Showing papers by "Bärbel Hahn-Hägerdal published in 1989"
TL;DR: Untreated spent sulfite liquor was fermented with five yeasts, Candida tropicalis, Pichia stipitis, Pachysolen tannophilus, Schizosaccharomyces pombe, Saccharomyceces cerevisiae, and a co-culture of P. tropicalis and P. tannophile, and the highest yield of ethanol, 0.41 g g− total sugar, was obtained with S. Cerevisiae.
102 citations
TL;DR: The amount of [C]maltose incorporated into the cell material of maltose-grown cells was four times greater than that of [D]glucose incorporated in the cellMaterial of glucose-grown Cells, indicating a difference in the utilization of the two carbon sources for energy metabolism.
Abstract: Homolactic fermentation of glucose and heterolactic fermentation of maltose with Lactococcus lactis 65.1 were confirmed. When moles of glucose were compared, the uptake rates of the two carbon sources were similar. The intracellular concentration of fructose-1,6-diphosphate (FDP) in maltose-assimilating cells was half of that in glucose-assimilating cells. Similarly, formation of FDP and lactate from maltose by extracts of maltose-grown cells was half of that formed from glucose by extracts of glucose-grown cells, indicating a difference in the utilization of the two carbon sources for energy metabolism. Concentrations of adenine nucleotides were similar in both types of cells. Glucose-1-phosphate was found in extracts of maltose-grown cells given maltose and, in addition, an inducible and low beta-specific phosphoglucomutase activity was observed. beta-Glucose-1-phosphate was not metabolized by cell extracts to either FDP or lactate, suggesting an alternative metabolic route. The amount of [C]maltose incorporated into the cell material of maltose-grown cells was four times greater than that of [C]glucose incorporated into the cell material of glucose-grown cells. The intracellular concentration of UTP was lower in maltose-assimilating cells than in glucose-assimilating cells. Cells grown on maltose were more spherical and less fragile than cells grown on glucose.
58 citations
TL;DR: In this article, xylulose was measured in a lignocellulose hydrolysate using HPLC with two hydrogen loaded ion exchange columns in series, in the concentration range appropriate for enzymatic xylose isomerization.
Abstract: In the concentration range appropriate for enzymatic xylose isomerization, xylulose was measured in a lignocellulose hydrolysate using HPLC with two hydrogen loaded ion exchange columns in series. Spent sulphite liquour (SSL) was used as a model for lignocellulose hydrolysates. In buffer the separation took 22 minutes and in SSL the analysis time was 47 minutes due to the presence of ethanol. The enzymatic isomerization of xylose to xylulose was followed directly in SSL, providing a method for the direct determination of xylose isomerase activity in lignocellulose hydrolysates.
23 citations
TL;DR: The perchloric acid extraction method for measuring concentrations of intracellular intermediary metabolites was adapted and optimized for Candida tropicalis and maximum metabolite concentrations as well as maximum ratio of Krebs cycle to glycolysis metabolites were found at 5 mM/h OTR.
Abstract: The perchloric acid extraction method for measuring concentrations of intracellular intermediary metabolites was adapted and optimized forCandida tropicalis. Cells were harvested by filtration and rapidly frozen in liquid nitrogen in order to image anin vivo situation. Intracellular metabolites were determined with NAD/NADH linked enzymatic assays and detected spectrofluorimetrically, which allowed determinations in the mM range. The assays allow measurements of 50–60 samples at the same time. Six different metabolites (fructose 1,6-diphosphate, pyruvate, phosphoenolpyruvate, citrate, malate and fumarate) could be determined in the same sample. The method was applied to study the relation of product formation and the intracellular intermediary metabolite concentrations inCandida tropicalis at varying degrees of oxygen limitation in xylose fermenting cells. Maximum metabolite concentrations as well as maximum ratio of Krebs cycle to glycolysis metabolites were found at 5 mM/h OTR, at which point maximum ethanol production was observed.
15 citations
TL;DR: In this paper, the production of β-glucosidase with Aspergillus phoenicis QM 329 was studied in two different aqueous two-phase systems: polyethylene glycol (PEG) 1550 7.5%/Dextran T2000 9.5%.
Abstract: The production of β-glucosidase withAspergillus phoenicis QM 329 was studied in two different aqueous two-phase systems: polyethylene glycol (PEG) 1550 7.5%/Dextran T2000 9.5% and PEG 8000 4%/polyvinyl alcohol (PVA) 14000 8%. The enzyme concentrations in the top phase of the phase systems were 3.4 IU/ml and 3.2 IU/ml, respectively, compared with 2.0 IU/ml obtained in a regular medium. The total amount of β-glucosidase obtained in the phase systems was 265 IU and 176 IU, respectively, compared with 200 IU in a regular medium.
12 citations
TL;DR: A pure d-xylulose and standard was produced by isomerization of d -xylose in a recirculating flow system incorporating an enzyme reactor containing immobilized xylose isomerase and was purified chromatographically.
12 citations
TL;DR: In this paper, Aspergillus phoenicis QM 329 was found to grow in the shape of beads in shake flasks and in an air-lift fermentor.
Abstract: Aspergillus phoenicis QM 329 was found to grow in the shape of beads in shake flasks and in an air-lift fermentor. Initial culture pH, pH profile during cultivation, carbon source, inoculum size and fermentor configuration influenced the retainment of the β-glucosidase activty in the mycelium. Glucose and soluble starch produced beads with the highest activity and the best stability. Glucose-derived beads were more homogeneous in size and shape than the starch-derived beads. These beads kept their integrity for 10 d at 50° C. After 48 h hydrolysis of 50 g/l cellobiose 75% of the initial enzyme activity remained. The beads could be air-dried and alcohol-sterilized with only minor loss of activity. The size of the beads could be controlled by varying the size of the conidia inoculum. In an air-lift fermentor with a working volume of 1500 ml,900 ml beads with an average diameter of 2 mm (estimated to 37–45,000 beads) were produced in less than 3 d with glucose as carbon source. The beads held a β-glucosidase activity of 0.140 IU/bead determined with the pNP assay.
9 citations