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Gschwendtner, S. ; Alatossava, T.* ; Kublik, S. ; Fuka, M.M.* ; Schloter, M. ; Munsch-Alatossava, P.*

N2 gas flushing alleviates the loss of bacterial diversity and inhibits psychrotrophic Pseudomonas during the cold storage of bovine raw milk.

PLoS ONE 11:e0146015 (2016)
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The quality and safety of raw milk still remains a worldwide challenge. Culture-dependent methods indicated that the continuous N2 gas-flushing of raw milk reduced the bacterial growth during cold storage by up to four orders of magnitude, compared to cold storage alone. This study investigated the influence of N2 gas-flushing on bacterial diversity in bovine raw-milk samples, that were either cold stored at 6°C or additionally flushed with pure N2 for up to one week. Next-generation sequencing (NGS) of the V1-V2 hypervariable regions of 16S rRNA genes, derived from amplified cDNA, which was obtained from RNA directly isolated from raw-milk samples, was performed. The reads, which were clustered into 2448 operational taxonomic units (OTUs), were phylogenetically classified. Our data revealed a drastic reduction in the diversity of OTUs in raw milk during cold storage at 6°C at 97% similarity level; but, the N2-flushing treatment alleviated this reduction and substantially limited the loss of bacterial diversity during the same cold-storage period. Compared to cold-stored milk, the initial raw-milk samples contained less Proteobacteria (mainly Pseudomonadaceae, Moraxellaceae and Enterobacteriaceae) but more Firmicutes (mainly Ruminococcaceaea, Lachnospiraceae and Oscillospiraceaea) and Bacteroidetes (mainly Bacteroidales). Significant differences between cold-stored and additionally N2-flushed milk were mainly related to higher levels of Pseudomononadaceae (including the genera Pseudomonas and Acinetobacter) in cold-stored milk samples; furthermore, rare taxa were better preserved by the N2 gas flushing compared to the cold storage alone. No major changes in bacterial composition with time were found regarding the distribution of the major 9 OTUs, that dominated the Pseudomonas genus in N2-flushed or non-flushed milk samples, other than an intriguing predominance of bacteria related to P. veronii. Overall, this study established that neither bacteria causing milk spoilage nor any well-known human pathogen or anaerobe benefited from the N2 gas flushing even though the N2-flushed and non-flushed cold-stored milk differed in bacterial counts by up to 104-fold.
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Publication type Article: Journal article
Document type Scientific Article
Language
Publication Year 2016
HGF-reported in Year 2016
ISSN (print) / ISBN 1932-6203
Journal PLoS ONE
Quellenangaben Volume: 11, Issue: 1, Pages: , Article Number: e0146015 Supplement: ,
Publisher Public Library of Science (PLoS)
Publishing Place Lawrence, Kan.
Reviewing status Peer reviewed
POF-Topic(s) 30202 - Environmental Health
Research field(s) Environmental Sciences
PSP Element(s) G-504700-002
PubMed ID 26730711
Scopus ID 84953791548
Erfassungsdatum 2016-01-07