Norman B. Jansen

Effect of oxygen uptake rate on ethanol production by a xylose-fermenting yeast mutant,Candida sp. XF217

SummaryThe fermentation of D-xylose by theCandida sp. mutant XF217 was studied at different oxygen uptake rates by controlling dissolved oxygen tension or agitation rate. The ethanol yield increases as the oxygen uptake rate decreases. The ethanol production rate is maximized at an oxygen uptake rate of 9–12 millimole/L/hour. Xylitol and cell mass production and cell morphology are also affected by oxygen level.

A model of acetic acid and 2,3-butanediol inhibition of the growth and metabolism ofKlebsiellaoxytoca

SummaryThe main product of fermentation byKlebsiellaoxytoca is 2,3-butanediol. This organism also produces acetic acid, ethanol, and acetoin. In this report, product inhibition due to 2,3-butanediol and acetic acid is considered. Although the acetate ion has little effect on growth, acetic acid is a strong inhibitor. Acetic acid inhibits growth more strongly than it inhibits respiration. The neutral product 2,3-butanediol is not a strong inhibitor; its effect on growth is no more than is expected by the decrease in water activity it causes. The effect of 2,3-butanediol on respiration can also be explained by a decreased water activity. It appears that it is possible to accumulate as much as 130 g/L butanediol while as little as 0.45 g/L acetic acid completely inhibits growth.

Use of porous glass fiber as a support for biocatalyst immobilization

SummaryPorous glass fiber has a very high surface area and good mechanical properties that make it an excellent support for biocatalyst immobilization. By packing aligned glass fibers in a tubular reactor such that the fibers are all parallel to the axis of the tube, the resulting pressure drop is considerably smaller than for a similar bed of packed beads. The utility of this support was demonstrated by immobilizing α-glucoamylase by silane-glutaraldehyde coupling, and measuring its activity toward converting maltose to glucose. Using optimized immobilization conditions, an enzyme loading of 1.5 mg protein perm2 surface area was obtained, with an activity of 370 units/g glass at 50°C. The half-life of the immobilized glucoamylase was more than twice as long as that of the free enzyme.

Ethanol inhibition of D-xylulose fermentation by Schizosaccharomyces pombe

SummaryThe kinetics of the utilization of D-xylulose by the yeast Schizosaccharomyces pombe has been examined under anaerobic batch conditions. The inhibitory effect of ethanol on xylulose uptake and ethanol production was studied at pH 6.0 and 30°C. Ethanol had little or no effect on the sugar uptake rate, but end product inhibition was observed on ethanol production. This non-competitive inhibition was linear with respect to ethanol concentration between 0 and 60 g/l. A kinetic model for the alcoholic fermentation of xylulose is presented.

Kinetic studies of the enzymatic isomerization of xylose

Abstract d -Xylose isomerase catalyses the conversion of the common pentose, d -xylose, to its keto-isomer, d -xylose. This reaction is of interest because many microorganisms that are unable to metabolize d -xylose can utilize d -xylulose. The kinetics of a commonly used immobilized whole-cell isomerase, Sweetzyme Q, have been determined from initial rate studies on the forward and reverse reactions. The effect of pH, temperature, and substrate and product concentration on enzyme activity have all been examined. Reaction rates were modelled with the Michaelis-Menten equation. Using constants determined from Lineweaver-Burk plots, the rate equation accurately simulated experimental conversion data.

Hydrolysis of maltose and cornstrarch by glucoamylase immobilized in porous glass fibres and beads

Glucoamylase (1,4 α-d glucan glucohydrolase, EC 3.2.1.3) was covalently immobilized on porous glass fibres and beads. The size of the glass beads (125 μm) was chosen to be small enough to avoid diffusional resistance. A comparison of both supports was established and discussed. Enzyme loadings were similar, 1·70–1·85 mg protein/m2 for fibres and 1·65 mg protein/m2 for beads. A 28% w/v maltose and 39% w/v α-amylase-hydrolysed dextrin 12 DE (Dextrose equivalent) syrups were used as model and real feed substrates respectively. A 98·8% maltose conversion was obtained with the glass fibre reactor. However, the hydrolysis of the dextrin syrup (12 DE, 39% dissolved solids, pH 4·5) was incomplete (93·5% conversion with the same reactor and 91·2% with the glass bead reactor). Glucose production from this syrup was poor for both systems: 85·7 and 83·9% respectively. The continuous operational enzyme stability was found to be highly dependent on substrate concentration, up to 57 days being achieved with a feed of 27·6% w/v maltose solution at pH 4·5 and 50°C.

Methane generation from chemically pretreated cellulose by anaerobic fluidized-bed reactors

Abstract Alkali cooking of cellulose at 10% (w/v) consistency, performed at 250°C, gives a liquor containing organic acids as main components (lactic, acetic and succinic acids). A synthetic substrate, representative of this liquor, was used as feed for two anaerobic fluidized-bed reactors operating at 35°C. The effects of hydraulic retention time and influent substrate concentration on substrate consumption and methane generation were studied. Organic removals of up to 95% and methane generation rates of 1·09 litres CH 4 litre R −1 day −1 were achieved at a retention time ( θ R ) of 8·3h and at an influent substrate concentration of 1400 mg COD litre −1 . At θ R = 3·5 h, conversion decreased to 60%. When feeding the cooked liquor, conversions were slightly lower, around 50% at θ R = 4 h and 1300 mg COD litre −1 of influent substrate concentration. However, the methane volumetric production rate was as high as 2·5 litres CH 4 litre R −1 day −1 under the same conditions. The results suggest that alkaline cooking with subsequent methane fermentation offers a viable process for the treament of cellulosic materials, such as municipal solid waste.

Utilization of a wood-based syrup as a fermentation carbon source

SummaryAn industrial by-product stream consisting primarily of α- and β-methyl xylosides supported microbial growth provided the treated syrup was diluted such that the osmotic pressure was within the range tolerated by the particular microorganism used. A culture screening study identified two organisms that efficiently utilized both α- and β-methyl xyloside. Xylose, α-, and β-methyl xylosides were all utilized simultaneously during batch growth ofArthrobacter sp. in a controlled-pH fermentor, although xylose was consumed faster than either xyloside. In addition,Arthrobacter sp. produced glucose isomerase when grown on the syrup.

A MODEL FOR THE GROWTH AND PRODUCT KINETICS OF FACULTATIVE ANAEROBES BASED ON ATP SYNTHESIS AND CONSUMPTION

ABSTRACT A mathematical model based on the production and consumption of ATP is presented which attempts to simulate the batch fermentation kinetics of Klebsiella pneumoniae. The chief utility of the model is its apparent ability to predict the non-linear way the product yields vary during oxygen limited growth when two different energy producing pathways are active.