Resolubilization of Protein from Water-Insoluble Phlorotannin-Protein Complexes upon Acidification
Vissers, Anne M. ; Blok, Annelies E. ; Westphal, Adrie H. ; Hendriks, Wouter H. ; Gruppen, Harry ; Vincken, Jean Paul - \ 2017
Journal of Agricultural and Food Chemistry 65 (2017)44. - ISSN 0021-8561 - p. 9595 - 9602.
complexation - pH - phlorotannins - reversibility - solubility
Marine phlorotannins (PhT) from Laminaria digitata might protect feed proteins from ruminal digestion by formation of insoluble non-covalent tannin-protein complexes at rumen pH (6-7). Formation and disintegration of PhT-protein complexes was studied with β-casein (random coil) and bovine serum albumin (BSA, globular) at various pH. PhT had similar binding affinity for β-casein and BSA as pentagalloyl glucose, as studied by fluorescence quenching. The affinity of PhT for both proteins was independent of pH (3.0, 6.0, and 8.0). In the presence of PhT, the pH range for precipitation of tannin-protein complexes widened to 0.5-1.5 pH units around the isoelectric point (pI) of the protein. Complete protein resolubilization from insoluble PhT-protein complexes was achieved at pH 7 and 2 for β-casein and BSA, respectively. It was demonstrated that PhT modulate the solubility of proteins at neutral pH and that resolubilization of PhT-protein complexes at pH deviating from pI is mainly governed by the charge state of the protein.
Mobile and immobile adhesion of staphylococcal strains to hydrophilic and hydrophobic surfaces
Boks, N.P. ; Kaper, H.J. ; Norde, W. ; Mei, H.C. van der; Busscher, H.J. - \ 2009
Journal of Colloid and Interface Science 331 (2009)1. - ISSN 0021-9797 - p. 60 - 64.
bacterial adhesion - biofilm reactors - infections - attachment - deposition - reversibility - substrata - energies - system - flow
Staphylococcus epidermidis adheres to hydrophilic glass and hydrophobic dimethyldichlorosilane (DDS)-coated glass in similar numbers, but in different modes. Real-time observation of staphylococcal adhesion under a shear rate of 15 s(-1) revealed different adhesion dynamics on both substrata. The number of adsorption and desorption events to achieve a similar number of adhering bacteria was twofold higher on hydrophilic than on hydrophobic DDS-coated glass. Moreover. 22% of all staphylococci on glass slid over the surface prior to adhering on a fixed site ("mobile adhesion mode"), but mobile adhesion was virtually absent (1%) on DDS-coated glass. Sliding preceded desorption on hydrophilic glass in about 20% of all desorption events, while on hydrophobic DDS-coated glass 2% of all staphylococci desorbed straight from their adhesion site. Since acid-base interactions between the staphylococci and a hydrophobic DDS-coating are attractive, it is suggested that these interactions facilitate a closer approach of the bacteria and therewith enhance immobile adhesion at local, high affinity sites. Alternatively, if the local site is low affinity, this may lead to desorption. In the absence of attractive acid-base interactions, as on hydrophilic glass, bacteria can be captured in the minimum of the DLVO-interaction energy curve, but this does not prevent them from sliding under flow at a fixed distance from a substratum surface until immobilization or desorption at or from a local high or low affinity site, respectively.
My voyage of discovery to proteins in flatland ... and beyond
Norde, W. - \ 2008
Colloids and Surfaces. B: Biointerfaces 61 (2008)1. - ISSN 0927-7765 - p. 1 - 9.
bovine pancreas ribonuclease - solid liquid interfaces - human-plasma albumin - model proteins - homomolecular exchange - polystyrene surfaces - serum-albumin - adsorption - reversibility - macromolecule
A kinetic model for the glucose/glycine Maillard reaction pathways
Martins, S.I.F.S. ; Boekel, M.A.J.S. van - \ 2005
Food Chemistry 90 (2005)1-2. - ISSN 0308-8146 - p. 257 - 269.
