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Thermal stability of red algal galactans: Effect of molecular structure and counterions
Abstract
Thermal degradation of κ-, ι-, λ-carrageenans, furcellaran, funoran and agarose samples in dry and sol states was investigated. The polysaccharides subjected to heat treatment were characterized by ¹H NMR, ¹³C NMR and FTIR spectroscopy, size exclusion chromatography and static rheometry methods The microstructure of galactan gels was studied using a cryofixation method in combination with freeze-drying and SEM techniques. Thermal stability at high temperatures decreases in the order of agarose > furcellaran > funoran > κ-carrageenan > λ-carrageenan > ι-carrageenan for dry preparations. The respective sequence for sol state is ι-carrageenan > λ-carrageenan > κ-carrageenan > furcellaran > funoran > agarose. The presence of methoxy groups stabilizes algal polysaccharides whereas divalent cations as counterions increase the susceptibility towards thermal degradation. In dry state the thermal treatment leads to significant desulfation of the galactan before the complete depolymerization occurs. Depending on the sulfation degree and the presence of 3,6-anhydrogalactose residues in the galactan, a notable amount of 5-hydroxymethylfurfural (yield 0.7–21.8%) is formed during the decomposition in sol state.
... Depolymerization not only lowers gel strength and viscosity, care should be also taken since degraded fractions (10-20 kDa) are not authorized for food use, although interesting activities can be obtained for these degraded fractions, including antitumor, antiviral, antibacterial or antioxidant [7,11,23]. ...
... Degradation is also influenced by the sulfation degree and presence of 3,6-anhydrogalactose, which is highly unstable in its free form at high temperatures. The formation of 5-hydroxymethylfurfural may occur both in the solid and in the soluble state, during the treatment with subcritical water under argon atmosphere and it is promoted by anhydrogalactose residues whilst being hindered by sulfation and OMe substituents [23]. The release of sulfate groups occurs in moderate acidic media, before complete depolymerization, with the most susceptible groups being the sulfate esters adjacent to the anomeric carbon [23]. ...
... The formation of 5-hydroxymethylfurfural may occur both in the solid and in the soluble state, during the treatment with subcritical water under argon atmosphere and it is promoted by anhydrogalactose residues whilst being hindered by sulfation and OMe substituents [23]. The release of sulfate groups occurs in moderate acidic media, before complete depolymerization, with the most susceptible groups being the sulfate esters adjacent to the anomeric carbon [23]. The acid polysaccharide extracted after high-pressure homogenization contains mainly galactose and small proportions of rhamnose, xylose, mannose, and glucose. ...
... The elevated and uneven conditions during direct drying may initiate the degradation of polysaccharide macromolecules and consequently can affect the gels' rheological and mechanical properties. Robal et al. [17] have studied carrageenans' thermal stability in dry and sol states. They found that degradation during heat treatment in the dry state depends on the galactan's sulphur content and decomposition begins at lower temperatures for more sulphated preparations. ...
... Compared with non-treated Fur (Figure 1), three additional peaks, at 90.4, 87.2 and 82.8 ppm (DA-C1, DA-C4, and DA-C3, respectively), appeared, indicating the formation of oligosaccharides with decreasing terminal 3,6-anhydro-α-D-galactose residues [38]. Similarly to Robal et al.'s work [17], concurrent β-D-galactose and β-D-galactose-4-sulphate anomeric signals became segregated, with the latter showing slightly higher peaks in the spectrum. Also, a decrease in anomeric carbon of 3,6-anhydro-α-D-galactose residue at 95.0 ppm was observed, which can be explained by galactan desulphation [17]. ...
... Similarly to Robal et al.'s work [17], concurrent β-D-galactose and β-D-galactose-4-sulphate anomeric signals became segregated, with the latter showing slightly higher peaks in the spectrum. Also, a decrease in anomeric carbon of 3,6-anhydro-α-D-galactose residue at 95.0 ppm was observed, which can be explained by galactan desulphation [17]. ...
