Rheology and microstructure of mixtures of iota and kappa-carrageenan

Helicity degree of carrageenan conformation determines the polysaccharide and water interactions

The polysaccharide in solution at critical concentration, Cc (g/L), is assimilated to a nano hydrogel (nHG) made of a single polysaccharide chain. Taking as reference the characteristic temperature of 20 ± 2 °C at which kappa-carrageenan (κ-Car) nHG swelling is greater with a Cc = 0.55 ± 0.05 g/L, the temperature of the minimum deswelling in the presence of KCl was found at 30 ± 2 °C for 5 mM with a Cc = 1.15 ± 0.05 g/L but not measurable above 100 °C for 10 mM of which Cc = 1.3 ± 0.05 g/L. Lowering the temperature to 5 °C, contraction of the nHG and further coil-helix transition with self-assembly increases the sample's viscosity, which steadily evolves with time in a logarithmic scale. Accordingly, the relative increment of the viscosity per unit of concentration, R_v (L/g), should increase in agreement with increasing polysaccharide concentration. But the R_v decreases for κ-Car samples above 3.5 ± 0.5 g/L in the presence of 10 mM KCl under steady shear 15 s^-1. This reflects a decrease of κ-Car helicity degree knowing that the polysaccharide is rather hydrophilic when its helicity degree is the lowest.

From Seaweeds to Hydrogels: Recent Progress in Kappa-2 Carrageenans

Hybrid carrageenans, also called kappa-2 (K2) or weak kappa, are a class of sulfated polysaccharides with thermo-reversible gelling properties in water and are extracted from a specific family of red seaweeds. K2 are known in the industry for their texturizing properties which are intermediate between those of kappa-carrageenans (K) and iota-carrageenans (I). As such, K2 are gaining industrial interest, as they can replace blends of K and I (K + I) in some niche applications. Over the last decade or so, some progress has been made in unravelling K2's chemical structure. The understanding of K2 gel's structure-rheological properties' relationships has also improved. Such recent progress is reported here, reviewing the literature on gelling K2 published since the last review on the topic. The focus is on the seaweeds used for extracting K2, their block copolymer chemical structures, and how these impact on the gel's formation and rheological properties. The outcome of this review is that additional rheological and structural studies of K2 hydrogels are needed, in particular to understand their viscoelastic behavior under large deformation and to unravel the differences between the texturizing properties of K2 and K + I.

Effects of Alkaline Solvent Type and pH on Solid Physical Properties of Carrageenan from Eucheuma cottonii

The effects of alkali type and pH on the physical properties of carrageenan have been extensively studied. However, their effects on certain characteristics of solid-state properties of carrageenan have not been identified. This research aimed to investigate the effect of alkaline solvent type and pH on the solid physical properties of carrageenan isolated from Eucheuma cottonii. Carrageenan was extracted from the algae using NaOH, KOH, and Ca(OH)₂ at pHs of 9, 11, and 13. Based on the results of preliminary characterization, including yield, ash content, pH, sulphate content, viscosity, and gel strength, it was found that all samples followed Food and Agriculture Organization (FAO) specifications. The swelling capacity of carrageenan based on the type of alkali was KOH > NaOH > Ca(OH)₂. The FTIR spectra of all samples were in agreement with that of standard carrageenan. The molecular weight (MW) of carrageenan using KOH as the alkali followed the order pH 13 > pH 9 > pH 11, while using NaOH, the order was pH 9 > pH 13 > pH 11, and while using Ca(OH)₂, the order was pH 13 > pH 9 > pH 11. The results of the solid-state physical characterization of carrageenan with the highest MW in each type of alkali showed that the morphology of carrageenan using Ca(OH)₂ has a cubic shape and is more crystal-like. The order of crystallinity of carrageenan using different types of alkali was Ca(OH)₂ (14.44%) > NaOH (9.80%) > KOH (7.91%), while the order of density was Ca(OH)₂ > KOH > NaOH. The order of solid fraction (SF) of the carrageenan was KOH > Ca(OH)₂ > NaOH, while the tensile strength when using KOH was 1.17, when using NaOH it was 0.08, and while using Ca(OH)₂, it was 0.05. The bonding index (BI) of carrageenan using KOH = 0.04, NaOH = 0.02, and Ca(OH)₂ = 0.02. The brittle fracture index (BFI) of the carrageenan was KOH = 0.67, NaOH = 0.26, and Ca(OH)₂ = 0.04. The order of carrageenan solubility in water was NaOH > KOH > Ca(OH)₂. These data can be used as the basis for the development of carrageenan for excipients in solid dosage forms.

