Willem Stevens - Academia.edu (original) (raw)

Papers by Willem Stevens

Asian Journal of Food and Agro-Industry, 2011

Waste and Biomass Valorization, Aug 26, 2021

Sustainable development regarding safely reusing waste and the transformation of waste to valuabl... more Sustainable development regarding safely reusing waste and the transformation of waste to valuable products is emerging as a strong trend. This study presents a potential source for chitin/chitosan products, such as moulted shrimp shells collected from solid waste in intensive aquaculture. The conditions for chitin extraction from these moulted shells were gentler compared to conventional peeling shrimp shells. The chemical structure, morphology, and purity of raw materials and prepared products were characterized by FTIR, XRD, NMR, SEM measurements. The prepared chitin and chitosan had a high purity with a very low ash (less than 0.5 wt%) and protein residues (less than 0.6 wt%), along with their medium viscosity and low crystallinity. This current study has provided a potential source and the proper extraction approach for large-scale chitin and chitosan production from moulted shrimp shells. Besides, these findings suggest a strategy for sustainable aquaculture by using solid wastes to produce value-added products.

Carbohydrate Research, Mar 1, 2020

In this study, pretreatment procedures have been investigated preceding the standard production o... more In this study, pretreatment procedures have been investigated preceding the standard production of chitin and chitosan. These steps can be used in industrial processes to preserve raw shrimp shells as long as the amount of material is not enough for one production batch. After these treatments, shrimp shells are clean and are facile for further demineralization, deproteinization and deacetylation processes. The prepared chitin and chitosan show a high purity with very low ash (less than 0.3%) and protein residues (less than 0.5%), along with their high molecular weight and high crystallinity. This modified approach has potential for application in large-scale production due to its ease of operation and reduction of environmental concerns.

Materials Science and Technology, Sep 1, 2008

... A label free electrosensing immunosensor is proposed based on the electrode modification ... ... more ... A label free electrosensing immunosensor is proposed based on the electrode modification ... alginatepoly-L-lysine (AL) composite used in the development bioartificial liver ... the improvement of cellular proliferation, differentiation and hemocompatibility.164,166 Pectin is another ...

Cold Spring Harbor Symposia on Quantitative Biology, 1970

The concept of operon was proposed to explain the coordinated activity of a cluster of closely li... more The concept of operon was proposed to explain the coordinated activity of a cluster of closely linked genes, as exemplified by the lactose operon (Jacob et al., 1960; Jacob and Monod, 1961a, b). The operon was defined as a polarized unit of coordinated transcription ...

Asian Institute of Technology eBooks, 1996

Biochimica Et Biophysica Acta - General Subjects, Feb 1, 1971

Applied Microbiology and Biotechnology, Dec 13, 2000

Factors affecting Lactobacillus fermentation of shrimp waste for chitin and protein liquor produc... more Factors affecting Lactobacillus fermentation of shrimp waste for chitin and protein liquor production were determined. The objective of the fermentation is medium conditioning by Lactobacillus through production of proteases and lowering of the pH. The efficiency was tested by conducting fermentation of biowaste in 1-1 beakers with or without pH adjustment using different acids. Addition of 5% glucose to the biowaste supported the growth of lactic acid bacteria and led to better fermentation. Among four acids tested to control pH at the start and during fermentation, acetic acid and citric acid proved to be the most effective. In biowaste fermented with 6.7% L. plantarum inoculum, 5% glucose, and pH 6.0 adjusted with acetic acid, 75% deproteination and 86% demineralization was achieved. Replacement of acetic acid by citric acid gave 88% deproteination and 90% demineralization. The fermentation carried out in the presence of acetic acid resulted in a protein fraction that smelled good and a clean chitin fraction.

Encyclopedia of Marine Biotechnology

Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen. Series C. Biological and medical sciences, 1971

