Use of chemically modified chitosan beads for sorption and enzyme immobilization

Broad-spectrum pH functional chitosan-phosphatase beads for the generation of plant-available phosphorus: utilizing the insoluble P pool

Utilization of organic phosphates and insoluble phosphates for the gradual generation of plant-available phosphorus (P) is the only sustainable solution for P fertilization. Enzymatic conversions are one of the best sustainable routes for releasing P to soil. Phosphatase enzyme aids in solubilizing organic and insoluble phosphates to plant-available P. We herein report the preparation of highly functional chitosan beads co-immobilized with acid phosphatase and alkaline phosphatase enzymes via a glutaraldehyde linkage. The dual enzyme co-immobilized chitosan beads were characterized using Fourier-transform infrared (FTIR), thermogravimetric (TGA), and scanning electron microscopy-energy dispersive x-ray (SEM-EDX) analyses to confirm the immobilization. The co-immobilized system was found to be active for a broader pH range of ∼4-10 than the individually bound enzymes and mixed soluble enzymes. The bound matrix exhibited pH optima at 6 and 9, respectively, for acid and alkaline phosphatase and a temperature optimum at 50°C. The phosphate-solubilizing abilities of the chitosan-enzyme derivatives were examined using insoluble tri-calcium phosphate (TCP) for wide pH conditions of 5.5, 7, and 8.5 up to 25 days. The liberation of phosphate was highest (27.20 mg/mL) at pH 5.5 after the defined period. The residual soil phosphatase activity was also monitored after 7 days of incubation with CBE for three different soils of pH ∼5.5, 7, and 8.5. The residual phosphatase activity increased for all the soils after applying the CBE. The germination index of the Oryza sativa (rice) plant was studied using different pH buffer media upon the application of the CBE in the presence of tri-calcium phosphate as a phosphate source. Overall, the dual-enzyme co-immobilized chitosan beads were highly effective over a wide pH range for generating plant-available phosphates from insoluble phosphates. The chitosan-enzyme derivative holds the potential to be used for sustainable phosphorus fertilization with different insoluble and organic phosphorus sources.

Deproteinization of Shrimp Shell Waste by Kurthia gibsonii Mb126 immobilized chitinase

This work was aimed at immobilization, characterization, and utilization of chitinase from Kurthia gibsonii Mb126. Immobilization of Kurthia gibsonii Mb126 chitinase on glutaraldehyde treated chitosan was carried out with immobilization yield of 106%. The optimal factors of the immobilization technique such as concentration of glutaraldehyde, chitinase concentration, and immobilization time were evaluated. After optimizing process parameters of immobilization (Glutaraldehyde concentration 4%, chitinase conc. 60mg, immobilization time 30min.), the specific activity of immobilized chitinase improved to 4.3-fold compared to the free form of chitinase. Temperature and pH optima of the immobilized chitinase and free enzyme were same i.e., 7.5 and 40°C respectively. The relative activity of immobilized chitinase remained 90% at 40°C, at 50°C, and at 60°C for 120 min. In the pH range from 5.5 to 8, the immobilized chitinase retained 100% activity. The results confirmed that the pH stability and thermal stability of chitinase increased by immobilizing chitinase on chitosan. The immobilized enzyme system maintained 90% of its efficiency even after 16 successive reaction cycles. The immobilized chitinase maintained 78% of its activity even after 20 months. Fermentation of prawn shell waste with immobilized chitinase indicated a high level of deproteinization. Deproteinization experiments were carried out with 5mL (0.4 mg/mL ) of immobilized and free chitinase on 300 mg/mL of prawn shell waste for 20 days without any additional supplements at 40°C and 6.5 pH. Protein content was reduced from 38.4 to 0.8% with immobilized chitinase. Results suggests the possibility of using immobilized enzymes to remove the prawn shell waste from the environment. To the best of our knowledge there was no such study about the deproteinization of prawn shell waste using immobilized chitinase till the date.

