Influence of pH, pectin and Ca concentration on gelation properties of low-methoxyl pectin extracted from Cyclea barbata Miers

Hydrogels formed with shellac and zein: pH-responsiveness, rheology, and gelation mechanism

Hydrogels responsive to pH have unique applications. Shellac is a pH-responsive molecule soluble above pH 7 but insoluble in acidic conditions. However, shellac-based hydrogels responding to pH have not been reported. In this study, 0.50-4.0 % w/v zein was incorporated in 4 % w/v shellac solutions to form hydrogels during pH-shifting from 12.0 to 6.2-6.4 enabled by gradual and uniform acidification due to hydrolysis of glucono-δ-lactone. These hydrogels maintained their volume when immersed in phosphate buffer at pH 7.0 but shrank at pH 6.0 and 6.5 and swelled or dissolved at pH 7.5 and 8.0. Increasing zein concentration led to greater changes in the hydrogel volume responding to pH changes. An increase in zein concentration facilitated gelation but excess zein weakened the network according to dynamic rheological tests and texture profile analyses. Molecularly, the alkaline pH led to multiple shellac molecules covalently bonded with zein according to gel electrophoresis. Analyses of hydrogel volume changes responding to NaCl, sodium dodecyl sulfate, and urea revealed the primary role of hydrophobic interaction and the secondary role of hydrogel bonds in forming hydrogels. These hydrogels with pH-responsiveness around pH 7.0 may find novel food and non-food applications.

The influence of pH and calcium ions on the gelation of low methoxy pectin from potato

In this study, pectin was extracted from potato with the hydrolysis of cellulose, as well as its acid-induced and Ca2+-induced gelation behavior was investigated, too. The gelation process of unhydrolyzed pectin might be used as a model for studying the gelation behavior and characteristic of pectin within the cell wall. The results showed that potato pectin solution (3%) could form a gel state at a minimal concentration of 0.25% CaCl2 or a maximum pH value of 4.60. Furthermore, acetic acid-induced and CaCl2-induced gels were both concentration-independent. Specifically, the gel strength increased with decreasing levels of pH and increasing concentrations of CaCl2. Moreover, CaCl2-induced gels exhibited superior gelation characteristics with a higher storage modulus (7.2 Pa), larger fractal dimension (2.58), smaller porosity (12.11%), shorter relaxation time T2, and a denser gel network structure. This disparity stemmed from different mechanism: acetic acid provided H+ to combine with free carboxyl groups on the pectin chains, reducing the repulsion between pectin molecules, narrowing chain spacing, and fostering hydrogen bond formation; whereas CaCl2 promoted gelation primarily via the information of the "egg box" structure involving non-covalent bonded calcium bridges. This research could provide a theoretical basis for acid-induced and Ca2+-induced gelation of unhydrolyzed pectin extracted from the cell wall.

Valorization of apple pomace: Structural and rheological characterization of low-Methoxyl Pectins extracted with green agents of citric acid/sodium citrate

Traditional production of low-methoxyl pectin (LMP) is labor-intensive and environmentally harmful. This study explores using citric acid/sodium citrate as a green extractant for valorizing LMPs from apple pomace. Two types of pectin, AP-5 and AP-8, were extracted at pH 5.0 and 8.0, resulting in LMPs with methoxylation degrees of 42.33 % and 34.68 %, respectively. Monosaccharide composition and SEC-MALLS analysis revealed that APs are rich in arabinose side chains and contain heterogeneous fractions, while FTIR spectra confirmed their low-methoxyl structure. Compared to the commercial low-methoxyl pectin, APs exhibited higher critical pH but lower critical Ca2+ levels for acid- and Ca2+-induced gels, where hydrogen bonding and electrostatic interactions were the dominant intermolecular forces. Notably, AP-8 and AP-5 demonstrated superior stability in acid- and Ca2+-induced gels. Additionally, combined acidic and Ca2+ conditions enhanced the gel strength and stability of APs. These findings highlight the potential of APs in developing novel, particularly low-calorie, food products.