In the production of biopolymers, the processing operations (e.g. extraction and drying) involve some degradation of the polysaccharide-causing structural and functional changes in final products. In this study, short-term heat treatment (75–115 °C, 15 min) influence on commercial carrageenans' — furcellaran, κ-carrageenan, ι-carrageenan and a κ/λ-carrageenan — structure, molecular weight and gel rheology was studied. Compared with other carrageenans, commercial furcellaran that had undergone multiple heatings at high temperatures during production was found to be susceptible to polymer degradation. Heat caused the desulphation and degradation of furcellaran galactans and the molecular weight was significantly decreased, causing a drop in viscosity and gel hardness. The loss of the network cross-linking of furcellaran gels was confirmed by scanning electron microscopy. Carrageenan gel storage modulus values decreased with the increase in the temperature of the treatment. The greatest decrease in storage modulus values occurred with κ/λ-carrageenan gels, followed by ι-carrageenan > furcellaran > κ-carrageenan.
... In the last years, there has been a worldwide increase in the demand for red seaweeds in the hydrocolloids industries (Robal, Truus, Volobujeva, Mellikov, & Tuvikene, 2017). Gigartina skottsbergii (Gigartinales, Rhodophyta) is considered to be one of the most important hybrid carrageenan producing red seaweed commercially in Chile (Buschmann, Correa, Westermeier, Hernández-González, & Norambuena, 2011). ...
... The carrageenan primary structures are based on an alternating disaccharide repeating sequence of 3-linked β-D-galactose and 4-linked α-D-galactose (Robal et al., 2017). The principal gelling carrageenans are kappa and iota disaccharide units, which present one and two sulfates groups per disaccharide repeat unit, respectively (Doyle, Giannouli, Rudolph, & Morris, 2010). ...
... The block length and the relative amount of kappa-and iotacarrageenan, as well as the relative content of more sulphated carrageenan units, depend on several factors such as the life stage or the family of the seaweeds (van de Velde, 2008;Souza, Hilliou, Bastos, & Gonçalves, 2011). A critically relevant characteristic of these carrageenans is their structural stability (Robal et al., 2017). Gels from carrageenan can be formed on cooling and melted on heating. ...
The effect of different counterions (Na⁺, K⁺ and Ca²⁺) on the sol-gel transition diagrams of kappa/iota-hybrid carrageenan isolated from Gigartina skottsbergii, together with the thermo-rheological features of the obtained gels are presented. Extraction yield (47.8 ± 3.5 g/100 g), molar fractions of kappa (62 ± 2) and iota (38 ± 2) and polymers with molecular masses between 7.5 10⁴ and 7 10³ g/mol were also determined for G. skottsbergii extracts. Gels formed in NaCl exhibited stable and weak gel properties. Gels made in KCl and CaCl2 featured stable and intermediate gel characteristics, except those formulated at the largest carrageenan and salt content that can be considered strong. All gels achieved stability after 15 min of maturation. No water syneresis was identified in tested gels. Gel setting and melting temperatures depended on the biopolymer and ionic contents. Gels formed in CaCl2 at the largest biopolymer content and ionic concentration showed thermo-reversible features.
... Values of the molar fractions of kappa-and iota-carrageenan disaccharide units determined by 1 [43], where alkali processing conditions were employed. The thermal treatment used during the microwave-assisted extraction seems to impact the purity of the recovered carrageenans since the impurities found in the samples tended to increase with increasing thermal processing conditions during the biopolymer extraction [44]. ...
... During the thermal decomposition of carrageenan in a sol state, the sulfation degree and the 3,6-anhydrogalactose content influenced the amount of 5-hydroxymethylfurfural (yield 0.7-21.8%) [44]. In our study, no degradation products were detected in the direct chromatographic analysis. ...
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.
... Hence, it is essential to understand the functionalities as well as the limitations of these substances for their practical use in consumer products. Polysaccharide degradation is a complex process affected by various factors such as temperature, pH, pressure, and presence of oxidizing agents [21]. Hence it is essential to maintain these factors under controlled conditions for increasing the shelf life of such products. ...
... Nevertheless, carrageenans used in many consumer products have not shown any adverse effects on the human skin. Carrageenans are stable in neutral or alkaline environments whereas their stability decreases when the pH is lower than 4.0 and under high temperatures causing polymer hydrolysis [21]. Currently, functionalizing biopolymers with structural modifications is an upcoming trend in biopolymer research. ...