Fabrication of stable electrospun blended chitosan-poly(vinyl alcohol) nanofibers for designing naked-eye colorimetric glucose biosensor based on GOx/HRP

In this study, designing of a stable electrospun blended chitosan (CS)-poly(vinyl alcohol) (PVA) nanofibers for colorimetric glucose biosensing in an aqueous medium was investigated. CS and PVA solutions were blended to acquire an optimum content (CS/PVA:1/4) and electrospunned to obtain uniform and bead-free CS/PVA nanofiber structures following the optimization of the electrospinning parameters (33 kV, 20 cm, and 1.2 ml.h^-1). Crosslinking process applied subsequently provided mechanically and chemically stable nanofibers with an average diameter of 378 nm. The morphological homogeneity, high fluid absorption ability (>%50), thermal (<230 °C) and morphological stability, surface hydrophilicity and degrability properties of cross-linked CS/PVA nanofiber demonstrated their great potential to be developed as an eye-readable strip for biosensing applications. The glucose oxidase (GOx) and horseradish peroxidase (HRP) was immobilized by physical adsorption on the cross-linked CS/PVA nanofiber. The glucose assay analysis by ultraviolet-visible (UV-Vis) spectrophotometry using the same enzymatic system of the proposed glucose strips in form of absorbance versus concentration plot was found to be linear over a glucose concentration range of 2.7 to 13.8 mM. The prepared naked eye colorimetric glucose detection strips, with lower detection limit of 2.7 mM, demonstrated dramatic color change from white (0 mM) to brownish-orange (13.8 mM). The developed cross-linked CS/PVA nanofiber strips, prepared by electrospinnig procedure, could be easily adapted to a color map, as an alternative material for glucose sensing. Design of a practical, low-cost, and environmental-friendly bio-based CS/PVA testing strips for eye readable detection were presented and suggested as an applicable medium for a wide range of glucose concentrations.

Immobilization of papain: A review

Papain is a cysteine protease from papaya, with many applications due to its broad specificity. This paper reviews for first time the immobilization of papain on different supports (organic, inorganic or hybrid supports) presenting some of the features of the utilized immobilization strategies (e.g., epoxide, glutaraldehyde, genipin, glyoxyl for covalent immobilization). Special focus is placed on the preparation of magnetic biocatalysts, which will permit the simple recovery of the biocatalyst even if the medium is a suspension. Problems specific to the immobilization of proteases (e.g., steric problems when hydrolyzing large proteins) are also defined. The benefits of a proper immobilization (enzyme stabilization, widening of the operation window) are discussed, together with some artifacts that may suggest an enzyme stabilization that may be unrelated to enzyme rigidification.

Enzyme immobilization on porous chitosan hydrogel capsules formed by anionic surfactant gelation

OBJECTIVES

Sodium dodecyl sulfate (SDS)-chitosan hydrogels have been employed for adsorption of anionic dyes and metallic substances. Two mutant forms of Thermoanaerobacter ethanolicus alcohol dehydrogenase (TeSADH) were used as model enzymes to develop a novel enzyme immobilization technique employing newly formulated porous chitosan hydrogels.

RESULTS

The enzyme immobilized on chitosan hydrogel capsules formed by 5 g/l SDS gelation and subsequent treatment with 0.05 M NaOH was 28-35% higher in NADPH production than that formed by 20 g/l SDS gelation only under the same conditions. A 48-h asymmetric biphasic reduction of acetophenone with immobilized TeSADH enzyme at 50 °C showed 68% increase in (R)-1-phenylethanol production than the free enzyme. Compared to the free enzyme which denatured and lost its activity at 80 °C, the immobilized enzyme retained about 25% of its initial activity after 2-h incubation.

CONCLUSION

In contrast to the conventional chitosan hydrogel which suffers thermal and operational stability, the newly formulated porous chitosan hydrogel capsules have excellent enzyme loading efficiency and stable at harsh temperatures. Especially, this newly developed enzyme immobilization method would be applicable for food processing.

Immobilization of bromelain on cobalt-iron magnetic nanoparticles (CoFe2O4) for casein hydrolysis

By means of recycling an enzyme, bromelain was used in casein hydrolysis facilitated by a nanobiocatalyst consisting of bromelain, CoFe2O4 magnetic nanoparticles, chitosan, and glutaraldehyde. Bromelain was immobilized on the chitosan cobalt-magnetite nanoparticle surface via covalent bonds to form the nanobiocatalyst. Immobilized bromelain showed 77% immobilization binding, retaining 85 ± 2% of the initial catalytic activity. Nanoparticles and immobilized bromelain were characterized using UV-Vis and IR spectroscopies, X-ray, square wave voltammetry (SWV), cyclic voltammetry (CV), vibrating-sample magnetization (VSM), and transmission electron microscope (TEM). The Michaelis-Menten constant (KM) and VMAX of the free and immobilized enzyme were calculated: KM = 2.1 ± 0.18 mM and 1.8 mM, respectively and VMAX = 6.08 x 10-2 ± 2.1 x 10-2 U/min and 6.46 ± 0.91 U/min, respectively. The thermal stability of the free enzyme was higher than the immobilized enzyme: 95-98% and 83-87%, respectively. An optimum pH of 6 and a temperature of 20 °C were determined in both cases. Immobilized bromelain maintained 50% of the initial catalytic activity after the fifth use. The immobilized bromelain proved to be effective and reusable for casein hydrolysis. As novel contribution the characterization by VOC and CV was carried out.

