Effect of environmental factors and carbohydrate on gellan gum production

Submerged culture fermentation studies were carried out in batch mode for optimizing the environmental parameters and carbon source requirement by Pseudomonas elodea for the production of gellan gum. The maximum production of gellan gum was obtained with 16-h-old culture and 8% inoculum at 30°C and pH 7.0 after 52 h of incubation (6.0 g/L). Of the various carbon sources tested, 2% sucrose, glucose, and soluble starch yielded considerably high amounts of gellan. Studies on the concentration of various carbohydrates on gellan gum production indicated that the optimum concentration of glucose and starch was 3%, whereas for sucrose it was 4%. The addition of glucose in the medium above 3% had a detrimental effect on gellan yield. The investigation of intermediate two-step addition of glucose under identical conditions of fermentation showed an enhanced production of gellan (8.12 g/L) as compared with the control (6.0 g/L). To optimize the recovery of gellan from fermented broth, different solvents were tested for precipitation of gellan gum. Among the various solvents tested, tetrahydrofuran gave better recovery of gellan (82%) as compared with the conventional solvent isopropanol (49%).     

Effect of surface attachment on synthesis of bacterial cellulose

Gluconacetobacter spp. synthesize a pure form of hydrophilic cellulose that has several industrial specialty applications. Literature reports have concentrated on intensive investigation of static and agitated culture in liquid media containing high nutrient concentrations optimized for maximal cellulose production rates. The behavior of these bacteria on semisolid and solid surfaces has not been specifically addressed. The species Gluconacetobacter hansenii was examined for cellulose synthesis and colony morphology on a range of solid supports, including cotton linters, and on media thickened with agar, methyl cellulose, or gellan. The concentration and chemical structure of the thickening agent were found to be directly related to the formation of contiguous cellulose pellicules. Viability of the bacteria following freezer storage was improved when the bacteria were frozen in their cellulose pellicules. This article was authored by a contractor of the US government under contract no. DEAC05-00OR22725. Accordingly, the US government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for US government purposes.     

Effect of polymer and ion concentration on mechanical and drug release behavior of gellan hydrogels using factorial design

Developing optimized hydrogel products requires an in-depth understanding of the mechanisms that drive hydrogel tunability. Here, we performed a full 4 × 4 factorial design study investigating the impact of gellan, a naturally derived polysaccharide (1%, 2%, 3%, or 4% w/v) and CaCl₂ concentration (1, 3, 7, or 10 mM) on the viscoelastic, swelling, and drug release behavior of gellan hydrogels containing a model drug, vancomycin. These concentrations were chosen to specifically provide insight into gellan hydrogel behavior for formulations utilizing polymer and salt concentrations expanding beyond those commonly reported by previous studies exploring gellan. With increasing gellan and CaCl₂ concentration, the hydrogel storage moduli (0.1–100 kPa) followed a power-law relationship and on average these hydrogels had higher liquid absorption capability and greater total drug release over 6 days. We suggest that the effects of gellan and CaCl₂ concentration and their interactions on hydrogel properties can be explained by various phenomena that lead to increased swelling and increased resistance to network expansion.     

The Preparation,Characterization and Properties of Catalase Immobilized on Crosslinked Gellan

In the present paper, the reaction of chemical immobilization of catalase on a crosslinked macromolecular carrier of a polysaccharide structure (gellan) is studied. The influence of some reaction parameters (enzyme/carrier, activator/carrier ratios, duration) on the activity of enzymatic products is analyzed. The kinetics of the biocatalytic process, stability under different pH and temperature conditions, and the inhibitors effect were studied for the immobilized enzymes.     

Stability and Rheological Properties of Suspended Pulp Particles Containing Orange Juice Stabilized by Gellan Gum

Gellan was used to suspend pulp particles in orange juice. Three groups of samples were prepared with 0%, 20%, and 40% orange juice concentrate and supplemented with gellan at different concentrations. A concentration-dependent increase in the size of gellan aggregates and gellan-protein assemblies was observed. Incorporation of gellan into the beverage with 0% juice concentrate changed the rheological behavior of sample to non-Newtonian shear-thinning fluid and increased its surface tension. When juice concentrate proportion was increased from 0% to 20%, the beverage viscosity increased. The highest gellan concentration resulted in a higher yield stress (σ₀) value and inhibited the pulp sedimentation completely.      

Alkaline phosphatase encapsulated in gellan-chitosan hybrid capsules

Alkaline phosphatase (ALP) was encapsulated in gellan-chitosan polyion complex (PIC) capsules using a convenient procedure. The recovery of ALP was about 50% when the capsules were prepared by dropping a solution of ALP and gellan mixture (ALP/gellan) into a chitosan solution. When p-nitrophenyl phosphate (p-NPP) and 5-bromo-4-chloro-3-indolyl phosphate (BCIP) were incubated with ALP/gellan-chitosan capsules as substrates for ALP, the transparent colorless capsules changed to yellow and blue, respectively. The encapsulation of ALP into the PIC capsules was also confirmed by SDS-PAGE and immunoblot analyses. The ALP and polypeptides of more than 30 kDa remained without release even after incubation at 4 degrees C for 14 d. The biochemical properties of the encapsulated ALP activity were similar to those of the intact enzyme. When the solution containing p-NPP was loaded on a column packed with ALP/gellan-chitosan capsules at 27 degrees C, approximately 75% of p-NPP was hydrolyzed by passing through the column. No significant leakage of ALP was observed during the procedure, indicating that the capsules were resistant to pressure in the chromatographic operation. Furthermore, 70% of the hydrolytic activity of the packed capsules remained after storage at 4 degrees C for one month. These results suggest that the polyion complex capsules could be useful materials for protein fixation without chemical modification. [Diagram: see text] Encapsulation of ALP into PIC capsules and the morphological changes seen in the absence of the ALP substrate and in the presence of p-NPP and BICP.     

