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Soutenance de thèse de Janine Deou

Vendredi 5 février à 14 heures

Janine DEOU soutiendra sa thèse intitulée "Control of the rheological behaviour of chocolate suspensions by optimizing the morphological properties of the particles" le vendredi 5 février 2021 à 14 heures par visioconférence.

Le jury sera composé de :

  • Xavier CHATEAU (Ecole des Ponts et Chaussées), Président du jury
  • Peter FISCHER (ETH Zurich), Rapporteur
  • Christophe LANOS (IUT Rennes), Rapporteur
  • Paul SMITH (Cargill), Examinateur
  • Joel WALLECAN (Cargill), Examinateur
  • Fabien DECLERCQ (Cargill), Invité 
  • Hela BESSAIES-BEY (Université Gustave Eiffel), Co-encadrante de thèse
  • Nicolas ROUSSEL (Université Gustave Eiffel), Directeur de thèse

Abstract :

The objective of this thesis is the formulation of fat-reduced chocolate and emulsifier free chocolate without affecting the viscosity and yield stress of the melt chocolate. To achieve these objectives, we control the rheological behaviour of chocolate suspensions by optimizing the morphological properties (particle size distribution, particle shape and maximum packing fraction) of sugar and cocoa powders. First, we develop appropriate protocols for the characterization of the morphological and rheological properties of chocolate suspensions. Then, we study the effect of the production process on the rheological and morphological properties of chocolate and show that viscosity depends on relative solid volume fraction (i.e., solid volume fraction to maximum packing fraction ratio) while yield stress depends on relative solid volume fraction and is inversely proportional to the particle mean size. Our experimental results show that the viscosity of melt chocolate suspension (i.e., sugar, cocoa, sugar and cocoa suspensions) can be related to the solid volume fraction and the maximum packing fraction by the phenomenological Krieger-Dougherty type equation. Moreover, we show that the maximum packing fraction of cocoa and sugar powders can be well predicted by the compressive packing model developed for the optimization of the mineral powdery materials used in construction materials. Finally, we exploit these results and models to attain the objectives of this thesis. We show that an accurate control of maximum packing fraction by adding “fine” cocoa particles allows for the decrease of the amount of fat in chocolate without affecting viscosity and chocolate solid composition. We moreover show that an accurate control of particle average size and maximum packing fraction by adding “coarse” sugar particles allows for the removal of the emulsifiers from chocolate without increasing the fat content of the suspension and affecting the viscosity and yield stress. Keywords: viscosity, yield stress, maximum packing fraction, particle size distribution optimization.