Atropos, gij waart godin van het noodlot en vrees'lijke rampspoed Gij waart bij machte ten gronde... more Atropos, gij waart godin van het noodlot en vrees'lijke rampspoed Gij waart bij machte ten gronde te richten, gij had een onzalige invloed Door tot de vader van goden en mensen het onheil te fluist'ren. Hiermee de sterv 'ling voorgoed aan zijn blinde bestemming te kluist 'ren En als extract van bell'donna verwijdend het oog der beminde, Zodat gij aanstaande man alswel vrouw in hun keuze verblindde Welk lot brengt U een bacil, die uit Hades rijk vrij is gegeven, Die in haar handen de schaar heeft, die knipt aan de draad van uw leven. * Voor stnictuurformules wordt verwezen naar tabel 5.6 en bijlage I. HOOFDSTUK 2 MATERIALEN EN METHODEN 2.1 NOMENCLATUUR Aangezien atropine een ester is van tropazuur, dat een optisch actief koolstofatoom bevat, komt het voor in twee optische isomeren. De aanduiding atropine wordt gebruikt voor racemisch atropine; de optische isomeren worden aangeduid met (-I-)-atropine en (-)-atropine, de natuurlijk voorkomende isomeer. De naam hyoscyamine, die ook aan de afzonderUjke stereo-isomeren van atropine wordt gegeven, zal hier niet worden gebruikt. De naam tropazuur wordt gebruUct voor het racemaat; de optische isomeren worden met {+)-en (-)-tropazuur aangeduid. (-)-tropazuur is de zuurcomponent van (-)-atropine en bezit de (S)-configuratie. Voorzover rüet de systematische naam van een verbinding is gebruikt, wordt voor structuurformules naar de substraat-specificiteitstabel in hoofdstuk 5 en naar bijlage I verwezen. Voor de aanduiding van organische zuren wordt de naam van het zuur gebruUct, ongeacht de dissociatietoestand onder de gebruikte proefomstandigheden. De enzymen atropine-esterase (AtrE), tropazuur-dehydrogenase (TDH), 2-fenyhnalonzuur-semi-aldehyde-decarboxylase (PDC) en fenyl-aceetaldehyde-dehydrogenase (PDH) worden gezamenlijk aangeduid met de tropazuur-enzymen. De afkortingen van enzymen, verbindingen, etc. zijn afgeleid van de Engelse benamingen. De afkortingen voor atropine, tropazuur, etc. worden uitsluitend gebruikt bij het beschrijven van het fenotype van de mutanten. 2.2 MATERIALEN De (-I-)-isomeer van atropine, (+)-en (-)-tropazuur en het 3-chinuclidinylbenzülaat werd beschücbaar gesteld door Drs. H.L. Boter (Chemisch Laboratorium RVO-TNO); (-)-atropine werd betrokken van de Nutritional Biochemicals Corporation (U.S.A.). Het N-methyljodide van het (-)-en (±)-atropine werd beschikbaar gesteld door Dr. F. Berends; Soman door Dr. P. Christen. Technisch tropazuur is betrokken van Mac-Farian Smith Ltd, (Schotland); dit werd tweemaal uit water omgekristaUiseerd. De synthese en de identificatie van 2-fenylmalonzuur-semi-aldehyde (pma) is beschreven in hoofdstuk 3. Fenylmalonzuur werd geïsoleerd uit de diethyl ester door alkalische hydrolyse en

Cold Spring Harbor Monograph Archive, 1971

Early in the productive growth cycle following infection, λ DNA can be found in doubly branched c... more Early in the productive growth cycle following infection, λ DNA can be found in doubly branched circular structures (Ogawa et al., 1968). The positions of branch points in these molecules suggest that each molecule carries two replication forks moving away from a locus in the region of genes O and P (Schnos and Inman, 1970). These suggestions have been substantiated and refined by measurements of replication in deletion prophages in the presence of helper (Stevens et al., this volume). The replication process can be divided into a step creating a replication fork (initiation) and the subsequent movement of the fork along the DNA template (progression or movement). Three λ genes ( N , O , and P ) are known to specify products that enter into the replication process. The host supplies the biosynthetic machinery for DNA precursors, and at least one gene product that is involved directly in replication of both the host chromosome and λ DNA beyond the precursor level (Hirota et al., 1968...

Progress in Brain Research, 1978

Publisher Summary This chapter discusses the experiments in which synapse formation and neurotran... more Publisher Summary This chapter discusses the experiments in which synapse formation and neurotransmission have been studied in tissue culture, using the ciliary ganglion of the chick embryo as a source of neurons. This ganglion was chosen because it contains only two types of cholinergic neurons, which in vivo form nicotinic neuromuscular junctions with the sphincter iridis and with the ciliary body of the chick, both composed of striated muscle fibers. In mixed cultures of ciliary ganglion plus skeletal muscle cells, functional nicotinic neuromuscular junctions are formed. Recent findings on the specificity of innervation by ciliary ganglia of mammalian and avian origin are also described in the chapter. In tissue culture, the chick ciliary ganglion forms functional junctions with skeletal muscle cells within 24 hours. The results suggest that most of the spontaneously occurring end-plate potentials are not under control of the perikaryon but are generated locally at the neuromuscular junction. Reduction of the amplitude of these end-plate potentials by an increase of the Mg2+/Ca2+ ratio in the bath suggests that some of these potentials are multiquantal in nature. Rabbit ciliary ganglion neurons that form muscarinic neuromuscular junctions with smooth muscle in vivo form functional nicotinic junctions with skeletal muscle fibers in culture.