Biogenic synthesized CuO nanoparticles and 5-fluorouracil loaded anticancer gel for HeLa cervical cancer cells

Cervical cancer remains a significant health challenge in developing countries are high due to low HPV vaccination rates, delayed diagnosis, and restricted healthcare access. Metal nanomaterials, such as copper oxide (CuO) nanoparticles (NPs), have shown significant promise in cancer therapy due to their ability to induce apoptosis. 5-Fluorouracil (5-Fu) enhances the cytotoxic effect against cervical cancer, working synergistically with CuO NPs to maximize the therapeutic impact while potentially reducing the 5-Fu's systemic side effects. This study explores the synergistic therapeutic potential of green-synthesized CuO NPs combined with 5-Fu in a gel formulation for targeted anticancer activity against HeLa cervical cancer cells. CuO NPs were synthesized using Trichosanthes dioica dried seeds extract and incorporated into a pectin-xanthan gum-based gel. The green-synthesized CuO NPs exhibited a zeta potential of -23.7 mV, a particle size of approximately 26 nm, and spherical morphology. Characterization studies, including FTIR, viscosity, spreadability, pH, and stability assessments, confirmed the gel's suitability for vaginal delivery. In-vitro drug release showed xanthan gum extended the release up to 8 h. The MTT assay revealed PXFCu6 gel's IC50 at 11.82 ± 0.22 μg/mL, significantly more cytotoxic to HeLa cells, being 3.62 times potent than CuO NPs (IC50: 42.8 ± 0.24 μg/mL) and 1.63 times potent than 5-Fu alone (IC50: 19.3 ± 0.49 μg/mL). The antibacterial assay showed no inhibition for the plain gel, but T. dioica-mediated CuO NPs exhibited inhibition of 22.35 ± 4.9 mm. PXFCu6 gel had the more potent inhibition at 52.05 ± 1.37 mm against Escherichia coli growth. The PXFCu6 gel showed better stability at 4 °C, maintaining viscosity, pH, and drug release, unlike 25 °C where a mild degradation occurred. This research highlights the potential of the CuO NPs-5-Fu gel as a novel, effective therapeutic strategy for cervical cancer treatment.

Exploring Noncentrifugal Sugar as a Partial Replacement for White Sugar in Low Methoxyl Pectin Confectionery Gels: Impacts on Physical and Rheological Properties

Noncentrifugal sugar (NCS) is an unrefined, dark brown sugar containing minerals and plant secondary metabolites, unlike refined white sugar (WS). This study explored using NCS in confectionary jellies as an alternative sugar. We used different concentrations of NCS and WS to prepare low methoxyl pectin (LMP) confectionery gels characterized by their physical and rheological properties along with time-domain nuclear magnetic resonance (TD-NMR) relaxometry. The strongest LMP gel, with a hardness of 0.94 N, was achieved by substituting 25% of WS with NCS at a low CaCl2 concentration (0.075 M). Gels with up to 50% WS replaced by NCS showed comparable hardness to standard LMP gels made solely with WS at a 0.15 M CaCl2 concentration, attributed to NCS's unique constituents. The NCS-WS gel exhibited the shortest T2 values (139.8 ms) and self-diffusion coefficient values (4.99 × 10-10 m2/s), indicating a denser, more cross-linked structure that restricted water mobility. These findings suggest NCS's complex role in affecting LMP gels' chemical and physical properties, highlighting its potential as a partial WS replacement in LMP gelation-based products, with an additional source of minerals and antioxidants.

Sequential extraction of hawthorn pectin: An attempt to reveal their original mode of being in plants and functional properties

Hawthorn is rich in pectin, which is much higher than most cultivated fruits, but conventional extraction methods do not meet the requirements of low energy consumption and green production. Pectin in hawthorn is divided into soluble and insoluble parts, and with the ripening of hawthorn, the original pectin is converted into soluble pectin and pectic acid under the action of enzymes. Therefore, based on the characteristics of hawthorn pectin, this study sequentially extracted hawthorn pectin using water-soluble pectin (WSP) and hot acid-soluble pectin (HAP) method, verifying the feasibility of extracting hawthorn pectin with pure water at room temperature, and systematically analyzing and comparing the physicochemical properties and functional characteristics of the two methods. The combination of texture analysis and gel rheology revealed that WSP formed a more uniform and dense network structure during the gelation process. Additionally, microscopic observations and emulsification index results indicated that the emulsion prepared with WSP (WSE) had a smaller particle size and better stability. This indicates that hawthorn pectin is suitable for extraction with pure water at room temperature, which can maintain its good physical properties while reducing energy consumption, providing a new approach for the large-scale extraction of pectin in the food industry.

