultivated individually in 10 ml trypticase soy broth supplemented with 0·6% yeast extract (TSB-YE; Difco) at 35°C. The cultures were transferred at three successive 24 h intervals. Each of the cell suspensions was centrifuged (2000 g for 15 min, at room temperature), the supernatant fluids discarded, and the cell sediments washed in 10 ml 0·1% peptone water. The centrifugation procedure was repeated, and the bacterial cell masses resuspended in 10 ml 0·1% peptone water. The inoculum, containing approximately 9·0 log10 CFU ml−1, was obtained by combining equal volumes of the five suspensions.

Inoculation and drying procedure

Inoculation was accomplished by applying 100 μl of the inoculum suspension using a micropipette in the form of 20 droplets evenly distributed onto the testing surface (i.e. the delineated 3·0 vs 2·0 cm surface area) of 12 green coconuts per repetition. Immediately upon inoculation, the green coconuts were placed into a drying chamber where they were kept for 24 h, at a temperature of 36 ± 3°C and relative humidity of 81 ± 7%.

Preparation of sanitizing solutions

The chlorinated solution was prepared by adding sodium hypochlorite (Indústria Anhembi, Osasco, SP, Brazil) to 1·8 l of a sterile 0·01 mol l−1 potassium phosphate buffer solution, yielding a sanitizing solution containing 200 mg l−1 residual chlorine and pH 6·5. The 80 mg l−1 peracetic acid solution was prepared by adding Tsunami 100, stock solution composed of acetic acid (15–40% w/w), hydrogen peroxide (7–13% w/w) and peracetic acid (10–30% w/w) (Ecolab Química Ltda, Rio de Janeiro, RJ, Brazil) to 1·8 l sterile-distilled water. The chlorinated solution was analysed by the method of the American Public Health Association (Bradley et al. 1992), whereas the peracetic acid solution was tested as recommended by the manufacturer. The test solutions were prepared 30 min before actual use in flasks with adequate light barrier properties and fitted with screw caps and transferred to the immersion vessel 1 min before initiating the experimental treatments.

Treatments

The treatments consisted in immersing the fruits for 2 min at room temperature (22 ± 4°C) in (i) sodium hypochlorite solution at pH 6·5 containing 200 mg l−1 residual chlorine, (ii) 80 mg l−1 peracetic acid solution, (iii) sterile-distilled water. Treatments studied refereed to those applied by juice industries and coconut water producers in Brazil (W.P. Tamega Jr, personal communication; Parish et al. 2006). The fruits were positioned so as to ensure complete immersion of the testing surface, at successive intervals of 15 min. The treatments were performed in triplicate. In each repetition, three green coconuts were subjected to analysis to determine the initial L. monocytogenes population, and three fruits were exposed to each of the treatments investigated, totalizing nine fruits per treatment.

Sample preparation for analysis

For the purpose of determining the initial L. monocytogenes populations and the populations still present after exposure to the sanitation treatments, the testing surface was removed using a sterilized knife and tweezers and placed into a Stomacher 400 bag containing 5·0 ml recovery solution, which consisted of 0·1% peptone water and a neutralizing agent (0·05 mol l−1 sodium thiosulphate) (Merck KGaA). Recovery of the bacterial cells was accomplished by vigorously rubbing the testing surface with the fingers against the outside of the Stomacher 400 bag for 1 min. Finally, the sample preparation procedure was concluded by agitating for 30 s. Preliminary tests indicated that manual rubbing resulted in greater recovery when compared to agitation of the Stomacher 400 (Seward Medical).

Microbiological analyses

The population of L. monocytogenes was determined by serial dilution (1 : 10) in 0·1% peptone water, followed by inoculation of the aliquots (0·1 ml in duplicate and 0·25 ml in quadruplicate) onto TSA-YE (Difco) and Oxford culture medium (OXA) (Oxoid), with incubation at 35°C for 48 h (Ryser and Donnelly 2001). Three isolated colonies from each treatment were subjected to biochemical confirmation (Pagotto et al. 2001).

Investigation into the inhibitory effects of plant fluids

Possible inhibitory effects on the L. monocytogenes strains exerted by plant sap/fluids released by rubbing the testing surface of the green coconuts and present in the recovery solution were analysed in accordance with the APHA (American Public Health Association) method for the determination of toxic substances in water (Marshall and Richardson 1992).

