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Effects of household washing on bacterial load and removal of Escherichia coli from lettuce and "ready-to-eat" salads

Uhlig, Elisabeth LU ; Olsson, Crister LU ; He, Jiayi; Stark, Therese; Sadowska, Zuzanna LU ; Molin, Göran LU ; Ahrné, Siv LU ; Alsanius, Beatrix and Håkansson, Åsa LU (2017) In Food Science and Nutrition 5(6). p.1215-1220
Abstract

Customer demands for fresh salads are increasing, but leafy green vegetables have also been linked to food-borne illness due to pathogens such as Escherichia coli O157:H7. As a safety measure, consumers often wash leafy vegetables in water before consumption. In this study, we analyzed the efficiency of household washing to reduce the bacterial content. Romaine lettuce and ready-to-eat mixed salad were washed several times in flowing water at different rates and by immersing the leaves in water. Lettuce was also inoculated with E. coli before washing. Only washing in a high flow rate (8 L/min) resulted in statistically significant reductions (p < .05), "Total aerobic count" was reduced by 80%, and Enterobacteriaceae count was reduced... (More)

Customer demands for fresh salads are increasing, but leafy green vegetables have also been linked to food-borne illness due to pathogens such as Escherichia coli O157:H7. As a safety measure, consumers often wash leafy vegetables in water before consumption. In this study, we analyzed the efficiency of household washing to reduce the bacterial content. Romaine lettuce and ready-to-eat mixed salad were washed several times in flowing water at different rates and by immersing the leaves in water. Lettuce was also inoculated with E. coli before washing. Only washing in a high flow rate (8 L/min) resulted in statistically significant reductions (p < .05), "Total aerobic count" was reduced by 80%, and Enterobacteriaceae count was reduced by 68% after the first rinse. The number of contaminating E. coli was not significantly reduced. The dominating part of the culturable microbiota of the washed lettuce was identified by rRNA 16S sequencing of randomly picked colonies. The majority belonged to Pseudomonadaceae, but isolates from Enterobacteriaceae and Staphylococcaceaceae were also frequently found. This study shows the inefficiency of tap water washing methods available for the consumer when it comes to removal of bacteria from lettuce. Even after washing, the lettuce contained high levels of bacteria that in a high dose and under certain circumstances may constitute a health risk.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
E. coli, Leafy green vegetables, Ready-to-eat, Rinsing, Water bath
in
Food Science and Nutrition
volume
5
issue
6
pages
1215 - 1220
publisher
Wiley-Blackwell
external identifiers
  • scopus:85030308500
  • wos:000415853500021
ISSN
2048-7177
DOI
10.1002/fsn3.514
language
English
LU publication?
yes
id
7e450ac1-fa50-4813-92c5-c2c0546ffe3a
date added to LUP
2017-10-16 14:56:09
date last changed
2018-02-18 22:20:38
@article{7e450ac1-fa50-4813-92c5-c2c0546ffe3a,
  abstract     = {<p>Customer demands for fresh salads are increasing, but leafy green vegetables have also been linked to food-borne illness due to pathogens such as Escherichia coli O157:H7. As a safety measure, consumers often wash leafy vegetables in water before consumption. In this study, we analyzed the efficiency of household washing to reduce the bacterial content. Romaine lettuce and ready-to-eat mixed salad were washed several times in flowing water at different rates and by immersing the leaves in water. Lettuce was also inoculated with E. coli before washing. Only washing in a high flow rate (8 L/min) resulted in statistically significant reductions (p &lt; .05), "Total aerobic count" was reduced by 80%, and Enterobacteriaceae count was reduced by 68% after the first rinse. The number of contaminating E. coli was not significantly reduced. The dominating part of the culturable microbiota of the washed lettuce was identified by rRNA 16S sequencing of randomly picked colonies. The majority belonged to Pseudomonadaceae, but isolates from Enterobacteriaceae and Staphylococcaceaceae were also frequently found. This study shows the inefficiency of tap water washing methods available for the consumer when it comes to removal of bacteria from lettuce. Even after washing, the lettuce contained high levels of bacteria that in a high dose and under certain circumstances may constitute a health risk.</p>},
  author       = {Uhlig, Elisabeth and Olsson, Crister and He, Jiayi and Stark, Therese and Sadowska, Zuzanna and Molin, Göran and Ahrné, Siv and Alsanius, Beatrix and Håkansson, Åsa},
  issn         = {2048-7177},
  keyword      = {E. coli,Leafy green vegetables,Ready-to-eat,Rinsing,Water bath},
  language     = {eng},
  number       = {6},
  pages        = {1215--1220},
  publisher    = {Wiley-Blackwell},
  series       = {Food Science and Nutrition},
  title        = {Effects of household washing on bacterial load and removal of Escherichia coli from lettuce and "ready-to-eat" salads},
  url          = {http://dx.doi.org/10.1002/fsn3.514},
  volume       = {5},
  year         = {2017},
}