Preparation of hydrogels based on pectin with different esterification degrees and evaluation of their structure and adsorption properties

Tunning the hydrophobic performance and thermal stability of pectin film by acetic anhydride esterification

Pectin, a polysaccharide found in plant cell walls, is characterized by a high abundance of hydroxyl groups and carboxylic acid groups, which results in a strong affinity for water and limits its suitability as a film material. This study aimed to modulate the esterification degree of PEC films by adjusting the concentration of acetic anhydride, and assess the impact of acetic anhydride esterification modification on the properties of the resultant PEC films. The results demonstrated successful grafting of acetic anhydride onto the galacturonic acid ring in the PEC molecule through the esterification process. The hydrophobicity, thermal stability, barrier properties, and mechanical properties of the esterified PEC films were investigated. Among the various concentrations tested, the E-PEC-0.25 film exhibited the highest contact angle of 103.46° and tensile strength of 33.44 MPa, showcasing optimal performance. The E-PEC-0.1 film achieved the highest esterification degree of 0.94 and elongation at a break of 21.11 %. It also exhibited the transparency of 11.66 and the lowest water vapor transmission rate of 0.56 g·mm/(m2·h·kpa). Additionally, TGA and DSC tests revealed enhanced thermal stability of the esterification-prepared films. These findings highlight the potential of acetic anhydride tuning as a promising strategy for optimizing pectin film production.

Physicochemical properties of pectin-Fe(III) gained by HG-type hawthorn with different esterification degree

In this study, the complexation ability of HG-type hawthorn pectin with trivalent iron ions after de-esterification was investigated. The moderate esterification reaction could significantly increase the iron content in HG-type hawthorn pectin. Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) experiments proved that -OH and -COOH in the pectin acted as a bridge connecting Fe3+ leading to the formation of β-FeOOH structure, and the trivalent iron ions were successfully complexed into the HG-type hawthorn pectin. In addition, infrared and ultraviolet spectroscopic scans, particle size, and potentiometric measurements were carried out to demonstrate the complexation coordination mechanism of hawthorn pectin with Fe3+, and there were differences in the complexation effect of HG-type hawthorn pectin with different degrees of esterification. The gelling properties of HG-type hawthorn pectin were subsequently verified by in vitro gastrointestinal tract simulation experiments to aid the smooth passage of ferric ions through the gastric juices and reduce irritation. The success of the experiments demonstrated that HG-type hawthorn pectin is an excellent raw material for metal complexation, and the degree of esterification is one of the important factors affecting its complexation effect, which proves its potential application value as an iron supplement.

Adsorption performance and mechanism of pectin modified with β-cyclodextrin for Zn2+ and Cu2

Removing heavy metals from aqueous solutions has drawn more and more attentions these years because of their serious global health challenge to human society. To develop an adsorbent with green, stable and high-efficiency for adsorption of heavy metals, pectin β-cyclodextrin composite was successfully prepared and used for Zn2+ and Cu2+ adsorption for the first time. Various variables that influence the adsorption performance were explored, and the optimal adsorption conditions were determined. According to the pseudo-second-order kinetic model, the adsorption process of Zn2+ and Cu2+ by the adsorbent was mainly chemical adsorption. The adsorbent adsorption process was an exothermic and non-spontaneous process. According to the Langmuir isotherm model, the maximum adsorption capacity was 12.51 ± 0.33 and 24.98 ± 0.23 mg/g for Zn2+ and Cu2+, respectively. The FTIR, EDX and XPS results revealed that the main mechanisms of removing pollutants by adsorbent were ion exchange and coordination. In addition, electrostatic attraction and chelation were present in the adsorption process. After five adsorption desorption cycles, the pectin β-cyclodextrin composite adsorbent still exhibited adsorption and regeneration capabilities. This study provides a low-cost, effective and simple method for preparation of modified pectin, which has excellent application potential in the removal of heavy metal ions from wastewater.

