Gelation conditions and transport properties of hollow calcium alginate capsules

The diameter, membrane thickness, and compression intensity of hollow Ca-alginate capsules were measured at different gelation conditions, such as the reactant concentration, dropping velocity, and gelation time. The optimum operation conditions for preparing capsules were determined at 100 g/L CaCl(2), 10 g/L sodium alginate (Na-alginate), a dropping velocity of 150 droplets/min, and a gelation time of 10 min. Diffusion of some saccharide and amino acid from bulk solution into capsules was investigated, and the diffusion coefficients were calculated by the developed mathematical model. All the tested substances can diffuse easily into the capsules. The combined diffusion coefficients of the capsule D(m) are 92-99% as large as their diffusion coefficients in pure water, while the diffusion coefficients in the capsule membrane D(1) are 60-95% as large as those. By employing polyethylene glycol (PEG) and bovine serum albumin (fraction V) (BSA(V)), the molecular weight cut-off of the capsule was determined. For linear macromolecules, hollow Ca-alginate capsules have a molecular weight cut-off of 4000. No diffusion of BSA(V) into the capsules was observed.     

Determination of diffusion coefficients and diffusion characteristics for chlorferon and diethylthiophosphate in Ca-alginate gel beads

Diffusion characteristics of chlorferon and diethylthiophosphate (DETP) in Ca-alginate gel beads were studied to assist in designing and operating bioreactor systems. Diffusion coefficients for chlorferon and DETP in Ca-alginate gel beads determined at conditions suitable for biodegradation studies were 2.70 x 10(-11) m(2)/s and 4.28 x 10(-11) m(2)/s, respectively. Diffusivities of chlorferon and DETP were influenced by several factors, including viscosity of the bulk solution, agitation speed, and the concentrations of diffusing substrate and immobilized cells. Diffusion coefficients increased with increasing agitation speed, probably due to poor mixing at low speed and some attrition of beads at high speeds. Diffusion coefficients also increased with decreasing substrate concentration. Increased cell concentration in the gel beads caused lower diffusivity. Theoretical models to predict diffusivities as a function of cell weight fraction overestimated the effective diffusivities for both chlorferon and DETP, but linear relations between effective diffusivity and cell weight fraction were derived from experimental data. Calcium-alginate gel beads with radii of 1.65-1.70 mm used in this study were not subject to diffusional limitations: external mass transfer resistances were negligible based on Biot number calculations and effectiveness factors indicated that internal mass transfer resistance was negligible. Therefore, the degradation rates of chlorferon and DETP inside Ca-alginate gel beads were reaction-limited.     

Oxygen diffusivity in gel beads containing viable cells

This article proposes a simple steady-state method for measuring the effective diffusion coefficient of oxygen (D(e)) in gel beads entrapping viable cells. We applied this method to the measurement of D(e) in Ca- and Ba-alginate gel beads entrapping Saccharomyces cerevisiae and Pseudomonas ovalis. The diffusivity of oxygen through gel beads containing viable cells was measured within an accuracy of +/-7% and found not to be influenced by cell density (0-30 g/L gel), cell type, and cell viability in gel beads. The oxygen diffusivity in the Ca-alginate gel beads was superior to that of the Ba-alginate gel beads, and the D(e) in the Ca-alginate gel beads nearly equalled the molecular diffusion coefficient in the liquid containing the gel beads. The oxygen concentration profile in a single Ca-alginate gel bead was calculated and compared to the distribution of mycelia of Aspergillus awamori grown in that gel bead. This procedure indicated that the oxygen concentration profile is useful for the estimation of the thickness of the cell layer in a gel bead. Numerical investigation revealed that high effectiveness factors, greater than 0.8, could be obtained using microgel beads with a radius of 0.25 mm.     

Determination of glucose and ethanol effective diffusion coefficients in Ca-alginate gel.

Glucose and ethanol diffusion coefficients in 2% Ca-alginate gel were measured using the experimental technique based on solute diffusion into or out of gel beads in a well-stirred solution. The aim of the study was to make the measurements under typical conditions found in alcoholic fermentations, such as the concentrations of glucose (100 g l-1) and ethanol (50 g l-1), the simultaneous counter-diffusion of glucose and ethanol, and the presence of cells in the gel beads at a level of 10(9) cells g-1 of beads. Previously, an evaluation of the error associated with the methodology used indicated how the experimental procedure would minimize the error. The individual measurement of glucose and ethanol coefficients in 2% Ca-alginate with no cells gave values of 5.1 and 9.6 x 10(-6) cm2 s-1, respectively, which are lower than those in water. When the effect of counter-diffusion was investigated, both coefficients decreased: glucose by 14% and ethanol by 28%. When cells were incorporated into the beads, only the ethanol coefficient decreased significantly, while the glucose coefficient apparently increased its value to 6.9 10(-6) cm2 s-1.     

