Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Influence of the overall charge and local charge density of pectin on the complex formation between pectin and beta-lactoglobulin
Sperber, B.L.H.M. ; Schols, H.A. ; Cohen Stuart, M.A. ; Norde, W. ; Voragen, A.G.J. - \ 2009
Food Hydrocolloids 23 (2009)3. - ISSN 0268-005X - p. 765 - 772.
bovine serum-albumin - whey proteins - aqueous-solution - acid - polyelectrolytes - coacervation - stabilization - conformation - carrageenan - dependence
The complex formation between ß-lactoglobulin (ß-lg) and pectin is studied using pectins with different physicochemical characteristics. Pectin allows for the control of both the overall charge by degree of methyl-esterification as well as local charge density by the degree of blockiness. Varying local charge density, at equal overall charge is a parameter that is not available for synthetic polymers and is of key importance in the complex formation between oppositely charged (bio)polymers. LMP is a pectin with a high overall charge and high local charge density; HMPB and HMPR are pectins with a low overall charge, but a high and low local charge density, respectively. Dynamic light scattering (DLS) titrations identified pHc, the pH where soluble complexes of ß-lg and pectin are formed and pH, the pH of phase separation, both as a function of ionic strength. pHc decreased with increasing ionic strength for all pectins and was used in a theoretical model that showed local charge density of the pectin to control the onset of complex formation. pH passed through a maximum with increasing ionic strength for LMP because of shielding of repulsive interactions between ß-lg molecules bound to LMP, while attractive interactions were repressed at higher ionic strength. Potentiometric titrations of homo-molecular solutions and mixtures of ß-lg and pectin showed charge regulation in ß-lg¿pectin complexes. Around pH 5.5¿5.0 the pKas of ß-lg ionic groups are increased to induce positive charge on the ß-lg molecule; around pH 4.5¿3.5 the pKa values of the pectin ionic groups are lowered to retain negative charge on the pectin. Since pectins with high local charge density form complexes with ß-lg at higher ionic strength than pectins with low local charge density, pectin with a high local charge density is preferred in food systems where complex formation between protein and pectin is desired.
Serum separation and structure of depletion- and bridging-flocculated emulsions: a comparison
Blijdenstein, T.B.J. ; Winden, A.J.M. van; Vliet, T. van; Aken, G.A. van - \ 2004
Colloids and Surfaces. A: Physicochemical and Engineering Aspects 245 (2004)1-3. - ISSN 0927-7757 - p. 41 - 48.
in-water emulsions - protein-stabilized emulsion - beta-lactoglobulin - polysaccharide - suspensions - carrageenan - interfaces - polymers - behavior - rheology
Stability against demixing, rheology and microstructure of emulsions that were flocculated by depletion or bridging were compared. Flocculation by depletion and bridging was induced by addition of the polysaccharide carboxy-methylcellulose (CMC) to emulsions that were stabilised by ß-lactoglobulin (ß-lg) at pH 6.7 and 3.0, respectively. Depletion-flocculated emulsions generally have a lower initial demixing rates than bridging-flocculated emulsions, but after long times they are compressed to a higher oil content by gravity. Differences in the initial demixing rate are shown to be caused by differences in porosity between the gels. In bridging-flocculated emulsions, large irreversible flocs are formed by flow during mixing, resulting in larger permeability than in depletion-flocculated emulsions. Rheological measurements showed that bridging-flocculated emulsions could withstand larger stresses than depletion-flocculated emulsions. Greater network strength and a lower probability of rearrangements explain why bridging-flocculation systems can retain more water at longer times. Keywords: Emulsions; Depletion; Bridging; Structure; Serum separation
Deacylation of antibiotic A40926 by immobilized Actinoplanes teichomyceticus cells in an internal-loop air-lift bioreactor
Jovetic, S. ; Bresser, L. de; Tramper, J. ; Marinelli, F. - \ 2003
Enzyme and Microbial Technology 32 (2003)5. - ISSN 0141-0229 - p. 546 - 552.
carrageenan - beads
A40926 is a natural glycopeptide antibiotic. It is a precursor of dalbavancin, a semi-synthetic second-generation glycopeptide in clinical development for the treatment of ß-lactam-resistant Staphyloccous aureus and Staphylococcus epidermidis infections. Deacylation of A40926, producing an intermediate useful for the synthesis of novel derivatives, can be carried out by the action of Actinoplanes teichomyceticus cells. Kinetics parameters for this particular deacylation reaction were obtained by fitting the experimental data to a Michaelis¿Menten kinetic model. The feasibility of A40926 deacylation by immobilized A. teichomyceticus cells in an air-lift bioreactor was examined. A single continuously operated air-lift reactor (ALR) was evaluated by a model describing diffusion and reaction in the biocatalyst beads. Model estimates were in a good agreement with experimental results. The system was operated continuously for 21 days with overall conversion above 60%.