Therapeutic efficacy of Strobilanthes urticifolia-infused pectin/polyacrylic acid hydrogel for targeted hepatorenal fibrosis mitigation: A multifaceted biomaterial approach

Pectin/polyacrylic acid (PPAA) hydrogel is a unique and versatile biomaterial with applications in drug delivery, wound healing, tissue engineering, and agriculture, owing to its tailored properties and multifunctional attributes. This study aims to harness the therapeutic potential of Strobilanthes urticifolia extract within a PPAA hydrogel matrix to attenuate liver and kidney fibrosis through targeted and sustained delivery of biologically active substances. PPAA hydrogel was prepared by free radical polymerization, followed by its porosity and swelling determination. The results depicted the porous nature of PPAA hydrogel and improved swelling properties at pH 7.4, confirming its drug delivery promise. The polyphenolic-enriched S. urticifolia extracts of leaf and flower were loaded onto PPAA hydrogel, and the loading efficiency was 87% (leaf) and 62.5% (flower). Moreover, slow-release studies showed controlled and prolonged release of polyphenols for 7 days. The polyphenolic-enriched hydrogel's microstructure was characterized using SEM, FTIR, and thermogravimetric analysis (TGA). SEM results revealed a highly porous structure of polyphenol enriched PPAA hydrogel, while FTIR analysis confirmed the presence of functional groups such as OH group of carboxylic acid, aliphatic CH2 stretching due to acrylic acid grafting with pectin, CO stretching due to acid linkage with pectin, CH of aromatic ring, and CH of carboxylate salt in PPAA hydrogel. TGA of PPAA hydrogel showed its stability up to 488°C. Additionally, the S. urticifolia extract loaded PPAA hydrogel displayed significant antibacterial properties and minimum inhibitory concentrations against both Gram-positive and Gram-negative bacteria. In vivo studies carried out on rats demonstrated that polyphenolic enriched PPAA hydrogel significantly attenuates liver and kidney fibrosis. Therefore, it is concluded from the present study that loading of polyphenolic enriched extract from leaves and flower of S. urticifolia enhanced the biomedical applications of PPAA hydrogel. RESEARCH HIGHLIGHTS: The PPAA hydrogel developed in this study exhibits a highly porous structure and improved swelling properties at physiological pH (7.4), making it an excellent candidate for drug delivery systems. S. urticifolia extracts, rich in polyphenols, were successfully incorporated into the PPAA hydrogel with high loading efficiencies of 87% for leaf and 62.5% for flower extracts. Loading of polyphenolic enriched extracts of S. urticifolia onto PPAA enhanced its biological activities such as antibacterial, hepatoprotective, and reno-protective activities as depicted by in vitro and in vivo studies.

Antimicrobial carbon dots/pectin-based hydrogel for promoting healing processes in multidrug-resistant bacteria-infected wounds

Multidrug-resistant (MDR) bacterial infections have become a significant threat to global healthcare systems. Here, we developed a highly efficient antimicrobial hydrogel using environmentally friendly garlic carbon dots, pectin, and acrylic acid. The hydrogel had a porous three-dimensional network structure, which endowed it with good mechanical properties and compression recovery performance. The hydrogel could adhere closely to skin tissues and had an equilibrium swelling ratio of 6.21, indicating its potential as a wound dressing. In particular, the bactericidal efficacy following 24-h contact against two MDR bacteria could exceed 99.99 %. When the hydrogel was applied to epidermal wounds infected with methicillin-resistant Staphylococcus aureus (MRSA) on mice, a remarkable healing rate of 93.29 % was observed after 10 days. This was better than the effectiveness of the traditionally used antibiotic kanamycin, which resulted in a healing rate of 70.36 %. In vitro cytotoxicity testing and hemolysis assay demonstrated a high biocompatibility. This was further proved by the in vivo assay where no toxic side effects were observed on the heart, liver, spleen, lung, or kidney of mice. This eco-friendly and easy-to-prepare food-inspired hydrogel provides an idea for the rational use of food and food by-products as a wound dressing to control MDR bacterial infections.

