Biomedical subjects

L A van der Wielen

Publications and source records attributed to L A van der Wielen.

7 recordsLinked to original sources

PubMed2000

Partitioning behavior of amino acids in aqueous two-phase systems with recyclable volatile salts.

As part of an ongoing research effort on aqueous two-phase systems (ATPSs) with volatile salts, this work describes the partitioning behavior of a series of amino acids, namely L-serine, glycine, L-alanine, L-valine, L-methionine, L-isoleucine, and L-phenylalanine, in these systems. The results show that amino acids partition in a similar way in polymer-volatile salt ATPSs and in traditional polymer-salt ATPSs. Increasing amino acid hydrophobicities lead to increasing partition coefficients. Moreover, the common linear relationship between the logarithm of the partition coefficient and the tie line length is observed here as well. Furthermore, the relation between relative partition coefficients and relative hydrophobicities of amino acids in the extraction systems investigated in this work is comparable to that in other extraction systems.

Amino Acids↗

PubMed2000

Isoelectric precipitation of soybean protein using carbon dioxide as a volatile acid.

A novel process is presented for the isoelectric precipitation of soy protein, using carbon dioxide as a volatile acid. By contacting a soy meal extract with pressurized carbon dioxide, the solution pH was decreased to the isoelectric region of the soy proteins. Complete precipitation of the precipitable soy proteins could be achieved for protein concentrations up to 40 g/l at pressures less than 50 bar. Isoelectric precipitation with a volatile acid enabled accurate control of the solution pH by pressure and eliminated the local pH overshoot, usual in conventional precipitation techniques. The advantage of the improved precipitation control was reflected by the morphology of the precipitate particles. Protein aggregates formed by CO2 were perfectly spherical whereas protein precipitated by sulfuric acid had an irregular morphology. The influence of process variables to control particle size is discussed.

Carbon Dioxide↗

PubMed2000

Novel simulated moving-bed method for reduced solvent consumption.

Simulated moving-bed (SMB) chromatography is attractive for reducing sorbent and solvent consumption relative to fixed-bed systems. In this contribution, we describe a novel and versatile method for further reducing solvent consumption in the case of reversed-phase chromatography. The method is based on the variation of the distribution coefficients of solutes to be separated upon varying the composition of a multi-component mobile phase. If the solvent strength of the desorbent is set higher than the solvent strength of the feed, the components will have smaller distribution coefficients in the extraction section of the SMB and hence will be more easily eluted. This will result in a lower desorbent flow and possibly also in a shorter desorbent zone, and, ultimately, in more concentrated products. The so-called "Triangle-method" by Storti et al. [AIChE J., 39 (1993) 471] to obtain the region of complete separation, is extended for this novel SMB method. Theoretical evaluation of the proposed methodology supports the anticipated solvent reduction relative to fixed-bed RP-HPLC for the cases of the purification of the polyketide antibiotic nystatin and the separation of bovine insulin from porcine insulin.

Animals↗

PubMed1998

Poly(ethylene glycol)-salt aqueous two-phase systems with easily recyclable volatile salts.

Aqueous two-phase systems (ATPSs) have great potential in the downstream processing of fermentation products. However, the consumption of large amounts of auxiliary materials limits application in industrial practice. Promising alternatives to the salts used so far are volatile salts such as ammonium bicarbonate and ammonium carbamate, which can be recycled to the extraction system as gaseous carbon dioxide and ammonia. In this work, it is demonstrated that ammonium carbamate in combination with poly(ethylene glycol) (PEG, molecular masses of 2000, 4000 and 10000) indeed produces aqueous two-phase systems (ATPSs) at a temperature of 25 degrees C and atmospheric pressure. Ammonium bicarbonate is clearly not suitable as a phase-forming salt, because of its too-low solubility in water.

Carbamates↗

PubMed1998

Centrifugal partition chromatographic reaction for the production of chiral amino acids.

The use of a centrifugal partition chromatographic reactor is investigated for the production of chiral amino acids from racemic mixtures. Chirally selective enzymatic hydrolysis of N-acetyl-L-methionine into acetic acid and L-methionine was carried out in the chromatographic reactor to demonstrate the concept of integrated reaction and separation in centrifugal partition chromatography (CPC). The products L-methionine and acetic acid, as well as the unconverted substrate, N-acetyl-D-methionine are obtained separately. An aqueous two-phase system, consisting of PEG 600, potassium phosphate and water was successfully applied as liquid-liquid two-phase system in CPC. A model is presented, which describes the reaction chromatograms on the basis of the independently measured partition and mass transfer coefficients of the individual (reacting) components. The model appears to be a valuable tool for optimizing the reaction-separation process.

Amino Acids↗

PubMed1997

Thermodynamics in biochemical engineering.

Equilibrium aspects in biotechnology and thermodynamics as the main theory underlying them have thus far received relatively little attention. As a consequence, design and development of biotechnological processes is still carried out today in an relatively empirical way. For this situation to improve, a wider and more systematic use of the thermodynamic aspects pertaining to biotechnology must be encouraged. Recognizing this need, the ESF program on Process Integration in Biotechnology developed an intensive advanced course which was held twice so far. The present contribution uses the course structure in order to give a short overview of the field and to identify research needs. The development of a rigorous thermodynamic description, for the exceedingly complex world of biotechnology, is indeed one of the major challenges today in establishing the scientific basis for rational efficient, and fast bioprocess development and design.

Biotechnology↗

PubMed1992

Integrated product formation and recovery in fermentation.

Fermentation processes are hampered by a variety of problems originating from the accumulation of products in the fermenter. Integration of fermentation and a primary product separation step can accelerate the product formation, improve the product yield, and facilitate downstream processing. The advantages of integrated bioprocesses, however, are counteracted by the incompatibility of the subprocesses. Over the past few years, research in this field has been directed towards the development of engineering tools to reduce integration problems, to select a suitable approach, and to predict the feasibility of the integrated process. More fundamental knowledge about metabolic pathways, control mechanisms, and process dynamics is needed in order to optimally design integrated systems.

Biotechnology↗