Gallic acid-functionalized soy protein-based multiple cross-linked hydrogel: Mechanism analysis, physicochemical properties, and digestive characteristics

New insights into the cross-linking mechanism of soybean protein-based double dynamic cross-linking hydrogels for the controlled delivery of curcumin

The growing demand for functional foods requires the development of advanced delivery systems for hydrophobic bioactive ingredients. To meet this demand, a novel dual-crosslinked hydrogel was designed using a mild gelation method, incorporating Schiff base and catechol-Fe3+ chelation bonds. The effect of the content of dynamic bonds on the physical properties and delivery characteristics of the hydrogel was systematically studied. The results show that the unique dual-crosslinked structure of the hydrogel imparts superior physicochemical properties and enhanced efficacy. Enhanced physicochemical properties include faster gelation time, stronger mechanical performance, a denser network structure, and improved self-healing ability. Furthermore, these hydrogels exhibit excellent thermal stability and water retention properties, with swelling behavior gradually weakening as the content of dynamic bonds increases. The SPD8@Fe1 hydrogels have optimal thermal stability (30.69 %), best mechanical properties (26.86 kPa) and low swelling rate (45.44 g/g). In vitro gastrointestinal digestion simulations indicate that these hydrogels can withstand damage caused by gastric conditions and sustain the release of curcumin under intestinal conditions, while also demonstrating excellent bile salt adsorption capacity. The hydrogel had good pH-dependent controlled-release ability for curcumin. By adjusting the content of dynamic bonds, the sustained release behavior of the hydrogel can be regulated. This work provides important insights into the structure-function relationship of hydrogels and valuable information for the design of functional delivery carriers for hydrophobic bioactive ingredients.

Effects of different binding strategies of D-galactose and glycinin on the thermal gelation behavior of the composite system

In this study, non-covalent and covalent interactions between D-galactose (DG) and glycinin (11S) were induced using a pH-shift method. This approach represents an innovative advancement in existing protein-monosaccharide binding strategies. Furthermore, the study investigated the resulting changes in gel behavior and the properties of the composite thermal gels. The solubility and Zeta-potential analysis showed that the non-covalent interaction (S-11S/DG) was more stable and less dispersed than the covalent interaction (S/DG-11S). Rheological results showed that S-11S/DG has higher viscosity and can form stable elastic gel after temperature program. FTIR and intermolecular force results indicated that both gels utilized disulfide bonds as the primary covalent force, with additional chemical bonds playing a secondary role in maintaining the stability of the gel network and surrounding water molecules. However, the S/DG-11S exhibits a looser structure, resulting in a less elastic and thinner network structure. In contrast, the S-11S/DG gel network demonstrated increased elasticity and support, enhancing its hardness, cohesion and water holding capacity. Thus, the pH-shifting-induced non-covalent gel system had more stable network structure and better properties than the pH-shifting-induced covalent gel system. This study offered new insights for constructing soybean protein gel systems and advancing the design of novel soybean protein products.

Composite gel based on κ-carrageenan-soybean isolate protein/soy protein fibrils: Focus on structural differences and gel properties

The effects of different concentrations of κ-carrageenan (κC) on the structure and gel properties of soybean protein isolate (SPI) and soybean protein fibrils (SPF) were investigated in this work. The interaction between κC and SPI/SPF was explored by SDS-PAGE, FTIR, fluorescence spectroscopy, surface hydrophobicity (H0). Results indicated that the binding of κC to SPI and SPF is mainly hydrogen bonding and hydrophobic interactions. With the increase of κC concentration, the fluorescence intensity and H0 of SPI/SPF-κC decrease. When κC was 8 mg/mL, the H0 of SPI/SPF-κC decreased by 53.56 % and 57.23 % respectively. The addition of κC increased the particle size and turbidity of SPI, while the opposite results for SPF. The gel properties of SPI/SPF-κC were evaluated by texture, rheology and LF-NMR. The results showed that the gel properties of SPF were better than those of SPI, and the addition of κC significantly increased the G', apparent viscosity and resistance to denaturation of the gel. When κC concentration was 8 mg/mL, the hardness of SPI/SPF-κC was 127.2 ± 5.82 g and 134.23 ± 5.89 g, respectively. In conclusion, the fibrillation of proteins and κC can effectively improve the gel properties of SPI gels, which provides a theoretical basis for expanding the high-value utilization of SPI and SPF.