The effective diffusion coefficient and the distribution constant for small molecules in calcium-alginate gel beads

The effective diffusion coefficient, D(e), and the distribution constant, K(i), 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 the gel beads were suspended. The effective diffusioncoefficients 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 onthe values of D(e) for the system of multiple solute diffusion; however, the values of K(i) were not significantly influenced. For the nine solutes tested, D(e) for 2% Ca-alginate gel beads was found to be approximately 85% of the diffusivity measured in water. The effects on D(e) and K(i), for lactose and lactic acid were determined for variations of alginate concentration, pH, temperature, and biomass content in the beads. D(e) decreased linearly for both lactose and lactic acid with increasing cell concentration in the Ca-alginate gel. K(i), was constant for both lactose and lactic acid with increasing cell concentration. D(e) was significantly lower at pH 4.5 than at pH 5.5 and 6.5 for both lactose and lactic acid. Furthermore, D(e) 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. (c) 1995 John Wiley & Sons Inc.     

Alginate as immobilization material: III. Diffusional properties

The rate of diffusion of serum albumin (MW 6.9 x 10(4) 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 the 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 approximately 23 kJ x mol(-1).     

Role of calcium alginate and mannitol in protecting bifidobacterium

Fourier transform infrared (FTIR) spectroscopy was carried out to ascertain the mechanism of Ca-alginate and mannitol protection of cell envelope components and secondary proteins of Bifidobacterium animalis subsp. lactis Bb12 after freeze-drying and after 10 weeks of storage at room temperature (25°C) at low water activities (a(w)) of 0.07, 0.1, and 0.2. Preparation of Ca-alginate and Ca-alginate-mannitol as microencapsulants was carried out by dropping an alginate or alginate-mannitol emulsion containing bacteria using a burette into CaCl(2) solution to obtain Ca-alginate beads and Ca-alginate-mannitol beads, respectively. The wet beads were then freeze-dried. The a(w) of freeze-dried beads was then adjusted to 0.07, 0.1, and 0.2 using saturated salt solutions; controls were prepared by keeping Ca-alginate and Ca-alginate-mannitol in aluminum foil without a(w) adjustment. Mannitol in the Ca-alginate system interacted with cell envelopes during freeze-drying and during storage at low a(w)s. In contrast, Ca-alginate protected cell envelopes after freeze-drying but not during 10-week storage. Unlike Ca-alginate, Ca-alginate-mannitol was effective in retarding the changes in secondary proteins during freeze-drying and during 10 weeks of storage at low a(w)s. It appears that Ca-alginate-mannitol is more effective than Ca-alginate in preserving cell envelopes and proteins after freeze-drying and after 10 weeks of storage at room temperature (25°C).     

Counter-diffusion of lactose and lactic acid in kappa-carrageenan/locust bean gum gel beads with or without entrapped lactic acid bacteria.

The effective diffusion coefficient (De) and equilibrium partition factor (Kp) for lactose and lactic acid in k-carrageenan (2.75% w/w)/locust bean gum (0.25% w/w) (LBG) gel beads (1.5-2.0 mm diameter), with or without entrapped Lactobacillus casei subsp. casei (L. casei), were determined at 40 degrees C. Results were obtained from transient concentration changes in well-stirred solutions of finite volume in which the beads were suspended. Mathematical models of unsteady-state diffusion into and/or from a sphere and appropriate boundary conditions were used to calculate effective diffusion coefficients of lactose and lactic acid from the best fit of the experimental solute concentration changes. The effective diffusivities of lactose and lactic acid were 5.73 x 10(-10) and 9.96 x 10(-10) m2 s-1, respectively. Furthermore, lactic acid was found to modify gel structure since lactose diffusion characteristics (De and Kp) differed significantly from an earlier study and in the literature. In gel beads heavily colonized with L. casei, the effective diffusion coefficients of lactose and lactic acid were respectively 17% and 24% lower than for cell-free beads. Partition coefficients also confirmed the obstruction effect due to the cells, and decreased from 0.89 to 0.79, and from 0.98 to 0.87, for lactose and lactic acid, respectively. External mass transfer was estimated by an unsteady-state model in infinite volume using the Biot number. The effect of external mass transfer resistance on De results and the data reported in the literature are discussed.     

