Synthesis and properties of maleic anhydride-modified agar with reversibly controlled gel strength

Agar-gelatin Maillard conjugates used for Pickering emulsion stabilization

A few protein- and polysaccharide-based particles have shown promising potential as stabilizers in multi-phase food systems. By incorporating polymer-based particles and modifying the wettability of colloidal systems, it is possible to create particle-stabilized emulsions with excellent stability. A Pickering emulsifier (AGMs) with better emulsifying properties was obtained by the Maillard reaction between acid-hydrolysed agar and gelatin. Laser confocal microscopy imaging revealed that AGMs particles can be used as solid emulsifiers to produce a typical O/W Pickering emulsion, with AGMs adsorbing onto the droplet surface to form a dense interfacial layer. Cryo-scanning electron microscopy analysis showed that AGMs self-assembled into a three-dimensional network structure, which prevented droplets aggregation through strong spatial site resistance, contributing to emulsion stabilization. These emulsions exhibited stability within a pH range of 1 to 11, NaCl concentrations not exceeding 300 mM, and at temperatures below 80 °C. The most stable emulsion oil-water ratio was 6:4 at a particle concentration of 0.75 % (w/v). AGMs-stabilized Pickering emulsion was utilized to create a semi-solid mayonnaise as a replacement for hydrogenated oil. Rheological analysis demonstrated that low-fat mayonnaise stabilized with AGMs exhibited similar rheological behavior to traditional mayonnaise, offering new avenues for the application of Pickering emulsions in the food industry.

Chemically modified seaweed polysaccharides: Improved functional and biological properties and prospective in food applications

Seaweed polysaccharides are natural biomacromolecules with unique physicochemical properties (e.g., good gelling, emulsifying, and film-forming properties) and diverse biological activities (e.g., anticoagulant, antioxidant, immunoregulatory, and antitumor effects). Furthermore, they are nontoxic, biocompatible and biodegradable, and abundant in resources. Therefore, they have been widely utilized in food, cosmetics, and pharmaceutical industries. However, their properties and bioactivities sometimes are not satisfactory for some purposes. Modification of polysaccharides can impart the amphiphilicity and new functions to the biopolymers and change the structure and conformation, thus effectively improving their functional properties and biological activities so as to meet the requirement for targeted applications. This review outlined the modification methods of representative red algae polysaccharides (carrageenan and agar), brown algae polysaccharides (fucoidan, alginate, and laminaran), and green algae polysaccharides (ulvan) that have potential food applications, including etherification, esterification, degradation, sulfation, phosphorylation, selenylation, and so on. The improved functional properties and bioactivities of the modified seaweed polysaccharides and their potential food applications are also summarized.

Fabrication, structure, characterization and emulsion application of citrate agar

In this study, citric acid successfully reacted with agar through the dry heat method, and citrate agar (CA) gel was used to stabilize O/W emulsions. The mechanisms of the CA structure and emulsion pH that affected emulsion stabilization were analyzed, and the application of CA gel emulsion (CAGE) was explored. Compared with native agar (NA), CA showed lower gel strength, higher transparency, and higher water contact angle. These changes indicate that a cross-linking reaction occurred, and it was demonstrated via FTIR and NMR. The emulsion properties were evaluated using particle size, ζ-potential, and the emulsification activity index. Results showed that CAGEs had a smaller particle size and lower ζ-potential than the native agar gel emulsion (NAGE). Meanwhile, confocal laser scanning microscopy confirmed that the CA gels stabilized the emulsions by forming a protective film around the oil droplets. Stability experiments revealed that CAGE (prepared with CA gel [DS = 0.145]) exhibited better stability than NAGE in the pH range of 3-11, and the rheological results further confirmed that the stability of the emulsions was influenced by the network structure and oil droplet interaction forces. Afterward, the application prospect of CAGE was evaluated by encapsulating vitamin D3 and curcumin.

