Production d'exopolysaccharides par fermentation avec des cellules immobilisées de LB. Rhamnosus RW-9595M d'un milieu à base de perméat de lactosérum
|Advisor:||Lacroix, Christophe; Champagne, Claude P.|
|Abstract:||A new method for EPS quantification based on ultrafiltration (UF) of fermented broth was developed. This method recovered between 83 and 104% of EPS in a solution with known concentration (40-1500 mg/l). The EPS production during batch fermentations was followed using the new method. The UF method was fast (8 h), accurate and simple, and required only small sample volumes (1 to 5 ml). Cultures were conducted in a supplemented whey permeate (SWP) medium containing 5 or 8% (w/w) whey permeate, 1% (w/w) yeast extract, minerals and Tween-80. Very high cell counts (1.3 · 1010 CFU/ml) and EPS productions (2350 mg/l) were obtained during batch fermentations with free cells. The cells were immobilized on solid supports and a method for immobilized biomass quantification, based on DNA analysis, was developed. This method measured a very high immobilized biomass of 8.5 · 1011 CFU/ml of support during repeated batch cultures. A high EPS concentration (1808 mg/l) was measured after the fourth cycle, with a very short incubation time (7 h) resulting in a high EPS volumetric productivity of 258 mg/l h. During continuous culture with free cells, an EPS production of 1808 mg/l and a volumetric productivity of 542.6 mg/l h was obtained for a dilution ratio (D) of 0.3 h-1. A 32-day continuous fermentation with cells immobilized in a two-stage bioreactor system was conducted. The influence of yeast extract concentration, temperature and dilution rate on the production of biomass, EPS and lactic acid was studied. A significant effect (P< 0.05) was found only for lactic acid but not for biomass or EPS production. A very high and stable immobilized biomass equal to 5.3 ± 1.8 · 1011 CFU/g support was measured. A physiological and morphological change of the culture with the loss of the capacity to produce soluble EPS (138 mg/l) was observed, resulting in the formation of macroscopic aggregates. With time, the aggregate concentration in the two reactors increased and the aggregates left the system in the effluent with a volumetric productivity between 5.68 and 49.54 g/l h. The aggregates contained 73.8% total biomass and 14.2% insoluble EPS (w/w). A viable biomass content of 4.32 ± 0.97 · 1012 CFU/g was also measured. These aggregates could find applications as synbiotic food-ingredients with very high active cell and EPS concentrations.|
|Document Type:||Thèse de doctorat|
|Open Access Date:||11 April 2018|
|Collection:||Thèses et mémoires|
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