Removal and recovery of uranium (VI) from aqueous solutions by immobilized Aspergillus niger powder beads

The immobilized Aspergillus niger powder beads were obtained by entrapping nonviable A. niger powder into Ca-alginate gel. The effects of pH, contact time, initial uranium (VI) concentration and biomass dosage on the biosorption of uranium (VI) onto the beads from aqueous solutions were investigated in a batch system. Biosorption equilibrium data were agreeable with Langmuir isotherm model and the maximum biosorption capacity of the beads for uranium (VI) was estimated to be 649.4?mg/g at 30?°C. The biosorption kinetics followed the pseudo-second-order model and intraparticle diffusion equation. The variations in enthalpy (26.45?kJ/mol), entropy (0.167?kJ/mol?K) and Gibbs free energy were calculated from the experimental data. SEM and EDS analysis indicated that the beads have strong adsorption capability for uranium (VI). The adsorbed uranium (VI) on the beads could be released with HNO₃ or HCl. The results showed that the immobilized A. niger powder beads had great potential for removing and recovering uranium (VI) from aqueous solutions.     

The molecular structure of low and high molecular weight levans synthesized by levansucrase

The levan synthesized by Bacillus subtilis levansucrase in the presence of alcohols was of only high molecular weight, while in solutions of high ionic strength only low molecular weight (MW) levan was produced. The addition of low MW levan to the enzyme reaction mixture at low ionic strength stimulated synthesis of a high MW levan, but the levan added was not incorporated into this high MW levan. Methylation analysis revealed that low MW levans contained glucose, which was isolated as 2,3,46-tetra-O-methyl alditol acetate showing that the glucose units existed as terminal residues. The molecular weight of levan estimated on the basis of glucose content coincided with that determined by the gel filtration method. Methylation analysis also revealed that the number of fructose residues of the linear fraction linked by leads to 6(F)2 leads to type bonds was 22 for levan with a molecular weight of (8.4(-22)) x 10(3), while it was 11 for that of 2,000 x 10(3). The number of (formula: see text) type branched residues increased with increase in the molecular weight of the levan synthesized.     

Immobilization of thermoalkalophilic recombinant esterase enzyme by entrapment in silicate coated Ca-alginate beads and its hydrolytic properties

Thermoalkalophilic esterase enzyme from Bal?ova (Agamemnon) geothermal site were aimed to be immobilized effectively via a simple and cost-effective protocol in silicate coated Calcium alginate (Ca-alginate) beads by entrapment. The optimal immobilization conditions of enzyme in Ca-alginate beads were investigated and obtained with 2% alginate using 0.5mg/ml enzyme and 0.7 M CaCl(2) solution. In order to prevent enzyme from leaking out of the gel beads, Ca-alginate beads were then coated with silicate. Enzyme loading efficiency and immobilization yield for silicate coated beads was determined as 98.1% and 71.27%, respectively and compared with non-coated ones which were 68.5% and 45.80%, respectively. Surface morphologies, structure and elemental analysis of both silicate coated and non-coated alginate beads were also compared using Fourier Transform Infrared Spectroscopy (FT-IR) and Scanning Electron Microscope (SEM) equipped with Energy-dispersive X-ray spectroscopy (EDX). Moreover, silicate coated alginate beads enhanced reusability of esterase in continuous processes compared to non-coated beads. The hydrolytic properties of free and immobilized enzyme in terms of storage and thermal stability as well as the effects of the temperature and pH were determined. It was observed that operational, thermal and storage stabilities of the esterase were increased with immobilization.     

Molecular Weight of Sindbis Virus Ribonucleic Acid as Measured by Polyacrylamide Gel Electrophoresis

The molecular weight (MW) of Sindbis virion ribonucleic acid (RNA) determined by gel electrophoresis was in a range of 3.89 x 10(6) to 4.45 x 10(6) daltons. Upon denaturation with urea, it separated into fragments having an MW of 1.76 x 10(6) daltons. Viral-specific Sindbis 26S RNA contained a major species having an MW of 1.76 x 10(6) daltons.     