Comparison on emulsifying and emulgelling properties of low methoxyl pectin with varied degree of methoxylation from different de-esterification methods

Low methoxyl pectin (LMP) with different degree of methoxylation (DM, 40-50 %, 20-30 % and 5-10 %) were prepared from commercially available citrus pectin using high hydrostatic pressure assisted enzymatic (HHP-pectin) and traditional alkaline (A-pectin) de-esterification method. The results showed that both de-esterification methods and DM exhibited LMPs with varied physicochemical, structural, and functional properties. As the DM decreased, LMP showed a decrease in molecular weight (Mw), while an increase in negative charges and rhamnogalacturonan I (RG-I) ratio, accompanied with better emulsion stability, emulsion gel strength and water-holding properties. Relative to A-pectin, HHP-pectin had higher Mw and lower RG-I side chain ratio, contributing to its better thermal stability, apparent viscosity, and emulgelling properties. HHP-pectin with lower DM (5-10 %) showed superior thickening, emulsifying and emulgelling properties, while that with higher DM (40-45 %) had superior thermal stability, which provided alternative for de-esterification and targeted structural modification of pectin.

Methyl jasmonate regulation of pectin polysaccharides in Cosmos bipinnatus roots: A mechanistic insight into alleviating cadmium toxicity

Methyl jasmonate (MeJA), a crucial phytohormone, which plays an important role in resistance to Cadmium (Cd) stress. The cell wall (CW) of root system is the main location of Cd and plays a key role in resistance to Cd toxicity. However, the mechanism effect of MeJA on the CW composition and Cd accumulation remain unclear. In this study, the contribution of MeJA in regulating CW structure, pectin composition and Cd accumulation was investigated in Cosmos bipinnatus. Phenotypic results affirm MeJA's significant role in reducing Cd-induced toxicity in C. bipinnatus. Notably, MeJA exerts a dual impact, reducing Cd uptake in roots while increasing Cd accumulation in the CW, particularly bound to pectin. The molecular structure of pectin, mainly uronic acid (UA), correlates positively with Cd content, consistent in HC1 and cellulose, emphasizing UA as pivotal for Cd binding. Furthermore, MeJA modulates pectin methylesterase (PME) activity under Cd stress, influencing pectin's molecular structure and homogalacturonan (HG) content affecting Cd-binding capacity. Chelate-soluble pectin (CSP) within soluble pectins accumulates a substantial Cd proportion, with MeJA regulating both UA content and the minor component 3-deoxy-oct-2-ulosonic acid (Kdo) in CSP. The study delves into the intricate regulation of pectin monosaccharide composition under Cd stress, revealing insights into the CW's physical defense and Cd binding. In summary, this research provides novel insights into MeJA-specific mechanisms alleviating Cd toxicity in C. bipinnatus, shedding light on complex interactions between MeJA, and Cd accumulation in CW pectin polysaccharide.

Ambient plasma treatment of pectin in aqueous solution to produce a polymer used in packaging

Water resistance, mechanical behavior and coloration of pectin needs to be tuned for packing utilization. Plasma was used for the treatment of natural products, but there is no research on its effect on the biomass in the presence of ammonia. Though the reaction of pectin (PE) and ammonia was known to impart the ammonolysis and de-esterification, the plasma treatment on PE solution containing ammonia was explored to exemplify the amination and polymerization of the carbohydrate at the ambient condition. The plasma treatment increased the coloration of the solution due to the deprotonation of PE for the production of more sp2 carbon. The film from the amination of PE showed higher hydrophobicity and water stability than the bare PE. The plasma treatment alone decreased the Young's modulus (4.3 MPa versus 22 MPa), while the nitrogen addition enhanced the Young's modulus to 160 MPa and increased the tensile strength (28.7 MPa versus 25.8 MPa of PE). The hydrogen bonds from the amine group induced a glass-to-rubber transition at 77.9 °C by the increasing the crosslinking. This work provided a facile way of aminating and conjugating the biomass in solution to produce polymer with improved mechanical properties using plasma and ammonia incorporation.

