Helena Kautola

Comparison of different strains of the yeast Yarrowia lipolytica for citric acid production from glucose hydrol.

Four commercial strains and two mutants of the yeast speciesYarrowia lipolytica were screened using batch fermentation. StrainY.lipolytica A-101-1.14 (induced with UV irradiation) was found to be the most suitable for citric acid production from glucose hydrol (39.9% glucose and 2.1% other sugars), a byproduct of glucose production from potato starch. The specific rate of total citric and isocitric acid production was 0.138 g/g.h, the yield on consumed glucose 0.93 g/g, and the productivity achieved was as high as 1.25 g/L.h All of the tested yeast strains were able to utilize only the glucose from the glucose hydrol medium. Thus, some residual higher oligosaccharides remained in the process effluent.

Itaconic acid production by immobilizedAspergillus terreus from xylose and glucose

SummaryAspergillus terreus NRRC 1960 spores were entrapped in calcium alginate gel beads or alternotely the fungal mycelium was immobilized either on Celite R-626 or in agar gel cubes, and the biocatalyst was employed both in repeated batch and in continuous column reactors to produce itaconic acid from D-xylose or D-glucose. The highest itaconic acid yield obtained in a submerged culture batch fermentation was 54.5% based on total initial glucose (55 g/l) with a volumetric productivity of 0.32 g/l h, and 44.8% from xylose (67 g/l) with a productivity of 0.20 g/l h. In a repeated batch fermentation mycelium immobilized in agar gel had a productivity of 0.112 g/l h, and mycelium grown from spores immobilized in calcium alginate gel 0.06 g/l h, both from xylose (60 g/l). With the best immobilized biocatalyst system used employing Celite R-626 as a carrier, volumetric productivities of 1.2 g/l h from glucose and 0.56 g/l h from xylose (both at 60 g/l) were obtained in continuous column operation for more than 2 weeks.

Fumaric acid production from xylose by immobilized Rhizopus arrhizus cells

SummaryThe production of fumaric acid by immobilized Rhizopus arrhizus TKK 204-1-1a mycelium was optimized in batch fermentations using statistical experimental design and empiric modelling. The maximum fumaric acid concentration was obtained at a xylose concentration of about 6% and a carbon:nitrogen ratio of about 160. In repeated batch fermentations with immobilized cells the highest volumetric productivity of fumaric acid reached was 87 mg/l per hour when the initial xylose concentration was 10%, the C:N ratio 160 and the residence time 1.75 days. The maximum product concentration was 16.4 g/l when the initial xylose concentration was 10%, the C:N ratio 160 and the residence time 10.25 days. The maximum yield from initial xylose (6.47%) was 23.7% with a product concentration of 15.3 g/l and volumetric productivity of 71 mg/l per hour at a residence time of 9 days and a C:N ratio of 188.3. Immobilization could increase the fumaric acid concentration to a level 3.4 times higher than that produced by free cells.

Itaconic acid production by immobilized Aspergillus terreus with varied metal additions

SummaryThe effect of trace and alkaline metals on itaconic acid production by polyurethane-foam-immobilized Aspergillus terreus was examined in repeated shake-flask cultures according to a statistical experimental design. An increase in the glucose or copper concentration increased the need for earth alkaline metals. The experimentally obtained highest itaconic acid concentration of 51 g/l from 15% glucose with a total productivity of 3.67 g/l per day was reached during the first 14-day batch fermentation. In the fourth batch the calculated highest itaconic acid concentration of 19 g/l was reached with 25% glucose, 5 g/l of magnesium sulphate, 13 mg/l of copper sulphate and 10 g/l of calcium chloride. The immobilization of the mycelium increased the itaconic acid concentration obtained by as much as eightfold.

Continuous itaconic acid production by immobilized biocatalysts

The continuous itaconic acid production from sucrose with Aspergillus terreus TKK 200-5-3 mycelium immobilized on polyurethane foam cubes was optimized in column bioreactors using statistical experimental design and empirical modelling. The highest itaconic acid product concentration calculated on the basis of the obtained model was 15.8 g l-1 in the investigated experimental area, when sucrose concentration was 13.5%, aeration rate 150 ml min-1 and residence time 178 h. From sucrose with immobilized A. terreus TKK 200-5-3 mycelium itaconic acid production was stable for at least 4.5 months in continuous column bioreactors. In comparison, using glucose as substrate and immobilized A. terreus TKK 200-5-1 mycelium as biocatalyst similar stability was obtained with higher product concentration. The omission of copper sulphate from the production medium gave the highest itaconic acid product concentration (26 g l-1) from 9% glucose with 0.25% ammonium nitrate and 0.095% magnesium sulphate.