Diffusion in kappa-carrageenan gel beads

Using a well-mixed and temperature-led vessel, the diffusion characteristics of various solutes into spherical kappa-carrageenan gel beads were experimentally investigated. The diffusion coefficient of glucose was markedly affected by the glucose concentration and the operating temperature. In all cases the diffusivity obtained was noticeably smaller than that of glucose in pure water. The experimental data also indicated an inverse relationship between the diffusivity and the polymer concentration used in the gel preparation. As well, the glucose diffusivity was affected by the presence of other solutes in the glucose solution. Electrolytes such as ammonium sulfate, KCl, and CaCl(2) were observed to enhance the diffusion coefficient. On the other hand, the addition of arginine or bovine serum albumin had an adverse effect on the diffusivity. No diffusion of albumin into the gel beads was observed, and such a solute created a significant mass transfer resistance during the diffusion process.     

Diffusion of (de)acylated antibiotic A40926 in alginate and carrageenan beads with or without cells and/or soybean meal

Effective diffusion coefficients (D(e)) of antibiotic A40926 and its deacylated derivative were determined in Ca-alginate (2% wt/wt) and kappa-carrageenan (2.6% wt/wt) gel beads with or without immobilized Actinoplanes teichomyceticus cells and/or soybean meal (SBM). The method used was based on transient concentration changes in a well-stirred antibiotic solution in which gel beads, initially free of solute, were suspended. Unsteady-state diffusion in a sphere was applied and D(e) determined from the best fit of experimental data. A40926 showed markedly different diffusion characteristics than its deacylated derivative. Diffusivity of deacyl-A40926 in alginate or carrageenan gel beads was six to seven times that of A40926. Large differences in partition coefficients (Kp) were also found. In case of beads without additions, A40926, in contrast to deacyl-A40926, strongly partitioned to the liquid phase. Introduction of SBM and/or mycelium in the gel beads decreased the effective diffusivity of deacyl-A40926, but increased its partitioning to the solid phase. Our findings indicate that a relatively moderate structural change of a lipoglycopeptide molecule could lead to a major change in its diffusion/partition characteristics.     

Diffusion of lactose in kappa-carrageenan/locust bean gum gel beads with or without entrapped growing lactic acid bacteria

Effective diffusion coefficients (De) of lactose in kappa-carrageenan (2.75% wt/wt)/locust bean gum (0.25% wt/wt) (LBG) gel beads (1.5-2.0-mm diameter)with or without entrapped lactic acid bacteria (LAB) were determined at 40 degrees C. The effects of lactose concentration, bacteria strain (Streptococcus salivarius subsp. thermophilus and Lactobacillus casei subsp. casei) and cell content at various steps of the fermentation process (after immobilization, pre-incubation of the beads and successive fermentations) were measured on De as a first step for process modelling. Results were obtained from transiend concentration changes n well-stirred lactose solutions in which the beads were suspended. A mathematical model of unsteady-state diffusion in a sphere was used, and De was obtained from the best fit of the experimental data. Diffusivity of lactose in cell-tree beads was significantly lower than in pure water mainly because of the obstruction effect of the polymer chains and the hydration region. Furthermore, effective diffusivity and equilibrium partition factor were independent of lactose concentration in the range from 12.5 to 50 g/L. No significant difference was found for De (effective diffusivity) and Kp (partition) coefficients between beads entrapping S. thermophilus (approximately 5 x 10(9) CFU/mL) and cell-free beads. On the other hand higher cell counts obtained with L. casei (close to 1.8 x 10(11) CFU/mL) increased mass transfer resistance resulting in lower effective diffusivities and Kp. Finally, the effects of the type of bacteria and their distribution in the beads on the diffusivity were also discussed.     

Poly(carbamoylsulfonate), a material for immobilization: Synthesis,diffusion- and mechanical properties

Summary A simple method is described for the synthesis of a material for immobilization, Poly(carbamoylsulfonate) (PCS). PCS is based on the synthesis of a hydrophilic polyether polyol and a polyisocyanate to the isocyanate-pre-polymer. The real diffusion coefficients of the PCS hydrogel are comparable with the values of Ca-alginate, the molecular weight cut-off can be found between myoglobine (MW 17000 g/mol) and albumine (MW 67000 g/mol). PCS hydrogels have optimal elastic properties (higher elongation at break and lower modulus of elasticity than other natural hydrogels) and therefore can be used for a matrix of biocatalysts in an agitated reactor as well as in a fluid-bed reactor.     