Pectin-Chitosan Hydrogel Beads for Delivery of Functional Food Ingredients

A common challenge in hydrogel-based delivery systems is the premature release of low molecular weight encapsulates through diffusion or swelling and reduced cell viability caused by the low pH in gastric conditions. A second biopolymer, such as chitosan, can be incorporated to overcome this. Chitosan is usually associated with colonic drug delivery systems. We intended to formulate chitosan-coated pectin beads for use in delaying premature release of the encapsulate under gastric conditions but allowing release through disintegration under intestinal conditions. The latter is of utmost importance in delivering most functional food ingredients. Therefore, this study investigated the impact of formulation and process conditions on the size, sphericity, and dissolution behavior of chitosan-coated hydrogel beads prepared by interfacial coacervation. The size and sphericity of the beads depend on the formulation and range from approximately 3 to 5 mm and 0.82 to 0.95, respectively. Process conditions during electro-dripping may be modulated to tailor bead size. Depending on the voltage, bead size ranged from 1.5 to 4 mm. Confocal laser scanning microscopy and scanning electron microscopy confirmed chitosan shell formation around the pectin bead. Chitosan-coated beads maintained their size and shape in simulated gastric fluid but experienced structural damage in simulated intestinal fluid. Therefore, they represent a novel delivery system for functional food ingredients.

Natural herb wormwood-based microneedle array for wound healing

Artemisia argyi, commonly known as wormwood, is a traditional Chinese herbal food and medicine celebrated for its notable antibacterial and anti-inflammatory properties. This study explores a novel delivery method for wormwood, aiming for more convenient and versatile applications. Specifically, we present the first investigation into combining wormwood with microstructures to create a microneedle (MN) patch for wound healing. The wormwood microneedle (WMN) patch is formulated with milled wormwood sap, calcium carbonate, and sodium hyaluronate. The addition of 0.3% (w/v) sodium hyaluronate enhances the mechanical strength of the WMN patch. Pectin, derived from wormwood, is combined with calcium carbonate to create a gelatinous and solidified substance. The WMN patch exhibits a well-defined shape and sufficient mechanical strength to penetrate the epidermis, as confirmed by our results. In vitro experiments demonstrate the biocompatibility of the WMN patch with fibroblasts and highlight its antibacterial and anti-inflammatory properties. Furthermore, the patch facilitates collagen deposition at the wound site. In an excisional rat model, the WMN patch significantly accelerates the wound closure rate compared to the control group. Our findings suggest that the WMN patch has the potential to serve as a natural treatment for wound healing. Additionally, this approach can be extended to other biologically active substances with similar physiochemical characteristics in future applications.

Tailoring microstructure and mechanical properties of pectin cryogels by modulate intensity of ionic interconnection

Porous morphology and mechanical properties determine the applications of cryogels. To understand the influence of the ionic network on the microstructure and mechanical properties of pectin cryogels, we prepared low-methoxyl pectin (LMP) cryogels with different Ca2+ concentrations (measured as R-value, ranging from 0 to 2) through freeze-drying (FD). Results showed that the R-values appeared to be crucial parameters that impact the pore morphology and mechanical characteristics of cryogels. It is achieved by altering the network stability and water state properties of the cryogel precursor. Cryogel precursors with a saturated R-value (R = 1) produced a low pore diameter (0.12 mm) microstructure, obtaining the highest crispness (15.00 ± 1.85) and hardness (maximum positive force and area measuring 2.36 ± 0.31 N and 12.30 ± 1.57 N·s respectively). Hardness showed a negative correlation with Ca2+ concentration when R ≤ 1 (-0.89), and a similar correlation with the porosity of the gel network when R ≥ 1 (-0.80). Given the impacts of crosslinking on the pore structure, it is confirmed that the pore diameter can be designed between 56.24 and 153.58 μm by controlling R-value in the range of 0-2.