Functionality differences between esterified and pregelatinized esterified starches simultaneously prepared by octenyl succinic anhydride modification and its application in dough

Octenyl succinic anhydride (OSA)-modified starches have gained widespread interest, but the modification can produce two starches with different states ignored. Herein, the two types of starches, esterified starch (ES) and pregelatinized esterified starch (PES), prepared by OSA modification were separated, and their structural and functional characteristics were comprehensively explored. Results showed that compared with native starch (NS), ES and PES exhibited high water-holding capacity, solubility, and swelling power and significantly decreased pasting temperature and thermal stability. Dynamic rheological tests illustrated that OSA modification changed the rheological behavior of starches. Fourier transform infrared spectroscopy confirmed that PES with higher degree of substitution showed more obvious ester carbonyl and carboxylate groups than ES. Laser confocal micro-Raman spectroscopy revealed that the short-range molecular order of ES, especially PES, decreased after modification. X-ray diffraction indicated that OSA modification disrupted the crystalline structure of starch, and that more amylose-lipid complex was formed in PES. Scanning electron microscopy showed that OSA modification eroded starchs surface and reduced its smoothness, and significantly disrupted PES integrity. ES and PES could be developed as food additives for retrogradation inhibition of dough. These results provide new insights into OSA modification and expand its functional application in foods.

Hydrophobic modified agar: Structural characterization and application in encapsulation and release of curcumin

In this study, three kinds of anhydrides with different structures were introduced into agar molecules to study the effects of varying degrees of substitution (DS) and anhydride structures on the physicochemical properties and curcumin (CUR) loading capacity. Increasing the carbon chain length and saturation of the anhydride affects the hydrophobic interaction and hydrogen bonding of the esterified agar, thereby changing the stable structure of the agar. Although the gel performance declined, the hydrophilic carboxyl group and the loose porous structure provide more binding sites for the adsorption of water molecules, hence providing excellent water retention (1700 %). Next, CUR was used as a hydrophobic active ingredient to study agar microspheres' drug encapsulation and in vitro release ability. Results showed that the excellent swelling and hydrophobic structure of esterified agar could promote the encapsulation of CUR (70.3 %). The release process is controlled by pH, and the release of CUR under weak alkaline conditions is significant, which can be explained by the pore structure, swelling characteristics, and carboxyl binding of agar. Therefore, this study shows the application potential of hydrogel microspheres in loading hydrophobic active ingredients and sustained release and provides the possibility for the application of agar in drug delivery systems.

Synthesis, characterization, antibacterial and emulsifying properties of agar benzoate

Agar benzoate (AB) with different degrees of substitution (DS) was synthesized by the esterification of agar and benzoic anhydride in aqueous solution. The DS could be regulated by adjusting composition ratio, pH, and temperature. Its chemical structure was determined by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR). ¹³C NMR spectrum of the AB suggested the main substitution occurred at the C-6 in the d-galactopyranose. Cryo-scanning electron microscopy (Cryo-SEM) showed that the aperture of AB was larger than that of agar. The thermal performance of AB decreased slightly, but this did not affect its performance. AB showed the highest relative antibacterial activity against Escherichia coli, S. aureus and Alternaria alternata, reaching 100 % (AB 20 g/L), 100 % (AB 40 g/L) and 19.35 % (7 d incubation), respectively. Moreover, the obtained AB possessed good emulsion stability. These antibacterial AB have broad application prospects in the field of fruit and vegetable preservation.

Super absorbent glutaric anhydride-modified agar: Structure, properties, and application in biomaterial delivery

Agar was modified with glutaric anhydride (GA) in this study to expand its application in food and medicine. Glutaric anhydride-modified agar (GAR) can maintain high gel strength (1247.4 g/cm²) and improved transparency (82.7 %). The esterified agar formed by GA further formed a cross-linking molecule structure by increasing the reaction temperature. Notably, excellent freeze-thaw stability (24.1 %) and swelling property (3116.6 %) of GAR indicated that the carboxyl-terminal of modified agar improves its affinity with water. Therefore, satisfactory water permeability and expansive stone enable agar films to achieve high water absorption. Furthermore, GAR films exhibit a specific absorption capacity of tetracycline hydrochloride in weak acid solution, thereby suggesting its potential application as a sustainable drug delivery carrier. Finally, the structure of the modified agar was analyzed to explain the mechanism of binding water. Cryo-scanning electron microscopy (SEM) depicted the porous structure of the agar gel responsible for swelling, drug loading, and release. Low-field NMR results showed that GA improves agar gel's binding and free water content. According to our research results, these GAR hydrogel membranes with excellent properties have the potential to be used as effective drug delivery materials.