Molecular multiplicity of nuclease TT1 from Thermus thermophilus HB8

Purified nuclease TT1 from Thermus thermophilus HB8 has multimolecular weight forms, each of which is composed of three different subunits, alpha (10.8 x 10(4)), beta (7.8 x 10(4)), and gamma (4.1 x 10(4)). The molecular weights of this enzyme were estimated by gel filtration, polyacrylamide gel electrophoresis and equilibrium sedimentation. It was found that most of the enzyme has a molecular weight of about 22 x 10(4) being a monomer having the subunit composition of alpha beta gamma. The remaining part of the enzyme has larger molecular weights and is considered to be size-isomers of alpha beta gamma. The alpha-helical content, 5.5--6.5%, and the beta-structure, about 28%, were estimated from the CD spectrum at 4 degrees C.     

Biosorption of Cr (VI) with Trichoderma viride immobilized fungal biomass and cell free Ca-alginate beads

Ability of Cr (VI) biosorption with immobilized Trichoderma viride biomass and cell free Ca-alginate beads was studied in the present study. Biosorption efficiency in the powdered fungal biomass entrapped in polymeric matric of calcium alginate compared with cell free calcium alginate beads. Effect of pH, initial metal ion concentration, time and biomass dose on the Cr (VI) removal by immobilized and cell free Ca-alginate beads were also determined. Biosorption of Cr (VI) was pH dependent and the maximum adsorption was observed at pH 2.0. The adsorption equilibrium was reached in 90 min. The maximum adsorption capacity of 16.075 mgg(-1) was observed at dose 0.2 mg in 100 ml of Cr (VI) solution. The high value of kinetics rate constant Kad (3.73 x 10(-2)) with immobilized fungal biomass and (3.75 x 10(-2)) with cell free Ca- alginate beads showed that the sorption of Cr (VI) ions on immobilized biomass and cell free Ca-alginate beads followed pseudo first order kinetics. The experimental results were fitted satisfactory to the Langmuir and Freundlich isotherm models. The hydroxyl (-OH) and amino (-NH) functional groups were responsible in biosorption of Cr (VI) with fungal biomass spp. Trichoderma viride analysed using Fourier Transform Infrared (FTIR) Spectrometer.     

Molecular weight distribution and solution properties of silk fibroins with different dissolution conditions

Four regenerated silk fibroin (SF) samples were prepared under different dissolution conditions and their molecular weight (MW) distributions and solution properties in water and formic acid were examined. SFL, produced by dissolving in LiBr aqueous solution for 6h, showed the highest MW level. In the three SFC samples, produced by dissolving SF in CaCl(2)/H(2)O/EtOH solution for dissolution times ranging from 3 to 180 min, the MW of the SFs decreased with increasing dissolution time and a new band appeared at low MW. Interestingly, SFL presented as a relatively transparent aqueous solution with 10-30 nm particle size, whereas the three SFC samples exhibited a turbid solution with 100-300 nm particle size. SF formic acid solutions showed a higher viscosity than SF aqueous solutions and exhibited almost Newtonian fluid behavior, whereas SF aqueous solutions displayed abrupt shear thinning in the low shear rate region (0.1-3 s(-1)).     

Diffusivity of Cu(2+) in calcium alginate gel beads

A linear absorption model (LAM) is used to describe the process of metal binding to spherically shaped biopolymers particles. The LAM was solved using a numerical algorithm which calculates diffusivities of metal ion in biopolymer gels. It assumes attainment of rapid metal-biopolymer binding equilibrium accompanied by rate limiting diffusion of the metal ions through the gel. The model was tested using batch experiments in which copper (Cu(2+)) binding with calcium alginate beads was investigated. Biopolymer density in the beads was varied between 2% and 5%. The diffusion coefficient of Cu(2+) calculated from the LAM ranged from 1.19 x 10(-9) to 1.48 x 10(-9) m(2) s(-1) (average 1.31 +/- 0.21 x 10(-9) m(2) s(-1)), independent of biopolymer density. The LAM has theoretical advantages over the shrinking core model (shell progressive model). The latter calculated an unreasonable exponential increase in the diffusion coefficient as density of alginate polymer in the bead increased. (c) 1993 John Wiley & Sons, Inc.