Electrical conductivity,impedance, and percolation behavior of carbon nanofiber and carbon nanotube containing gellan gum hydrogels

The electrical impedance behavior of gellan gum (GG), GG–carbon nanotube, and GG–carbon nanofiber hydrogel composites is reported. It is demonstrated that the impedance behavior of these gels can be modeled using a Warburg element in series with a resistor. Sonolysis (required to disperse the carbon fillers) does not affect GG hydrogel electrical conductivity (1.2 ± 0.1 mS/cm), but has a detrimental effect on the gel's mechanical characteristics. It was found that the electrical conductivity (evaluated using impedance analysis) increases with increasing volume fraction of the carbon fillers and decreasing water content. For example, carbon nanotube containing hydrogels exhibited a six‐ to sevenfold increase in electrical conductivity (to 7 ± 2 mS/cm) at water content of 82%. It is demonstrated that at water content of 95 ± 2% the electrical behavior of multiwalled nanotube containing hydrogels transitions (percolates) from transport dominated by ions (owing to GG) to transport dominated by electrons (owing to the carbon nanotube network). © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 864–871     

Surface modification by deposition of IPA plasma and gellan gum/chitosan hybrid hydrogel onto thermoplastic polyurethane for controlled release of N‐acetylcysteine

A thin film system composed of gellan gum and chitosan was fabricated through a combination of polyelectrolyte blend and hybrid hydrogel gelation for controlled release of drug. In this study, precursor isopropyl alcohol (IPA) was used to plasma deposit on the surface of thermoplastic polyurethane (TPU) to form a hydrophilic film. The features of the thin film were evaluated using water contact angle (WCA) measurement, scanning electron microscopy (SEM), Fourier transform infra‐red (FTIR), UV/Vis spectroscopy, and studies of controlled release of drugs. The hybrid hydrogel, pH‐sensitive, was tested at pH values of 1.2 and 7.4 of buffer solution and at a temperature of 37°C to observe its swelling ratio and drug delivery properties with N‐acetylcysteine as a drug material for controlled release. Furthermore, at pH 7.4, the hybrid hydrogel has an outstanding release ratio of up to about 90% absorption amounts of N‐acetylcysteine after 8 hr. The mechanism of drug release from thin film devices (n = 0.684) is anomalous (non‐Fickian) transport, the value of n lies between 0.43 and 0.85.     

Local chain mobility of gellan in aqueous systems studied by fluorescence depolarization

The local chain mobility of a gellan, an electrolyte polysaccharide, in aqueous systems was examined with respect to the effect of the temperature, the concentration of gellan (c(G)), and the concentration of added salt (c(S)). The relaxation time of local motion was estimated for fluorescein isothiocyanate (FITC)-labeled-gellan by the fluorescence depolarization technique, and the chain mobility was discussed. The relaxation time increased with decreasing temperature, in particular when accompanying the coil-helix transition due to the great difference in chain mobility between the coil and the helical conformations. The effect of c(G) was observed for gellan solutions even below the critical concentration of chain entanglement (2 wt.-%) for well-expanded nonelectrolyte polymers with size similar to that of the gellan. This suggests that the actual excluded volume of gellan is larger than that of nonelectrolyte polymers due to the electrostatic repulsion between segments. The relaxation time for 0.2 wt.-% systems of gellan in coil conformation is independent of c(S), whereas a c(S) dependence of the relaxation time is clearly observed for 0.5 wt.-% systems. The degree of expansion of the gellan chain is independent of the shielding effect of cations on the electrostatic repulsion between gellan segments due to the stiffness of gellan chain. On the other hand, the c(G) as well as the c(S) dependence of the chain mobility is clearly observed for gellan in the helical conformation, examined over the concentration range, probably due to the partial aggregation of helices induced by the attractive interaction between gellan segments.     

Graphene oxide–gellan gum–sodium alginate nanocomposites: synthesis,characterization, and mechanical behavior

This paper reports the preparation and characterization of graphene oxide–gellan gum–sodium alginate nanocomposites (GO–GG–Alg). The nanocomposites were prepared by a simple solution mixing-evaporation method. Fourier transform infrared spectroscopy, X-ray diffractions, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, thermal gravimetric analysis, and mechanical testing were conducted to study the structure and properties of the nanocomposites. The obtained findings reveal that gellan gum, sodium alginate, and graphene oxide are able to form a homogeneous mixture. Small amount of GO loading on GO–GG–Alg drastically improves its tensile strength and Young’s modulus. Detailed material characteristics of the nanocomposites are addressed.