The impact of seaweed life phase and postharvest storage duration on the chemical and rheological properties of hybrid carrageenans isolated from Portuguese Mastocarpus stellatus

Structure and properties of polysaccharides from tetrasporophytes of Mazzaella parksii

The structure and anti-SARS-CoV-2 activity of sulfated polysaccharides (Mzpt) obtained in high yield (60 %) from tetrasporophytes of Mazzaella parksii were studied. Stepwise fractionation with KCl showed that Mzpt consisted of eight (MzptF1-MzptF8) carrageenans fractions, differing in structure and molecular weight. The yield of non-gelling MzptF8 was 58.1 % of the original Mzpt. According to IR and NMR spectroscopies, gelling MzptF1 and MzptF2 were mainly kappa/iota/nu-carrageenans. MzptF7 included mainly lambda-carrageenan and in smaller quantities kappa-, iota-, mu- and nu-carrageenans. MzptF8 had a complex composition and included gamma-carrageenan, unsulfated carrageenan, probably, delta-carrageenan and also structural elements of xi-, psi- and omicron-carrageenans. According to atomic force microscopy data, MzptF8 involved several polymer chains associated with each other in a disordered structure, in contrast to MzptF2, which formed three-dimensional networks. Unlike ribavirin and remdesivir, Mzpt was not cytotoxic to Vero E6 cells at concentrations >2000 μg mL-1. Mzpt was shown to inhibit SARS-CoV-2 replication in a dose-dependent manner in CPE inhibition and RT-PCR assays. IC50 was 92.0 μg mL-1, SI - 22. At concentration 250 μg mL-1, Mzpt caused the highest reduction in viral RNA levels with an inhibition coefficient of 31.1 % and exhibited significant inhibition of the early stages of virus-cell interaction.

Eco-friendly kappa-carrageenan-nano zerovalent iron hydrogel water and wastewater purification

Sustainable water management is crucial for reducing environmental impact, improving public health, and contributing to the United Nations' Sustainable Development Goals (SDGs). This study introduces a novel hydrogel composite membrane for wastewater treatment and desalination. The membrane was fabricated by cross-linking kappa-carrageenan (κC) with nano-zerovalent iron (nZVI) using polyethyleneimine (PEI) to produce a porous structure hydrogel membrane of high water flux and contaminant rejection via adsorption and reduction processes, leveraging the properties of kappa carrageenan and nZVI. Experiments showed an increased water flux and rejection rate for the hydrogel membrane by increasing the pressure from 10 psi to 30 psi. In initial tests with 2 g/L of NaCl or MgSO4, the membrane exhibited 98 % rejection of divalent Mg2 + ions and 90 % rejection of Na+ ions at 30 psi and 17.98 L/M2H water flux. The hydrogel's contaminant separation mechanisms involve a combination of size exclusion, electrostatic repulsion, and hydrophilic-hydrophobic polarity rejection. Leachate wastewater treatment by the membrane achieved 11 L/m2h water flux at 30 psi and an outstanding rejection rate of more than 98 % for divalent ions, such as Li+, Pb2+, Cd2+, Co2+, and Cu2+, and 61 % rejection of organic matter of 165.68 mg/L initial concentration. Due to membrane fouling, the water flux decreased in the second and third filtration cycles, while membrane rejection remained unchanged. The dead-end filtration mode facilitated metal ions recovery at the end of the experiments, recording 68.32 % and 66.31 % recovery for lead and lithium ions. This novel hydrogel provides a promising and sustainable solution for water purification and valuable heavy metals recovery from solutions to support the circular economy.

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.

Carrageenans and Their Oligosaccharides from Red Seaweeds Ahnfeltiopsis flabelliformis and Mastocarpus pacificus (Phyllophoraceae) and Their Antiproliferative Activity

Comparative structural analysis of gelling polysaccharides from A. flabelliformis and M. pacificus belonging to Phyllophoraceae and the effect of their structural features and molecular weight on human colon cancer cell lines (HT-29, DLD-1, HCT-116) was carried out. According to chemical analysis, IR and NMR spectroscopies, M. pacificus produces kappa/iota-carrageenan with a predominance of kappa units and minor amounts of mu and/or nu units, while the polysaccharide from A. flabelliformis is iota/kappa-carrageenan (predominance of iota units) and contains negligible amounts of beta- and nu-carrageenans. Iota/kappa- (Afg-OS) and kappa/iota-oligosaccharides (Mp-OS) were obtained from the original polysaccharides through mild acid hydrolysis. The content of more sulfated iota units in Afg-OS (iota/kappa 7:1) was higher than in Mp-OS (1.0:1.8). The poly- and oligosaccharides up to 1 mg/mL did not show a cytotoxic effect on all tested cell lines. Polysaccharides showed an antiproliferative effect only at 1 mg/mL. Oligosaccharides had a more pronounced effect on HT-29 and HCT-116 cells than the original polymers, while HCT-116 cells were slightly more sensitive to their action. Kappa/iota-oligosaccharides exhibit a greater antiproliferative effect and more strongly decrease the number of colonies forming in HCT-116 cells. At the same time, iota/kappa-oligosaccharides inhibit cell migration more strongly. Kappa/iota-oligosaccharides induce apoptosis in the SubG0 and G2/M phases, while iota/kappa-oligosaccharides in the SubG0 phase.

