Self-assembled pH-stable gellan/κ-carrageenan bigel: Rheological studies and viscosity prediction by neural network.

The current study focused on analysing and predicting the effect of physicochemical parameters on the rheological properties of the novel polysaccharide-based bigel. This is the first study to report a bigel fabricated entirely from polysaccharides and develop a neural network to predict the modulation in its rheology. This bi-phasic gel had gellan and κ-carrageenan as the constitutive elements in the aqueous and the organic phase, respectively. Physicochemical studies revealed the influence of organogel in eliciting high mechanical strength and smooth surface morphology to the bigel. Furthermore, variation in physiochemical parameters indicated the bigel's inertness towards change in pH of the system. However, variation in temperature led to a noticeable change in the rheology of the bigel. It was observed that after gradual decline, the bigel regained its original viscosity as the temperature increased beyond 80 °C. Insights from this study can pave way for the development of highly-stable polysaccharide bigels.

Green Synthesis of pH-Responsive, Self-Assembled, Novel Polysaccharide Composite Hydrogel and Its Application in Selective Capture of Cationic/Anionic Dyes.

Dyes are one of the most hazardous chemicals causing significant environmental pollution and affecting water quality. Majority of the existing methods for dye removal and degradation involve synthetic membranes and use of hazardous chemicals, further resulting in secondary pollution. The present study reports polysaccharide based novel composite hydrogel as biodegradable matrix for pH-responsive selective adsorption of cationic/anionic dyes. This membrane showed pH-responsive adsorption of methyl green (MG) and methyl orange (MO) with similar adsorption equilibrium, i.e., 315 and 276 mg g-1, respectively. Interestingly, selective adsorption at different pH has allowed separation of dye mixtures that holds incredible industrial importance for dyes recovery. The hydrogel matrix was able to completely separate MG, a model cationic dye at neutral pH from the dye mixture whereas, it was possible to remove 60% MO, a model anionic dye at acidic pH. Furthermore, comprehensive isothermal and kinetic studies of adsorption revealed that Freundlich isotherm describing the multilayer coverage and pseudo-second-order kinetics were followed. Thermodynamic studies indicated that the adsorption process was spontaneous and endothermic. In fact, the membrane was reusable for at least ten cycles and exhibited desorption efficiency of 80 and 60% for MO and MG, respectively, which may be further recycled to make the process environmentally sustainable. Overall, this study proposes an inexpensive, simple, biologically safe, and efficient adsorbent material for dye effluent treatment.

Recent advances in composite hydrogels prepared solely from polysaccharides.

The proliferating demand for sustainable, biodegradable, and biologically safe materials has triggered the development of polysaccharide-based hydrogels. The translation of research on single polysaccharide-based hydrogels into their desired clinical or industrial application is minimal. This is attributable to their lack of mechanical strength, inadequate stability, and constrained the possibility of their modulation to obtain the desired property. Polysaccharide-based composite hydrogels (PCHs) have proven their mantle to counteract this issue while expanding the horizons for their applications. PCHs can be fabricated by physical and/or chemical interlinking techniques, which entails the association of macromolecular chain linkages. The resulting composites can impart remarkably higher stability and elevate the suitability and efficiency of the system. Owing to these advantages, the research on PCHs has been gaining momentum. They are emerging as a lucrative alternative for the conventional molecules used for the fabrication of such materials. The review would initially focus on providing a detailed outlook for the various physical/chemical techniques involved in the preparation of PCHs. Subsequently, the characterization techniques used to understand the structural and chemical behavior of PCHs would be discussed. The article would also elaborate on the various fields of application and the possible areas for future research of PCHs.

Synthesis and rheological characterization of a novel shear thinning levan gellan hydrogel.

Shear thinning hydrogels are majorly employed in biomedical and cosmetic industry. However, the application of such chemically modified hydrogels is limited due to their high gelation time and chemical toxicity. The present study attempts to address these issues by synthesizing a novel quick setting, non-toxic hydrogel composed of biodegradable polysaccharides, levan and gellan. Comprehensive rheological analysis was conducted to understand the shear thinning and self-healing behaviour of the hydrogel. Frequency sweeps indicated that remarkable mechanical properties were exhibited by the composite hydrogels. Furthermore, the hydrogel exhibited an ease of injectability as demonstrated by strain sweep experiments. This study can, therefore, act as a pioneer for establishment of natural polysaccharide-based shear thinning hydrogels for possible application in various sectors.

pH mediated rheological modulation of chitosan hydrogels.

Chitosan (CS) hydrogels are used widely for multifarious applications in diverse fields due to the property of pH responsiveness. This study aims to explain the sensitivity of CS hydrogels to alteration in pH due to change in the concentration of acetic acid, which is a solvent for CS. Studies on changes in rheological properties in this regard are still scarce. The present study evaluated the change in rheological properties of the CS hydrogels by studying the flow behaviour, creep recovery and thixotropic property. The obtained data were used to fit mathematical models, like power law model and Herschel-Bulkley model to gain a vivid understanding of the rheological properties of CS hydrogel. Overall analyses revealed that the CS hydrogels, irrespective of the pH, were highly elastic in nature and exhibited significant creep recovery. However, the steady flow behaviour and thixotropy varied substantially with variation in pH.

