Gellan Gum Gels Research Articles

The inactivation of Escherichia coli O157:H7 during pulsed electric field (PEF) treatment in a static chamber

The inactivation of Escherichia coli O157:H7 by pulsed electric field (PEF) processing as a function of electric field strength (15–30 kV cm −1), pulse number (1–20), temperature (5–65°C) and pH (3·5 and 6·8) was studied using a commercially available pulser, a static chamber and gellan gum gel as a suspension medium. The custom-designed static chamber achieved near-isothermal treatment conditions while eliminating flow field effects. Gellan gum gel was used to suspend the bacteria for treatment. It allowed uniform distribution of bacteria and neither inhibited nor promoted bacterial growth. The combination of equipment design and experimental protocol allowed the contribution of electrical (PEF) and thermal energy to be measured separately. In water-based gel, a maximum of 3 log reductions were achieved by PEF energy. Greater inactivation was observed at a treatment temperature of 55°C, but the additional inactivation was attributable entirely to thermal energy. Microbial injury was also observed at this temperature. At 60°C and above, complete inactivation was achieved, but this was attributable entirely to thermal energy. In water-based gellan gum gel adjusted to pH 3·5, again a 3 log reduction was achieved by PEF. In gel made from freshly squeezed apple juice naturally having the same pH, however, a maximum of 1·5 log reduction was observed. Published by Elsevier Science Ltd.

The effect of potassium salt on the structural characteristics of gellan gum gel

Gellan gum in aqueous solution undergoes gelation by adding the metal salts. The cross-linking domain structure in various concentrations of potassium salt was observed by small angle X-ray scattering. The results were analyzed by means of molecular models of associated double helices. It found that the gelation yielded the mono-layer flat particles constructed by side-by-side aggregation of double helices at lower salt concentration and then they grew up to the multi-layer aggregates by a further addition of salt.

Influence of low sucrose concentrations on the compression resistance of gellan gum gels

Effects of the addition of low-sucrose concentrations (100–250 g/l) to gellan gels at different concentrations (3, 7.5, and 12 g/l) on compression parameters were studied. True stress and strain values were obtained from compression up to rupture tests and the modulus of deformability from compression up to 10% deformation. True rupture stress and deformability modulus values increased and true rupture strain values decreased with addition of sucrose for the higher gellan concentrations gels (7.5 and 12 g/l), resulting in stronger, firmer and more brittle gels.

Particle and matrix gels of gellan gum: effects of filler particles on rheological properties of matrix gels

The effects of particle gels (PG) on rheological properties of gellan gum gels were studied as a function of PG ratio by measuring the stress–strain curves, dynamic viscoelasticity, syneresis and by the sensory evaluation. Matrix gel (MG) used in the experiments was 0.6 wt% gellan gum gel added with 5 mM CaCl 2 (MG(0.6%–5 mM)) or 0.8 wt% gel added with 5 mM CaCl 2 (MG(0.8%–5 mM)). MG(0.6%–5 mM) was filled with particle gels of 0.6 wt% gellan gum added with 5 mM CaCl 2 (PG(0.6%–5 mM)) or with 2 mM CaCl 2 (PG(0.6%–2 mM)). MG(0.8%–5 mM) was filled with PG(0.8%–5 mM) or PG(0.8%–2 mM). Breaking stress, breaking strain, breaking energy and dynamic viscoelasticity of all kinds of gels containing PG decreased with increasing PG content. The sample size dependence of breaking stress of gels containing PG was more intense than that of gels without PG. These results may indicate that particle gels act as inactive filler in the matrix gel. Storage Young's modulus of MG(0.8%–5 mM) without PG increased with increasing temperature from 10 to 40°C and then decreased with further temperature increase to 60°C. The degree of variations of storage Young's modulus with temperature reduced, as the PG content increased. The degree of syneresis increased with an increase in the PG content during storage for 5 h. Gels were identified as soft, brittle, rough and not elastic with an increase in the PG content by the sensory evaluation.

