Mapping the Complex Phase Behaviors of Aqueous Mixtures of κ-Carrageenan and Type B Gelatin

Multivariable analysis of egg white protein-chitosan interaction: Influence of pH, temperature, biopolymers ratio, and ionic concentration

The influence of pH, temperature, biopolymer ratio, total concentration, and ionic concentration on the interaction between egg white protein (EWP) and chitosan (CS) was investigated through turbidity, zeta potential, and state diagram in our research. In addition, phase behavior was observed under various conditions. The turbidity of EWP remained low (turbidity < 0.03) and basically unchanged at a wide range of pH (4.0-8.0), while the turbidity of CS was slightly higher (turbidity < 0.2) after pH 7.0 than before. Moreover, under the same conditions, a sharply rising peak pattern was observed for the complex between EWP and CS. The maximum turbidity value was observed at 55 °C, and the temperature had a mild effect on turbidity. The optimum EWP to CS ratio was found to be 12:1 based on the turbidity curves and state diagrams influenced by different biopolymer mixing ratios. With the enhanced concentrations of total biopolymer, the maximum turbidity rose insignificantly above 0.1%.

Ultrasonic-assisted glycosylation with κ-carrageenan on the functional and structural properties of fish gelatin

BACKGROUND

Fish gelatin (FG) has multifunctional properties similar to mammalian gelatin (MG), and it has been recognized as the optimal alternative to MG. While its poor surface-active and gelling properties significantly limit its application values, glycosylation has been successfully used to increase surface-active properties of FG, but the influence of ultrasonic-associated glycosylation (UAG) on the gelling and structural characteristics of FG is still rarely reported. This article explores UAG (100-200 W, 0.5-1 h) with κ-carrageenan (κC) on the functional properties (emulsifying, gelling and rheological properties) and structural characteristics of FG.

RESULTS

The longer time and higher power of ultrasonics accelerated the glycosylation reaction with an increase in glycosylation degree and browning index values. Compared with original FG, FG-κC mixture and bovine gelatin, UAG-modified FG possessed higher emulsification activity index, emulsion stability index, gel strength, hardness and melting temperature values. Among them, gelatin modified by appropriate ultrasonic conditions (200 W, 0.5 h) had the highest emulsifying and gelling properties. Rheological results showed that UAG contributed to the gelation process of gelatin with advanced gelation time and endowed it with high viscosity. Structural analysis indicated that UAG promoted κC to link with FG by the formation of covalent and hydrogen bonds, restricting more bound and immobilized water in the gels, exhibiting higher gelling properties.

CONCLUSION

This work showed that UAG with κC is a promising method to produce high gelling and emulsifying properties of FG that could replace MG. © 2023 Society of Chemical Industry.

pH-induced complex coacervation of fish gelatin and carboxylated chitosan: phase behavior and structural properties

The aim of this study was to investigate the phase behavior and structural properties of fish gelatin complex coacervation with carboxylated chitosan as a function of pH by varying the amount of carboxylated chitosan added (0-0.25%, w/v) while keeping the fish gelatin concentration constant at 0.667% (w/v). Zeta potential indicated that electrostatic interaction drove the complex coalescence of fish gelatin and carboxylated chitosan to form soluble or insoluble complexes. The turbidity of the fish gelatin-carboxylated chitosan complex system was greatest at a carboxylated chitosan concentration of 0.2%. UV and fluorescence spectroscopy indicated that the carboxylated chitosan changed the tertiary conformation of fish gelatin. Circular dichroism showed that complexation of fish gelatin with carboxylated chitosan resulted in a shift from the α-helix to the β-sheet structure of fish gelatin. In particular, at pH 5, the fish gelatin complexed with carboxylated chitosan had a disordered structure. X-ray diffraction and scanning electron microscopy of the composite coacervates both investigated that electrostatic interaction between the two replaced molecular interaction within the carboxylated chitosan to form a new lamellar porous structure. These findings may in future enable the use of fish gelatin-carboxylated chitosan complex systems in the design of new food matrices.