Insights into the Acid-Induced Gelation of Original Pectin from Potato Cell Walls by Gluconic Acid-δ-Lactone

The acid-induced gelation of pectin in potato cell walls has been gradually recognized to be related to the improvement in the cell wall integrity after heat processing. The aim of this study was to characterize the acid-induced gelation of original pectin from a potato cell wall (OPP). Rheological analyses showed a typical solution-sol-gel transition process of OPP with different additions of gluconic acid-δ-lactone (GDL). The gelation time (Gt) of OPP was significantly shortened from 7424 s to 2286 s. The complex viscosity (η*) of OPP gradually increased after 4000 s when the pH was lower than 3.13 and increased from 0.15 to a range of 0.20~6.3 Pa·s at 9000 s. The increase in shear rate caused a decrease in η, indicating that OPP belongs to a typical non-Newtonian fluid. Furthermore, a decrease in ζ-potential (from -21.5 mV to -11.3 mV) and an increase in particle size distribution (from a nano to micro scale) was observed in OPP after gelation, as well as a more complex (fractal dimension increased from 1.78 to 1.86) and compact (cores observed by cryo-SEM became smaller and denser) structure. The crystallinity of OPP also increased from 8.61% to 26.44%~38.11% with the addition of GDL. The above results call for an investigation of the role of acid-induced OPP gelation on potato cell walls after heat processing.

Laccase-Induced Gelation of Sugar Beet Pectin-Curcumin Nanocomplexes Enhanced by Genipin Crosslinking

Research on the use of polysaccharides as hydrophobic bioactive carriers instead of proteins is still scarce. Sugar beet pectin (SBP) contains a small amount of protein and is a potential carrier for loading curcumin. In this work, SBP encapsulation, genipin crosslinking, and laccase-induced gelation were used to develop novel jelly food and improve the stability of curcumin without the incorporation of oil. By mixing the SBP solution (40 mg/mL) with curcumin powder (25 mg/mL SBP solution), an SBP-curcumin complex (SBP-Cur) was fabricated with a loading amount of 32 mg/g SBP, and the solubility of curcumin improved 116,000-fold. Fluorescence spectroscopy revealed that hydrophobic interactions drove the complexation of curcumin and SBP. Crosslinked by genipin (10 mM), SBP-Cur showed a dark blue color, and the gel strength of laccase-catalyzed gels was enhanced. Heating and UV radiation tests suggested that the genipin crosslinking and gelation strategies substantially improved the stability of curcumin. Because of the unique UV-blocking capacity of blue pigment, crosslinked samples retained 20% more curcumin than control samples. With the enhanced stability of curcumin, the crosslinked SBP-curcumin complexes could be a functional food ingredient used in functional drinks, baked food, and jelly food.

A Review of Pectin-Based Material for Applications in Water Treatment

Climate change and water are inseparably connected. Extreme weather events cause water to become more scarce, polluted, and erratic than ever. Therefore, we urgently need to develop solutions to reduce water contamination. This review intends to demonstrate that pectin-based materials are an excellent route to detect and mitigate pollutants from water, with several benefits. Pectin is a biodegradable polymer, extractable from vegetables, and contains several hydroxyl and carboxyl groups that can easily interact with the contaminant ions. In addition, pectin-based materials can be prepared in different forms (films, hydrogels, or beads) and cross-linked with several agents to change their molecular structure. Consequently, the pectin-based adsorbents can be tuned to remove diverse pollutants. Here, we will summarize the existing water remediation technologies highlighting adsorption as the ideal method. Then, the focus will be on the chemical structure of pectin and, from a historical perspective, on its structure after applying different cross-linking methods. Finally, we will review the application of pectin as an adsorbent of water pollutants considering the pectin of low degree methoxylation.