Exploration of polysaccharide based nanoemulsions for stabilization and entrapment of curcumin.

This study was focussed on developing polysaccharide based nanoemulsion (P-NE) encapsulating curcumin. Two different carrier oil, olive and castor oil, and various polysaccharides like, levan, fucoidan, alginate, guar gum and κ-carrageenan were evaluated for their entrapment efficiency for curcumin. The prepared nanoemulsions with fucoidan and κ-carrageenan were found to have relatively better properties than nanoemulsions prepared with Tween 20. The lowest particle size after ultrasonication was observed when fucoidan was employed as emulsifying agent. Rheological and thermodynamic analyses confirmed better stability of P-NE. Additionally, encapsulation efficiency (EE) of polysaccharides was comparable to Tween 20 with κ-carrageenan exhibiting significantly higher EE than Tween 20. Synergistic increase in the antioxidant potential of the P-NE containing curcumin was also noteworthy. The structural interaction for the observation was proven by FT-IR analysis. The study, first of its kind, was able to evaluate efficiency of different polysaccharides for emulsification of curcumin, without the use of any coemulsifier.

Synthesis of a novel gellan-pullulan nanogel and its application in adsorption of cationic dye from aqueous medium.

The current study focused on synthesizing a novel gellan-pullulan composite nanogel via chemical crosslinking with DPPH. The physical and rheological properties of the synthesised nanogel was assessed by determining its particle size, zeta potential and effect of temperature and stress on viscosity of nanogels. Furthermore, the novel nanogel was assessed for its ability to ameliorate water resources by efficiently adsorbing cationic dyes. Methylene blue (MB) was used as a model cationic dye compound in the study. The adsorption capacity of nanogels for MB was evaluated by fitting different isotherm models and understanding thermodynamics and kinetics of the process. It was revealed from the overall analysis that nanogels had the property to adsorb MB in multilayer alignment. The gellan-pullulan composite nanogel was found to have better adsorption capability as compared to native gellan nanogel. This is the first report of gellan-pullulan nanogel and its application for cationic dye adsorption.

Understanding the Effect of Impeller Configurations on Pullulan Production by Aureobasidium Pullulans RBF 4A3.

Mass transfer is one of the most important factors involved in viscous fermentation processes, like production of pullulan. Impellers play a crucial role in maintaining homogeneity and better mass transfer conditions during the fermentation process. The present study attempted to evaluate the efficiency of impellers with diverse configurations during pullulan fermentation. Initially, the mass transfer coefficients of 10 selected impellers were evaluated in an aqueous system. Among these, three impellers, namely, single helical ribbon, Rushton turbine, and Smith turbine impellers, were found to be more efficient and were further employed in the pullulan fermentation process. The results suggested that the single helical ribbon impeller was able to provide 24% higher pullulan production as compared to the Rushton turbine and Smith turbine impellers. The single helical ribbon was able to maintain the critical demand of dissolved oxygen in fermentation broth. Therefore, it may be commented that the single helical ribbon impeller configuration is suitable for higher production of pullulan during the fermentation process.

Synthesis and rheological studies of a novel composite hydrogel of xanthan, gellan and pullulan.

Hydrogels are three dimensional polymeric structures and are of great importance to industrial sector due to their signature physiochemical and mechanical properties. Use of natural polysaccharides as the components of hydrogel composite is of great interest due to their non-toxic nature, biodegradability, biocompatibility and viscoelastic properties. The present study reports a novel hydrogel composed of xanthan, gellan and pullulan. Unlike, pullulan and xanthan, this tri-composite formed a stable gel having high water retention ability and swelling ratio. The synergistic effects of individual components of the hydrogel on viscoelastic properties and flow behaviour were also studied. The hydrogel composite also indicated swelling ratio in alkaline environment attributed to the ionisation of hydrogel components in response to the presence of OH moieties. Overall results indicated that the composite hydrogel can have plausible application in food industry as it displays viscoelastic nature and flow behaviour index (n) values for composites within the desirable range.

Purification, characterization and functional properties of exopolysaccharide from a novel halophilic Natronotalea sambharensis sp. nov.

An exopolysaccharide producing strain AK103T was isolated from Sambharlake, Rajasthan, India. Based on polyphasic taxonomy, the strain AK103T was found to be a novel species for which the name Natronotalea sambharensis sp. nov. is proposed. The strain was able to secrete (1.2 gL-1) EPS under optimum conditions. The FT-IR spectroscopy revealed that EPS had carboxyl, hydroxyl, carbonyl and sulfate ester groups. The high performance liquid chromatography (HPLC), gel permeation chromatography (GPC) and NMR revealed that the exopolysaccharide was composed of mannose, glucose and glucuronic acid with a molecular weight of 4.6 × 106 KDa. This novel EPS was designated as Nat-103. Interestingly, the EPS was found to have antioxidant activity and in vitro antioxidant studies showed that DPPH (2,2-diphenyl-1-picrylhydrazyl) activity increased in a dose dependent manner. Furthermore, EPS Nat-103 was able to produce gold nanoparticles which were further characterized by FT-IR, DLS and Zeta potential (ZP).

