Willibaldo Schmidell

Volumetric oxygen transfer coefficients (kLa) in batch cultivations involving non-Newtonian broths

The oxygen transfer in non-Newtonian fermentation broths of Aspergillus awamori, during batch cultivations in conventional 10 l bioreactor has been investigated. Values of the volumetric oxygen transfer coefficient (kLa), obtained at various impeller speeds, air flow rates and at distinct initial substrate concentrations were correlated with operational variables, geometric parameters of the system and physical properties of the broths utilising rigorous techniques in order to obtain a set of reliable and accurate data. An experimental device was constructed for on-line rheological measurements, and the apparent dynamic viscosity was determined from the broth rheograms. In order to measure power requirements, a torque meter was developed and non-Newtonian fluids with rheological characteristics similar to the Aspergillus fermented broths were utilised to obtain reference curves and correlations in the fermentor where the cultivations took place. Gas balancing method and a modified dynamic method were utilised simultaneously to determine kLa values. The rigorous methods thus developed allowed adequate evaluation of the oxygen transfer in the cultivations and also permitted good fits of four different traditional correlations for kLa to the experimental data.

Influence of carbon and nitrogen sources on glucoamylase production byAspergillus in batch process

SummaryGlucoamylase production kinetics was greatly affected by medium composition. While maltose and cassava flour induced glucoamylase synthesis, fructose clearly repressed it, reaching a maximum enzyne activity value (Am) of only 6% of those obtained with the former carbon sources. Among the nitrogen sources the best result was obtained with urea, reaching Am values of about 40% higher than those obtained with ammonium sulphate.

Estimation of the rheology of glucoamylase fermentation broth from the biomass concentration and shear conditions

Fermentation broths from nine Aspergillus awamori cultivations, carried out under different agitation and aeration conditions and distinct initial substrate concentrations, were characterized using a continuous on-line rheometer. A single correlation between the consistency index (K) and the biomass concentration (X), including the agitation (N) and aeration (Q) conditions fitted the experimental data reasonably well, showing that the shear conditions imposed on the broth influence in a significant way the mycelial morphology and, therefore, the broth rheology.

The effect of dissolved oxygen concentration control on cell growth and antibiotic retamycin production in Streptomyces olindensis So20 fermentations

Cell growth and retamycin production in Streptomyces olindensis So20 were studied at different dissolved oxygen levels during fermentation. The profiles for cell growth and retamycin production in an experiment with dissolved oxygen control at 5% air saturation during production were similar to those in an experiment without dissolved oxygen control. However, despite slower cell growth, a twofold increase in the final retamycin concentration was achieved when dissolved oxygen was controlled at 100% during the growth phase, compared to a base experiment (no DO control). Therefore, the results revealed that retamycin production was dependent on dissolved oxygen concentration during the growth phase, even with sufficient oxygen. On the other hand, a large oxygen supply during the production phase did not contribute to an improvement in retamycin production.

Effect of yeast extract on glucoamylase synthesis byAspergillusawamori NRRL 3112

SummaryGlucoamylase synthesis is strongly affected by yeast extract concentration (CE). An eight fold increase in CE caused a two fold increase in the maximum glucoamylase activity value (Am) for the cultivations conducted with an initial glucose concentration (GO) of about 20 g/l, and a four fold increase in Am in the runs with a Go value of about 40 g/l. Five mathematical correlations are presented, showing a very good adjustment to the experimental results.

RELATIONSHIP BETWEEN MORPHOLOGY, RHEOLOGY AND GLUCOAMYLASE PRODUCTION BY Aspergillus awamori IN SUBMERGED CULTURES

The influence of inoculum preparation on Aspergillus awamori morphology, broth rheology and glucoamylase synthesis in submerged cultures was investigated. A series of runs were performed in fermenters, using initial total reducing sugar concentrations of 20 g/L and 80 g/L. The inocula were prepared in a rotary shaker, at 35oC and 200 rev/min, using a spore concentration of 9.2 x 105 spores/mL and varying both cultivation time and medium pH during the spore germination step. Three types of inocula were used: inoculum cultivated for 24 hours at an initial pH of 5.0, and inocula cultivated for 7 hours at both a pH of 2.5 and a pH of 5.5. Regarding glucoamylase production, the inoculum which provided the best results was shaker cultivated for 7 hours at a pH of 2.5. This inoculum produced glucoamylase of about 1,221 U/L in the fermenter, which was between 20% and 30% higher than those obtained using other inocula.