n-(1-deoxy-d-fructos-1-yl)-glycine degradation pathways - casein systems - amadori compounds - glucose - reversibility - melanoidins - acrylamide - products - (glucose - aldoses
A comprehensive kinetic model for the glucose/glycine Maillard reaction is proposed based on an approach called multiresponse kinetic modelling. Special attention was paid to reactants, intermediates and end products: -fructose, N-(1-deoxy--fructos-1-yl)-glycine (DFG), 1-deoxy-2,3-hexodiulose and 3-deoxy-2-hexosulose, formic and acetic acid, methylglyoxal and 5-hydroxymethylfurfural (HMF). The organic acids were found to be stable end products, 3-deoxy-2-hexosulose was found to be involved in colour formation by reaction with glycine. It is suggested to consider acetic acid as an indicator of the progress of the Maillard reaction at pH 6.8. The significance of reversibility of formation of DFG was studied by kinetic model discrimination. The results suggested that the reaction path from DFG into its parents, glucose and glycine, is not important from a quantitative point of view, even though it does happen. The proposed model was updated and strained by varying one of the most important reaction conditions, the temperature. The estimated rate constants showed an Arrhenius type temperature dependence and the model performed well for all studied temperatures (80, 90, 100, 110 and 120 °C). Striking differences were found in temperature dependencies of the various reaction steps. More than just a fitting procedure, multiresponse modelling was shown to be a powerful tool in unravelling complicated reaction routes as occur in the Maillard reaction.
Model films of cellulose. I. Method development and initial results
Gunnars, S. ; Wågberg, L. ; Cohen Stuart, M.A. - \ 2002
Cellulose 9 (2002). - ISSN 0969-0239 - p. 239 - 249.
adsorption - reversibility - kinetics
This report presents a new method for the preparation of thin cellulose films. NMMO (N- methylmorpholine- N-oxide) was used to dissolve cellulose and addition of DMSO (dimethyl sulfoxide) was used to control viscosity of the cellulose solution. A thin layer of the cellulose solution is spin- coated onto a silicon oxide wafer and the cellulose is precipitated in deionised water. The cellulose film is anchored onto the silicon oxide wafer by a saturated polymer layer. Among many different polymers tested, PVAm (polyvinylamine) and G- PAM (glyoxalated- polyacrylamide) worked well. The preparation of cellulose model films described in this paper resulted in films with thicknesses in the range 20- 270 nm and the thickness can be controlled by altering the concentration of cellulose solution by addition of different amounts of DMSO. The films were cleaned in deionised water and were found to be free from solvents by ESCA analysis and contact angle measurements. The molecular weight distribution of the cellulose surface material shows that there is only minor breakdown of the cellulose chains, mainly by cleavage of the longest molecular mass fraction and without creation of low molecular mass oligomers of glucose.
Effects of hydrodynamic mixing intensity coupled with ionic strength on the initial stage dynamics of bridging flocculation of polystyrene latex particles with polyelectrolyte
Adachi, Y. ; Matsumoto, T. ; Cohen Stuart, M.A. - \ 2002
Colloids and Surfaces. A: Physicochemical and Engineering Aspects 207 (2002)1-3. - ISSN 0927-7757 - p. 253 - 261.
cationic polyelectrolytes - adsorbed macromolecules - structural relaxation - humic-acid - adsorption - kinetics - polymers - spheres - reversibility - aggregation
Effects of hydrodynamic mixing intensity on the initial stage dynamics of bridging flocculation induced by adsorbing polyelectrolyte were analyzed as an extension of previous report on the effect of ionic strength (J. Coll. Int. Sci. 204 (1998) 328). Mixing condition were changed by adopting forked flask of varying depth, mounted on an end-over-end rotation apparatus. At low ionic strength, no significant influence due to the difference of mixing intensity was observed. Flocculation proceeded in a way consistent with the picture of kinetically-controlled polymer adsorption and ultimate degree of flocculation increased with increasing mixing intensity. At high ionic strength, a qualitatively different behavior of the progress of flocculation was found. At higher mixing intensity, flocculation started slowly, implying a flat conformation of the adsorbing polyelectrolyte in the beginning of adsorption. This result was interpreted as an immediate spreading of attached polyelectrolyte chains on the bare surface. However, a remarkable enhancement of the rate of flocculation sets in after a while. The point of this onset roughly corresponds to the half coverage of the surface. This is an indication of the formation of a thicker adsorption layer presumably caused by the fact that pre-adsorbed chains hamper the spreading of new comers in their neighborhood. These results mean that the rate of reconfirmation is a function of surface coverage. It was also confirmed that the ultimate degree of flocculation converged to a constant level independent of mixing intensity, implying a complete relaxation of the meta-stable state. These observations are explained in terms of the effect of salt on (i) polyelectrolyte conformation and (ii) strength of the ion pair bond between charged segments and charged groups on the particle surface.