Anti-methicillin resistance Staphylococcus aureus and in vitro toxicology evaluation of corilagin-loaded gelatin/agar microspheres with potential biotextile applications

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged since the early 1960s. The increasing resistance of pathogens to currently used antibiotics requires the urgent discovery of new antimicrobials effective in combating drug-resistant bacteria. From past to present, medicinal plants are useful to cure human diseases. Corilagin (β-1-O-galloyl-3,6-(R)-hexahydroxydiphenoyl-d-glucose), commonly found in Phyllanthus species, exerts potentiating effect on β-lactams against MRSA. However, its biological effect may not be fully utilized. Therefore, incorporating microencapsulation technology with the delivery of corilagin would be more effective in utilizing the potential effect on biomedical applications. This work reports the development of a safe micro-particulate system which combined agar with gelatin as wall matrix materials for topical delivery of corilagin in order to eliminate the potential toxicity of the crosslinker formaldehyde. The optimal parameters for microsphere preparation were identified and the particle size of optimal microspheres was 20.11 μm ± 3.58. Antibacterial studies revealed that micro-trapped corilagin (minimum bactericidal concentration, MBC = 0.5 mg/mL) possessed a higher potency against MRSA than free corilagin (MBC = 1 mg/mL). The in vitro skin cytotoxicity showed the safety of the corilagin-loaded microspheres for topical applications, with approximately 90 % of HaCaT cell viability. Our results demonstrated the potential of corilagin-loaded gelatin/agar microspheres for the applicable bio-textile products to treat drug-resistant bacterial infections.

Chemical modifications in the structure of marine polysaccharide as serviceable food processing and preservation assistant: A review

Marine polysaccharides are a kind of natural polysaccharides which isolated and extracted from marine organisms. Now some marine polysaccharides, such as chitosan, sodium alginate and agar, have been proven to exhibit antibacterial, antioxidant functions and biocompatibility, which are often used to preserve food or improve the physicochemical properties of food. However, they still have the defects of unsatisfactory preservation effect and biological activity, which can be remedied by its modification. Chemical modification is the most effective of all modification methods. The advances in common chemical modification methods of chitosan, sodium alginate, agar and other marine polysaccharides and research progress of modified products in food processing and preservation were summarized, and the influence of additional reaction conditions on the existence of chemical modification sites of polysaccharides was discussed. The modification of functional groups in natural marine polysaccharides leads to the change of molecular structure, which can improve the physical, chemical and biological properties of marine polysaccharides. Chemically modified products have been used in various fields of food applications, such as food preservatives, food additives, food packaging, and food processing aids. In general, chemical modification has excellent potential for food processing and preservation, which can improve the function of marine polysaccharides.

Preparation of macroporous rigid agarose microspheres by pre-crosslinking with cyclic anhydride

In this study, a new method for preparing macroporous rigid agarose microspheres was developed by one-step pre-crosslinking method with cyclic anhydride. Three different cyclic anhydrides, namely, maleic anhydride, succinic anhydride, and glutaric anhydride, were used to pre-crosslink agarose. The reaction temperature and the amount of cyclic anhydride in the pre-crosslinking process were optimized to endow agarose with stronger cross-linking. Under the optimal cross-linking condition, macroporous rigid agarose microspheres with homogeneous particle size were successfully obtained by adjusting emulsification method. Cryo-scanning electron microscopy was used to characterize the morphology of cross-linked agarose gel and microspheres. The addition of cyclic anhydride increased the gel aperture of cross-linked agarose microspheres, thereby making the macropores in the microspheres more dense and enhancing the mass transfer in the particles. Under low pressure, the cross-linked agarose microsphere column can effectively separate model proteins at linear flow rates three times higher than the agarose microsphere column. These results indicate that the developed agarose microspheres are a promising high-speed chromatographic medium.