Dilute solution properties of κ-carrageenan polysaccharides: effect of potassium and calcium ions on chain conformation

To gel or not to gel - Tuning the sulfation pattern of carrageenans to expand their field of application

Carrageenans represent a major cell wall component of red macro algae and, as established gelling and thickening agents, they contribute significantly to a broad variety of commercial applications in the food and cosmetic industry. As a highly sulfated class of linear polysaccharides, their functional properties are strongly related to the sulfation pattern of their carrabiose repeating units. Therefore, the biocatalytic fine-tuning of these polymers by generating tailored sulfation architectures harnessing the hydrolytic activity of sulfatases could be a powerful tool to produce novel polymer structures with tuned properties to expand applications of carrageenans beyond their current use. To contribute to this vision, we sought to identify novel carrageenan sulfatases by studying several putative carrageenolytic clusters in marine heterotrophic bacteria. This approach revealed two novel formylglycine-dependent sulfatases from Cellulophaga algicola DSM 14237 and Cellulophaga baltica DSM 24729 with promiscuous hydrolytic activity towards the sulfated galactose in the industrially established ι- and κ-carrageenan, converting them into α- and β-carrageenan, respectively, and enabling the production of a variety of novel pure and hybrid carrageenans. The rheological analysis of these enzymatically generated structures revealed significantly altered physicochemical properties that may open the gate to a variety of novel carrageenan-based applications.

Carboxymethyl hydroxypropyl guar gum physicochemical properties in dilute aqueous media

We investigate carboxymethyl hydroxypropyl guar gum (CMHPG) solution properties in water and NaCl, KCl, and CaCl2 aqueous solutions. The Huggins, Kraemer, and Rao models were applied by fitting specific and relative viscosity of CMHPG/water and CMHPG/salt/water to determine the intrinsic viscosity [η]. The Rao models yielded better results (R2 = 0.779-0.999) than Huggins and Kraemer equations. [η] decreased up to 84% in salt solution over the range 0.9-100 mM compared to water. Salt effects screened the CMHPG charged side groups chains leading to a compacted structure. In 0.9 mM NaCl(aq), the hydrodynamic coil radius (Rcoil) was 28% smaller and 45% smaller in 100 mM NaCl solution relative to water. Similar decreases were seen in KCl and CaCl2 solutions. KCl and CaCl2 were more effective than NaCl. CMHPG is salt-tolerant and shows comparatively less viscosity change than native guar gum, with modest reduced viscosity increases with CMHPG dilution at all salt concentrations. The electrostatic interactions were effective up to 100 mM salt. The activation energy of viscous flow for CMHPG solutions was computed and compared to measured xanthan gum and several literature values. These data show that the barrier to CMHPG flow is higher than for xanthan gum.

Salt and Temperature Effects on Xanthan Gum Polysaccharide in Aqueous Solutions

Xanthan gum (XG) is a carbohydrate polymer with anionic properties that is widely used as a rheology modifier in various applications, including foods and petroleum extraction. The aim was to investigate the effect of Na+, K+, and Ca2+ on the physicochemical properties of XG in an aqueous solution as a function of temperature. Huggins, Kraemer, and Rao models were applied to determine intrinsic viscosity, [η], by fitting the relative viscosity (ηrel) or specific viscosity (ηsp) of XG/water and XG/salt/water solutions. With increasing temperature in water, Rao 1 gave [η] the closest to the Huggins and Kraemer values. In water, [η] was more sensitive to temperature increase (~30% increase in [η], 20-50 °C) compared to salt solutions (~15-25% increase). At a constant temperature, salt counterions screened the XG side-chain-charged groups and decreased [η] by up to 60% over 0.05-100 mM salt. Overall, Ca2+ was much more effective than the monovalent cations in screening charge. As the salt valency and concentration increased, the XG coil radius decreased, making evident the effect of shielding the intramolecular and intermolecular XG anionic charge. The reduction in repulsive forces caused XG structural contraction. Further, higher temperatures led to chain expansion that facilitated increased intermolecular interactions, which worked against the salt effect.

The Impact of Divergent Algal Hydrocolloids Addition on the Physicochemical, Viscoelastic, Textural, and Organoleptic Properties of Cream Cheese Products

The aim of the current study was to evaluate the addition of different algal hydrocolloids (κ-carrageenan, ι-carrageenan, furcellaran, and sodium alginate) at three different concentrations (0.50, 0.75, and 1.00% w/w) on the physicochemical, viscoelastic, textural, and organoleptic properties of model cream cheese (CC) samples. On the whole, the highest viscoelastic moduli and hardness values of the CC samples were reported when κ-carrageenan was used. Furthermore, increasing the concentrations of the tested hydrocolloids led to increases in the viscoelastic moduli and hardness values of CC. Recommendations for softer-consistency CC production include the application of κ-carrageenan at a concentration of 0.50-0.75% (w/w) or the use of furcellaran and sodium alginate at a concentration of 1.00% (w/w). For the production of CC with a more rigid consistency, it is recommended to apply κ-carrageenan at a concentration higher than 0.75% (w/w).