Colorimetric films of carboxymethyl cellulose and sodium alginate incorporating Spirulina extract (phycobiliproteins) and gallic acid for real-time shrimp freshness monitoring

This study developed edible colorimetric films by incorporating 1 % ultrasonic-assisted aqueous extract of Spirulina platensis (UAAESP; 76.83 % protein), and 0.125-0.250 % gallic acid (GA) into 2 % carboxymethyl cellulose (CMC) and sodium alginate (SA) matrices. The films were evaluated for structural, optical, mechanical, antimicrobial, antioxidant, and calorimetric properties. UAAESP exhibited a blue-grey colour at pH 3-9 and yellowish-green at pH 10, reflecting higher UV-visible absorption. The addition of 1 % UAAESP and 0.25 % GA reduced moisture content (7.73 %), water solubility (12.06 %), and water vapor and oxygen permeability, while increasing film thickness (10.97 %) and tensile strength (38.53 %). Film opacity increased due to the blue colour of UAAESP. SEM showed homogeneous surfaces, with minor cracks in cross-sections, while FTIR confirmed strong physical interactions between CMC, SA, UAAESP, and GA. Antioxidant activity improved with UAAESP and higher GA levels, while 0.25 % GA expanded inhibition zones by 74.25 % and 81.09 % against S. aureus and E. coli. The GA not only improve the antioxidant and antimicrobial activities but also sensitize the UAAESP incorporated in the matrices to better sense the spoilage levels. The films' colour changes (blue, bluish-grey, dark grey) corresponded shrimp spoilage levels. Thus, UAAESP-GA films offer real-time freshness indicators and sustainable, recyclable alternatives to plastic packaging.

Inclusion of chitosan in Tenebrio molitor larva protein hydrogels improved the rheological and gel properties of the composite hydrogels

Tenebrio molitor protein (TMP) is a highly promising alternative protein resource. However, hydrogels formed from TMP alone typically exhibit fragility and brittleness, limiting their development and application. This study investigated the effects of varying chitosan (CS) concentrations on the mechanical properties of TMP hydrogels. We found that CS concentrations between 0.5 and 1.5 % greatly improved the mechanical properties, water-holding capacity (WHC), and rheological properties of the TMP/CS composite gels. Specifically, the incorporation of 1.5 % CS improved the storage modulus of the gel, enhanced the interaction between water and proteins, and yielded a WHC of 53.32 %. Furthermore, the addition of 1.5 % CS altered the secondary structure and spatial conformation of the protein, with a β-folding content of 43.27 %, leading to a significant enhancement of hydrophobic interactions and hydrogen bonding in the composite gel system and the formation of a dense and stable gel network structure. However, the addition of excessive CS (2.0 % ~ 3.0 %) led to phase separation of the gel system, which decreased gel strength and increased the viscosity of composite gels. In conclusion, optimized CS incorporation offers a viable theoretical basis for the development of new TMP-based food formulations.

Hydrogel formed in situ through Schiff base reaction between gallic acid-grafted soybean protein isolate and oxidized dextran: Interactions, physicochemical properties, and digestive characteristics

