Anthocyanins concentration by adsorption onto chitosan and alginate beads: Isotherms, kinetics and thermodynamics parameters

NADES-based extraction optimization and enrichment of Cyanidin-3-O-galactoside from Rhododendron arboreum Sm.: Kinetics and thermodynamics insights

Cyanidin-3-O-galactoside (Cy3-gal) is the most widespread anthocyanin that has been found to be applicable to nutraceutical and pharmaceutical ingredients. Nevertheless, the process of separation and purification, susceptibilities to heat, and pH inactivation present some limitations. In the present study, natural deep eutectic solvents (NADES) with an ultrasonic-assisted extraction method were briefly studied, and the recovery of Cy3-gal from Rhododendron arboreum was highlighted. The NADES, consisting of choline chloride and oxalic acid (1:1), was screened out as an extractant, and single-factor experiments combined with a two-site kinetic model were employed to describe the extraction process. Further, the work investigated ultrasound-assisted adsorption/desorption to efficiently purify Cy3-gal using macroporous resins. The optimal extraction conditions to attain maximum Cy3-gal yield was 30% water in a 50:1 (mL/g) solvent-to-sample ratio, 11.25 W/cm3 acoustic density, and 50% duty cycle for 16 min of extraction time. Under these conditions, the results revealed 23.07 ± 0.14 mg/g of Cy3-gal, two-fold higher than the traditional solvents. Furthermore, of the different resins used, Amberlite XAD-7HP showed significantly (p < 0.05) higher adsorption/desorption capacities (12.82 ± 0.18 mg/g and 10.97 ± 0.173 mg/g) and recovery (48.41 ± 0.76%) percent over other adsorbents. Experiments on the degrading behavior (40-80 °C) of the recovered Cy3-gal were performed over time, and the first-order kinetic model better explained the obtained data. In conclusion, the study asserts the use of ultrasonication with NADES and XAD-7HP resin for the improved purification of Cy3-gal from the crude extract.

Preparation and characterization of cellulose nanocrystals with high stability from okara by green solvent pretreatment assisted TEMPO oxidation

Because the traditional preparation methods of cellulose nanocrystals (CNCs) involve chemical pollution issues, in this study, two typical green solvents, alkali/urea solvent (AUS) and deep-eutectic solvent (DES), were used to dissolve insoluble soybean fibers (ISF) extracted from okara and prepare regenerated CNCs (AUS/CNC and DES/CNC), which were further modified by TEMPO oxidation (AUS/T-CNC and DES/T-CNC). The recoveries of AUS and DES were 82.58 % and 84.00 %, respectively. Chemical composition analysis showed high cellulose purity (>95 %) of the regenerated CNCs. FTIR, XRD and 13C NMR analysis indicated the cellulose structure and polymorph of CNCs. Thermal analysis revealed that the maximum degradation peak of regenerated CNC shifted to a lower temperature. AFM revealed that CNCs exhibited rod-like fiber structures, while AUS-pretreated CNCs exhibited some special spherical fibers. TEMPO oxidation showed an enhancement effect on the characteristics of AUS/T-CNC and DES/T-CNC; DES/T-CNC exhibited higher stability and apparent viscosity than AUS/T-CNC. The DES/T-CNC-based cryogel displayed a higher adsorption capacity for anthocyanin (0.40 g/g) and curcumin (1.09 g/g) with good controlled release capacity. These results indicated that green solvent pretreatment-assisted TEMPO oxidation is a new environmentally friendly and low-cost method for the preparation of CNCs and shows excellent potential in the field of drug loading and controlled release.

Magnetic Hydrogel Beads as a Reusable Adsorbent for Highly Efficient and Rapid Removal of Aluminum: Characterization, Response Surface Methodology Optimization, and Evaluation of Isotherms, Kinetics, and Thermodynamic Studies