Statistical analysis

The experimental data relative to the initial and after treatment L. monocytogenes populations on the testing surfaces were converted to logarithmic values and analysed by analysis of variance (anova). A comparison of means was performed using the Tukey test, with the least significant difference set at the 5% level of significance. All calculations were performed using the sas, ver. 6·11, software package (SAS Institute, Inc.).

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. References

Influence of the experimental conditions on the quantification of Listeria monocytogenes

There was no significant difference (P < 0·05) between the counts of L. monocytogenes strains dispersed for 15, 30 and 60 min, in the plant sap/fluid and in 0·1% peptone water enumerated on TSA-YE and OXA (data not shown).

The population of the L. monocytogenes strain cocktail inoculated onto the testing surface of green coconuts (100 μl suspension) was 8·6 log10 CFU per fruit, when determined by plating the inoculum on TSA-YE. After drying the inoculum, a cell concentration of 6·8 log10 CFU per fruit was recovered. On OXA selective culture medium, the population of the L. monocytogenes strain cocktail inoculated onto the testing surface was 8·5 log10 CFU per fruit and did not differ (P < 0·05) from the population determined by plating on nonselective culture medium. However, after drying of the inoculum, the cell concentration on OXA was 6·0 log10 CFU per fruit, significantly different (P < 0·05) from the count on TSA-YE.

The enumeration of L. monocytogenes on nonselective medium (TSA-YE) were greater than (P < 0·05) those on selective culture medium (OXA), in all treatments investigated (Table 1). Thus, the enumeration on TSA-YE was used to calculate the degree of sanitization brought about by the chemical treatments investigated in this study.

Table 1.   Recovery of Listeria monocytogenes before and after sanitation treatments of green coconuts in nonselective (TSA-YE) and selective (OXA) culture media
MediumTreatment (log10 CFU per fruit)*
ControlH2OHOCl2PAA
  1. TSA-YE, trypticase soy agar yeast extract; OXA, Oxford culture medium.

  2. *L. monocytogenes populations recovered before (Control) and after immersion of the fruits for 2 min at room temperature in water (H2O), in a sodium hypochlorite solution containing 200 mg l−1 residual chlorine and pH 6·5 (HOCl2), and in a 80 mg l−1 peracetic acid solution (PAA).

  3. †Means and standard deviation of L. monocytogenes populations from three fruits in triplicate. Means followed by the same letter in the same column (comparison between means) and in the same row (comparison between treatments) do not differ from each other (P < 0·05).

TSA-YE6·8 ± 0·2 a†5·1 ± 0·3 b4·1 ± 0·82 c2·1 ± 0·5 d
OXA6·0 ± 0·4 a4·6 ± 0·2 b3·3 ± 0·42 c1·6 ± 0·4 d

Influence of the treatments on the sanitization green coconuts

The reductions in the populations of L. monocytogenes brought about by the treatments investigated and quantified on TSA-YE are depicted in Fig. 1. Immersing green coconuts in water for 2 min was a less effective treatment, resulting in a 1·7 log10 CFU per fruit reduction of the L. monocytogenes population whereas the chemical treatments significantly reduced L. monocytogenes population in green coconuts. The treatment with a solution of sodium hypochlorite (200 mg l−1 residual chlorine and pH 6·5) for 2 min produced a reduction of 2·7 log10 CFU per fruit in the population of L. monocytogenes. The treatment with a solution of peracetic acid (80 mg l−1) for 2 min brought about a reduction of 4·7 log10 CFU per fruit in the population of L. monocytogenes. There was significant difference between the treatments (P < 0·05) in that immersion in a peracetic acid solution was more effective than in a sodium hypochlorite solution.

image

Figure 1.  Reduction in Listeria monocytogenes populations on the surface of green coconuts immersed for 2 min in water (H2O), a hypochlorite solution containing 200 mg l−1 residual chlorine and pH 6·5 (HOCl2), and a solution of 80 mg l−1 peracetic acid (PAA).

Download figure to PowerPoint

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. References

Influence of the experimental conditions on the quantification of Listeria monocytogenes

It was concluded that the plant fluids released by rubbing the fruit surface did not exert any inhibitory or lethal effect on the L. monocytogenes strains used in this study. The inhibitory effects of plant fluids may lead to overestimation of the degree of lethality of the sanitization treatments (Beuchat et al. 2001).

