Contribution de protéases pariétales dans l'activité des systémes protéolytiques de surface de Lactobacillus helveticus et streptococcus thermophilus en matrice laitière

Abstract : Dairy products (cheeses, yoghurt, fermented milk…) represent 10% of our food. These products are appreciated thanks to their flavor, their texture and their health benefits. These characteristics are due to various compounds like peptides which come from the cutting of milk protein by enzymes. These enzymes come from the milk, are added during the fabrication or come from bacteria. To understand and to master the dairy products fabrication is essential to develop the food of tomorrow. The fabrication of fermented dairy products as cheese begins with the cutting or proteolysis of caseins, the major milk proteins, thanks to enzymes called proteinases. Some of them are attached at the surface of lactic acid bacteria which are used at the beginning of the cheese fabrication, as Streptococcus thermophilus or Lactobacillus helveticus. S. thermophilus possess one cell envelop proteinase, PrtS, already well-studied unlike L. helveticus which possess four cell envelop proteinases, PrtH, PrtH2, PrtH3 and PrtH4, which were not studied separately yet. The aim of this thesis work is to better understand the proteolytic properties of L. helveticus and S. thermophilus and identify how their proteinases adjust the hydrolysis profile of caseins in a dairy matrix. Two strategies were selected: to express one of the proteinases of L. helveticus in S. thermophilus to study it independently from the others and study each proteinase in strains which only express one proteinase gene
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Xavier Lecomte. Contribution de protéases pariétales dans l'activité des systémes protéolytiques de surface de Lactobacillus helveticus et streptococcus thermophilus en matrice laitière. Alimentation et Nutrition. Université de Lorraine, 2014. Français. ⟨NNT : 2014LORR0271⟩. ⟨tel-01751307⟩

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