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How Vacuum and MAP Packed Meat Spoils

22 May 2015

Spoilage of modified atmosphere (MAP) or vacuum-packaged meat is often caused by psychrotrophic lactic acid bacteria (LAB).

Lactic acid bacteria contamination occurs during the slaughter or processing of meat, according to a new study Taxonomy And Diversity Of Coccal Lactic Acid Bacteria Associated With Meat And The Meat Processing Environment by Riitta Rahkila from the University of Helsinki Finland.

During storage lactic acid bacteria become the dominant microbiota due to their ability to grow at refrigeration temperatures and to resist the microbial inhibitory effect of CO2.

Spoilage is a complex phenomenon caused by the metabolic activities and interactions of the microbes growing in late shelf-life meat which has still not been fully explained.

In the research, the taxonomic status of unknown bacterial groups isolated from late shelf-life meat and meat processing environment was resolved by the polyphasic approach.

Five isolates from a broiler processing plant represented a novel Enterococcus species which phylogenetic analyses showed to be located within the Enterococcus avium group.

The name Enterococcus viikkiensis was proposed for this species.

In addition to enterococcal studies, the taxonomy of the Leuconostoc gelidum group was revised.

Twenty isolates from packaged meat were shown to represent a novel subspecies within L. gelidum, for which the name Leuconostoc gelidum subsp. aenigmaticum was proposed.

The novel subspecies was closely related to both L. gelidum and Leuconostoc gasicomitatum. Phylogenetic analyses and DNA-DNA reassociation studies led to the reclassification of Leuconostoc gelidum and Leuconostoc gasicomitatum as Leuconostoc gelidum subsp. gelidum and Leuconostoc gelidum subsp. gasicomitatum.

In the third part of the thesis, Lactococcus piscium was shown to form a significant part of the LAB population in a variety of MAP meat in late shelflife.

This formerly neglected species in meat spoilage studies grew together with leuconostocs and contributed to spoilage when inoculated into pork.

Numerical analysis of ribopatterns, and/or multilocus sequence typing of several housekeeping genes were shown to differentiate species/subspecies of enterococci and lactococci well.

Finally, a novel MLST scheme was developed and the population structure within 252 strains of the spoilage bacterium Leuconostoc gelidum subsp. gasicomitatum from meat and vegetable sources was investigated. Indication of niche specificity was observed, as well as a very low level of genetic material exchange within the three subpopulations.

Further Reading

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May 2015

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