Conducting experiments utilizing a small surface area of green coconuts not only facilitates the handling of the sample specimens (i.e. large fruits) and the cell recovery procedures, but also reduces the recovered natural microbial load. For that reason, the number of L. monocytogenes cells greatly exceeded that of natural microbiota, thereby enabling reliable enumeration on nonselective medium.

The difference between the populations of L. monocytogenes strains inoculated onto the testing surface and after drying the inoculums may be attributed to both incomplete removal of bacterial cells adhered to the epidermis of the fruit and to bacterial death or cell stress during drying. The difference between the counts on TSA-YE and OXA may indicate that some L. monocytogenes may have been injured and had not been able to form visible colonies in the presence of selective substances (Beuchat et al. 2006).

The greater recovery of the L. monocytogenes strains on the nonselective medium were compared to selective medium indicates that part of the bacterial population was stressed and unable to form visible colonies in the presence of selective substances. The presence of stressed bacterial cells may lead to overestimation of the degree of lethality of the sanitization treatments (Beuchat et al. 2001). This fact justifies the use of a nonselective culture medium to calculate the degree of disinfection brought about by the chemical treatments investigated in this study.

Influence of the treatments on the sanitization green coconuts

The disinfection achieved by immersion in plain water can be attributed to the merely physical removal or detachment of the bacterial cells from the fruit surface by the rinsing procedure. However, in this case, the water itself becomes a potential source of contamination or recontamination of the fruits, thereby evidencing the primary function of sanitizers: to maintain and preserve the microbiological quality of water (Brackett 1999; Venkitanarayanan et al. 2002).

Brackett (1987) found that a residual chlorine concentration of 50 mg l−1 in a potassium phosphate buffer caused more than 5 log10 reductions of L. monocytogenes suspensions in water. Higher chlorine concentrations are typically recommended, because in the case of commercial products the lower effectiveness of chlorine on surfaces should be taken into account, along with its consumption and instability (Dychdala 1991).

The results found in this study for the treatment with the sodium hypochlorite solution were according to generic estimates reported by Burnett and Beuchat (2000). They concluded that effectiveness of chlorinated solutions on fruits and vegetables translates into microbial reductions varying between 2 and 3 log10 cycles.

The greater efficacy of peracetic acid when compared to immersion in water and in a solution of sodium hypochlorite may be associated with the hydrophobic nature of its molecule (Fatemi and Frank 1999), which enables greater penetration into the hydrophobic multilayer cuticle of fruits’ and vegetables’ epidermis.

A series of limitations make comparisons between the results produced by disinfection treatments of fruits and vegetables somewhat difficult because the substantial variations that may occur or affect the experimental conditions. These variations include the type of produce, the test micro-organism, preparation of the inoculum, the inoculation method, storage of the fruit/vegetable before treatment, treatment conditions, recovery procedures and microbiological analysis procedures (Beuchat et al. 2001). However, Rodgers et al. (2004) reported a reduction in the population of L. monocytogenes (initial population of 6 log10 CFU g−1) to nondetectable levels in apples, cantaloupes, strawberries and lettuce leafs after 5-min immersion in solutions of chlorinated trisodium phosphate (200 mg l−1 residual chlorine) and peracetic acid (80 mg l−1).

The results of this study demonstrate that chemical treatments with solutions of either sodium hypochlorite or peracetic acid are effective to sanitize young green coconut. Although immersion in a solution of peracetic acid produced a greater reduction in L. monocytogenes counts, sanitation with a solution of sodium hypochlorite also produced satisfactory results.