Renewable marine polysaccharides for microenvironment-responsive wound healing

Marine polysaccharides (MPs) are an eco-friendly and renewable resource with a distinctive set of biological functions and are regarded as biological materials that can be in contact with tissues and body fluids for an extended time and promote tissue or organ regeneration. Skin tissue is easily invaded by the external environment due to its softness and large surface area. However, the body's natural physiological healing process is often too slow or suffers from the incomplete restoration of skin structure and function. Functional wound dressings are crucial for skin tissue engineering. Herein, popular MPs from different sources are summarized systematically. In particular, the structure-effectiveness of MP-based wound dressings and the physiological remodeling process of different wounds are reviewed in detail. Finally, the prospect of MP-based smart wound dressings is stated in conjunction with the wound microenvironment and provides new opportunities for high-value biomedical applications of MPs.

Sulfate groups position determines the ionic selectivity and syneresis properties of carrageenan systems

The salt sensitivity and selectivity feature of α-carrageenan (α-Car) were investigated and compared with κ-carrageenan (κ-Car) and iota-carrageenan (ι-Car). These carrageenans are identified by one sulfate group on the 3,6-anhydro-D-galactose (DA) for α-Car, D-galactose (G) for κ-Car and on both carrabiose moieties (G and DA) for ι-Car. The viscosity and temperature, where order-disorder transition have been observed, were greater in presence of CaCl₂ for α-Car and ι-Car compared with KCl and NaCl. Conversely, the reactivity of κ-Car systems were greater in presence of KCl than CaCl₂. Unlike κ-Car systems, the gelation of α-Car in presence of KCl was observed without syneresis. Thus, the position of sulfate group on the carrabiose determines the importance of counterion valency too. The α-Car could be a good alternative to κ-Car to reduce the syneresis effects.

Rheological study of α- and κ-carrageenan expansion in solution as effects of the position of the sulfate group

The viscosity of carrageenan solutions in the coil state was greater for α-carrageenan (α-Car) compared with that for κ-carrageenan (κ-Car); thus, the impact of one sulfate group on 3,6-anhydro-D-galactose was compared with the impact of one sulfate group on D-galactose units of the carrabiose residues. The thermal expansion coefficient of the solutions, B₂ × T_c, characterizes the way the viscosity decreases because of extension of the physical bonds of the systems to their rupture point (T_c) under increasing temperature. The T_c and B₂ × T_c of water were equal to (100 ± 5) °C and (1.57 ± 0.05) × 10^-2/°C, respectively. The T_c of the α-Car and κ-Car systems increased after the addition of CaCl₂ and KCl, respectively, and with increasing polysaccharide concentration. However, the B₂ × T_c of the α-Car and κ-Car systems were rather sensitive to CaCl₂ and KCl, respectively. In the overall solutions examined, the expansion of α-Car systems was found to be between 1.5 × 10^-2/°C and 1.61 × 10^-2/°C, greater than the expansion of κ-Car systems, which was between 1.5 × 10^-2/°C and 1.2 × 10^-2/°C. Thus, α-Car is a good alternative to κ-Car for reducing syneresis phenomena, and its sensitivity as ι-Car to divalent cations would be due to the anhydro cycle.

Characterization of a Novel Carrageenan-Specific Carbohydrate-Binding Module: a Promising Tool for the In Situ Investigation of Carrageenan

Carrageenan is a commercially important polysaccharide widely applied in the food industry. Specific probes are critical tools for the in situ investigation of polysaccharides, whereas the carrageenan-specific probes are limited at present. Carbohydrate-binding modules (CBMs) could serve as specific probes for the in situ investigation of polysaccharides. In the present study, an unknown function module from the κ-carrageenase Cgk16A was cloned and expressed in Escherichia coli. The expressed protein Cgk16A-CBM92 could specifically bind to carrageenan. Its novelty sheds light on a new CBM family (CBM92) as the founding member. Furthermore, a fluorescent probe was successfully constructed by fusing Cgk16A-CBM92 with a green fluorescent protein. The application potential of Cgk16A-CBM92 as a probe served in the in situ visualization of carrageenan was evaluated. The discovery of Cgk16A-CBM92 provided a promising tool for the in situ investigation of carrageenan.

