Diffusion of solutes in agarose and alginate gels:1H and23Na PFGSE and23Na TQF NMR studies (original) (raw)
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Biotechnology and Bioengineering, 1995
The effective diffusion coefficient, 0, and the distribution constant, Ki for selected mono-and disaccharides and organic acids were determined in homogeneous calcium-alginate gel with and without entrapped bacteria. Results were obtained from transient concentration changes in well-stirred solutions of limited volume, in which t h e gel beads were suspended. The effective diffusion coefficients and the distribution constants were estimated by fitting mathematical model predictions to the experimental data using a nonlinear model fitting program (MODFIT). Both single solute diffusion and multiple solute diffusion were performed. A small positive effect was obtained on the values of 0, for the system of multiple solute diffusion; however, the values of Ki were not significantly influenced. For the nine solutes tested, D, for 2% Ca-alginate gel beads was found to be approximately 85% of t h e diffusivity measured in water. The effects on 0, and Ki for lactose and lactic acid were determined for variations of alginate concentration, pH, temperature, and biomass content in the beads. 0, decreased linearly for both lactose and lactic acid with increasing cell concentration in the Ca-alginate gel. Ki was constant for both lactose and lactic acid with increasing cell concentration. 0, was significantly lower at pH 4.5 than at pH 5.5 and 6.5 for both lactose and lactic acid. Furthermore, 0, seemed to decrease with increased alginate concentration in the range of 1% to 4%. The diffusion rate increased with increasing temperature, and the activation energy for the diffusion process for both lactose and lactic acid was constant in the temperature range tested.
Diffusion of glucose and maltose in polyacrylamide gel
Enzyme and Microbial Technology, 2004
The diffusion of glucose and maltose in different polyacrylamide gels (PAAG) was investigated. The method applied was non-steady-state diffusion into gel beads from a finite solution. The diffusion coefficients were determined applying Crank's solution of the diffusion equation. It was found that the diffusion coefficients in PAAG were about 15-85% lower than the corresponding coefficients in water, depending on gel composition. The influence of different factors, such as monomer concentration, cross-linking ratio, temperature, concentration of the diffusing substance, ionic strength, and the amount of the entrapped enzyme were tested.
Alginate as immobilization material: III. Diffusional properties
Biotechnology and Bioengineering, 1992
The rate of diffusion of serum albumin (MW 6.9 lo4 D) out of beads of calcium alginate gels depends upon the concentration and uronic acid composition of the alginate (ManA/GulA ratio), the conditions under which t h e beads are produced, the pH, and the temperature. The diffusion coefficient decreases with increasing alginate concentration, and (ManA/GulA) ratio and with decreasing pH. Diffusion out of the beads, in which the alginate is uniformly distributed (homogeneous gel), is faster than out of the beads in which the alginate is concentrated at the surface (inhomogeneous gel). The temperature dependence of the diffusion coefficient follows the Arrhenius law, with an activation energy of-23 kJ. mol-'.
Molecular Diffusion in Polysaccharide Gel Systems as Observed by NMR
2009
The diffusion coefficients D of dendrimers in agar gel and pullulan in gellan gel were determined by pulsed field gradient spin-echo (PFGSE) NMR measurements. The ratio of D to D 0 (diffusion coefficient in dilute solution) was used to estimate mesh size. The mesh size increased as the temperature fell below the gelling temperature, suggesting that the solute polysaccharides are involved in aggregation. Changes in mesh size explain the experimental results of water exudation from a stored agar gel under compression and the heat resistance of gellan gel in the presence of divalent cations.