Independently of the sanitizing solution employed to sanitize the surface of the fruits, it should be stressed that the reduction achieved are insufficient to ensure coconut water free of micro-organisms, including pathogenic bacteria (Harris et al. 2006). In spite of this, the sanitation of green coconut is one of the most important control measures to prevent the contamination of coconut water, specially the beverage that is packaged, stored and consumed fresh.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. References
  • Abreu, L.F., Araújo, A.V.C., Araújo, E.A.F., El-Aouar, A.A., Neumann, D. and Silva, M.A.A.P. (2005) Perfil sensorial e aceitabilidade de amostras de água de coco obtidas por diferentes processos de fabricação. Bol Cent Pesqui Process Aliment 23, 397412.
  • Beuchat, L.R., Ward, T.E. and Pettigrew, C.A. (2001) Comparison of chlorine and a prototype produce wash product for effectiveness in Killing Salmonella and Escherichia coli O157:H7 on alfalfa seeds. J Food Prot 64, 152158.
  • Beuchat, L.R., Farber, J.M., Garrett, E.H., Harris, L.J., Parish, M.E., Suslow, T.V. and Busta, F.K. (2006) Standardization of a method to determine the efficacy of sanitizers in inactivating human pathogenic microorganisms on raw fruits and vegetables. Compr Rev Food Sci Food Saf 2, 174178.
  • Brackett, R.E. (1987) Antimicrobial effect of chlorine on Listeria monocytogenes. J Food Prot 50, 9991003.
  • Brackett, R.E. (1999) Incidence, contributing factors, and control of bacterial pathogens in produce. Postharvest Bio Technol 15, 305311.
  • Bradley, R.L. Jr, Arnold, E. Jr, Barbano, D.M., Semerad, R.G., Smith, D.E., Vines, B.K. and Case, R.A. (1992) Chemical and physical methods. In Standard Methods for the Examination of Dairy Products, 16th edn ed. Marshall, R.T.. pp. 433531. Washington, DC: American Public Health Association.
  • Burnett, S.L. and Beuchat, L.R. (2000) Human pathogens associated with raw produce and unpasteurized juices, and difficulties in decontamination. J Ind Microbiol Biotechnol 25, 281287.
  • Chen, J., Luo, X., Jiang, L., Jin, P., Wei, W., Liu, D. and Fang, W. (2009) Molecular characteristics and virulence potential of Listeria monocytogenes isolates from Chinese food systems. Food Microbiol 26, 103111.
  • Dychdala, G.R. (1991) Chlorine and chlorine compounds. In Disinfection, Sterilization, and Preservation, 4th edn ed. Block, S.S. pp. 131151. Philadelphia: Lea & Febiger.
  • Fatemi, P. and Frank, J.F. (1999) Inactivation of Listeria monocytogenes/Pseudomonas biofilms by peracid sanitizers. J Food Prot 62, 761765.
  • Fenlon, D.R. (1999) Listeria monocytogenes in the natural environment. In Listeria, Listeriosis, and Food Safety, 2nd edn ed. Ryser, E.T. and Marth, E.H.. pp. 2138. New York: Marcel Dekker, Inc.
  • Fortes, E.P., Lima, A., Cronemberg, M.G.O. and Crispim, L.S. (2006) Qualidade físico-química e microbiológica das águas-de-coco envasadas e comercializadas em Teresina, Piauí. Hig Aliment 20, 8790.
  • Frassetti, J., Tórtora, J.C.O. and Gregório, S.R. (2003) Aceitação da água de coco in natura e processada. In 17th Congresso Brasileiro de Ciência e Tecnologia de Alimentos. p. 3.87. Fortaleza, Ceara, Brazil. August 8–10, 2003.
  • Fröder, H., Martins, C.G., Souza, K.L.O., Landgraf, M., Franco, B.D.G.M. and Destro, M.T. (2007) Minimally processed vegetable salads: microbial quality evaluation. J Food Prot 70, 12771280.
  • Gandhi, M. and Chikindas, M. (2007) Listeria: a foodborne pathogen that knows how to survive. Int J Food Microbiol 113, 115.
  • Harris, L.J., Farber, J.N., Beuchat, L.R., Parish, M.E., Suslow, T.V., Garret, E.H. and Busta, F.F. (2006) Outbreaks associated with fresh produce: Incidence, growth, and survival of pathogens in fresh and fresh-cut produce. Compr Rev Food Sci Food Saf 2, 78141.