Herein, we developed multifunctional hydrogels formed between soybean protein (SPI)-gallic acid conjugate and oxidized dextran (ODex) via a Schiff base reaction. The effects of ODex on the morphology, structure, and functional properties of the hydrogels were elucidated. The results showed that the crosslinking modes in the hydrogels include hydrogen bonding, Schiff bases, Michael addition, and π-π stacking. The synergistic crosslinking of gallic acid and ODex conferred the hydrogels with an appropriate equilibrium swelling ratio, dense morphology, excellent mechanical properties, high thermal stability, and water-holding properties. When the addition of ODex was 0.8 (w/w), the hydrogel had a higher crosslinking degree (76.31 %), smaller average pore diameter (0.322 μm), and higher zero shear viscosity (748.5 mPa. s). In addition, in vitro digestion tests showed that hydrogel degradation was delayed upon increasing the degree of crosslinking, which improved the hydrogel's capacity to adsorb bile salts and control the release of curcumin. This study provides a theoretical basis for the design of high-quality protein hydrogels and other multifunctional materials suitable for various applications.

Effects of pH shift and D-galactose on network structure of glycinin gel and diffusion behavior of non-network proteins

To reduce the content of non-network proteins in protein-based gels, a synergistic approach involving pH shift and D-galactose (DG) was developed herein to obtain elastic gels with dense networks. The results revealed that the combined effect of pH shift and DG promoted the formation of additional disulfide bonds and chemical bonds between molecules, resulting in a denser, and highly elastic gel network, which immobilized more aggregates, leading to a significant reduction in non-network protein content, and enhancing the functional properties of the gel. Moreover, non-network proteins primarily consisted of subunit A4 (mostly Glu and Asp), while the subunit B was the primary polypeptide forming the gel network. Therefore, the removal of the non-network protein has no significant effect on the microstructure, water holding capacity, elasticity, and recovery of the gel. Comprehensively, the combination of pH shift and DG generated a positive synergistic effect of the glycinin hydrogel network structure.

Biomimetic Design of Underwater Adhesives Based on Tea Polyphenol-Modified Gelatin

Although many tissue adhesives with good biocompatibility are currently available, their lack of wet adhesion capacity significantly hinders their clinical application. Therefore, further development and exploration of new medical adhesives are necessary. Inspired by the adhesion mechanism of marine mussels, through modifying gelatin protein with gallic acid (GA) for wet adhesion and cross-linking gelatin (Gel) molecular chains with tea polyphenols (TP), the adhesive TP-GA/Gel was developed. The adhesive exhibited an adhesion strength of up to 130.47 kPa to porcine skin tissues and maintained a high adhesion state in various aqueous environments, demonstrating excellent and reproducible adhesion. Additionally, TP-GA/Gel possessed outstanding antimicrobial, antioxidant, and biocompatibility properties. In an in vivo wound healing study with SD rats, the wound area treated with TP-GA/Gel adhesive decreased from 10.3 mm2 to 0.9 mm2 after 15 days, promoting effective and scarless wound healing. These results highlight the promising clinical potential of TP-GA/Gel as a medical adhesive.

A review on polysaccharide-based delivery systems for edible bioactives: pH responsive, controlled release, and emerging applications

pH changes occur during bodily lesions, presenting an opportunity for leveraging pH-responsive delivery systems as signals for a targeted response. This review explores the design and application of pH-responsive delivery systems based on natural polysaccharides for the controlled release of bioactives. The article examines the development of diverse delivery carriers, including nanoparticles, nanofibers, nanogels, core-shell carriers, hydrogels, emulsions as well as liposomes and their capacity to respond to pH variations, enabling the precise and targeted delivery of bioactives within the human body. These polysaccharide-based delivery systems can be made pH-responsive by modulating the charge of polybasic or polyacidic polysaccharides, inducing swelling of the carrier and subsequent release of the encapsulated bioactives. These pH-responsive systems show promise in stabilizing under acidic conditions for enhanced retention in the stomach during oral delivery while also enabling targeted release at low pH sites such as tumors and wounds, thereby accelerating wound healing and aiding in cancer therapy and inflammation treatment. pH can co-respond with a variety of stimuli, including temperature, enzymes and reactive oxygen species, enabling more precise responses to the microenvironment for targeted delivery. It provides solid theoretical foundations for the advancement of personalized nutrition and therapeutics through controlled and responsive release technologies.