Naturally-derived biopolymers: Potential platforms for enzyme immobilization

Naturally-derived biopolymers such as alginate, chitosan, cellulose, agarose, guar gum/guaran, agar, carrageenan, gelatin, dextran, xanthan, and pectins, etc. have appealed significant attention over the past several years owing to their natural abundance and availability all over the years, around the globe. In addition, their versatile properties such as non-toxicity, biocompatibility, biodegradability, flexibility, renewability, and the availability of numerous reactive sites offer significant functionalities with multipurpose applications. At present, intensive research efforts have been focused on engineering enzymes using natural biopolymers as novel support/composite materials for diverse applications in biomedical, environmental, pharmaceutical, food and biofuel/energy sectors. Immobilization appears as a straightforward and promising approach to developing biocatalysts with improved catalytic properties as compared to their free counterparts. Biopolymers-assisted enzymes are more stable, robust, and recoverable than that of free forms, and can be employed for continuous biocatalytic reactions. The present review highlights the recent developments and use of biopolymers and their advanced composites as support carriers for the immobilization of a variety of different enzymes to develop biocatalysts with desired catalytic activity and stability characteristics for emerging applications.

Scanning electrochemical microscopy imaging of poly (3,4-ethylendioxythiophene)/thionine electrodes for lactate detection via NADH electrocatalysis

Herein we report the use of scanning electrochemical microscopy (SECM) together with electrochemical and spectroscopic techniques to develop and characterise a stable and uniformly reactive chemically modified platinum electrode for NADH electrocatalysis. In order to achieve this, a range of different approaches for thionine entrapment within an electropolymerised poly (3,4-ethylendioxythiophene) (PEDOT) film were evaluated using SECM imaging in the presence of NADH, demonstrating the uniformity of the reactive layer towards NADH oxidation. The effect of electrolyte type and time scale employed during PEDOT electropolymerisation was examined with respect to thionine loading and the resulting charge transport diffusion coefficient (D_CT) estimated via chronoamperometry. These studies indicated a decrease in D_CT as thionine loading increased within the PEDOT film, suggesting that charge transport was diffusion limited within the film. Additionally, thionine functionalised nanotubes were formed, providing a stable support for lactate dehydrogenase entrapment while lowering the rate of thionine leaching, determined via SECM imaging. This enabled lactate determination at E_app = 0.0 V vs Ag/AgCl over the range 0.25-5 mM in the presence of 1 mM NAD⁺.

A review on agro-industrial waste (AIW) derived adsorbents for water and wastewater treatment

There is a large amount of studies surrounding the usage of agro-industrial waste (AIW) for the adsorptions of organic pollutants (dyes) and inorganic pollutants (heavy metals) in water/wastewater. This method is normally treated as an alternative approach to the conventional water/wastewater treatment. However, there are some increasing interests for investigators to identify novel adsorption materials for pollutants removal. It is particularly noteworthy that most AIW wastes are not currently used at the original state, but modified in a variety of ways to reinforce the porosity and adsorption surface area of the material. Nanostructuring, activation, carbonization, and grafting are some common modification technologies of agricultural waste adsorbents. Besides, the characteristic, preparation and application of adsorbents from various industrial wastes, including natural materials and biosorbents, were summarized. Additionally, the challenges and perspectives for future researches of waste-derived adsorbents were studied. This review provides an important insight on using AIWs as precursor materials for preparing adsorbents in water/wastewater treatment.

Magnetic nanoparticles: a versatile carrier for enzymes in bio-processing sectors

Many industrial processes experience the advantages of enzymes which evolved the demand for enzymatic technologies. The enzyme immobilisation technology using different carriers has trustworthy applications in industrial biotechnology as these techniques encompass varied advantages such as enhanced stability, activity along with reusability. Immobilisation onto nanomaterial is highly favourable as it includes almost all aspects of science. Among the various techniques of immobilisation, the uses of nanoparticles are remarkably well perceived as these possess high-specific surface area leading to high enzyme loadings. The magnetic nanoparticles (MNPs) are burgeoning in the field of immobilisation as it possess some of the unique properties such as high surface area to volume ratio, uniform particle size, biocompatibility and particularly the recovery of enzymes with the application of an external magnetic field. Immobilisation of industrially important enzymes onto nanoparticles offers overall combined benefits. In this review, the authors here focus on the current scenario in synthesis and functionalisation of MNPs which makes it more compatible for the enzyme immobilisation and its application in the biotechnological industries.