Biopolymers such as alginate and gelatin have attracted much attention because of their exceptional adsorption properties and biocompatibility. The magnetic hydrogel beads produced and used in this study had a core structure composed of magnetite nanoparticles and gelatin and a shell structure composed of alginate. The combination of the metal-ion binding ability of alginate and the mechanical strength of gelatin in magnetic hydrogel beads presents a new approach for the removal of metal from water sources. The beads were designed for aluminum removal and fully characterized using various methods, including Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy-energy-dispersive X-ray spectroscopy, vibrating sample magnetometry, microcomputed tomography, and dynamic mechanical analysis. Statistical experimental designs were employed to optimize the parameters of the adsorption and recovery processes. Plackett-Burman Design, Box-Behnken Design, and Central Composite Design were used for identifying the significant factors and optimizing the parameters of the adsorption and recovery processes, respectively. The optimum parameters determined for adsorption are as follows: pH: 4, contact time: 30 min, adsorbent amount: 600 mg; recovery time: reagent 1 M HNO3; and contact time: 40 min. The adsorption process was described by using the Langmuir isotherm model. It reveals a homogeneous bead surface and monolayer adsorption with an adsorption capacity of 5.25 mg g-1. Limit of detection and limit of quantification values were calculated as 4.3 and 14 μg L-1, respectively. The adsorption process was described by a pseudo-second-order kinetic model, which assumes that chemisorption is the rate-controlling mechanism. Thermodynamic studies indicate that adsorption is spontaneous and endothermic. The adsorbent was reusable for 10 successive adsorption-desorption cycles with a quantitative adsorption of 98.2% ± 0.3% and a recovery of 99.4% ± 2.6%. The minimum adsorbent dose was determined as 30 g L-1 to achieve quantitative adsorption of aluminum. The effects of the inorganic ions were also investigated. The proposed method was applied to tap water and carboy water samples, and the results indicate that magnetic hydrogel beads can be an effective and reusable bioadsorbent for the detection and removal of aluminum in water samples. The recovery values obtained by using the developed method were quantitative and consistent with the results obtained from the inductively coupled plasma optical emission spectrometer.

Computational design of a chitosan derivative for improving the color stability of anthocyanins: Theoretical calculation and experimental verification

The objective of this study was to design a chitosan (CS) derivative with good protective effect on the color stability of anthocyanins (ACNs) under accelerated storage. The binding affinities and interactions of 12 organic acids with cyanidin-3-O-glucoside (C3G) were evaluated using quantum mechanics method. Sinapic acid (SinA) showing the strongest interaction with C3G was selected for the synthesis of SinA-grafted-CS (SinA-g-CS), which was further characterized by FTIR and 1H NMR. Under accelerated storage conditions (40 °C), SinA-g-CS significantly improved the color stability of black rice anthocyanins (BRA) in the presence of l-ascorbic acid (pH 3.0), and showed a better protective effect than that of CS. Moreover, molecular dynamics simulation analysis showed SinA-g-CS formed more hydrogen bonds with C3G than CS. Our study demonstrated that SinA-g-CS designed by computational methods can effectively protect ACNs from degradation, and has the potential to be used in ACN-rich beverages as a replacement for CS.

Chitosan as a Tool for Sustainable Development: A Mini Review

New developments require innovative ecofriendly materials defined by their biocompatibility, biodegradability, and versatility. For that reason, the scientific society is focused on biopolymers such as chitosan, which is the second most abundant in the world after cellulose. These new materials should show good properties in terms of sustainability, circularity, and energy consumption during industrial applications. The idea is to replace traditional raw materials with new ecofriendly materials which contribute to keeping a high production rate but also reducing its environmental impact and the costs. The chitosan shows interesting and unique properties, thus it can be used for different purposes which contributes to the design and development of sustainable novel materials. This helps in promoting sustainability through the use of chitosan and diverse materials based on it. For example, it is a good sustainable alternative for food packaging or it can be used for sustainable agriculture. The chitosan can also reduce the pollution of other industrial processes such as paper production. This mini review collects some of the most important advances for the sustainable use of chitosan for promoting circular economy. Hence, the present review focuses on different aspects of chitosan from its synthesis to multiple applications.

Green metallochromic cellulose dipstick for Fe(III) using chitosan nanoparticles and cyanidin-based natural anthocyanins red-cabbage extract

Environmentally-friendly, cyanidin(Cy)-based anthocyanin isolated from red-cabbage served as a spectroscopic probe imprinted onto chitosan nanoparticles (CsNPs), which were in turn integrated onto cellulose paper strip (CPS) as a host matrix to develop a metallochromic solid state sensor for real-time selective determination of ferric ions in an aqueous medium. The ferric transition metal ions in aqueous environments were detected using a novel, simple, portable, fast responsive, low-cost, real-time, environmentally safe, reversible and colorimetric sensor based on chitosan nanoparticles as a hosting biopolymer and cyanidin phenol chromophore as a biomolecular probe. In order to use the cyanidin biomolecule as a pH indicator and chelating agent, it was purified from red-cabbage and added into the CsNPs biosensor film. The colorimetric shift increased in direct proportion to the ferric ion concentration. As a result, the current research that was both qualitative and quantitative was carried out. While the Cy-CsNPs-CPS sensor showed high selectivity for ferric ions, no color change was detected for other metal cations. It was discovered that the detection process occurred as a result of a coordination complex formed between the active sites of phenolic cyanidin and Fe(III) ions.