Differences in polymorphonucleocyte function and local inflammatory response between horses and ponies
Wilmink, J.M. ; Veenman, J.N. ; Boom, R. ; Rutten, V. ; Niewold, T.A. ; Broekhuisen-Davies, J.M. ; Lees, P. ; Armstrong, S. ; Weeren, P.R. van; Barneveld, A. - \ 2003
Equine Veterinary Journal 35 (2003)6. - ISSN 0425-1644 - p. 561 - 569.
tumor-necrosis-factor - peritoneal-macrophages - human-monocytes - equine models - assay - interleukin-1 - contraction - carrageenan - mediators - invitro
Reasons for performing study: Wound healing proceeds faster in ponies than in horses and complications during healing, such as wound infection, occur less frequently in ponies. Earlier studies suggested that this difference might be related to differences in the initial post traumatic inflammatory response. Hypothesis: That polymorphonuclear leucocyte (PMN) function and profiles of humoral factors in local inflammatory processes are different in horses and ponies. Methods: PMNs were isolated from venous blood of horses and ponies. Chemotaxis and reactive oxygen species (ROS) production was determined. Tissue cages were implanted in limbs and necks of horses and ponies and injected with carrageenan and, 3 weeks later, with LPS. In sequential samples of inflammatory exudate, the numbers of macrophages and PMNs and the production of PGE2, TNF¿, IL-1, IL-6 and chemoattractants were determined. Results: In vitro ROS production of PMNs was significantly higher in ponies than in horses, whereas in vitro PMN chemotaxis was significantly lower in ponies. In the tissue cages for both stimuli, the production of IL-1 and chemoattractants was significantly higher in ponies than in horses and remained so towards the end of the observation period in ponies. Conclusions: This study demonstrated a higher production of various inflammatory mediators by pony leucocytes. Despite the lower in vitro chemotaxis of pony PMNs, this higher in vivo production resulted in a stronger initial inflammatory response in ponies, as has been reported in studies on wound healing, through the attraction of leucocytes and triggering of the production of other cytokines. A stronger initial inflammation may promote healing by more rapid elemination of contaminants and earlier transition to repair. Potential relevance: Modulation of the initial inflammatory response might therefore be a valid option for therapeutic intervention in cases of problematic wound healing. Further, the intraspecies differences in leucocyte function may have an impact on many fields in equine medicine.
Phase separation induced fractionation in molar mass in aqueous mixtures of gelatin and dextran
Edelman, M.W. ; Tromp, R.H. ; Weenen, H. - \ 2003
Physical Review. E, Statistical nonlinear, and soft matter physics 67 (2003)2. - ISSN 1539-3755 - 11 p.
locust bean gum - 2-phase systems - temperature - carrageenan - equilibria - protein
An overview of the effects of phase separation of aqueous mixtures of gelatin and dextran on the fractionation in molar mass of these two components is given. Molar mass distributions in coexisting phases were investigated using size exclusion chromatography with multiangle laser light scattering. The initial molar mass of the native material, concentration, and temperature were varied. The results show a strong fractionation in molar mass for both components. The molar mass of the native material and concentration appeared to be the only factors that affected the final molar mass distributions, temperature having no effect. The results show that in the molar mass range where fractionation is the strongest, i.e., roughly below the maximum in the distribution, fractionation is governed by a Boltzmann factor e-¿G/kT, where ¿G denotes the free energy involved in transferring a polymer with a certain length from the enriched to the depleted phase, and in this case turns out to be proportional to the molar mass. Comparison of the results of phase separation with results on dialysis shows that water affinity is not the driving force for the phase separation of gelatin and dextran in aqueous solution. The gelation properties of gelatin in both phases were also determined. The gelation properties of gelatin in the coexisting phases differ from those of native gelatin. In particular, the gelatin in the gelatin-poor phase shows strong differences compared to the native material.
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