Bioaugmentation strategy employing a microbial consortium immobilized in chitosan beads for oil degradation in mesocosm scale

A bacterial consortium composed by four metagenomic clones and Bacillus subtilis strain CBMAI 707, all derived from petroleum reservoirs, was entrapped in chitosan beads and evaluated regarding hydrocarbon degradation capability. Experiments were carried out in mesocosm scale (3000L) with seawater artificially polluted with crude oil. At different time intervals, mesocosms were sampled and subjected to GC-FID and microbiological analyses, as total and heterotrophic culturable bacterial abundance (DAPI and CFU count), biological oxygen demand (BOD) and taxonomic diversity (massive sequencing of 16S rRNA genes). The results obtained showed that degradation of n-alkane hydrocarbons was similar between both treatments. However, aromatic compound degradation was more efficient in bioaugmentation treatment, with biodegradation percentages reaching up to 99% in 30days. Community dynamics was different between treatments and the consortium used in the bioaugmentation treatment contributed to a significant increase in aromatic hydrocarbon degradation.

Cytotoxicity and cellular uptake of ZnS:Mn nanocrystals biofunctionalized with chitosan and aminoacids

Highly luminescent, manganese doped, zinc sulphide (ZnS:Mn) nanocrystals biofunctionalized with chitosan and various aminoacids such as L-citrulline, L-lysine, L-arginine, L-serine, L-histidine and glycine were synthesized by chemical capping co-precipitation method at room temperature, which is a simple and cost effective technique. The synthesized nanocrystals were structurally characterized by TEM, XRD, EDXS and FT-IR spectroscopy techniques. They possess high colloidal stability with strong orange red photoluminescence emission at 598 nm. The intensity of orange red emission has been observed to be maximum in L-citrulline capped ZnS:Mn nanocrystals in which the emission at 420 nm is effectively quenched by surface passivation due to capping. Taking into consideration the prospects of these highly luminescent, bio-compatible ZnS:Mn nanocrystals in bio-imaging applications, cytotoxicity studies were conducted to identify the capping combination which would accomplish minimum toxic effects. ZnS:Mn nanocrystals biofunctionalized with chitosan, L-citrulline, glycine, L-artginine, L-serine and L-histidine showed least toxicity up to 10 nM concentrations in mouse fibroblast L929 cells, which further confirms their cytocompatibility. Also the ZnS:Mn nanocrystals biofunctionalized with l-arginine showed maximum uptake in in vitro studies carried out in human embryonic kidney cells, HEK-293T, which shows the significant role of this particular amino acid in fetoplacental nutrition. The present study highlights the suitability of aminoacid conjugated ZnS:Mn nanocrystals, as promising candidates for biomedical applications.

Synergistic removal of dyes by Myrothecium verrucaria immobilization on a chitosan–Fe membrane

A kind of novel, environmental friendly and efficient hybrid for the fungus and chitosan–Fe membrane has been fabricated by the alginate approach for efficient removal of aqueous dyes.

Size-dependent optical properties of bio-compatible ZnS:Mn nanocrystals and their application in the immobilisation of trypsin

Chitosan capped zinc sulphide nanocrystals doped with manganese (ZnS:Mn) have been synthesised by chemical capping co-precipitation method and structurally characterised by XRD, TEM and EDXS techniques. The dependence of optical properties on the size of these bio-compatible ZnS:Mn nanocrystals was investigated by UV/Vis and photoluminescence (PL) spectroscopic techniques in aqueous solvents. A variation in molar concentration of the precursor, sodium sulphide, from 0.125 to 0.01 mol L(-1) is accompanied by a decrease in particle size. The excitonic peak in the UV/Vis spectra is found to be blue shifted with a decrease in size of the nanocrystals due to confinement effects. In the present study, trypsin was immobilised onto ZnS:Mn nanocrystals using glutaraldehyde (GA) as cross-linker, which was confirmed by photoluminescence (PL) and Fourier transform infrared (FTIR) spectroscopic studies. Results indicate that the activity of trypsin, immobilised onto chitosan modified nanocrystals, has improved upon cross-linking, which suggests that the immobilised trypsin has become more stable and active. This work highlights the prospects of potential applications of immobilised trypsin in therapeutic and diagnostic fields.