Supramolecular Structure and Mechanical Performance of κ-Carrageenan-Gelatin Gel

In this work, by means of complex physicochemical methods the structural features of a composite κ-carrageenan–gelatin system were studied in comparison with initial protein gel. The correlation between the morphology of hydrogels and their mechanical properties was demonstrated through the example of changes in their rheological characteristics. The experiments carried out with PXRD, SAXS, AFM and rheology approaches gave new information on the structure and mechanical performance of κ-carrageenan–gelatin hydrogel. The combination of PXRD, SAXS and AFM results showed that the morphological structures of individual components were not observed in the composite protein–polysaccharide hydrogels. The results of the mechanical testing of initial gelatin and engineered κ-carrageenan–gelatin gel showed the substantially denser parking of polymer chains in the composite system due to a significant increase in intermolecular protein–polysaccharide contacts. Close results were indirectly followed from the SAXS estimations—the driving force for the formation of the common supramolecular structural arrangement of proteins and polysaccharides was the increase in the density of network of macromolecular chains entanglements; therefore, an increase in the energy costs was necessary to change the conformational rearrangements of the studied system. This increase in the macromolecular arrangement led to the growth of the supramolecular associate size and the growth of interchain physical bonds. This led to an increase in the composite gel plasticity, whereas the enlargement of scattering particles made the novel gel system not only more rigid, but also more fragile.

Modulation of Molecular Structure and Mechanical Properties of κ-Carrageenan-Gelatin Hydrogel with Multi-Walled Carbon Nanotubes

Hydrogels, three-dimensional hydrophilic water-insoluble polymer networks having mechanical properties inherent for solids, have attracted continuous research attention over a long time period. Here, we studied the structure and properties of hydrogel based on gelatin, κ-carrageenan and CNTs using the combination of SAXS, PXRD, AFM microscopy, SEM and rheology methods. We have shown that the integration of polysaccharide and protein in the composite hydrogel leads to suppression of their individual structural features and homogenization of two macromolecular components into a single structural formation. According to obtained SAXS results, we observed the supramolecular complex, which includes both polysaccharide and protein components associated with each other. It was determined that hydrogel structure formed in the initial solution state (dispersion) retains hydrogel supramolecular structure under its cooling up to gel state. The sizes of dense cores of these polyelectrolyte complexes (PEC) slightly decrease in the gel state in comparison with PEC water dispersion. The introduction of CNTs to hydrogel does not principally change the type of supramolecular structure and common structural tendencies observed for dispersion and gel states of the system. It was shown that carbon nanotubes embedded in hydrogel act as the supplementary template for formation of the three-dimensional net, giving additional mechanical strengthening to the studied system.

Water-soluble caffeic acid-dopamine acid-base complex exhibits enhanced bactericidal, antioxidant, and anticancer properties

Despite the highly potent biological characteristics, the poor water-solubility of caffeic acid (CA) limits its applications in various domains. Here, we present a facile approach, wherein CA has been treated with dopamine hydrochloride (Dopa.HCl) to obtain a water-soluble acid-base complex, which does not possess any covalent bond between the individual components and thus retains their nativity. Simple mixing of CA and Dopa.HCl did not provide water solubility to CA, but the complex became readily soluble in water when the mineral acid was scavenged using sodium bicarbonate. The obtained CA-Dopa complex had been characterized using FT-IR, ¹H NMR, ¹³C NMR, 2D ¹H-¹H NOESY NMR, XPS, and DSC techniques. The complex was found to exhibit excellent bactericidal, antibiofilm, antioxidant, and anticancer properties in the physiologically relevant pH range of 5.5 to 7.5. The results have revealed the high potential of the simple acid-base complex of CA in diverse domains.

Extremely stretchable and tough hybrid hydrogels based on gelatin, κ-carrageenan and polyacrylamide

Nowadays, several approaches are being suggested to endow hydrogels with improved mechanical properties for practical applications as cartilage and skin replacements, soft electronics, and actuators. However, it remains a challenge to develop DN gels with both high fracture toughness and fracture stretch. Here, we introduce (bio)polyelectrolyte complexes (PECs) consisting of gelatin and κ-carrageenan as the first brittle network and covalently crosslinked polyacrylamide (PAAm) as the second stretchable network to fabricate a highly stretchable and notch-insensitive gelatin/κ-carrageenan/PAAm hydrogel. The unprecedented high stretchability (∼51.7) is ascribed to the reduction of stress concentration and defects in the network structure through the fracture of the PEC gel. In addition, a high fracture toughness (∼16053.34 J m^-2) is achieved by effective energy transfer between the PECs and PAAm gel due to their covalent crosslinking, and efficient energy dissipation through destroying inter- and intramolecular interactions in the PEC gel.