Controlled drug release from gels using surfactant aggregates: I. Effect of lipophilic interactions for a series of uncharged substances

Gels are often used for the delivery of drugs because they have rheological properties that will give a long residence time. Most pharmaceutical gels consist of ∼99% water and a polymer matrix that will not hinder the release of drugs with a small molecular weight. To fully take advantage of the residence time, it is necessary to have a sustained drug release. In this paper it is suggested that surfactant micelles can be used to control the release from gels. The in vitro release under physiological conditions of five parabens from four different poly(acrylic acid) gels (Carbopol 934, 940, 1342) and one gellan gum (Gelrite) gel was measured using a USP dissolution bath modified for gels, and the diffusion coefficients were calculated. The diffusion coefficient of uncharged parabens was generally lower in gels with lipophilic modifications, such as C1342, and the greatest effect was seen for butylparaben, with a diffusion that was 25% lower than that in C934 (lacking lipophilic modification). Addition of surfactant micelles to gels delayed the release of all the uncharged drugs in all types of gels studied. The slowest release was seen for butylparaben in a lipophilically modified gel with micelles present. The diffusion coefficient in such a system was almost 30 times smaller than that in C934 without micelles. © 2001 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:1216–1225, 2001

Measurement of stress and strain during tensile testing of gellan gum gels: effect of deformation speed

Tensile tests were carried out on gellan gum gels of concentration 2% in order to observe the relation between deformation speed and deformation properties such as tensile modulus and rupture strain. The primary objective of this experiment is to show the validity of the measurement for the actual strain and strain rate during tensile tests. The tensile modulus decreased with decreasing deformation speed, showing the viscoelastic character of the gel, while the stress–strain curve was linear. The results were interpreted in terms of linear viscoelasticity theory. The instantaneous modulus was calculated and compared with the storage modulus found in the literature. A guide value of the relaxation time was also calculated and shown to be much larger than the observation time.

Rb+ and Na+ spin relaxation in aqueous gellan solutions and implication of selective site binding of alkali metal ions.

87Rb NMR was applied to investigate the site binding of Rb+ ions in gellan gum gels. The temperature dependence of the transverse and longitudinal relaxation NMR relaxation rates of 87Rb+ ion and 23Na+ ion have been compared in aqueous 5% (w/v) rubidium-type and sodium-type gellan. In each sample, the relaxation rates were sensitive to the conformation (helix or random coil). In rubidium-type gellan, significant line-broadening effects (losses in intensity) were found, which is due to the presence of cation-binding sites in the ordered conformation. In sodium-type gellan, such an enhancement of the relaxation was not observed. These results indicated that gellan gum produced highly selective binding sites for alkali metal ions, in which Rb+ ion bound more strongly than Na+ ion. The 87Rb NMR line shift suggested selective site binding of ions to form the cross-linking domains in gellan gels.

Diffusion of sucrose and aspartame in kappa-carrageenan and gellan gum gels

In the process of sweetness release from the food to the human papillae, diffusion of the sweetener through the food is one of the steps. Information on diffusion behaviour of small molecules like sucrose has been studied mainly in connection with blanching or osmotic processes. In this paper, diffusion constants ( D) of both sucrose (100 and 150 g/l) and aspartame (0.8 and 1.2 g/l) in model systems—kappa-carrageenan and gellan gum gels at two different concentrations—have been determined at 37°C (mouth temperature). Mean D values for sucrose (5.9–7.3×10 −10 m 2 s −1) and for aspartame (6.1–7.7×10 −10 m 2s −1) in soft kappa-carrageenan gels were significantly higher than in the other gels (3.8–5.1×10 −10 m 2s −1 for sucrose and 3.9–5.9×10 −10 m 2s −1 for aspartame). Higher concentrations of sweetener detected in the diffusing medium in the case of soft kappa–carrageenan gels could be partially affected by incipient melting of the gel. Upper values in these ranges corresponded to higher initial sweetener contents.