Facile construction of lignin-based network composite hydrogel for efficient adsorption of methylene blue from wastewater

Adsorption method is an effective approach to treat wastewater containing methylene blue. Herein, a cost-effective and eco-friendly lignin-based network composite hydrogel adsorbent (PAA@SML) was constructed by using polyacrylic acid (PAA) to crosslink with sulfomethylated lignin (SML) via free radical polymerization for adsorption of methylene blue (MB) from wastewater. The constructed PAA@SML-0.2 exhibited remarkable adsorption performance towards removal of MB, with a maximum theoretical adsorption capacity of 777.1 mg·g-1. The improved efficiency can be attributed to the well-established network structure and abundant hydrophilic functional groups present in the adsorbent, promoting the interaction between methylene blue (MB) molecules and the adsorption sites of the adsorbent. The adsorption process of the adsorbent for MB followed the pseudo-second-order kinetic and the Langmuir isotherm models, which illustrated the adsorption process attributed to monolayer chemisorption. Mechanism investigation confirmed that the adsorption of MB by PAA@SML-0.2 primarily relied on hydrogen bonding and electrostatic interactions. Moreover, the recyclability test demonstrated excellent regeneration usability and stability of PAA@SML-0.2, and the adsorption capacity maintained above 74.0 % after five cycles. This constructed lignin-based network composite hydrogel is considered to have great potential in the treatment of organic dye in wastewater.

Physicochemical properties and Pb2+ adsorption capacity of freeze-dried hawthorn pectin fractions by gradient ethanol precipitation

Three fractions of FHP20, FHP40 and FHP60 were obtained from freeze-dried hawthorn pectin by gradient ethanol precipitation (20-60 %), and their physicochemical properties and adsorption performance on Pb²⁺ were investigated. It was found that the content of galacturonic acid (GalA) and esterification of FHP fractions gradually reduced with the increase of ethanol concentration. FHP60 had the lowest molecular weight (60.69 × 10³ Da), and the composition and proportion of monosaccharides were significantly different. The experimental results of Pb²⁺ adsorption showed that the adsorption process fitted well with the Langmuir monolayer adsorption and the pseudo-second-order models. Our findings suggested that pectin fractions with good homogeneity of molecular weight and chemical construction can be obtained by gradient ethanol precipitation, and hawthorn pectin could be developed as a potential adsorbent for Pb²⁺ removal.

Low-temperature plasma modification, structural characterization and anti-diabetic activity of an apricot pectic polysaccharide

To fully research the anti-diabetic activity of apricot polysaccharide, low temperature plasma (LTP) was used to modify apricot polysaccharide. The modified polysaccharide was isolated and purified using column chromatography. It was found that LTP modification can significantly improve the α-glucosidase glucosidase inhibition rate of apricot polysaccharides. The isolated fraction FAPP-2D with HG domain showed excellent anti-diabetic activity in insulin resistance model in L6 cell. We found that FAPP-2D increased the ADP/ATP ratio and inhibited PKA phosphorylation, activating the LKB1-AMPK pathway. Moreover, FAPP-2D activated AMPK-PGC1α pathway, which could stimulated mitochondrial production and regulate energy metabolism, promoting GLUT4 protein transport to achieve an anti-diabetic effect. The Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy data showed that the LTP modification could increase the CH bond content while decreasing the C-O-C/C-O bond content, indicating that LTP destroyed the C-O-C/C-O bond, which enhanced the anti-diabetes activity of the modified apricot pectin polysaccharide. Our findings could pave the way for the molecular exploitation of apricot polysaccharides and the application of low-temperature plasma.

