In the future the demand for ethanol is expected to increase greatly due to the rising energy requirements in the world. Lignocellulosic materials are a suitable and potentially cheap feedstock for sustainable production of fuel ethanol, since vast quantities of agricultural and forest residues are available in many countries. However, there are several problems involved in the utilization of lignocellulosic raw materials as sugar source. The most common way of releasing the simple sugars in the material is by dilute acid hydrolysis. This procedure is relatively simple and cheap, but in addition to the sugars it creates inhibitory compounds. These inhibitors make it very hard for the yeast to ferment the hydrolyzate and detoxification is often necessary. One way to overcome this problem is to encapsulate the yeast. Encapsulation is an attractive method since it improves the cells stability and inhibitor tolerance, increases the biomass amount inside the reactor, and decreases the cost of cell recovery, recycling and downstream processing. However, the method does not yet permit long-term cultivation since the capsules used so far are not robust enough. Therefore more studies have to be conducted in order to find methods which produce mechanically robust capsules. The main goal of this paper is to find a suitable method to produce robust capsules using different concentration of the chemicals at different pH and also implementing some modifications such as addition of cross-linkers in preparation procedure. In this paper comparison of three different encapsulation techniques were studied based on the mechanical robustness of the capsules. The three different techniques were calcium mineralized alginate-chitosan capsules, alginate capsules coated with 2% chitosan (2% AC) and genipin crosslinked alginate-chitosan (GCAC) capsules. The results indicate that GCAC capsules are most robust and were good enough for prolonged use since most of the capsules were not deformed in mechanical strength test. There were slight differences in the diameter and membrane thickness before and after swelling. No negative influence was observed on the yeast growth when applying the cross-linker. The results of this study will hopefully add valuable information and helps in further studies using other cross-linkers to prepare robust capsules. / Program: Industrial Biotechnology

Dans le contexte énergétique et climatique mondial, le coût élevé des enzymes Cellulolytiques (cellulases) freine le développement des bioraffineries lignocellulosiques, pour produire des biocarburants et composés chimiques à partir d'une matière première végétale renouvelable. L'objectif de ce travail est de caractériser et de modéliser le métabolisme du micro-organisme Trichoderma reesei, afin d'optimiser le protocole industriel de production de cellulases. Cette étude a été réalisée sur des milieux modèles représentatifs de ceux attendus à l'échelle industrielle. Tout d'abord, la stoechiométrie des réactions de croissance et de production a été établie, puis une étude cinétique a été menée pour mesurer précisément le comportement du micro-organisme à forte induction de la production de cellulases. Le modèle résultant a été utilisé pour optimiser le protocole industriel de production. Ensuite, l'intégration de cette étape dans une bioraffinerie lignocellulosique a été étudiée, avec l'effet sur le métabolisme i) des mélanges de sucres disponibles, ii) des composés inhibiteurs issus de la dégradation de la lignocellulose, et iii) du changement d'échelle. Ces travaux ont fait progresser de façon substantielle les connaissances du métabolisme de T. reesei en ce qui concerne la production de cellulases, et les modèles développés sont des outils d'aide rationnelle à la définition d'un procédé de production de cellulases intégré dans une bioraffinerie lignocellulosique. / In the global energetic and climatic context, the high cost of the cellulolytic enzymes (cellulases) postpones the development of lignocellulosic biorefineries, dedicated to produce biofuels and chemical compounds from renewable vegetable feedstocks. The aim of this work was to measure and model the metabolism of the micro-organism Trichoderma reesei, in order to optimize the industrial protocol for the production of cellulase. This study was carried out using synthetic media representative of industrial ones. First, the stoichiometries of growth and protein production reactions were determined. Then, a kinetic study was conducted to precisely measure the specific rates of T. reesei at high induction of cellulase production. The resulting model was used to optimize the industrial production protocol. Finally the integration of this step in a lignocellulosic biorefinery was studied by determining the impacts on the metabolism of i) available sugar mixtures, ii) inhibitory compounds from lignocellulosic biomass degradation, and iii) scale-up. These results significantly contributed to improve the knowledge of T. reesei metabolism on cellulase production. The developed models are rational tools for the optimization of a cellulase production protocol suited to lignocellulosic biorefineries.