Apatite-Forming Ability of Polymers with Carboxy Groups in Simulated Body Fluid

Apatite-polymer composites with analogous structure to that of the natural bone are desired to be developed, since such composites are believed to show biological and mechanical properties similar to those of the natural bone. In the present study, apatite-forming ability of various kinds of polymers with or without carboxy (COOH) groups in simulated body fluid (SBF) was investigated. Carboxymethyl- (CM)- chitin and gellan gum gels, which have COOH groups, formed apatite on their surfaces within 3 d, when they were previously treated with saturated Ca(OH){sub 2} solution. Calcium alginate gel with COOH groups formed apatite on its surface within 7 d without the Ca(OH){sub 2}-treatment, since calcium ions are previously incorporated into the gel structure in the gel-forming process. In contrast, curdlan gel without COOH groups did not form that the COOH groups on a polymer surface are effective for the apatite nucleation and the apatite-forming ability of the polymer can be improved by incorporation of the calcium ions. In conclusion, these types of polymers are promising candidates for obtaining apatite-polymer composites with bonelike structure by a biomimetic process. (orig.)

COMPARATIVE STUDY OF LARGE STRAIN METHODS FOR ASSESSING FAILURE CHARACTERISTICS OF SELECTED FOOD GELS

ABSTRACTVane rheometry was compared with uniaxial compression and torsion in evaluating the effects of strain rate on failure shear stress and deformation of soybean protein (tofu) and gellan gum gels. A Haake VT 550 viscotester was used for torsion and vane tests, and compression was performed with an Instron/MTS universal testing machine. Strain or angular deformation at failure was independent of strain rate in the three testing modes. In vane rheometry, failure shear stress increased with increasing low shear rates (< 0.100 s−1) and was rate independent at higher rates. This strain rate dependency was also evident in compression, varying with the material. For torsion, fracture stress appeared to be rate independent. Shear fracture stresses measured in torsion and compression were in good agreement at strain rates above 0.025 s−1 and 0.100 s−1 for tofu and gellan gels, respectively. Shear stresses from the vane method were lower than shear stresses of torsion and compression. Similar texture maps of the food gels studied were generated by plotting stress and strain or angular deformation values of the three testing methods. The findings validate the vane technique as an alternative to torsion and compression for rapid textural characterization of viscoelastic foods.

NEW PARAMETERS FOR INSTRUMENTAL TEXTURE PROFILE ANALYSIS: INSTANTANEOUS AND RETARDED RECOVERABLE SPRINGINESS

ABSTRACTCylindrical samples of gelatin, K‐carrageenan/locust bean gum and gellan gum gels were subjected to two successive cycles of compression at three predetermined deformation levels corresponding to 25, 50 and 75% of their respective degrees of compression at failure. Values of “recoverable instantaneous springiness” (Sins) and “recoverable retarded springiness” (Sret) were measured. Values of Sins and Sret for the gelatin samples were similar and close to 1, indicating a very fast and almost complete recovery of their initial height. By contrast, for K‐carrageenan/locust bean gum and gellan gels the values of Sins and Sret were quite different, indicating that recovery was retarded. These parameters seem to be a good index of the relative magnitude of elastic and viscous components of foods. This was confirmed by relaxation tests.

Effect of conformation and molecular weight of co-solute on the mechanical properties of gellan gum gels

The mechanical properties of 0.5% gellan systems in the presence of a range of commonly used co-solutes, from monomeric sugars (glucose and fructose) and disaccharides (sucrose and maltose), to starch hydrolysates (corn syrups and maltodextrins), have been studied up to 60% w/w addition. Their effects are discussed in terms of co-solute concentration, conformation, configuration and M w. Addition of co-solute generally resulted in a lowering of the calcium required for maximum network strength accompanied by at least a three-fold decrease in the maximum measured Young’s modulus from 0 to 60% and an increase in the yield strain at the maximum modulus. This argues for limited aggregation of the polymer chains, which create a more flexible network in the high solids environment. At 60% solids, gel modulus decreases in the order: fructose>glucose>sucrose, which reflects a reduced level of aggregation due to different ring conformation and molecular weight of the co-solute. The network firmness recovered partially in the presence of maltose, which has a smaller hydration layer than sucrose, with the greater number of available water molecules facilitating more stable gellan structures. The recovery of Young’s modulus continued with corn syrup and maltodextrin, which was rationalised on the basis of partial phase separation between gellan chains and the polymeric fractions of the starch hydrolysates.