Production of 2,3-Butanediol from Sucrose by Klebsiella pneumoniae NRRL B199 in Batch and Fed-Batch Reactors

In batch mode, Klebsiella pneumoniae growth and 2,3-butanediol/acetoin formation are increasingly inhibited by initial sucrose concentrations (S0) over 60 g/L. At non inhibitory conditions, a maximum sucrose consumption rate of 1,5 g/L/h was measured. With S0=204 g/L however, this rate decreased to 0.15 g/L/h. K. pneumoniae fermented 204 g/L sucrose to produce 84.3 g/L of a mixture 2,3-butanediol/acetoin with a yield of 0.41 g/g and a productivity of 1.06 g/L/h. Higher oxygen transfer rates improved the overall process rate but the product yield was reduced. Avoiding substrate inhibition, by performing the fermentation in fed-batch mode, a final 2,3-butanediol/acetoin concentration of 80.0 g/L was achieved. In this case, a productivity of 2.63 g/L/h and a product yield of 0.37 g/g were calculated.

Effect of the air supply on the production of 2,3-butanediol by Klebsiella pneumoniae NRRL B199

Klebsiella pneumoniae was cultivated on sucrose in batch, under five quite different oxygen transfer conditions. Depending on the oxygen supply, three different phases could occur. With oxygen in solution, cell growth is exponential and butanediol/acetoin production depends on the oxygen transfer coefficient (KLa). A higher KLa can completely hinder the butanediol formation. When dissolved oxygen concentration is zero, the growth becomes linear and the product formation has its greatest specific rate (μp) as a function of KLa. The maximum μp is dependent on the KLa of each experiment. Below its maximum value, μp is a function of the specific oxygen uptake rate (QO2). Under a very low oxygen supply, cell growth is suppressed and diol/acetoin formation rates decrease. A theoretical interpretation of the results is proposed.

CONSTRUCTION AND OPERATION OF AN IMPELLER RHEOMETER FOR ON-LINE RHEOLOGICAL CHARACTERIZATION OF NON-NEWTONIAN FERMENTATION BROTHS

The present work describes the development and operation of a continuous rotational impeller rheometer for on-line rheological measurements in fermentation broths. In an initial step three devices were calibrated, two of them utilizing helical ribbon impellers and the third a six-bladed impeller. The calibration constants obtained were within the range mentioned in the literature, showing consistency with the methodology employed. In the sequence, the system with one of the helical ribbon impellers (HR39) was selected for on-line continuous rheological measurements due to its small dimensions and its wide measurement range. Finally, the performance of the proposed device, in terms of rheological measurements in Aspergillus awamori broths, was compared to that of a commercial bench rheometer. The comparison of on-line and off-line rheological measurements showed a good agreement between both measurement techniques. Furthermore, results suggest that the proposed on-line rheometer features higher sensitivity and easier operation than the commercial rheometer

INFLUENCE OF PHOSPHATE CONCENTRATIONS ON GLUCOAMYLASE PRODUCTION BY Aspergillus awamori IN SUBMERGED CULTURE

The aim of this work was to study the influence of phosphate concentrations on glucoamylase production by the fungus Aspergillus awamori. In culture media containing cassava flour, different levels of phosphates were tested and the fungal responses to increasing levels (whether or not coupled to pH adjustment throughout the run) were assessed in terms of the resulting glucoamylase production. Phosphate increments, associated with pH readjustments throughout the run, yielded around 1,200 U/L of quite stable glucoamylase activity in the broth, while under a conventional condition (low phosphate without pH readjustment), enzymatic activity was around 350 U/L, which decayed dramatically towards the end of the cultivation