Ameliorative effects of L-arginine? On heat-induced phase separation of Aristichthys nobilis myosin are associated with the absence of ordered secondary structures of myosin

This investigation aimed to study the potential mechanism of L-arginine (L-Arg) on the heat-induced phase separation phenomenon of myosin from the perspective of conformational changes of myosin. L-Arg ameliorated the phase separation of myosin after a two-step heating procedure via suppression of heat-induced aggregation of myosin. The effect of L-Arg on the heating of myosin at high temperatures (75-85 °C) was more pronounced than that in the setting stage (35-45 °C), suggesting that the ameliorative effects of L-Arg on the heat-induced phase separation of myosin are mainly attributed to the inhibition of rod-rod cross-linking between denatured myosin molecules. Additionally, L-Arg without pH modification exhibited an increased ability to suppress the gelation of myosin compared with pH modification, indicating that both pH effects and the particular structure of L-Arg play noticeable roles in the suppression of myosin gelation. Far-UV circular dichroism, intrinsic fluorescence spectroscopy and differential scanning calorimetry demonstrated that L-Arg induced the absence of ordered secondary structures of myosin molecules, especially β-sheets, and thus generated a looser protein structure, which may represent the dominant suppression mechanisms of L-Arg on the heat-induced aggregation of myosin. This work provided support for the use of L-Arg as a food additive, and the results of this study will be attractive to the meat and beverage products.

Modified Fish Gelatin as an Alternative to Mammalian Gelatin in Modern Food Technologies

This review considers the main properties of fish gelatin that determine its use in food technologies. A comparative analysis of the amino acid composition of gelatin from cold-water and warm-water fish species, in comparison with gelatin from mammals, which is traditionally used in the food industry, is presented. Fish gelatin is characterized by a reduced content of proline and hydroxyproline which are responsible for the formation of collagen-like triple helices. For this reason, fish gelatin gels are less durable and have lower gelation and melting temperatures than mammalian gelatin. These properties impose significant restrictions on the use of fish gelatin in the technology of gelled food as an alternative to porcine and bovine gelatin. This problem can be solved by modifying the functional characteristics of fish gelatin by adding natural ionic polysaccharides, which, under certain conditions, are capable of forming polyelectrolyte complexes with gelatin, creating additional nodes in the spatial network of the gel.

Hyaluronic acid/lysozyme self-assembled coacervate to promote cutaneous wound healing

Traditional hydrogel dressings are limited in practical applications due to the complexity of the preparation and low biocompatibility. So, there is an urgent need to design wound dressing with simple preparation method, higher biocompatibility, and superior therapeutic effect. Additionally, using a polysaccharide/protein mixture system is an attractive method to prepare the gel. In this study, a simple mixture of hyaluronic acid/lysozyme (HL) was used to obtain the HL coacervate gel. HL coacervate has suitable viscoelasticity and excellent adhesion on the skin tissue. We demonstrated its highly efficient self-healing property to overcome fracture or deformation. HL coacervate showed a significant effect on promoting wound healing in a full-thickness skin defect model. Compared to the commercial 3M dressing, it has faster epithelial tissue regeneration and stronger collagen deposition. In addition, cytotoxicity and organ toxicity tests indicated its high safety. In summary, HL coacervate has broad clinical application prospects as a wound dressing material.

Formation of Higher Structural Levels in λ-Carrageenan Induced by the Antimalarial Drug Chloroquine

The linear polysaccharide λ-carrageenan is the only one among the carrageenans not forming secondary, tertiary, and quaternary structures in the presence of inorganic ions. Chloroquine (CQ) is a well-established antimalaria drug also recently discussed in therapeutics against the COVID-19 pandemic. The interaction of this polysaccharide-ionic drug pair was investigated by combining UV-vis spectrophotometry and atomic force microscopy (AFM) imaging. A decrease of the UV peak assigned to free CQ and the occurrence of isosbestic points indicate the formation of complexes. High-resolution AFM height images revealed an increasing height of the single polysaccharide chains in the random coil state upon addition of CQ, indicating the formation of a secondary structure, followed by higher hierarchical aggregates. The disappearance of higher-ordered structures and the recovery of polysaccharide chains with primary structure were observed by introducing inorganic cations (Na⁺, K⁺, Ca²⁺), replacing the condensed CQ and paving the way to reversible ion-induced drug release.