Plant Science, 2006

The effect of shrimp and fungal chitosan on the growth and development of orchid plant meristemic... more The effect of shrimp and fungal chitosan on the growth and development of orchid plant meristemic tissue in culture was investigated in liquid and on solid medium. The growth of meristem explants into protocorm-like bodies in liquid medium was accelerated up to 15 times in the presence of chitosan oligomer, the optimal concentration being 15 ppm. The 1 kDa shrimp oligomer was slightly more effective compared to 10 kDa shrimp chitosan and four times more active compared to high molecular weight 100 kDa shrimp chitosan. The 10 kDa fungal chitosan was more effective compared with 1 kDa oligomer. The development of orchid protocorm into differentiated orchid tissue with primary shoots and roots was studied on solid agar medium. The optimal effect, the generation of 5-7 plantlets in 12 weeks was observed in the presence of 20 ppm using either 10 kDa fungal or 1 kDa oligomer shrimp chitosan. The data are consistent with preliminary results from field experiments and confirm unequivocally that a minor amount of chitosan has a profound effect on the growth and development of orchid plant tissue.

Experimental Neurology, 1978

The influence of various neural explants on the morphology and the survival of chick muscle fiber... more The influence of various neural explants on the morphology and the survival of chick muscle fibers was studied. A method was developed to evaluate the condition of the muscle fibers using the following four morphological parameters : cross striation, thickness, number of fibers, and absence of vacuoles. Chick as well as mouse spinal cord explants appeared to have a distinct favorable influence on the muscle fibers. Chick ciliary ganglia and mouse cortex explants had less effect and chick sympathetic ganglia and mouse dorsal root ganglia had no effect. Innervation by spinal cord neurons did not lead to a change in resting membrane potential of the muscle fibers. The amount of cross striation in muscle fibers in the vicinity of mouse spinal cord explants was positively correlated with the frequency of spontaneous end-plate potentials in these muscle fibers. d-Tubocurarine did not interfere with the trophic support of muscle cells by nerve cells, although it reversibly blocked neuromuscular transmission throughout the experiment. This demonstrates that neither the acetylcholine receptor nor the activity induced in the muscle fiber mediate the trophic action. The data suggest that a humoral trophic factor, released at the neuromuscular junction or at a region of close cell-cell contact, is needed for normal development and maintenance of muscle fiber morphology.

Brain Research, 1979

Electrophysiological and pharmacological properties of neuromuscular junctions formed in tissue c... more Electrophysiological and pharmacological properties of neuromuscular junctions formed in tissue culture between chick ciliary ganglia and chick skeletal muscle cells have been studied. Functional neuromuscular junctions are formed already within 24 h. No functional acetylcholine (ACh) esterase is present at these end-plates. The neurites conduct action potentials to the neuromuscular junctions, where EPPs are generated. Tetrodotoxin (TTX) blocks this nerve conduction but in the presence of TTX MEPP-like potentials remain whose amplitudes are lowered when the Mg2+/Ca2+ ratio in the medium is raised. It is speculated that these large TTX-resistant potentials are multiquantal. The relatively high resting membrane potential in non-innervated muscle fibers was not changed by innervation. ACh-sensitivity was determined by iontophoretical application of ACh to the myotubes. Non-innervated myotubes exhibited an evenly distributed ACh-sensitivity. Local differences in ACh-sensitivity were always gradual and never exceeded a factor of 3. Innervation did not alter the overall ACh-sensitivity, but on functionally innervated muscle cells loci hypersensitive to ACh were found. Hypersensitivity was located within sharply defined areas. Apparently the parasympathetic neurons of the ciliary ganglion are able to form functional neuromuscular junctions with skeletal muscle cells in tissue culture and to induce the formation of regions of high ACh-sensitivity.