Alcoholic fermentation of D-xylose by immobilizedPichia stipitis yeast

SummaryPichia stipitis NRRL Y-7124 yeast cells were for the first time immobilized both in agar gel beads and on fine nylon net for ethanol fermentation on D-xylose, in order to investigate the possibility of using the biocatalyst for improved utilization of the biomass pentose fraction. With free cells the initial xylose level affected little ethanol production, with a maximum of 22 g/l ethanol obtained in 5 days on 5% and of 40 g/l in 8 days on 10% xylose, and an average volumetric productivity of about 0.22 g/lh. The maximum ethanol concentration of 19.5% on 5% xylose with the nylon net attached cells in a continuous packed-bed column reactor was obtained with 35 h residence time. The volumetric productivities of 0.56 g/lh at 19.5 g/l ethanol and 1.0 g/lh at 15.0 g/l ethanol were markedly higher than those obtained with free cells. The stability of the immobilized biocatalyst was excellent. The same reactor could be used for at least 80 days without significant activity loss.

Itaconic acid production by immobilizedAspergillus terreus on sucrose medium

SummaryThe itaconic acid production by immobilizedAspergillus terreus TTK 200-5-3 mycelium was optimized in shake flask fermentations using statistical experimental design and empirical modelling. The maximum itaconic acid concentration was calculated to be 13.3 g/l in the investigated experimental area when initial sucrose concentration was 10%, ammonium nitrate concentration 0.275% and initial pH 3. The itaconic acid product concentration using immobilized mycelium was about double of that obtained with the free mycelium.

Itaconic acid production from xylose in repeated-batch and continuous bioreactors

SummaryItaconic acid production from xylose by immobilized Aspergillus terreus TKK 200-5-2 mycelia was optimized both in repeated shake-flask fermentations and in continuous column bioreactors using statistical experimental design and empirical modelling. Using continuous 9-1 scale air-lift bioreactors, a pH of 2.5, aeration rate of 0.6 v/v per minute and residence time of 160 h gave the highest itaconic acid concentration. In air-lift bioreactors a cubic carrier size of 0.5 cm gave a 3.3-fold higher product concentration than 1-cm cubes. Packed-bed column reactors had a higher production rate than air-lift reactors.

Studies on citric acid production with immobilized Yarrowia lipolytica in repeated batch and continuous air-lift bioreactors

Citric acid was produced from glucose in repeated-batch shake-flask and continuous air-lift cultivations by calcium-alginate-immobilized Yarrowia lipolytica A-101 yeast. The medium composition was systematically studied in a batch system by using experimental design and empiric modelling. The highest citric acid product concentration of 39 g/l was reached with a medium containing 150 g/l of glucose, 0.105 g/l of potassium dihydrogen phosphate, 0.84 g/l of magnesium sulphate and 21 mg/l of copper sulphate (5.2 mg/l of copper). The results were further improved by hardening the alginate carrier beads with glutaraldehyde, and by activation of the immobilized biocatalyst in a nutrient solution. In continuous air-lift bioreactors with varying height-to-diameter ratio the highest productivity of 350 mg/l per hour with a dilution rate of 0.023 l/h and a citric acid product concentration of 12 g/l was reached with a ratio of 3.

Production of citric acid with immobilized Yarrowia lipolytica

SummaryCitric acid was produced with immobilized Yarrowia lipolytica yeast in repeated batch-shake-flask and air-lift fermentations. In active and passive immobilization methods calcium alginate, κ-carrageenan, polyurethane gel, nylon web and polyurethane foams were tested as carriers in repeated-batch fermentations. The highest citric acid productivity of 155 mg l−1 h−1 was reached with alginate-bead-immobilized cells in the first batch. A decrease in bead diameter from 5–6 mm to 2–3 mm increased the volumetric citric acid productivity threefold. In an air-lift bioreactor the highest citric acid productivity of 120 mg l−1 h−1 with a product concentration of 16.4 g l−1 was obtained with cells immobilized in κ-carrageenan beads.