Synthesis and Characteristics of a pH-Sensitive Sol-Gel Transition Colloid for Coal Fire Extinguishing

Coal fires, most of which are triggered by the spontaneous combustion of coal, cause a huge waste of resources and release poisonous and harmful substances into the environment, seriously threatening the safety of industrial production. Gel flame retardant plays a core role in coal fire prevention and extinguishing. Most gel flame retardants used in coal fires possess good sealing and oxygen isolation properties, but it is difficult for them to flow deep into fire areas due to their low fluidity. Some fire extinguishing agents with good fluidity lack leak-blocking performance. In order to simultaneously improve the fluidity, leakage sealing, and oxygen isolation effects of coal fire extinguishing colloids, a novel, pH-sensitive, sol-gel transition colloid was prepared using low methoxyl pectin (LMP), calcium bentonite (Ca-Bt), sodium bentonite (Na-Bt), and water as the main components. When the initial sol-state colloid absorbed acid gas products from coal combustion, the pH value decreased and a large amount of Ca²⁺ in Ca-Bt precipitated, thus immediately growing calcium bridges with LMP molecules that formed a three-dimensional network structure for gelation. The optimum ratio of the new colloid was determined through X-ray diffraction, tube inversion, shock shear-temperature scanning, and genetic algorithm. By testing the fire extinguishing performance of the colloid, the findings proved that the product had good oxygen isolation performance, strong adhesion ability, high thermal stability, and strong inhibition effects on coal combustion.

Gelation behavior and mechanism of Nicandra physalodes (Linn.) Gaertn. seeds pectin induced by Glucono-delta-lactone

In this study, the physicochemical properties of pectin from Nicandra physalodes (Linn.) Gaertn. seeds (NPGSP) were analysed firstly, and the rheological behavior, microstructure and gelation mechanism of NPGSP gels induced by Glucono-delta-lactone (GDL) were investigated. The hardness of NPGSP gels was increased from 26.27 g to 226.77 g when increasing GDL concentration from 0 % (pH = 4.0) to 1.35 % (pH = 3.0), and the thermal stability was improved. The peak around 1617 cm^-1 was decreased as the adsorption peak of the free carboxyl groups was attenuated with addition of GDL. GDL increased the crystalline degree of NPGSP gels, and its microstructure exhibited more smaller spores. Molecular dynamics was performed on systems of pectin and gluconic acid (GDL hydrolysis product), indicating that inter-molecular hydrogen bonds and van der Waals forces were the main interactions to promote gels formation. Overall, NPGSP has the potential commercial value for developing as a thickener in food processing.

Pectin gels based on H+/(NH4)2SO4 and its potential in sustained release of NH4. Int J Biol Macromol 2022;208:486-493. [PMID: 35304200 DOI: 10.1016/j.ijbiomac.2022.03.062] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

A gelling strategy for HP was proposed in this study, ammonium sulfate (AS) as a co-solute could induce the gelling of HP in acidic environment. The solubility and Zeta potential of HP dramatically decreased in AS solution, which indicated AS could promote the aggregation of HP. The rheological results confirmed the gelling of HP (G' > G″) with AS: 25-30 wt% and pH ≤ 3.0, and the gel strength is mainly depended on HP rather than AS concentration. Smaller AS crystals (SEM) and reduced T₂ values (LF-NMR) were observed in HP gels, suggested the gel network of HP could limit the migration of AS and water. Finally, it was found that the release process of NH₄⁺ in HP + AS gel was lagged behind that of pure AS, which verified the potential of HP + AS gel in the field of sustained-release fertilizers.

Hydrogels based on low-methoxyl amidated citrus pectin and flaxseed gum formulated with tripeptide glycyl-l-histidyl-l-lysine improve the healing of experimental cutting wounds in rats