Soybean protein isolate/dialdehyde sodium alginate hydrogels based on dynamic imine bond cross-linking: Synthesis and properties

A soybean protein isolate (SPI)-based hydrogel with controllable properties was prepared under mild conditions using a simple mixing method with dialdehyde sodium alginate (DSA) as an eco-friendly macromolecular crosslinker. DSA was successfully synthesized via periodate oxidation. Analysis of the structure of the SPI/DSA hydrogel indicated that a 3D network was formed between SPI and DSA through dynamic imine and hydrogen bonds. The analysis of the physicochemical properties of the hydrogels showed that the micropore size, mechanical properties, and the swelling and release behavior of the hydrogels could be effectively regulated by changing the DSA content. When 3.0 wt% DSA was added, the hydrogel exhibited a dense and homogeneous network structure with optimal gel properties, which enabled the controlled release of curcumin. This effective structure is mainly attributed to the synergistic effect of short- and long-range chemical and physical crosslinking. Overall, the SPI/DSA hydrogels are effective carriers for the controlled release of bioactive compounds.

Schiff Base Mediated Food-Derived Peptide Supramolecular Self-Assembly as Curcumin Carriers

The fusion assembly strategy of supramolecular chemistry combined with dynamic covalent chemistry has provided novel insights into the design of precision nutrition and intelligent drug delivery carriers. This work involved the development of a supramolecular self-assembly originating from entropy- and enthalpy-driven dynamic covalent bonding on Schiff bases between egg white-derived peptide Gln-Ile-Gly-Leu-Phe (QIGLF) and glutaraldehyde (GA), denoted QIGLF-GA. The assembly exhibited outstanding assembly characteristics and multiwavelength autofluorescence properties. Benefiting from the potent facilitation of the dynamic covalent interaction of Schiff base on the noncovalent assembly force network, QIGLF-GA was afforded an encapsulation capacity of curcumin (Cur) of more than 22% (≫ 10%) and rationally inhibited P-glycoprotein-mediated cellular efflux and markedly elevated the efficacy of Cur in overcoming the intestinal epithelial absorption barrier to the circulation with the help of endocytosis. Furthermore, QIGLF-GA-Cur features responsive release under weakly acidic conditions, which dramatically contributes to the intracellular bioavailability of Cur.

Ultrasound-assisted modification of soybean protein isolate with L-histidine: Relationship between structure and function

Herein, the effects of ultrasound-assisted L-histidine (L-His) on the physicochemical properties and conformation of soybean protein isolate (SPI) were investigated. Particle size, zeta potential, turbidity, and solubility were used to evaluate protein aggregation, and the relationship between structural and functional changes of the proteins was characterized using spectral analysis, surface hydrophobicity, emulsification, and antioxidant properties. After ultrasound-assisted L-His treatment, SPI exhibited a smaller particle size, higher solubility, and more homogeneous micromorphology owing to the decrease in alpha-helix content and subsequent increases in zeta potential and active sulfhydryl content. In addition, spectral analysis showed that L-His and SPI could form a complex, which changed the microenvironment of the amino acid residues in SPI, thus improving its emulsification and antioxidant properties. At the concentration of L-His was 0.3 % w/w, the nanocomplex had a smaller particle size (140.03 nm), higher ζ-potential (-23.63 mV), and higher emulsification stability (22.48 min).

Effect of sodium alginate block type on the physicochemical properties and curcumin release behavior of quaternized chitosan-oxidized sodium alginate Schiff base hydrogels

Controlling bioactive ingredients release by modulating the 3D network structure of cross-linked hydrogels is important for functional food development. Hereby, oxidized sodium alginate (OSA) with varying aldehyde contents was formed by periodate oxidation of sodium alginate (SA) with different β-d-mannuronic acid (M) and α-l-guluronic acid (G) ratios (M/G = 1:2, 1:1, and 2:1) and its structure was characterized. Moreover, hydrogels were prepared via Schiff base and electrostatic interactions between quaternized chitosan (QCS) and OSA. The properties of hydrogels such as microstructure, thermal stability, swelling and controlled release were investigated. The results showed that OSA with M/G = 1:2 had the highest content of aldehyde groups, and the hydrogel formed by it and QCS had higher thermal stability and a denser network structure with the lowest equilibrium swelling rate, which could better control the release of curcumin. Additionally, it had good self-healing and can recover rapidly after the rupture of its network structure.

