Submerged citric acid fermentation: rheological properties ofAspergillus niger broth in a stirred tank reactor

Abstract

A large number of submerged citric acid fermentations in a beet molasses substrate was studied.The development of Aspergillus niger from conidia to pellets was followed. Rheological characteristics of the fermentation broth including the pellets were determined. The results obtained confirm the fact that the non-Newtonian pseudoplastic behaviour of the fermentation broth was due to the presence of mycelial pellets. The most significant changes in rheological properties occurred during the period of maximal citric acid production and increase in biomass.

Effect of biomass concentration and mycelial morphology on fermentation broth rheology

“…Allen and Robinson (1990) found that n fell rapidly from a value of 1 at the beginning of a fermentation to around 0.4 at 8 g L −1 and thereafter remained stable. Similar findings were also reported by Berovic et al (1991) and Warren et al (1994). The method used to measure the rheology in this study did not allow accurate measurements to made below 8 to 10 g L −1 and, consequently, measurements were only made once n had begun to stabilize.…”

Effect of transport phenomena of Cladosporium cladosporioides on decolorization and chemical oxygen demand of distillery spent wash

“…But it was observed that only between 4th and 5th day; the pellet was rigid and firm; and then, it lost its rigidity for the remaining period. It was reported that during the development of A. niger, it lasted for 36 h to form spherical pellet with short and thick peripheral hyphae (Berovic et al 1991). In our investigation, pellets formation started at the end of 2nd day.…”

“…The fermentation broth is a suspension of microorganisms, substrate and organic contents of the distillery spent wash along with melonidine pigment the color causing biopolymer. Earlier reports revealed that an important feature of a batch fermentation process is the change in rheological behavior during fermentation due to the change in substrate composition, biomass concentration, and morphology of the microorganisms (Berovic et al 1991). It is evident from Fig.…”

“…The rheological behavior is closely related to the morphology and biomass concentrations (Blanch and Bhavaraju 1976;Charles 1978;Metz et al 1979;Tucker and Thomas 1993). The broth rheology determines the transport phenomena in bioreactors and is considered to be the key factor for getting an improved yield of the targeted product (Berovic et al 1991;Gehrig et al 1998). Generally two types of growth forms the filamentous and pelleted can be observed during a fungal fermentation.…”

Imobilização de células microbianas e suas aplicações biotecnológicas

“…Outro metabólito de interesse é a produção de ácido cítrico pelo fungo Aspergillus niger, o qual ocorre quando este microrganismo se encontra na forma de "pellets" (BEROVIC et al, 1991).…”