Stabilization and Dispersion of OSA Starch-Coated Titania Nanoparticles in Kappa-Carrageenan-Based Solution

Titania is a white pigment used widely in papermaking, paints and cosmetic industries. Dispersion and stabilization of high concentration titania in water-based system remains a great bottleneck in industry nowadays, because aggregation of titania nanoparticles results in severe adverse effects to gloss, opacity, tint strength, color distribution and storage stability of end products. Because kappa-carrageenan (κ-CG) has excellent rheological properties such as emulsification, gelation, stability and so on, it has the ability to form gel and increase the viscosity of aqueous solution. In this work, Octenyl succinic anhydride (OSA) starch was utilized as wall material to encapsulate titania pigments using electrostatic spray drying processing. Transmission electron microscopy (TEM) showed that titania pigments were coated by OSA starch, with a final form of nanoparticle. Accelerating stability test found that around 60% OSA starch–titania particles were stably dispersed in κ-CG-based solution. All materials used in this work were natural ingredient, which would be preferred by cosmetic industry and consumers. The technique used in the present study could potentially be extended to other pigments for similar purpose.

Structure-Elastic Properties Relationships in Gelling Carrageenans

Gelling carrageenans are polysaccharides extracted from the Gigartinales order of red algae. These are additives used essentially in the food industry for texturizing, stabilizing or gelling various formulations. Although a consensual gel mechanism has been reached which encompasses a coil-to-helix transition followed by the self-assembling of helices in a network, the structure–elastic relationships in the network are still to be clearly established. This paper reviews the reports in which carrageenan gel structures have been systematically compared with gel elastic properties. The focus is on the sizes documented for structural units, such as strands, aggregates, voids or network meshes, as well as on the reported linear and nonlinear elastic characteristics. The insufficient rationalization of carrageenan gel elasticity by models which take on board mechanically relevant structural features is underlined. After introducing selected linear and nonlinear elastic models, preliminary results comparing such models to structural and rheological data are presented. In particular, the concentration scaling of the strain hardening exhibited by two types of carrageenan gels is discussed.

Dual stimuli-sensitive carrageenan-based formulation for additive manufacturing

The design and development of controlled release systems of molecules of interest (nutrients, flavors, and drugs) have attracted significant attention over several years. Herein, we report a formulation of dual temperature and electro responsive κ- and ι-carrageenan based hydrogel for efficient food material and drug delivery. The microstructure and the thermal behavior of the hydrogel were characterized. The in-vitro drug release from the hydrogel was also studied. Using this carrageenan-based formulation and folic acid as the drug model, a high drug loading, and a sustained release because of either electric field or temperature were observed. In principle, the proposed formulation does not rely on 3D printing to perform its function; however, it adds to the feedstocks for 3D printing in the food and pharmaceutical industries. For the future, this could allow potentially more complex smart structures to be created from this material, further tuning release behavior.

Influence of two functional dextrins on the gel properties of kappa-carrageenan

The physicochemical properties of κ-carrageenan (KC) can be improved by incorporation with small-molecule cosolvents. The texture and rheological properties, micromorphology, and crystallinity of KC incorporating indigestible dextrin (IDD) and beta-limit dextrin (BLD) were investigated. The rheological properties and sol-gel transition temperatures of the gels were slightly improved and the hardness of KC gels was significantly increased after the two dextrins were mixed in. Fourier transform infrared spectroscopy results indicated hydrogen-bonding interactions were strengthened in the presence of the dextrins. Confocal laser scanning microscope images revealed that a more homogenous structure was formed of the KC gel after the addition of dextrins. Moreover, X-ray diffraction patterns indicated the crystallinity of KC gel decreased upon dextrin addition. At the same dextrin content, IDD exerted a greater influence than BLD. IDD contents exceeding 3% (w/w) led to undesirable effects, whereas up to 5% (w/w) of BLD could be added. The two dextrins affected the rearrangement of the KC random coils in the sol state, and facilitated aggregation of the KC chains during cooling to form gel network structures after gelation. Therefore, the appropriate addition of these two dextrins can improve the texture and stability of KC gels and expand their application in functional foods.

