Isolation of a respiratory-deficient Kluyveromyces fragilis mutant for the production of ethanol from Jerusalem artichoke

A respiratory-deficient, mutant of Kluyveromyces fragilis was isolated using a ethidium bromide mutagenesis. It was characterized by a loss of cytochromes a + a3 and by an improvement of its inulinase activity. Under anaerobic conditions this mutant was always better than the wild strain for ethanol production especially from Jerusalem artichoke extracts containing large amounts of high polyfructosans ("early" extracts).     

Bioactive polymers XXX. Immobilization of invertase on the diazonium salt of 4-aminobenzoylcellulose

Invertase was immobilized on diazotized 4-aminobenzoylcellulose. The optimum coupling conditions, namely enzyme concentration, time, and pH, were determined. The temperature and pH value for the maximum activity of the immobilized enzyme were determined and the apparent Michaelis constant was estimated.     

Mathematical modelization of a packed-bed reactor performance with immobilized yeast for ethanol fermentation

The performance of a continuous vertical packed-bed reactor with yeast immobilized in carrageenan gel beads is reported. The study focuses on the mathematical modelling of the steady-state fermentor behavior by means of a tanks-in-series model which includes the intrinsic kinetic model and the external mass transfer and internal diffusion-reaction conditions in the beads.     

A process for protein enrichment of cassava by solid substrate fermentation in rural conditions

An artisanal static process for protein enrichment of cassava by solid-state fermentation, developed in laboratory and tested on pilot units in Burundi (Central Africa), provides enriched cassava containing 10.7% of dry matter protein versus 1% before fermentation. Cassava chips, processed into granules of 2-4-mm diameter, are moistened (40% water content) and steamed. After cooling to 40 degrees C, cassava is mixed with a nutritive solution containing the inoculum (Rhizopus oryzae, strain MUCL 28627) and providing the following per 100 g dry matter: 3.4 g urea, 1.5 g KH(2)PO(4), 0.8 g MgSO(4).7H(2)O, and 22.7 g citric acid. For the fermentation, cassava, with ca. 60% moisture content, is spread in a thin layer (2-3 cm thick) on perforated trays and slid into an aerated humidified enclosure. The incubation lasts +/- 65 h. The production of protein enriched cassava is 3.26 kg dry matter/m(2) tray. The effects of the variation of the nutritive solution composition and the inoculum conservation period on the protein production are equally discussed.     

Purification and partial characterization of a cellodextrin glucohydrolase (beta-glucosidase) from Trichoderma reesei strain QM 9414

A beta-glucosidase (E.C. 3.2.1.21) was isolated from the culture filtrate of fungus Trichoderma reesei QM 9414 grown in continuous culture with biomass retention. The crude extracellular enzyme preparation was fractionated by a three-step purification procedure [chromatography on Fractogel HW-55 (S) and Bio-Gel A 0.5 plus final preparative isoelectric focusing] to yield three beta-glucosidases with isoelectric points at pH 8.4, 8.0, and 7.4. Only one enzyme (pi 8.4) met the stringent criterion of being homogeneous according to titration curve analysis. This enzyme was then characterized not to be a glycoprotein, although the native protein contained 35% carbohydrate (as glucose). It was found to have an apparent molar mass of 7 x 10(4) g/mol (SDS-PAGE), exhibited its optimum activity towards cellobiose at pH 4.5 and 70 degrees C (30 min test), and lost less than 3% activity at 50 degrees C over a period of 7 h. The K(M) values towards cellobiose and p-nitrophenyl-beta-D-glucopyranoside were determined to be 0.5mM and 0.3mM, respectively. The enzyme hydrolyzed cellodextrins (cellotriose to cellooctaose) by sequentially splitting off glucose units from the nonreducing end of the oligomers. The extent of the observed transfer reactions varied with the initial substrate concentration. No enzyme activity towards microcrystalline cellulose or carboxymethylcellulose could be detected. The classification of the enzyme as beta-glucosidase or exo-beta-1,4-glucan glucohydrolase is discussed with respect to the exhibited hydrolytic activities.     

Spore production of Penicillium roqueforti by solid state fermentation: Stoichiometry, growth and sporulation behavior

The development of Penicillium roqueforti on buckwheat seeds proceeds roughly into four steps, involving a lag phase and three growth phases. First, it appears as a spore germination and external colonization of the grains by the mycelium. Then, mainly external sporulation and internal colonization of the seeds occur and finally internal sporulation takes place. The Stoichiometry of the growth and the sporulation is established. Kinetic experiments performed in a fixed bed reactor show that the growth of the microorganism (biomass production) may be estimated by the protein content of the medium. This growth occurs with a very low mu(max) value close to 0.030 h(-1). The chitin content of the medium is an indicator of the sporulation, just as the metabolic liquor (mainly water) produced during the course of a cultivation. The values of the observed respiratory quotient are close to those predicted by stoichiometry.     

Enzymic interesterification of fats: Laboratory and pilot-scale studies with immobilized lipase from Rhizopus arrhizus

An immobilized lipase suitable for fat interesterification has been prepared by precipitation with acetone of a commercial lipase from Rhizopus arrhizus onto diatomaceous earth. As observed previously with a less active enzyme from Aspergillus sp., the interesterification activity was enhanced by addition of purified lipase or by high loadings of commercial enzyme. The interesterification activities reached maximum values in both cases. For immobilized preparations with purified enzyme, interesterification activity was also enhanced by the presence of a precoat of glutaraldehyde cross-linked commercial lipase. A 2.9-L column of immobilized lipase was used to interesterify batches of shea oleine (67 kg) and shea oil (40 kg). Little activity was lost processing shea oleine, but slow poisoning of the bed occurred when shea oil was fed to the column.     

Continuous production of L-phenylalanine by transamination

L-Phenylalanine was produced continuously from L-as-partate and phenylpyruvate by transaminase from a newly screened Pseudomonas putida strain. The process was carried out with an isolated enzyme in homogeneous phase in an enzyme membrane reactor and with immobilized whole cells in a stirred tank reactor, respectively. Due to the difference in transport resistance, the productivity of the free enzyme in homogeneous phase (72 mmol/L h) was about 3 times higher than the productivity achieved using immobilized cells. However, a better stability of the biocatalyst was observed with immobilized cells.