Optimization and characterization of high internal phase double emulsion (HIPDE) stabilized by with soybean protein isolate, gallic acid and xanthan gum

This study aims to formulate a stable high internal phase double emulsion (HIPDE) using soybean protein isolate (SPI), gallic acid (GA), and xanthan gum (XG). To prepare HIPDE, W1/O was formulated with the water phase dispersed in the oil phase using polyglycerol polyricinoleate (PGPR) as a stabilizer. Thereafter, W1/O dispersed in W2 (SPI solution) was used. To stabilize the HIPDE, GA was added in W1 (0 or 1 %), XG was added in W2 (0 or 1 %), and the pH of the W phases was adjusted to acidic, neutral, and basic. The samples containing GA in W1 and XG in W2 did not phase out during the storage periods and maintained a higher ζ-potential value, a higher apparent viscosity, and a more sustainable droplet compared to others. These results were derived by the interaction between SPI and XG, SPI and GA, or GA and PGPR. Physicochemical crosslinks were formed, such as gallate-derived groups, SPI-GA complexation (Michael addition, Shiff base reaction), and hydrogen bonding. In conclusion, applying the SPI, GA, and XG to HIPDE would contribute to various industries such as food, medicine, and cosmetics.

Gallic acid: design of a pyrogallol-containing hydrogel and its biomedical applications

Polyphenol hydrogels have garnered widespread attention due to their excellent adhesion, antioxidant, and antibacterial properties. Gallic acid (GA) is a typical derivative of pyrogallol that is used as a hydrogel crosslinker or bioactive additive and can be used to make multifunctional hydrogels with properties superior to those of widely studied catechol hydrogels. Furthermore, compared to polymeric tannic acid, gallic acid is more suitable for chemical modification, thus broadening its range of applications. This review focuses on multifunctional hydrogels containing GA, aiming to inspire researchers in future biomaterial design. We first revealed the interaction mechanisms between GA molecules and between GA and polymers, analyzed the characteristics GA imparts to hydrogels and compared GA hydrogels with hydrogels containing catechol. Subsequently, in this paper, various methods of integrating GA into hydrogels and the applications of GA in biomedicine are discussed, finally assessing the current limitations and future development potential of GA. In summary, GA, a natural small molecule polyphenol with excellent functionality and diverse interaction modes, has great potential in the field of biomedical hydrogels.

Construction of protein-, polysaccharide- and polyphenol-based conjugates as delivery systems

Natural polymers, such as polysaccharides and proteins, have been used to prepare several delivery systems owing to their abundance, bioactivity, and biodegradability. They are usually modified or combined with small molecules to form the delivery systems needed to meet different needs in food systems. This paper reviews the interactions of proteins, polysaccharides, and polyphenols in the bulk phase and discusses the design strategies, coupling techniques, and their applications as conjugates in emulsion delivery systems, including traditional, Pickering, multilayer, and high internal-phase emulsions. Furthermore, it explores the prospects of the application of conjugates in food preservation, food development, and nanocarrier development. Currently, there are seven methods for composite delivery systems including the Maillard reaction, carbodiimide cross-linking, alkali treatment, enzymatic cross-linking, free radical induction, genipin cross-linking, and Schiff base chemical cross-linking to prepare binary and ternary conjugates of proteins, polysaccharides, and polyphenols. To design an effective target complex and its delivery system, it is helpful to understand the physicochemical properties of these biomolecules and their interactions in the bulk phase. This review summarizes the knowledge on the interaction of biological complexes in the bulk phase, preparation methods, and the preparation of stable emulsion delivery system.