Structural characteristics of crosslinking domain in gellan gum gel

AbstractGellan gum samples having different counterions of TMA+ (tetramethyl‐ammonium ion), Na+, K+ and Cs+ were prepared, and the small‐angle X‐ray scattering was observed from the aqueous solutions of those samples. A sharp peak appears in the SAXS profile at low temperature, indicating the electrostatic interaction between the domains composed of multiple gellan gum chains. The SAXS profile revealed a rigid rod‐like characteristics of gellan gum chain. The cross‐sectional radius of gyration was evaluated from the scattering profiles, and the gelation mechanism was discussed from the change of the cross‐sectional radius of gyration upon gel‐sol transition. Taking the difference of the scattering power of counter ions into account, the ion condensation due to gelation was evaluated from the excess scattering of Cs+ gellan gum with respect to K+ gellan gum in respective aqueous solutions.

The network structure of gellan gum hydrogels based on the structural parameters by the analysis of the restricted diffusion of water

Gellan gum gels formed with potassium and calcium ions were investigated by the pulsed field gradient (PFG) stimulated echo NMR method. The structure of the gel network of the gellan gum gel was discussed on the basis of the interbarrier distance, a, the permeability of the barrier, p, and the actual diffusion coefficient of water, D 0. These structural parameters were estimated by the analysis of the restricted diffusion of water in the gel network. Three different types of gel, namely, weak gel, true gel and brittle gel, were obtained at various concentrations of the gel-promoting cation. Interestingly, the topological structure of the network in each type of gel as reflected by the structural parameters is identical in K +-bridged gels and Ca 2+-bridged gels, although the absolute concentration of the cation needed to form the different network types is quite different. It is assumed that the binding structures at the crosslink and at the bridge between the helices are different between the type of cation. Nevertheless, structural properties of the network such as the average distance between junction zones and the permeability of the junction zone were independent of the type of gel-promoting cation. The change in the overall gel architecture formed by the junction zones in the gelation process seems to be identical in the cases of monovalent and divalent cations and the difference is only the gel-forming efficacy of cations.

Rheological and thermal studies of gel-sol transition in gellan gum aqueous solutions

The rheological and thermal properties of sodium-form gellan gum solutions with and without sodium chloride, potassium chloride, calcium chloride and magnesium chloride were studied by dynamic viscoelastic measurement and differential scanning calorimetry. Temperature dependence of the loss modulus G″ for gellan gum solutions of lower concentrations without salt showed one step-like change at a certain temperature, however, that for concentrated gellan gum solutions (> 2.0%) showed two step-like changes. The higher temperature process was attributed to the helix-coil transition, and was found in between the exothermic and endothermic peak temperatures T s and T m observed in cooling and heating DSC curves, while the lower temperature process was attributed to the sol-gel transition. Temperature dependence of G″ for gellan gum solutions of higher concentrations (> 3.2%) showed a large hysteresis, moreover, the temperature at which G″ showed the second step decrease in the heating process shifted to higher temperatures with increasing concentration of gellan gum. The cooling or heating DSC curves for gellan gum solutions of lower concentrations showed a single exothermic or endothermic peak, and both T s and T m shifted to higher temperatures, and both exothermic and endothermic enthalpies increased with increasing concentration of gellan gum. However, for a gellan gum solution with a concentration higher than 3.2%, two endothermic peaks were observed on heating while the cooling curve showed only one exothermic peak. The lower temperature endothermic peak corresponds to the first step decrease of G″ in the heating process, and the higher temperature endothermic peak corresponds to the second step decrease of G″. The viscoelastic behavior of gellan gum solutions was influenced much more strongly by divalent cations than by monovalent cations. DSC heating curves for a 1% gellan gum solution in the presence of sufficient monovalent cations showed multiple endothermic peaks, however, these multiple peaks were observed at significantly higher temperatures than those for a gellan gum solution of high concentration (3.2%) without salts. The endothermic peaks in the presence of sufficient divalent cations in the heating DSC curve were too broad to be resolved from the baseline, however, many small peaks were observed at higher temperatures and the largest endothermic peak was observed at a temperature higher than 100 °C. Therefore, although divalent cations promote the formation of thermally stable junction zones much more strongly than monovalent cations, the gellan gum gels containing divalent cations may also consist of physical junction zones of hydrogen bonds because these junction zones can be unzipped on heating to 120 °C.

