Exopolysaccharide production by Enterobacter A47: optimization of cultivation conditions and study of polymer functional properties

Dissertação para obtenção do Grau de Mestre em Biotecnologia

FucoPol is a fucose-containing biopolymer produced by the bacterium Gram-negative, Enterobacter A47 DSM 23139. It is an exopolysaccharide (EPS) composed of neutral sugars (fucose, galactose, glucose), an acidic sugar (glucuronic acid), and also non-saccharide substituents (acetate, pyruvate and succinate). In this work, two primary objectives were considered: the optimization of EPS production by varying two different parameters, and the functional properties’ assessment of different EPS produced by the bacterium. In the optimization study, the influence of different dissolved oxygen concentrations (controlled at 10, 30 and 60% of air saturation), and the impact of phosphate concentration reduction in the culture medium (5.25 and 3.81 g L-1) were assessed. The objective was to evaluate not only the effect of both parameters on cellular growth and exopolysaccharide-synthesis, but also to determine their influence in EPS chemical composition. The best results were obtained with DO at 10%, with the highest EPS production (6.11 g L-1), and although a reduction of phosphate concentration didn’t affect the EPS production, it reduced the exopolysaccharide’s fucose content to 24%mol. Secondly, the functional properties of nine distinct exopolysaccharides synthesized by Enterobacter A47 under different cultivation conditions were evaluated. Rheologically, most of the EPS polymer solutions showed shear-thinning behavior, wherein EPS-s, EPS-g and GNEX achieved the highest apparent viscosity (0.2 - 0.3 Pa.s) at lower shear rates (0.3 to 1 s-1). Also, most of the polymers presented emulsifying capacity at different temperatures. Concerning the film-forming capacity, EPS-s, EPS-g and EPS-x films demonstrated to have good mechanical properties and high water vapour permeability. And, all polymers described flocculating activity at 0.01% of EPS, which was significantly diminished at lower concentration, 0.001%.