Electrostatic complexation of β-lactoglobulin aggregates with κ-carrageenan and the resulting emulsifying and foaming properties

The electrostatic complexation of protein and polysaccharide and the functional properties of the complexes are significantly affected by the structure of protein aggregates and are important in the development of new food ingredients. In this work, natural globular β-lactoglobulin (NGBLG), β-lactoglobulin nanoparticles (BLGNP), and β-lactoglobulin fibrils (BLGF) were prepared and complexed with κ-carrageenan (κ-car). Phase diagrams of the NGBLG-, BLGNP-, and BLGF-κ-car systems were established and divided into 4 regions: mixed soluble polymers (I), intramolecular soluble complex (II), intermolecular soluble complex (III), and intermolecular insoluble complex (IV). Aggregation shifted the boundaries of regions III and IV of BLGF- or BLGNP-κ-car to lower pH and higher protein aggregates/κ-car weight ratio (r), especially for BLGF-κ-car. The emulsifying and foaming properties of the 3 mixed systems were investigated in regions I and II. Complexes in region II had significantly better emulsifying properties than the corresponding mixtures in region I and the pure protein aggregates. Interestingly, phase separation resulted in different effects on the foaming properties of the 3 BLG-κ-car complexes, in which BLGF-κ-car complexation in region II decreased the foaming properties in region I but the complexation of NGBLG-κ-car and BLGNP-κ-car in region II increased the foaming properties. The BLGF-κ-car complex in regions I and II provided the best emulsifying and foaming properties. Interfacial data both on oil-water and air-water interfaces overall explained the emulsifying and foaming properties of the complexes.

A new alternative insight of nanoemulsion conjugated with κ-carrageenan for wound healing study in diabetic mice: In vitro and in vivo evaluation

Astaxanthin and alpha-tocopherol have attracted great attention because of their properties for the management of wound healing in diabetics. This study aimed to investigate the wound healing study of astaxanthin and alpha-tocopherol with κ-carrageenan nanoemulsion (AS-TP@KCNE) and to perform a histopathological study on streptozotocin (STZ)-induced diabetic mice. AS-TP@KCNE were also evaluated with aim of maintaining an effective and prolonged antidiabetic potential. KC@SENE and KC@USNE were obtained by spontaneous and ultrasonication emulsification methods and were characterized for stability, pH, particle size, and zeta potential by standard analysis. In vitro cytotoxicity and wound healing results demonstrated less toxicity and faster cell migration for the nanoemulsions at different concentrations. Based on the promising results, transdermal administration of AS-TP@KCNE can significantly restore the body weight, reduce fasting blood glucose levels, and improve glucose tolerance, which improved the ability to quickly heal of wounds in diabetic mice compared to control. In conclusion, the present study shows that the AS-TP@KCNE are biocompatible and possess healing properties that accelerate wound closure and exhibited better control of hyperglycemia and more superbly reversed the diabetes mellitus complications than STZ-induced diabetic mice. These results suggested that AS-TP@KCNE could be a promising platform for wound healing applications for diabetics.

Self-assembled gelatin-ι-carrageenan encapsulation structures for intestinal-targeted release applications

In this work, natural biopolymeric encapsulation structures were developed through the self-assembly of gelatin and ι-carrageenan in aqueous solutions. The interactions of this binary system and of a ternary system containing a polyphenol-rich extract were deeply explored for the development of intestinal delivery systems. The processing of the structures (extrusion vs. freeze-drying) greatly influenced release properties, explained by the specific interactions between gelatin and polyphenols, thus allowing for tuning the processing conditions depending on the desired target application. Release was further controlled by incorporating a divalent salt, giving raise to extract-loaded ι-carrageenan/gelatin capsules with adequate release profiles for intestinal targeted delivery. These results demonstrate the potential of exploiting biopolymer interactions for designing bioactive delivery systems using environmentally friendly processes which do not involve the use of toxic or harsh solvents or cross-linkers.

Effects of conformational ordering on protein/polyelectrolyte electrostatic complexation: ionic binding and chain stiffening

Coupling of electrostatic complexation with conformational transition is rather general in protein/polyelectrolyte interaction and has important implications in many biological processes and practical applications. This work studied the electrostatic complexation between κ-carrageenan (κ-car) and type B gelatin, and analyzed the effects of the conformational ordering of κ-car induced upon cooling in the presence of potassium chloride (KCl) or tetramethylammonium iodide (Me₄NI). Experimental results showed that the effects of conformational ordering on protein/polyelectrolyte electrostatic complexation can be decomposed into ionic binding and chain stiffening. At the initial stage of conformational ordering, electrostatic complexation can be either suppressed or enhanced due to the ionic bindings of K⁺ and I⁻ ions, which significantly alter the charge density of κ-car or occupy the binding sites of gelatin. Beyond a certain stage of conformational ordering, i.e., helix content θ > 0.30, the effect of chain stiffening, accompanied with a rapid increase in helix length ζ, becomes dominant and tends to dissociate the electrostatic complexation. The effect of chain stiffening can be theoretically interpreted in terms of double helix association.