Fermentation: the development of "good" bacteria to the detriment of others
During the manufacture of fermented meat products such as dried sausage, fermentation is due to the development of so-called lactic acid bacteria, which are present in large numbers and prevent the growth of other species. Among the bacteria used in meat fermentation, Lactobacillus sakei is the most widely used in Europe, while Pediococcus pentosaceus tends to be used in the United States.
Lactobacillus sakei was described for the first time in rice alcohol, or saké, hence its name*. Since then, it has been shown that this is a bacterium typical of meat because it is almost always found in meat products, and frequently in raw fish-based products.
A team of INRA researchers has sequenced and analysed the genome of Lactobacillus sakei in order to answer a crucial question: what are the important functions coded by this genome which could explain why it is so well adapted to meat?
By comparing it with other bacteria, the researchers observed three principal and original functions:
- L. sakei is capable of optimally using the nutrient molecules present in meat in order to develop;
- it is also better than other bacteria at resisting the challenging environmental conditions (cold, presence of salt or spices, varying oxygen levels) encountered during the preservation of meat products;
- finally, it can produce substances capable of killing other bacterial species.It is the combination of these three characteristics, some of which were not suspected prior to sequencing of the genome, which means that this bacterium has many advantages if it is used as a biological meat preservative.
These properties have now provided clues as to which physicochemical parameters (such as temperature, the addition of spices or other compounds such as salt, gaseous environment) could be adjusted to allow the development of L. sakei to the detriment of other species. The researchers are also considering the selection of strains endowed with a series of properties which would confer an advantage over other pathogenic or food-spoiling species.
A new function for L. sakei: the preservation of meat and fish
As for the preservation of meat or fish-derived products, use of this type of bacterium can now be envisaged not just to ferment products but also to preserve their microbiological quality. In this case, these bacteria must be present but must not develop in excessive quantities, not affect the organoleptic qualities of the product (colour, flavour, texture) and must prevent the growth of undesirable micro-organisms.
To achieve this, the lactic acid bacterium Lactobacillus sakei is a good candidate: it is the typical bacterial species of meat environments, it is the most common flora in a certain number of products (dried sausage, vacuum-packed meats), it is resistant to the presence of salt, low water levels and low temperatures (conditions which often prevail during preservation) and has an inhibitory effect on the development of other bacteria.
Furthermore, it was recently shown that this bacterium is found in the digestive tract of healthy humans. It is probable that in this case, its source may be dietary, so that this bacterium is a long-standing companion to man.
* It does not participate in the production of saké but tends to be a contaminant.
Scientific contact:
Monique ZAGOREC
INRA - Unité de recherche Flore Lactique et Environnement Carné (FLEC)
Domaine de Vilvert
78350 Jouy en Josas
Tel. :+3301 34 65 22 89
Fax : +331 34 65 21 05
monique.zagorec@jouy.inra.fr
site web de l'unité : http://www.jouy.inra.fr/unites/flec
Source :
The genome sequence of the meat-borne lactic acid bacterium Lactobacillus sakei 23K. Nature Biotechnology, DOI 10.1038/nbt1160 advance online publication du 6 novembre 2005, http://www.nature.com/nbt/journal/vaop/ncurrent/index.htmlStéphane Chaillou1, Marie-Christine Champomier-Vergès1, Monique Cornet1, Anne-Marie Crutz-Le Coq1, Anne-Marie Dudez1, Véronique Martin1, Sophie Beaufils1, Emmanuelle Darbon-Rongère1, Robert Bossy2, Valentin Loux2 and Monique Zagorec1 (1)Unité Flore Lactique et Environnement Carné. INRA Domaine de Vilvert, Jouy-en-Josas (2)Mathématique, Informatique et Génome. INRA Domaine de Vilvert, Jouy-en-Josas |
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