Studies of the mixing character and flow distribution in mycelial fermentation broths

Abstract

The influence of two mixing systems on the principal parameters of mycelial fermentations of Aspergillus niger, Fusicoccwn amygdali Del. and Fusarium moniliforme Sheld. as well as their metabolite citric acid, fusicoccin and gibberellic acid production was analyzed from the viewpoint of flow energy distribution in a bioreactor. The growth and metabolite synthesis during fermentation was compared' under different mixing conditions in the fermenter FU-8 with a turbine mixing system (TMS) and a counterflow mixing system (CMS). It was found that the growth, productivity and respiration characteristics as well as the morphology of these cultures varied dependent on the mixing system and agitation regime used. The counterflow mixing system was more favourable for large agglomerates (F. amygdali) or soft pellets (A. niger) forming fungi, while the turbine mixing system was more effective for F. moniliforme growing in the form of small clumps and f m l y dispersed hyphae. Flow characteristics under different mixing conditions were analyzed in a model fermenter. The kinetic energy of flow fluctuations was measured in gassed and ungassed water and different fermentation broth systems by using a Stimng Intensity Measuring Device (SIMD-Fl). The difference of the energy values at different points was better expressed in the fementer with a turbine mixing system in comparison with that having a counterflow mixing system. High viscous F. amygdali and A. niger broth provided higher energy values compared to water and low viscous F. moniliforme broth. It was observed that the intensity of growth and the intensity of the synthesis decreased at very high energy values, which was obviously connected to the influence of the irreversible shear stress on the mycelial morphology.

Excess turbulence as a cause of turbohypobiosis in cultivation of microorganisms

“…In conditions where the intensity of local turbulence is high but insufficient for the mechanical disruption of the cultivated cells, changes in the cell morphology were often observed [2,56,62,[66][67][68][69][70][71][72][73][74][75][76]. Simultaneously with morphological adjustment, the physiological character, namely, the productivity of metabolite synthesis [66,67,69,72,73,76], biological activity [70,74,77] and enzyme activity [71] also changed.…”

“…Simultaneously with morphological adjustment, the physiological character, namely, the productivity of metabolite synthesis [66,67,69,72,73,76], biological activity [70,74,77] and enzyme activity [71] also changed. Hence, these morphological changes may be regarded to be not a simple result of the mechanical deformation of cells, but a reaction to the changes in cultivation conditions.…”

EFFECT OF THE OPERATIONAL CONDITIONS ON THE L-LACTIC ACID PRODUCTION BYRhizopus oryzaeEFECTO DE LAS CONDICIONES DE OPERACIÓN EN LA PRODUCCIÓN DE ACIDO L-LÁCTICO PORRhizopus oryzaeEFECTO DAS CONDICIÓNS DE OPERACIÓN NA PRODUCCIÓN DE ACIDO L-LÁCTICO PORRhizopus oryzae

“…The size of mycelial pellet varied from a diameter of 1 to 10 mm. The filamentous growth forms a homogeneous suspension that can disperse throughout the liquid medium resulting in highly viscous broth, which has a negative impact on the mass transfer properties, difficulting the large scale production in the traditional stirred tanks (Vanags et al, 1995). If the fermentations require oxygen transfer such as in the lactic acid production by Rhizopus oryzae, the problem is more important (Du et al, 1998).…”