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Bacterial abilities to adhere to food components : extent, characterisation, and sensitivity to shear stress

Abstract : In the last decade, there has been an increasing interest in the potential health effects associated with consumption of Lactic Acid Bacteria (LAB) in foods. Adhesive interactions between bacteria and food components are likely to play a key role on bacterial probiotic action by modulating both bacterial protection and distribution within food matrices. Research presented in this thesis aims a better understanding of these interactions to help optimizing functional food design. Indeed, the adhesive behavior of most LAB, as well as the impact of adhesive interactions on food structuration, remain mostly unknown. Furthermore, some food manufacturing steps, such as spray-drying, may induce stress on bacteria, which can cause partial loss of bacterial adhesive capacities. In case of bacteria integrated within an adhesive matrix, the effect of adhesive interactions on bacterial protection from stress can also be questioned. A high-throughput screening method was first designed to screen quickly a hundred of strains for their adhesive affinities towards a given range of biomolecules of interest. This method was then applied to a 73-LAB strains collection which allowed identifying common characteristics amongst adhesive strains, especially in terms of adhesion specificity. Two studies (experimental and theoretical) were performed in parallel to determine the impact of shear stress on bacterial functionality and bacterial chains integrity. These studies suggest that the stress-induced breaking-down process of bacterial chains can be thought of as a functionality protective process. The proposed model predicts regioselectivity of damages inflicted to bacterial cells within a chain, which intensity would vary with chain length. When applied to bacteria-spherical component adhesive interactions within a food matrix submitted to shearing, the model suggests an unfavorable impact of adhesion on bacterial cell damages, which would be all the more important than spheres are big. This multidisciplinary research project points out several key findings that may help with designing more efficient food matrices for optimized LAB delivery.
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Faustine Gomand. Bacterial abilities to adhere to food components : extent, characterisation, and sensitivity to shear stress. Food engineering. Université de Lorraine, 2019. English. ⟨NNT : 2019LORR0123⟩. ⟨tel-02499669⟩

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