Structural peculiarities of carrageenans from Far Eastern red seaweed Mazzaella parksii (Gigartinaceae)

The sulfated polysaccharides from cystocarpic plants of Mazzaella parksii were studied. Fractionation at a given KCl concentration allowed us to assume, and stepwise fractionation to prove, that these polysaccharides consisted of several carrageenans that differed in structure and molecular weight. As a result of stepwise fractionation with KCl, nine gelling (1-9) and one non-gelling (10) fractions were obtained. Using IR spectroscopy, it was shown that fractions 3, 4 and 5 were kappa/iota-, kappa- and kappa/beta-carrageenans, respectively. The structures of the main fractions 1, 2, 9 and 10 were investigated in more detail by methylation, NMR spectroscopy and mass spectrometry. Fractions 1 and 2 were hybrid kappa/iota-carrageenans with kappa:iota ratio 79:21 and 63:37, respectively. At the same time, fraction 9 contained kappa-, iota- and small amounts of nu-carrageenans. The fraction 10 had complex structure and was built from kappa-, iota-, beta-, mu- and nu-carrageenans and included agar-like structure, which explained the inability of this fraction to gel at 15 % KCl. It was shown that isolated polysaccharides activated the classical pathway of complement system, increasing the concentration of C1 inhibitor of serine protease by 50 % compared with the negative control.

Microwave-Assisted Extraction of Carrageenan from Sarcopeltis skottsbergii

The development of greener processes for the sustainable utilization of raw materials is increasingly demanded for environmental and economic reasons. A rapid and chemical-free technique was proposed for the extraction of hybrid kappa/iota (6/4) carrageenan from Sarcopeltis (ex Gigartina) skottsbergii. After separation, carrageenans were analyzed by Fourier transform infrared attenuated total reflectance, high-performance size-exclusion chromatography, and rheology. Maximum carrageenan extraction yields up to 63-64% were obtained operating at 110 or at 160 °C, for 5-7 min considering the sum of the heating and cooling periods, but the extraction of the phenolic fraction was favored at 220 °C. The recovered carrageenan showed apparent viscous values around 10³ mPa at the lowest tested shear rates (0.1 1/s) and could be suitable to formulate films. Furthermore, those carrageenans obtained under 140 °C showed gel characteristics without previous separation from the liquid extract, avoiding ethanolic precipitation and energy consumption. The antiradical properties correlated with the phenolic content in the liquid phase, but no influence of temperature on the reducing properties was observed. The microwave-assisted hydrothermal treatment could be an efficient tool without needing chemicals for the extraction of carrageenans, which showed adequate rheological properties for commercial uses.

Improved extraction of carrageenan from red seaweed (Chondracantus canaliculatus) using ultrasound-assisted methods and evaluation of the yield, physicochemical properties and functional groups

Red seaweed Chondracanthus canaliculatus, an underexploited algae species, was used as a potential source for the obtaining of carrageenan. Seaweed was treated under alkaline conditions using ultrasound alone or combined with conventional procedures, to improve the yield extraction. Color, syneresis behavior, water retention capacity, and functional groups of the gelling and non-gelling fractions of carrageenan were determined; these properties were compared with those of commercial carrageenans named A and B. Ultrasound alone or with heat significantly (p < 0.05) increased the yield extraction up to 41-45% and influenced color parameters, in comparison with conventional treatments. Functional groups kappa and iota, and alginates, were confirmed in both carrageenan fractions. Syneresis behavior was well fitted to a third-degree polynomial equation within days 1 to 6, after which, it reached a plateau. While, the use of ultrasound at room temperature gave carrageenan properties more similar to those of the commercial carrageenan type A.

Hybrid carrageenans: isolation, chemical structure, and gel properties

Hybrid carrageenan is a special class of carrageenan with niche application in food industry. This polysaccharide is extracted from specific species of seaweeds belonging to the Gigartinales order. This chapter focuses on hybrid carrageenan showing the ability to form gels in water, which is known in the food industry as weak kappa or kappa-2 carrageenan. After introducing the general chemical structure defining hybrid carrageenan, the isolation of the polysaccharide will be discussed focusing on the interplay between seaweed species, extraction parameters, and the hybrid carrageenan chemistry. Then, the rheological experiments used to determine the small and large deformation behavior of gels will be detailed before reviewing the relationships between gel properties and hybrid carrageenan chemistry.