Polysaccharide production: Experimental comparison of the performance of four mixing devices

Abstract

This investigation was undertaken with the objective to compare experimentally the performance of four different mixing devices for the production of the polysaccharide pullulan with Aureobasidium pullulans (2552). Fermentations were performed using identical bioreactors with respectively an assembly of three Rushton turbines (RTB), a helical ribbon impeller (HR) and two different reciprocating plates (RPB1, RPB2). Each mixing vessel had identical geometry and working volume (18 L). These four fermentations were performed with an equal level of power input per unit volume (1000 W/m 3 ) and gas¯ow rate (0.5 vvm, 9 L/min). For each system, the evolution of biomass, polysaccharide concentration, dissolved oxygen and agitation speed or frequency were recorded as a function of time along with the rheological properties of the culture broths.The type of mixing device used had a signi®cant impact on the rate of biomass production and on polysaccharide physical properties. However, the rate of polysaccharide production appears to be less sensitive to the bioreactor design. The overall productivity, which represents the ability of micro-organisms to convert rapidly substrate into biomass and polysaccharide, was maximised using the RPB2 system. The quality of the synthesised polysaccharide, in terms of viscosity producing power, was highest using the HR system but the overall productivity was very low. Thus, the best compromise between productivity and product quality was achieved with the RPB2.

Excess turbulence as a cause of turbohypobiosis in cultivation of microorganisms

“…If the enzyme activity of cells changes, then the amount and content of the metabolism product also must change. This relationship is confirmed by the aforementioned and other studies [85][86][87][88], in which the main criterion of the evaluation of the results is the amount and quality of the synthesised product.…”

“…In some studies [71,86,88,96], the influence of stirring intensity on the molecular mass and physicochemical properties of the synthesised product has been established.…”

Vitis vinifera culture in a non-conventional bioreactor: the reciprocating plate bioreactor

“…Experiments in our laboratory with Aspergillus niger [unpublished results] and Aureobasidium pullulans [22] already showed that the perforation diameter of the plates could have a profound impact on the product concentration and quality. Using a plate with larger perforations also decreases the level of shear stress to which the microorganisms are subjected.…”

Studies on the optimal culture conditions of <i>Aureobasidium pullulans</i> to produce exopolysaccharides

“…The high price of pullulan is attributed mainly to the difficulties in its production through fermentation such as high broth viscosity, low product yield, pigmentation, and product degradation [4]. Many factors can influence the pullulan production, including strain [5], temperature [6], pH [7], dissolved oxygen (DO) level (influenced by agitation, aeration) [8], substrate [9,10], trace element [11], fermentation model [12], mixing device [13], and so on. Lots of scientists and enterprisers in the world focus on it, but its synthetic mechanism of polysaccharide is still unknown, and there are different reports about its industrial fermentation.…”