Carrageenan-based physically crosslinked injectable hydrogel for wound healing and tissue repairing applications

In this study, a novel injectable hydrogel based on iota and kappa carrageenan, locust bean gum and gelatin was prepared for wound healing and tissue repairing applications. This injectable hydrogel was obtained via physical crosslinking. FTIR analysis confirmed the physical interaction between the biopolymeric components of the hydrogel. The prepared injectable hydrogel exhibited shear-thinning characteristics and could be injected for minimally invasive applications. Also, the hydrogel showed a porous structure, physiological and mechanical stability and biocompatibility. The in vitro cell culture studies showed that fibroblasts were able to grow, adhere and spread inside the hydrogel, indicating that hydrogel could support tissue repair. Moreover, hydrogel could be useful for the delivery of biomolecules. Vascular endothelial growth factor was encapsulated within the hydrogel and subsequently released, which accelerated the migration of human umbilical vein endothelial cells and facilitated in vitro wound healing. Overall, the results indicate that hydrogel can be a potential injectable delivery vehicle for wound healing and tissue repair.

Latest advances in imaging techniques for characterizing soft, multiphasic food materials

Over the last two decades, the development and production of innovative, customer-tailored food products with enhanced health benefits have seen major advances. However, the manufacture of edible materials with tuned physical and organoleptic properties requires a good knowledge of food microstructure and its relationship to the macroscopic properties of the final food product. Food products are complex materials, often consisting of multiple phases. Furthermore, each phase usually contains a variety of biological macromolecules, such as carbohydrates, proteins and lipids, as well as water droplets and gas bubbles. Micronutrients, such as vitamins and minerals, might also play an important role in determining and engineering food microstructure. Considering this complexity, highly advanced physio-chemical techniques are required for characterizing the microstructure of food systems prior to, during and after processing. Fast, in situ techniques are also essential for industrial applications. Due to the wide variety of instruments and methods, the scope of this paper is focused only on the latest advances of selected food characterization techniques, with emphasis on soft, multi-phasic food materials.

Facile and Green Fabrication of Carrageenan-Silver Nanoparticles for Colorimetric Determination of Cu2+ and S2

In the present work, silver nanoparticles (AgNPs) were prepared by a simple and green method using carrageenan as reducing and capping agent. The as-synthesized carrageenan-AgNPs was demonstrated as an effective duel colorimetric sensing for selective and sensitive recognition of Cu²⁺ and S²⁻, which could be used to detect these ions with naked eyes. In addition, the possible sensing mechanism was that Cu²⁺ ions caused serious aggregation of carrageenan-AgNPs, which led to the color change of carrageenan-AgNPs. AgNPs were etched by S²⁻ forming Ag₂S, which played an important role in the determination of S²⁻ ions. Furthermore, it has been successfully applied to the determination of Cu²⁺ and S²⁻ in tap water and lake water, showing its great potential for the analysis of environmental water samples.

Effect of Carrageenans on Vegetable Jelly in Humans with Hypercholesterolemia

Changes in lipid profile constitute the main risk factor for cardiovascular diseases. Algae extracted carrageenans are long-chain polysaccharides and their ability to form gels provides for the formation of vegetable jelly. The objective was to evaluate the bioactive potential of carrageenan (E407) in the lipid profile, after ingestion of jelly. A total of 30 volunteers of both sexes, aged 20-64 years and with total cholesterol (TC) values ≥200 mg/dL, who ingested 100 mL/day of jelly for 60 days, were studied. All had two venous blood collections: before starting the jelly intake and after 60 days. At both times, TC, high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C) and triglycerides (TG), were evaluated using commercial kits and spectrophotometer. The statistics were performed using the SPSS 25.0 software and p < 0.05 were considered statistically significant. Serum values after 60 days of jelly intake revealed a statistically significant decrease in TC levels (5.3%; p = 0.001) and LDL-C concentration (5.4%; p = 0.048) in females. The daily intake of vegetable jelly for 60 days showed a reduction in serum TC and LDL-C levels in women, allowing us to conclude that carrageenan has bioactive potential in reducing TC concentration.