  • Hoffmann, F.L., Coelho, A.R., Mansor, A.P., Takahashi, C.M. and Vinturim, T.M. (2002) Qualidade microbiológica de amostras de água de coco vendidas por ambulantes na cidade de São João do Rio Preto - SP. Hig Aliment 16, 8792.
  • Hollingsworth, P. (2000) Functional beverage juggernaut faces tighter regulations. Food Technol 54, 5054.
  • Jayalekshmy, A., Arumughan, C., Narayanan, C.S. and Mathew, A.G. (1986) Changes in the chemical composition of coconut water during maturation. J Sci Technol 23, 203207.
  • Kohler, J. (2008) Coconut water and McDonald`s. http://itisdrinkable.blogspot.com/2008/09/coconut-water-and-mcdonalds.html, (accessed 4 February 2009).
  • Leite, C.C., Assis, P.N., Silva, M.D., Sant`Ana, M.E.B. and Santana, L.R.R. (2000) Avaliação microbiológica da água de coco produzida e comercializada na cidade de Salvador – BA. Hig Aliment 14, 6466.
  • Little, C.L., Taylor, F.C., Sagoo, S.K., Gillespie, I.A., Grant, K. and McLauchlin, J. (2007) Prevalence and level of Listeria monocytogenes and other Listeria species in retail pre-packaged mixed vegetable salads in the UK. Food Microbiol 24, 711717.
  • Marshall, R.T. and Richardson, G.H. (1992) Media. In Standard Methods for the Examination of Dairy Products, 16th edn ed. Marshall, R.T. pp. 85101. Washington, DC: American Public Health Association.
  • Melo, N.P.M., Cardonha, A.M.S. and Oliveira, A.C.F. (2003) Qualidade microbiológica das águas de coco envasadas e comercializadas na cidade de Natal - RN. Hig Aliment 17, 113114.
  • Pagotto, F., Daley, E., Farber, J. and Warburton, D. (2001) Isolation of Listeria monocytogenes from all food and environmental samples. Government of Canada, Health Products and Food Branch. http://www.hc-sc.ca/food.aliment (accessed 2 November 2007).
  • Parish, M.E., Beuchat, L.R., Suslow, T.V., Harris, L.J., Garrett, E.H., Farber, J.N. and Busta, F.F. (2006) Methods to reduce/eliminate pathogens from fresh and fresh-cut produce. Compr Rev Food Sci Food Saf 2, 161173.
  • Richardson, S.D. (2003) Disinfection by-products and other emerging contaminants in drinking water. Trends Anal Chem 22, 666684.
  • Rodgers, S.L., Cash, J.N., Siddiq, M. and Ryser, E.T. (2004) A comparison of different chemical sanitizers for inactivating Escherichia coli O157:H7 and Listeria monocytogenes in solution and on apples, lettuce, strawberries and cantaloupe. J Food Prot 67, 721731.
  • Ryser, E.T. and Donnelly, C.W. (2001) Listeria. In Compendium of Methods for the Microbiological Examination of Foods, 4th edn ed. Downes, F.P. and Ito, K.. pp. 343356. Washington, DC: American Public Health Association.
  • Schlech, W.F., Lavigne, P.M., Bortolussi, R.A., Allen, A.C., Haldane, E.V., Wort, A.J., Hightower, A.W., Johnson, S.E. et al. (1983) Epidemic listeriosis - evidence for transmission by food. N Engl J Med 308, 203206.
  • Slutsker, L. and Schuchat, A. (1999) Listerioses in humans. In Listeria, Listeriosis, and Food Safety, 2nd edn ed. Ryser, E.T. and Marth, E.H.. pp. 7596. New York: Marcel Dekker, Inc.
  • Varma, J.K., Samuel, M.C., Marcus, R., Hoekstra, R.M., Medus, C., Segler, S., Anderson, B.J., Jones, T.F. et al. (2007) Listeria monocytogenes infection from foods prepared in a commercial establishment: a case–control study of potential sources of sporadic illness in the United States. Clin Infect Dis 44, 521528.
  • Venkitanarayanan, K.S., Lin, C.-H., Bailey, H. and Doyle, M.P. (2002) Inactivation of Escherichia coli O157:H7, Salmonella Enteritidis and Listeria monocytogenes on apples, oranges, and tomatoes by lactic acid with hydrogen peroxide. J Food Prot 65, 100105.
  • Walter, E.H.M., Kabuki, D.Y., Esper, L.M.R., Sant’Ana, A.S. and Kuaye, A.Y. (2009) Modelling the growth of Listeria monocytogenes in fresh green coconut (Cocos nucifera L.) water. Food Microbiol 26, 653657.
  • Wei, C.-I., Cook, D.L. and Kirk, J.R. (1985) Use of chlorine compounds in the food industry. Food Technol 39, 107115.