Textural and structural properties of a κ-carrageenan-konjac gum mixed gel: effects of κ-carrageenan concentration, mixing ratio, sucrose and Ca2+ concentrations and its application in milk pudding

BACKGROUND

Mixtures of carrageenan and konjac gum are useful for specific applications in gel-based foods. Focusing on the changes of textural and structural properties, the effects of κ-carrageenan and konjac ratio and sucrose and Ca²⁺ concentrations on mixed gels were studied in this research. Furthermore, application of κ-carrageenan-konjac gum mixed gel to milk puddings was investigated.

RESULTS

There was a better synergistic effect when the ratio of κ-carrageenan and konjac was 7:3. The mixed gel containing 10 g kg^-1 κ-carrageenan-konjac gum was characterized by higher hardness, chewiness, adhesiveness and resilience and denser network structure. Besides, the addition of 5-10 wt% sucrose or 0.02 wt% Ca²⁺ could enhance the hardness, chewiness and adhesiveness of the mixed gel, as well as affording a denser network structure. For milk pudding, moderate hardness, chewiness and resilience could be obtained by adding 1.5 g kg^-1 κ-carrageenan-konjac gum mixture.

CONCLUSIONS

This research provides useful information for the formation of κ-carrageenan-konjac gum gel and its application in milk pudding. © 2020 Society of Chemical Industry.

Biocompatible Crosslinked Nanofibers of Poly(Vinyl Alcohol)/Carboxymethyl-Kappa-Carrageenan Produced by a Green Process

This study presents a new type of biocompatible nanofiber based on poly(vinyl alcohol) (PVA) and carboxymethyl-kappa-carrageenan (CMKC) blends, produced with no generation of hazardous waste. The nanofibers are produced by electrospinning using PVA:CMKC blends with ratios of 1:0, 1:0.25, 1:0.4, 1:0.5, and 1:0.75 (w/w PVA:CMKC) in aqueous solution, followed by thermal crosslinking. The diameter of the fibers is in the nanometer scale and below 300 nm. Fourier transform infrared spectroscopy shows the presence of the carboxyl and sulfate groups in all the fibers with CMKC. The nanofibers from water-soluble polymers are stabilized by thermal crosslinking. The incorporation of CMKC improves cytocompatibility, biodegradability, cell growth, and cell adhesion, compared to PVA nanofibers. Furthermore, the incorporation of CMKC modulates phenotype of human adipose-derived stem cells (ADSCs). PVA/CMKC nanofibers enhance ADSC response to osteogenic differentiation signals and are therefore good candidates for application in tissue engineering to support stem cells.

Carboxymethyl-kappa-carrageenan: A study of biocompatibility, antioxidant and antibacterial activities

Chemical modification of polysaccharides is an important route to enhance, develop or change polysaccharide properties. In this study, carboxymethylation of kappa-carrageenan (KC) with monochloroacetic acid was performed to achieve different degrees of substitution (DS) of carboxymethyl-kappa-carrageenan (CMKC). The degree of substitution ranged from 0.8 to 1.6 and was calculated from the ¹H NMR spectra. The chemical structure of the CMKCs was further characterized by FT-IR, and ¹³C NMR. FT-IR confirmed the carboxymethylation. Carboxymethylation increased viscosity of KC in water and decreased viscosity of KC in synthetic human sweat. Tests with human adipose derived stem cells showed higher viability and lower cytotoxicity for CMKCs when compared to KC. CMKCs showed no hemolytic activity to human red blood cells. CMKCs have increased antioxidant activity compared to KC. In antibacterial assays, CMKCs with DS of 0.8, 1.0 and 1.2 exhibited growth inhibition against Staphylococcus aureus, Bacillus cereus, Escherichia coli and Pseudomonas aeruginosa. CMKC with DS ranging from 1.0 to 1.2 are good candidate biomaterials for cell-contacting applications.