TEXTURE OF SWEET ORANGE GELS BY FREE‐CHOICE PROFILING

ABSTRACTTexture of orange gels prepared with 15% fruit pulp, sucrose up to 55° Brix and five different gelling agents — kappa‐carrageenan, kappa‐carrageenan plus locust bean gum, alginate, gellan gum, and gellan, xanthan and locust bean gums — was studied by Free‐Choice Profile (FCP) analysis. Maximum rupture force and deformation at rupture were also determined by uniaxial compression in an Instron texturometer. Generalized Procrustes Analysis applied to FCP data permitted differentiation between samples and informed on the textural attributes responsible for the observed differences. Sensory differences were in general in accordance with mechanical differences. However, carrageenan and gellan gum gels were differentiated with the sensory method applied but not with mechanical tests.

Effects of pH, Potassium Chloride, and Sodium Chloride on the Thermal and Rheological Properties of Gellan Gum Gels

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEffects of pH, Potassium Chloride, and Sodium Chloride on the Thermal and Rheological Properties of Gellan Gum GelsHatsue Moritaka, Katsuyoshi Nishinari, Mika Taki, and Hiroyasu FukubaCite this: J. Agric. Food Chem. 1995, 43, 6, 1685–1689Publication Date (Print):June 1, 1995Publication History Published online1 May 2002Published inissue 1 June 1995https://doi.org/10.1021/jf00054a050RIGHTS & PERMISSIONSArticle Views621Altmetric-Citations60LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (562 KB) Get e-Alerts Get e-Alerts

Work Hardening Effects in Gellan Gum Gels1

Abstract Gellan gum is a bacterial polysaccharide that is marketed as a broad spectrum gelling agent. The shear and Young's moduli, and the fracture strength of gellan gels increase with increasing ionic strength, pass through maxima and then decrease to zero at higher ionic strength. The position of the maxima depend on the valency of added counterions and are virtually independent of polymer concentration. At low ionic strength the measured rheological parameters show small variability but these values become increasingly variable with increasing ionic strength. Stress relaxation experiments were carried out in order to examine the mechanical behaviour of gellan gels and to explain these effects. At low ionic strength the gels approximate to elastic solids whereas at high ionic strength the increased stress relaxation is colloid-like in behaviour. However, unlike colloidal dispersions, the magnitude of the stress relaxation decreases on successive applications of stress and the relaxation modulus increa...

ジェランガムのゲル化に及ぼすアンモニウム塩の影響

ジェランガムのゲル化に及ぼすアンモニウム塩の影響

Effect of potassium ions on the rheological and thermal properties of gellan gum gels

To clarify the effect of cations on the gelling ability of gellan gum, the cation-free gellan gum was prepared by treating with ethylenediaminetetraacetic acid and ethanol. Storage Young's modulus E′ and mechanical loss tangent tan δ were observed for cation-free gellan gum (F1) gels, non-treated gellan gum (F2) gels and potassium added F1 gels. E′ increased and tan δ decreased in the presence of potassium ions indicating the increase of the number of junction zones, and the critical polymer concentration below which no gelation occurs shifted to lower concentrations by adding cations. An endothermic peak accompanying gel-to-sol transition in heating differential scanning calorimetry curves shifted to higher temperatures by adding potassium ions. It was confirmed that potassium ions increase the number of junction zones and make the junction zones more heat resistant. F2 gels containing sodium, calcium and magnesium ions in addition to potassium ions showed multiple broad endotherms in addition to a main endothermic peak indicating that junction zones are made from various aggregations of double helices, with different bonding energies and/or different degrees of rotational freedom of parallel links consisting a single zipper.