A review on applicability of naturally available adsorbents for the removal of hazardous dyes from aqueous waste

The effluent water of many industries, such as textiles, leather, paper, printing, cosmetics, etc., contains large amount of hazardous dyes. There is huge number of treatment processes as well as adsorbent which are available for the processing of this effluent water-containing dye content. The applicability of naturally available low cast and eco-friendly adsorbents, for the removal of hazardous dyes from aqueous waste by adsorption treatment, has been reviewed. In this review paper, we have provided a compiled list of low-cost, easily available, safe to handle, and easy-to-dispose-off adsorbents. These adsorbents have been classified into five different categories on the basis of their state of availability: (1) waste materials from agriculture and industry, (2) fruit waste, (3) plant waste, (4) natural inorganic materials, and (5) bioadsorbents. Some of the treated adsorbents have shown good adsorption capacities for methylene blue, congo red, crystal violet, rhodamine B, basic red, etc., but this adsorption process is highly pH dependent, and the pH of the medium plays an important role in the treatment process. Thus, in this review paper, we have made some efforts to discuss the role of pH in the treatment of wastewater.

Conjugation of laccase from the white rot fungus Trametes versicolor to chitosan and its utilization for the elimination of triclosan

A commercial laccase from Trametes versicolor was conjugated with biopolymer chitosan using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) as the cross-linking agent. Laccase-chitosan conjugation strategies were tested using different molar ratios of glucosamine monomer/protein with different molar excess ratios of EDC relative to laccase. Immobilization techniques were developed to improve the stability against thermal and chemical denaturation, storage and reusability of this biocatalyst. The conjugation resulted in a solid biocatalyst with an apparent laccase activity of ±626 U/g, 12 and 60 folds higher in the conjugation efficiency of biocatalyst relative to the immobilized and free laccase activity respectively when compared with zero EDC/laccase ratio used in conjugation solution. The conjugated laccases formed successfully eliminated the emerging pollutant triclosan (TCS) from aqueous solutions, having a higher potential to transform TCS than free laccase. UPLC-QTOF results indicate the formation of TCS oligomers. Furthermore, they are the first evidence of direct dechlorination of TCS mediated by the oxidative action of laccases.

Applications of chitin- and chitosan-derivatives for the detoxification of water and wastewater--a short review

Chitin and chitosan-derivatives have gained wide attention as effective biosorbents due to low cost and high contents of amino and hydroxyl functional groups which show significant adsorption potential for the removal of various aquatic pollutants. In this review, an extensive list of chitin- and chitosan-derivatives from vast literature has been compiled and their adsorption capacities for various aquatic pollutants as available in the literature are presented. This paper will give an overview of the principal results obtained during the treatment of water and wastewater utilizing chitin and chitosan-derivatives for the removal of: (a) metal cations and metal anions; (b) radionuclides; (c) different classes of dyes; (d) phenol and substituted phenols; (e) different anions and other miscellaneous pollutants. The review provides a summary of recent information obtained using batch studies and deals with the various adsorption mechanisms involved. It is evident from the literature survey that chitin- and chitosan-derivatives have shown good potential for the removal of various aquatic pollutants. However, still there is a need to find out the practical utility of such developed adsorbents on commercial scale.

Hydrocolloid gel particles: formation, characterization, and application

Hydrocolloid gel particles of micron and sub-micron size are particularly attractive for use in many applications in the food, agricultural, pharmaceutical, and chemical industries, due to their biocompatibility, perception as "natural" materials, and soft-solid texture. Industrial applications for such particles include uses as texturizers in confectionery and cosmetic products, slow-release encapsulation agents for flavors, nutrients, and pharmaceutical products, and thickeners in soups and sauces. Properties such as particle size, hardness, shape, texture, and molecular release rates can be important for individual applications. In addition, product formats will determine specific needs for physical form (e.g. dry or wet) and compatibility with other components. The diverse range of potential applications for hydrocolloid gel particles provide a driver for understanding-led tailoring of raw material and process conditions. This review introduces some of the materials that are used to form hydrocolloid gel particles and the corresponding gel formation mechanisms. One issue of importance in the production of hydrocolloid gel particles is the control of particle properties, such as release profiles, strength, and detectability within products. An alternative technique to traditional methods of hydrocolloid gel particle production is evaluated and a model for control of particle size, and subsequently other particle properties, is proposed. Key properties of hydrocolloid gel particles are identified and characterization methods for evaluating these properties are described.