High sugar content impacts microstructure, mechanics and release of calcium-alginate gels
Food Hydrocolloids, 2018
The use of calcium-alginate gels as carriers of food and pharmaceutical compounds is of great interest due the versatile properties of such systems. In this work, we investigated the influence of sugars (glucose:fructose) as co-solutes (15-60 % (wt)) on the physico-chemical properties of calciumalginate gel particles. Sugar concentrations above 15 % (wt) reduced extensibility of alginate molecules, as shown by intrinsic viscosity measurements, and lead to a more open or less connected gel network with aggregated alginate strands. Furthermore, it is shown for the first time that sugar impacted swelling-deswelling ability of calcium alginate gels under simulated gastric (pH 1.2) and intestinal (pH 6.6) conditions. Release of sugar from calcium alginate gels with 15 % (wt) and 30 % (wt) sugar was close to Fickian diffusion mechanism, in both simulated gastric and intestinal fluid, with diffusion coefficient close to that previously reported for calcium-alginate gels with lower sugar contents. However, release from 60 % (wt) gels in gastric fluid was slower than for 15 and 30 % (wt) and, there was a drastic shrinkage of the gels under acid conditions. In intestinal fluid 60 % (wt) gels showed slower release than gels with lower sugar content, this was hypothesised to be due to the lower surface area of these gels. Understanding the structure-function relationship of these gels is key to the successful design of delivery systems for food and biotechnological applications.
Crosslinking Kinetics of Thermally Preset Alginate Gels
Journal of Food Science, 1994
The Sharp-Interface model was used to describe the crosslinking kinetics of thermally preset calcium alginate gel at constant temperature. The model assumes diffusion of calcium ions through a preformed gel of sodium alginate and a selected carrier, and an instantaneous reaction between the calcium and sodium alginate. The proposed model was experimentally verified using two different carriers at the following concentrations: agar 0.6(g/100 mL)-0.8(g/100 mL), and gelatine 4(g/100 mL); sodium alginate concentrations were 1(g/100 mL) and 1.5(g/100 mL), while a 2(g/100 mL) calcium lactate solution was used as calcium ion source. The diffusion coefficient of calcium ion was determined using a cell diffusion model. The model can be used to predict processing effects on food gels.
Glucose oxidase release from calcium alginate gel capsules
Enzyme and Microbial Technology, 2000
Diffusion of glucose oxidase within calcium alginate gel capsules has been assayed and the experimental data fitted to a simple semi-empirical power equation, which is used to analyse the solute release from polymeric devices. It was found that an increase in the concentration of sodium alginate and calcium chloride gives rise to a reduction in the enzyme leakage. This was verified when glucose oxidase (GOD) diffusion percentages were compared in capsules with thicknesses of the same order of magnitude but obtained under different experimental conditions. So, the use of sodium alginate and calcium chloride solutions of concentrations 0.5% w/v and 2.6% w/v, respectively, lead to a diffusion percentage of 25 Ϯ 2. This percentage was reduced to 8 Ϯ 3 when sodium alginate and calcium chloride concentrations were fixed at 1% w/v and 4% w/v, respectively, even though the thicknesses of the capsules were of the same order of magnitude.
Reaction and diffusion in a gel membrane reactor containing immobilized cells
Biotechnology and Bioengineering, 1992
To investigate the effect of diffusional limitations and heterogeneous cell distribution in a gel-immobilized cell system, a gel membrane reactor has been constructed. The reactor consists essentially of a gel layer with immobilized cells, flanked by two well-mixed chambers. Through one chamber substrate is pumped, and this chamber is the equivalent of the outside of a spherical gel bead. The second closed measuring chamber contains a small quantity of liquid that can equilibrate with the inside surface of the membrane, eventually after a long transient. Analysis of the liquid in this chamber can give direct information on substrate and product concentrations at the gel surface, and is an indication of the situation in the center of a gel bead. The gel membrane reactor appears to be an excellent tool to study diffusion and reaction in a gel-containing immobilized cells. A mathematical model with timeand positiondependent cell concentration and diffusion coefficient is described. Experimental data show the effective diffusion coefficient of glucose in an alginate gel to decrease with yeast cell concentration. Moreover, kinetic parameters could be determined, using the mathematical model. Microscopic analysis confirmed the proliferation of the gel-entrapped microorganisms in the outer layer of the matrix, as predicted by the model. Potentially, this type of reactor has a clear potential to study the physiology of gel-immobilized Cells. 0 1992 John Wiley & Sons, Inc.