Effet barrière

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L'effet barrière, ou encore "barrière naturelle", est un phénomène connu tant en biologie (agroalimentaire, santé, écologie) qu'en chimie où on parle volontiers de réaction barrière[1], où un à plusieurs facteurs (agent chimique, agent physique, agent biologique) s'opposent à un changement d'état (diffusion, détérioration, etc.) d'un sujet (aliment, organisme vivant, répartition de population, etc.).

Agroalimentaire

Au cours de l'histoire de l'humanité sont retrouvées de nombreuses traces de transformation et conservation des aliments. Parmi les nombreux témoignages qui en sont retrouvés, les poteries en particulier sont utilisées dès le Paléolithique pour ce faire.

Nos aliments subissent divers processus afin de préserver leur innocuité tant au cours de la transformation que pendant le transport et le stockage afin d'une part d'être consommés en toute sécurité, mais aussi pour préserver autant que possible leurs propriétés organoleptiques[2].

Plusieurs méthodes existent :

En France notamment, le décret 2007-628 et le décret n°88-1203 réglementent les fromages et les laits fermentés. Par exemple les yaourts ne peuvent être additionnés de conservateurs puisqu'ils possèdent une flore vivante servant normalement de barrière[4].

La préservation des aliments a malheureusement un certain coût environnemental[5], obligeant à repenser nos modes de production et recyclage.

Santé

Les exemples abondent dans le domaine de la santé.

Par exemple le microbiote intestinal conjugué au mucus intestinal constituent une barrière majeure pour contrer les pathogènes issus de l'alimentation. Cette barrière est à la fois d'ordre mécanique (paroi intestinale, mucus)[6], chimique (micropeptides antibactériens)[6], immunitaire (leucocytes, cellules dendritiques)[6], et microbiologique[7].

Écologie

La dénomination "barrière naturelle" recouvre de nombreuses fonctions en écologie. Le plus souvent il s'agit de facteurs physiques limitant les diffusions et mouvements de populations[8]. Ces facteurs peuvent être de toute nature : reliefs, fleuves, estuaires[9], températures, pression, hygrométrie, régime des vents ou des courants, etc. Le facteur orographique peut manifester un effet barrière pour les flux atmosphériques (masses d'air, vents), ayant une incidence sur la pluviométrie et les températures[10].

Cet effet barrière peut être causé par des superstructures anthropiques : barrages, routes, urbanisme, etc.

Chimie

Il peut exister plusieurs barrières à une réaction chimique. Parmi les exemples populaires est souvent cité le triangle du feu :

  • barrière énergétique (nécessite une énergie d'activation)
  • manque de réactifs
  • excès de produits dans une réaction partielle et réversible

Références

  1. ↑ « Calculation of Chemical Reaction Barrier Heights by Multiconfiguration Pair-Density Functional Theory with Correlated Participating Orbitals »(en)
  2. ↑ « Barrier-promoting efficiency of two bioactive flavonols quercetin and myricetin on rat intestinal epithelial (IEC-6) cells via suppressing Rho activation »(en)
  3. ↑ « Multilayer packaging: Advances in preparation techniques and emerging food application »(en)
  4. ↑ « La flore microbienne et les propriétés fonctionnelles des yaourts et laits fermentés »(fr)
  5. ↑ « Food Packaging—Roles, Materials, and Environmental Issues »(en)
  6. ↑ a b et c « Intestinal inflammation and mucosal barrier function »(en)
  7. ↑ « Role of the normal gut microbiota »(en)
  8. ↑ « Predicting thecontinuumbetween corridors andbarriers to animal movements using Step SelectionFunctions and Randomized Shortest Paths »(en)
  9. ↑ « More than meets the eye: The barrier effect of the Yangtze River outflow »(en)
  10. ↑ Gérard Beltrando, Les climats. Processus, variabilité et risques, Armand Colin, , p. 167

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