Hydrogels based on natural and modified polysaccharides represent growing group of suitable matrices for the construction of effective wound healing materials. Bioactive tripeptide glycyl-l-histidyl-l-lysine and amino acid α-l-arginine are known to accelerate wound healing and skin repair. In this study, hydrogels based on low-methoxyl amidated citrus pectin or flaxseed gum were prepared and used for the transport of these healing agents to the experimental cutting wounds affected by extensive skin damage. Fourier-transform infrared spectroscopy, rheology, differential scanning calorimetry, scanning electron microscopy, swelling and release tests confirmed that these hydrogels differed in structure and physical properties. The cationic tripeptide was found to bind to carboxylic groups in LMA pectin, and the C3OH hydroxyl and ring oxygen O5 are involved in this interaction. The pectin hydrogel showed high viscosity and strong elastic properties, while the flaxseed gum hydrogel was characterised as a viscoelastic system of much lower viscosity. The former hydrogel released the drugs very slowly, while the latter hydrogel demonstrated zero order releasing kinetics optimal for drug delivery. In the in vivo wound healing testing on rats, both polysaccharide hydrogels improved the healing process mediated by the mentioned biomolecules. The tripeptide applied in the hydrogels showed significantly higher healing degree and lower healing time than in the control animals without treatment and when it was applied in an aqueous solution. Despite the absence of a synergistic effect, the mixture of the tripeptide and α-l-arginine in the hydrogels was also quite effective in wound healing. According to histological analysis, complete healing was achieved only when using the tripeptide in the flaxseed gum hydrogel. These observations might have an important prospect in clinical application of polysaccharide hydrogels.

Egg-box model-based gelation of alginate and pectin: A review

Alginate and pectin are emblematic natural polyuronates that have been widely used in food, cosmetics and medicine. Ca-dependent gelation is one of their most important functional properties. The gelation mechanisms of alginate and pectin, known as egg-box model, were believed to be basically the same, because their Ca-binding sites show a mirror symmetric conformation. However, studies have found that the formation and the structure of egg-box dimmers between alginate and pectin were different. Very few studies have reviewed those differences. Therefore, this study was proposed to first summarize the intrinsic and extrinsic factors that can influence the gelation of alginate and pectin. The differences in the effect of these factors on the gelation of alginate and pectin were then discussed. Meanwhile, the similarity and difference in their gelation mechanism was also summarized. The knowledge gained in this review would provide useful information for the practical applications of alginate and pectin.

A new delivery system based on apple pomace-pectin gels to encourage the viability of antimicrobial strains

This work was aimed to investigate the concept of the valorization of apple processing by-products to produce a new preservation system based on apple pomace gels to encourage the viability of antimicrobial Lactobacillus strains. A high frequency (850 kHz) low power (1.3 W/cm²) ultrasound-stimulated cavitation was used for the structure modulating of gels under low-temperature (50 ℃) conditions. Medium esterified apple pectin was added to apple pomace to improve its texture properties and stability. The monitoring of the process of gelation was performed by using acoustic technique and method, based on the measurement of the distance (parameter h, mm) traveled by a free-falling module. The obtained data were then compared to gel texture measurements. The results suggest that low power ultrasound leads to a reduced jelly mass stickiness and increased gel hardness, compared to the thermally treated sample. The immobilization of probiotic cells in low pectin apple pomace gels did not sufficiently protect the microorganisms. The higher viability of immobilized Lactobacillus paracasei (54-77%) compared to L. plantarum (43-59%) was recorded after incubation at acidic conditions (pH 2.0). The most suitable system for preserving bacterial cells during storage can be the apple pomace-pectin gel containing up to 53% pectin as a stabilizer retaining 84% of viable cells after one-month storage at 4 ℃. The apple pomace-pectin hydrogels with gelation rate (dh/dt) of 0.03-0.05 mm/s can be used for the preservation of bacterial cells as a suitable functional ingredient for food.

The Effect of Concentration on the Cross-Linking and Gelling of Sodium Carbonate-Soluble Apple Pectins

The cross-linking and gelation of low-methoxy pectins are basic processes commonly used in different industries. The aim of this research was to evaluate the cross-linking process of the sodium carbonate-soluble pectins (named DASP) extracted from apples, characterized by a low degree of methylesterification as a function of its concentration in water (CDASP). The cross-linking process was studied with a dynamic light scattering method, atomic force microscope (AFM), viscosity and pH measurements. An increase in CDASP above 0.01% resulted in a decrease in the aggregation index (AI) and the change of its sign from positive to negative. The value of AI = 0 occurred at CDASP = 0.33 ± 0.04% and indicated the formation of a pectin network. An increase in CDASP caused the changes in viscosity of pectin solutions and the nanostructure of pectins spin-coated on mica observed with AFM, which confirmed results obtained. The hydrogen bonds were involved in the cross-linking process.