Structural Diversity in Galactans From Red Seaweeds and Its Influence on Rheological Properties

Galactans are important components of many plant cell walls. Besides, they are the major polysaccharides in extracellular matrixes from different seaweeds, and other marine organisms, which have an acidic character due to the presence of sulfate groups in their structures. In particular, most of the red seaweeds biosynthesize sulfated galactans with very special linear backbones, constituted by alternating (1→3)-β-d-galactopyranose units (A-unit) and (1→4)-α-galactopyranose residues (B-unit). In the industrially significant seaweeds as source of hydrocolloids, B-units belong either to the d-series and they produce carrageenans (as in the order Gigartinales), or to the l-series, and they are sources of agarose and/or structurally related polymers (i.e., Gelidiales, Gracilariales). In both cases, the latter units appear as cyclized 3,6-anhydro-α-galactose in certain amounts, which can be increased by alkaline cyclization of α-galactose 6-sulfate units. Besides, it has been clearly shown that some red algae produce different amounts of both galactan structures, known as d/l-hybrids. It is not yet clear if they comprise both diasteromeric types of units in the same molecule, or if they are mixtures of carrageenans and agarans that are very difficult to separate. It has been reported that the biosynthesis of these galactans, showing that the nucleotide transport for d-galactopyranose units is UDP-d-Gal, while for l-galactose, it is GDP-l-Gal, so, there is a different pathway in the biosynthesis of agarans. However, at least in those seaweeds that produce carrageenans as major galactans, but also agarans, both synthetic pathways should coexist. Another interesting characteristic of these galactans is the important variation in the sulfation patterns, which modulate their physical behavior in aqueous solutions. Although the most common carrageenans are of the κ/ι- and λ-types (with A-units sulfated at the 4- and 2-positions, respectively) and usually in agarans, when sulfated, is at the 6-position, many other sulfate arrangements have been reported, greatly influencing the functional properties of the corresponding galactans. Other substituents can modify their structures, as methyl ethers, pyruvic acid ketals, acetates, and single stubs of xylose or other monosaccharides. It has been shown that structural heterogeneity at some extent is essential for the proper functional performance of red algal galactans.

Rheological characteristics and chain conformation of mannans obtained from Saccharomyces cerevisiae

Mannans were extracted from S. cerevisiae, the rheological properties of mannan solutions were important in many industrial applications. In this paper, effects of mannans concentration, solution temperature, pH, salts and their concentrations on apparent viscosity were investigated. The conformational parameters of yeast mannans were determined by SEC-MALS-RI-DP. The Higiro's 1 and Higiro's 2 plots were obtained by capillary viscometry gave an intrinsic viscosity of 0.166 and 0.131dl/g. The yeast mannans solution showed Newtonian flow behavior at all the tested concentrations. The apparent viscosity of yeast mannans solution decreased continuously with the temperature increase (25°C-85°C) at a given shear rate. The viscosity did not change within the pH values of 4.0-10.0, however, it increased when the pH decreased from 4.0 to 2.0. The viscosity decreased with addition of CaCl₂ up to 10mM and remained constant above this concentration. The conformational parameters (derived from [η] vs M_w and R_g vs M_w) showed yeast mannans existed as a sphere-like shape with many shorter branches. The special flow behavior and conformation of yeast mannans may make it preferable polysaccharide in food industry.

Interaction between biopolyelectrolytes and sparingly soluble mineral particles

We investigate the complex physicochemical behavior of dispersions containing calcium carbonate (CaCO(3)) particles, a sparingly soluble mineral salt; and carrageenans, negatively charged biopolyelectrolytes containing sulfate groups. We reveal that the carrageenans suspend and stabilize CaCO(3) particles in neutral systems by absorbing on the particle surface which provides electrosteric stabilization. In addition, carrageenans provide a weak apparent yield stress which keeps the particles suspended for several months. The absorption measurements of carrageenan on the CaCO(3) particle indicate that more carrageenan is removed from the solution than expected from the case of a simple monolayer adsorption. Confocal laser scanning microscopy observations confirm that polyelectrolyte-containing precipitate is formed in both CaCO(3)-carrageenan and CaCl(2)-carrageenan mixtures. On the basis of these results, we confirm that in the presence of carrageenan some CaCO(3) dissolves and the Ca(2+) ions interact with the sulfate groups leading to aggregation and formation of particle-like structures. These new insights are important for fundamental understanding of other mineral-polyelectrolyte systems and have important implications for various industrial applications where calcium carbonate is used.

Carrageenan-based hydrogels for the controlled delivery of PDGF-BB in bone tissue engineering applications

One of the major drawbacks found in most bone tissue engineering approaches developed so far consists in the lack of strategies to promote vascularisation. Some studies have addressed different issues that may enhance vascularisation in tissue engineered constructs, most of them involving the use of growth factors (GFs) that are involved in the restitution of the vascularity in a damaged zone. The use of sustained delivery systems might also play an important role in the re-establishment of angiogenesis. In this study, kappa-carrageenan, a naturally occurring polymer, was used to develop hydrogel beads with the ability to incorporate GFs with the purpose of establishing an effective angiogenesis mechanism. Some processing parameters were studied and their influence on the final bead properties was evaluated. Platelet derived growth factor (PDGF-BB) was selected as the angiogenic factor to incorporate in the developed beads, and the results demonstrate the achievement of an efficient encapsulation and controlled release profile matching those usually required for the development of a fully functional vascular network. In general, the obtained results demonstrate the potential of these systems for bone tissue engineering applications.