Zwitterionic ammonium-sulfonato grafted cellulose for efficient thallium removal and adsorption mechanism study

Thallium (Tl) has posed serious impacts on human being concerning increasingly serious pollution in aqueous environments. However, little information on removal method than conventional heavy metals have been available. In the present work, zwitterionic N-(3-sulfonato-1-propyl)-N,N-dimethylammonium grafted cellulose fibre (DMAE-PS) has been fabricated. The chemical component, thermal stability and surface properties of as-prepared materials are identified by FT-IR, elemental analysis, TGA, XRD, BET and SEM. DMAE-PS is shown to be very efficient for removing Tl(I) from water samples with a loading capacity of 274.7 mg (Tl(I))·g^-1 (DMAE-PS)_, representing one of the best performances among bio-mass derived materials. The adsorption is consistent with the Freundlich model following a pseudo-second order (K₂ = 4.36 × 10^-4 g·mg^-1·min^-1, R² = 0.999) and two-step intra-particle diffusion kinetics. The selectivity towards Tl(I) is also remarkably, 1-2 orders (distribution ratio K_Tl/M = 14.85-289.29) of magnitude larger than competing metals (Zn²⁺, Cr³⁺, Mn²⁺, Cu²⁺ and Cd²⁺). The SEM, XPS and UV-visible spectrum collectively reveal that -SO₃^--Tl(I) ionic interaction is probably the main driving force for specific adsorption, which shows a high stability against pH variation. The fabricated DMAE-PS is a sustainable bio-adsorbent with synthetic availability, high removing capacity and strong selectivity, therefore, potentially feasible in treatment of Tl(I) polluted environmental samples.

Green and Superior Adsorbents Derived from Natural Plant Gums for Removal of Contaminants: A Review

The ubiquitous presence of contaminants in water poses a major threat to the safety of ecosystems and human health, and so more materials or technologies are urgently needed to eliminate pollutants. Polymer materials have shown significant advantages over most other adsorption materials in the decontamination of wastewater by virtue of their relatively high adsorption capacity and fast adsorption rate. In recent years, "green development" has become the focus of global attention, and the environmental friendliness of materials themselves has been concerned. Therefore, natural polymers-derived materials are favored in the purification of wastewater due to their unique advantages of being renewable, low cost and environmentally friendly. Among them, natural plant gums show great potential in the synthesis of environmentally friendly polymer adsorption materials due to their rich sources, diverse structures and properties, as well as their renewable, non-toxic and biocompatible advantages. Natural plant gums can be easily modified by facile derivatization or a graft polymerization reaction to enhance the inherent properties or introduce new functions, thus obtaining new adsorption materials for the efficient purification of wastewater. This paper summarized the research progress on the fabrication of various gums-based adsorbents and their application in the decontamination of different types of pollutants. The general synthesis mechanism of gums-based adsorbents, and the adsorption mechanism of the adsorbent for different types of pollutants were also discussed. This paper was aimed at providing a reference for the design and development of more cost-effective and environmentally friendly water purification materials.

Construction of double-network hydrogel based on low methoxy pectin/polyvinyl alcohol and its structure and properties

In this study, an interpenetrating double-network hydrogel (LMP/AA/PVAH) was prepared based on low methoxy pectin (LMP), acrylic acid (AA) and polyvinyl alcohol (PVA). The first rigid network of chemical crosslinking was constructed via free radical polymerization of LMP and AA, and the second of ductile physical crosslinking network was constructed via cyclic freeze-thaw of PVA. The first cycle hardness and elasticity of the LMP/AA/PVAH significantly increased from 13.08 N and 0 to 24.28 N and 0.79, respectively, when the second network structure was constructed in the hydrogel by PVA. Besides, the PVA network might enhance the ductile and limit the swelling of hydrogel. In addition, the adsorption properties of LMP/AA/PVAH were evaluated by adsorption of methylene blue (MB). The adsorption behavior of MB by LMP/AA/PVAH conformed to the pseudo-second-order kinetic model. Besides, after 4 cycles of adsorption, there was no significant difference in adsorption capacity of LMP/AA/PVAH. The results showed that LMP/AA/PVAH had good reusability.