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Application of Novel Plant Probiotics to Increase the Health Value of Ready-to-Eat Leafy Greens

de Mel, Rumathi LU orcid (2024)
Abstract
Ready-to-eat (RTE) leafy greens offer an appealing way to integrate leafy greens into meals. Unfortunately, these leafy greens can
get contaminated with human pathogens such as Salmonella, and Shiga toxin producing Escherichia coli (STEC) at any stage along the
manufacturing chain, potentially leading to serious foodborne diseases. Currently, there is no single step in the production and processing of RTE leafy vegetables that guarantees the elimination of all potential pathogens, leaving the final product susceptible to contamination. To address this challenge, this master’s thesis proposes a novel approach: the direct inoculation of previously evaluated plant probiotics on the day of delivery, known for their antagonistic effects... (More)
Ready-to-eat (RTE) leafy greens offer an appealing way to integrate leafy greens into meals. Unfortunately, these leafy greens can
get contaminated with human pathogens such as Salmonella, and Shiga toxin producing Escherichia coli (STEC) at any stage along the
manufacturing chain, potentially leading to serious foodborne diseases. Currently, there is no single step in the production and processing of RTE leafy vegetables that guarantees the elimination of all potential pathogens, leaving the final product susceptible to contamination. To address this challenge, this master’s thesis proposes a novel approach: the direct inoculation of previously evaluated plant probiotics on the day of delivery, known for their antagonistic effects against E. coli. The bacterial levels on the day of delivery and the best-before date were analyzed using viable cell count, quantitative polymerase chain reaction (qPCR), and Next Generation Sequencing (NGS).

The findings from the viable cell count revealed a consistent reduction in non-pathogenic E. coli for all the plant probiotic strains tested. Particularly, Bacillus coagulans LMG P-32205 and Pseudomonas cedrina LMG P-32207 showed the most significant effectiveness (p ≤ 0.01) throughout the shelf-life period. Additionally, qPCR analysis showed that Pseudomonas cedrina LMG P-32207 had higher concentrations on the last day of shelf-life compared to the control. Moreover, Illumina MiSeq sequencing revealed a lower relative abundance of pathogenic genera, especially Escherichia coli, in the microbiota of the leafy greens. The mixed salad and mixed lettuce samples inoculated with probiotics exhibited a higher relative abundance of Proteobacteria and Bacteroidetes compared to the control group. Over all trials, the top family with the highest relative abundance was Pseudomonadaceae.

The α-diversity exhibited variations only among mixed lettuce and mixed salad samples inoculated with probiotics. Higher β-diversity was observed in all mixed salad groups compared to day 1, as a shift to the right. Indicating that inoculation of probiotics and E. coli has induced substantial changes in the native microbiota of the mixed salad leaves. The effect of probiotic strains varied between different leafy green products, thus no conclusions could be drawn. Nonetheless, these results encourage the use of bacterial antagonists as part of a global solution to reduce the risk of human pathogens on leafy green vegetables. (Less)
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author
supervisor
publishing date
type
Thesis
publication status
published
subject
pages
48 pages
publisher
Lund University
language
English
LU publication?
no
id
6b9afe62-4b4a-449a-9442-167416cb62fb
alternative location
http://lup.lub.lu.se/student-papers/record/9154733
date added to LUP
2025-06-30 12:59:33
date last changed
2025-08-21 11:27:19
@misc{6b9afe62-4b4a-449a-9442-167416cb62fb,
  abstract     = {{Ready-to-eat (RTE) leafy greens offer an appealing way to integrate leafy greens into meals. Unfortunately, these leafy greens can<br/>get contaminated with human pathogens such as Salmonella, and Shiga toxin producing Escherichia coli (STEC) at any stage along the<br/>manufacturing chain, potentially leading to serious foodborne diseases. Currently, there is no single step in the production and processing of RTE leafy vegetables that guarantees the elimination of all potential pathogens, leaving the final product susceptible to contamination. To address this challenge, this master’s thesis proposes a novel approach: the direct inoculation of previously evaluated plant probiotics on the day of delivery, known for their antagonistic effects against E. coli. The bacterial levels on the day of delivery and the best-before date were analyzed using viable cell count, quantitative polymerase chain reaction (qPCR), and Next Generation Sequencing (NGS).<br/><br/>The findings from the viable cell count revealed a consistent reduction in non-pathogenic E. coli for all the plant probiotic strains tested. Particularly, Bacillus coagulans LMG P-32205 and Pseudomonas cedrina LMG P-32207 showed the most significant effectiveness (p ≤ 0.01) throughout the shelf-life period. Additionally, qPCR analysis showed that Pseudomonas cedrina LMG P-32207 had higher concentrations on the last day of shelf-life compared to the control. Moreover, Illumina MiSeq sequencing revealed a lower relative abundance of pathogenic genera, especially Escherichia coli, in the microbiota of the leafy greens. The mixed salad and mixed lettuce samples inoculated with probiotics exhibited a higher relative abundance of Proteobacteria and Bacteroidetes compared to the control group. Over all trials, the top family with the highest relative abundance was Pseudomonadaceae.<br/><br/>The α-diversity exhibited variations only among mixed lettuce and mixed salad samples inoculated with probiotics. Higher β-diversity was observed in all mixed salad groups compared to day 1, as a shift to the right. Indicating that inoculation of probiotics and E. coli has induced substantial changes in the native microbiota of the mixed salad leaves. The effect of probiotic strains varied between different leafy green products, thus no conclusions could be drawn. Nonetheless, these results encourage the use of bacterial antagonists as part of a global solution to reduce the risk of human pathogens on leafy green vegetables.}},
  author       = {{de Mel, Rumathi}},
  language     = {{eng}},
  month        = {{05}},
  publisher    = {{Lund University}},
  title        = {{Application of Novel Plant Probiotics to Increase the Health Value of Ready-to-Eat Leafy Greens}},
  url          = {{http://lup.lub.lu.se/student-papers/record/9154733}},
  year         = {{2024}},
}