Calcium peroxide aids tyramine-alginate gel to crosslink with tyrosinase for efficient cartilage repair

The innate cartilage extracellular matrix is avascular and plays a vital role in innate chondrocytes. Recapping the crucial components of the extracellular matrix in engineered organs via polymeric gels and bioinspired approaches is promising for improving the regenerative aptitude of encapsulated cartilage/chondrocytes. Conventional gel formation techniques for polymeric materials rely on employing oxidative crosslinking, which is constrained in this avascular environment. Further, poor mechanical properties limit the practical applications of polymeric gels and reduce their therapeutic efficacy. Herein, the purpose of this study was to develop a bioadhesive gel possessing dual crosslinking for engineering cartilage. Tyramine (TYR) was first chemically conjugated to the alginate (ALG) backbone to form an ALG-TYR precursor, followed by the addition of calcium peroxide (CaO₂); calcium ions of CaO₂ physically crosslink with ALG, and oxygen atoms of CaO₂ chemically crosslink TYR with tyrosinase, thus enabling dual/enhanced crosslinking and possessing injectability. The ALG-TYR/tyrosinase/CaO₂ gel system was chemically, mechanically, cellularly, and microscopically characterized. The gel system developed herein was biocompatible and showed augmented mechanical strength. The results showed, for the first time, that CaO₂ supplementation preserved cell viability and enhanced the crosslinking ability, bioadhesion, mechanical strength, chondrogenesis, and stability for cartilage regeneration.

Core-shell alginate beads as green reactor to synthesize grafted composite beads to efficiently boost single/co-adsorption of dyes and Pb(II)

A series of sodium alginate (SA) grafted polymer composite beads were synthesized by a solution free-radical graft polymerization reaction performed in a surface crosslinked alginate bead reactor. The outer surface of the precursor droplet containing reactants including SA, acrylamide (AM), N,N'-methylene-bis-acrylamide (MBA), ammonium persulfate (APS), sepiolite (SP) and gelatin (GE) was instantly crosslinked with Ca²⁺ ions to form a capsule-like bead when it was dropped into aqueous solution of calcium chloride, and simultaneously the reactants inside the capsule-like "bead reactor" were polymerized in-situ to form new composite beads with crosslinked network structure, abundant functional groups, single or co-adsorption ability and easily separable advantages. The optimal composite bead shows high adsorption capacity of 390.78, 1425.65 and 533.91 mg/g towards Methylene Blue (MB), Basic Fuchsin (BF) and Pb(II), respectively. After adsorption by the composite bead, 99.71% of MB, 99.99% of BF and 99.97% of Pb(II) were removed from original dye or Pb(II) solutions. Moreover, above 99.22% of BF and 95.33% of Pb(II) was co-removed from their binary mixture (BF concentration, 100 mg/L; Pb(II) concentration, 50 mg/L). This paper provides a simple green way to synthesize efficient and recyclable biopolymer-based adsorbents capable of purifying dyes and heavy metal ions in water.

Development of a biosponge based on Luffa cylindrica and crosslinked chitosan for Allura red AC adsorption

A new bioadsorbent from Luffa cylindrica and cross-linked chitosan was proposed in the present study. Luffa was used as a natural support medium for chitosan crosslinked with glutaraldehyde (LCsG) and epichlorohydrin (LCsE). Biosponges were applied to remove Allura red from aqueous solutions. LCsG and LCsE were produced using different concentrations of chitosan (1%, 3% and 5% (m v^-1)) and crosslinking agents (0.5%, 1.0% and 1.5% (v v^-1)). Based on the FT-IR spectra, functional groups characteristic of chitosan crosslinked with glutaraldehyde and epichlorohydrin confirmed the crosslinking. In addition, the biosorbent revealed highly efficient functional groups and morphology with irregularities favorable for adsorption. It was found that the increase in the percentage of glutaraldehyde and epichlorohydrin increased the sample's swelling degree, and the degree of cross-linking was greater than 80% for all LCsG. The results regarding the degree of swelling and degree of crosslinking corroborated with the evaluation of the biosponge's adsorptive potential. The Sips model predicted the equilibrium isotherms, with a maximum adsorption capacity of 89.05 mg g^-1 for LCsG and 60.91 mg g^-1 for LCsE. The new procedure was successful. Luffa was excellent support for chitosan, resulting in an attractive, low-cost bioadsorbent, preventing renewable sources.