Structural characterization and antioxidant potential of a novel anionic exopolysaccharide produced by marine Microbacterium aurantiacum FSW-25.

An exopolysaccharide (EPS) producing strain FSW-25 was isolated from the Rasthakaadu beach Kanyakumari, Tamil Nadu India. Based on polyphasic taxonomy, the strain FSW-25 was assigned to the genus Microbacterium and found to be the closest relative of the species aurantiacum. Large quantity of EPS (7.81 g/l) was secreted by the strain upon fermentation using Reasoner's 2A medium enriched with 2.5% glucose and was designated as Mi-25. FT-IR spectrum revealed presence of hydroxyl, carbonyl, carboxyl, methyl and sulfate functional groups in purified EPS. The EPS Mi-25 has a molecular weight of 7.0 × 106 Da and mainly comprises of glucuronic acid followed by glucose, mannose and fucose. Rheological study revealed that Mi-25 possesses significant viscosity with pseudoplastic nature. Interestingly, it was observed that the EPS Mi-25 has higher antioxidant activity as compared to xanthan. The characteristics of EPS Mi-25 suggested that, it can be used as a potential antioxidant with viscosifier properties in diverse industrial sectors.

Production, characterization and bio-emulsifying activity of a novel thermostable exopolysaccharide produced by a marine strain of Rhodobacter johrii CDR-SL 7Cii.

An exopolysaccharide (EPS) producing bacterial strain was isolated from the surface of marine macroalgae (Padina sp.). Based on polyphasic taxonomy, the strain CDR-SL 7Cii was assigned to the genus Rhodobacter and found to be the closest relative of the species Rhodobacter johrii. The strain was able to produce 6.2 g/l of EPS upon fermentation using R2A medium enriched with 2.5% glucose. FT-IR analysis revealed the presence of hydroxyl, carboxyl and diacyl-ester functional groups in the purified EPS. Further Chromatographic study revealed that R. johrii synthesized a high molecular weight anionic exopolysaccharide composed of glucose, glucuronic acid, rhamnose and galactose in a molar ratio of 3:1.5:0.25:0.25. The 1D and 2D NMR spectroscopy (COSY/HSQC) analysis revealed the presence of 1,6 linked-α-d-Glcp, 1,4 linked-ß-d-Glcp, 1,3 linked-ß-d-GlcA, 1,3 linked-ß-d-Galp, 1,6 linked-ß-d-Galf and 3-α-l-Rhmp residues. Moreover, the purified EPS has shown stability towards elevated temperature and also acted as a bio-emulsifier to create a high pH and temperature stable emulsion of hydrocarbon/water indicating its industrial potential. This is the first report of EPS production by a strain of Rhodobacter johrii.

Synthesis and rheological characterization of a novel thermostable quick setting composite hydrogel of gellan and pullulan.

Hydrogels have found applications in diverse industrial sectors and majority of them are chemically modified. However, recently demand for stable biocompatible non-toxic hydrogels has increased significantly. The current study is focused on synthesizing a novel composite hydrogel using gellan and pullulan, two commercially available biologically safe polysaccharides, without any chemical modifications. Furthermore, rheological behavior of the gellan-pullulan hydrogel was studied and power law and Arrhenius models were fit to understand consistency and flow behavior. Interestingly, this novel hydrogel was quick-setting and exhibited good crosslinking and maintained its elasticity at high temperature and frequency. Overall analysis of the rheological data suggested that the synthesized hydrogel can offer potential advantages over gellan hydrogel as it was found to be more thermostable and elastic. This is the first report of a composite hydrogel solely made of gellan and pullulan.

Extracellular polysaccharide production by a novel osmotolerant marine strain of Alteromonas macleodii and its application towards biomineralization of silver.

The present study demonstrates exopolysaccharide production by an osmotolerant marine isolate and also describes further application of the purified polysaccharide for production of colloidal suspension of silver nanoparticles with narrow size distribution. Phylogenetic analysis based on 16S r RNA gene sequencing revealed close affinity of the isolate to Alteromonas macleodii. Unlike earlier reports, where glucose was used as the carbon source, lactose was found to be the most suitable substrate for polysaccharide production. The strain was capable of producing 23.4 gl(-1) exopolysaccharide with a productivity of 7.8 gl(-1) day(-1) when 15% (w/v) lactose was used as carbon source. Furthermore, the purified polysaccharide was able to produce spherical shaped silver nanoparticles of around 70 nm size as characterized by Uv-vis spectroscopy, Dynamic light scattering and Transmission electron microscopy. These observations suggested possible commercial potential of the isolated strain for production of a polysaccharide which has the capability of synthesizing biocompatible metal nanoparticle.