The cosmetics industry is one of the most profitable in the world today. This multi-billion-dollar industry has a profound sociological impact worldwide. Its influence is global, with most individuals being concerned with conserving their physical appearance, beauty, and youth. The consumers’ desire for novel, better, and safer products has stimulated the utilization of natural-product-based cosmeceutical formulations over synthetic chemicals. With remarkable advancements in marine bioresource technology, algal polysaccharides have gained much attention as bioactive ingredients in cosmeceuticals. Algae biosynthesize a variety of polysaccharides including fucoidans, alginates, carrageenans, galactans, agar, porphyran, glucans, and ulvans, all of which exhibit distinctive structural and functional properties. Many of these materials have been proven to possess skin-protective effects, including anti-wrinkle, lightening, moisturizing, UV protective, antioxidative, and anti-inflammatory activity. Moreover, they have a wide spectrum of physicochemical properties, such as the ability to form hydrogels, which extend their utilization as emulsifiers, stabilizers, and viscosity controlling ingredients in cosmeceuticals. Accordingly, algal hydrocolloids and their synthetic derivatives can also be applied in tissue engineering and cosmetic surgery. The challenge is to increase awareness about these polysaccharides and consequently generate value-added products. This review discusses the beneficial biological and physicochemical properties of algal polysaccharides, highlighting their potential in cosmeceutical applications.
... For the rarely methoxylated galactans, K + as an example, is known to cause intense conformational changes in kappa-carrageenan and furcellaran whereas Ca 2+ predominantly influences iota-carrageenan. These cations change the coil-to-helix structure and induce gelation by aggregating their helices (Rhein-Knudsen et al., 2017;Robal, Truus, Volobujeva, Mellikov, & Tuvikene, 2017;Saluri, Kaljuvee, Paalme, Reile, & Tuvikene, 2021;Thrimawithana, Young, Dunstan, & Alany, 2010). As anticipated, a combination of K + and divalent Ca 2+ in this study, did not have much of a gelling influence on these heterogeneous fractions. ...
The effect of different cations (K+, Ca2+ and Ba2+) on the gel forming properties of sulfated polysaccharides isolated from the red epiphytic alga, Vertebrata lanosa, using a successive cold (25 °C) and hot (95 °C) alkaline extraction process is presented. The elucidation of their monomeric composition using a two-step reductive hydrolysis and structural analyses (1D and 2D NMR) revealed d-galactose (G) linked to 3,6-anhydro-l-galactose (LA) and also sulfated 3,6-anhydro-l-galactose (L6S) as the major monomers with some amounts of glucose, β-d-xylose, 6-O-methyl-d-galactose (G6M), 2-O-methyl-l-anhydrogalactose (LA2M) and l-arabinofuranose. This composition implied the presence of both diads of agaran types, funoran and porphyran in polysaccharides from Vertebrata lanosa. Similar to funorans, their gelation, was highly influenced in the presence of Ba2+ ions compared to other tested salts. 0.2 M of BaCl2 in the hot extracted fractions recorded storage modulus (Gʹ) to up to ∼80 Pa and increased complex viscosity to 16,000 mPa s compared to the <5 Pa storage modulus from pristine solutions with no added salts. Sulfate amount contained within these fractions ranged up to ∼30% with less than 1 % (gallic acid equivalent, GAE) total phenolic compounds. Some of these fraction, nonetheless, have shown good α-amylase and reactive oxygen species (ROS) inhibition activities thus suggesting a nutraceutical potential of hydrocolloids from this algal species.
... The 3,6-anhydro-α-D-galactopyranose residues are unstable at elevated temperatures and further degrade to 5-hydroxymethylfurfural (HMF) during the thermal treatment. Robal, Truus, Volobujeva, Mellikov, and Tuvikene (2017) reported that the thermal stability of algal galactans at high temperatures decreases in the order of agarose > κ-carrageenan > λ-carrageenan > ι-carrageenan. ...
Algal polysaccharides have become more popular in the food and packaging industry because of their excellent physicochemical properties. Further, the use of biodegradable, biobased polymers as an alternative renewable source for developing environmentally friendly materials has emerged as a substitute for non-renewable plastic materials. In this regard, algal polysaccharide-based biopolymers are highly studied in the development of novel packaging materials with the improved barrier, mechanical, antioxidant, and antimicrobial properties. In this review, major algal polysaccharides, such as galactans (agar, carrageenan), alginates, and ulvan, are mainly considered and will give information about their structure, properties, and applications in the food packaging industry.
... The improvement in thermal stabilities can be attributed to the algae associated chemical components of the CS/GT*m-Alg/ZnO based on earlier studies. 38 Figure 3A shows how the contact time affects the removal efficiency of BPA using CT/GT, CT/GT/ZnO, and CT/ GT*m-Alg/ZnO beads through the presentation of the results of corresponding experiments. Various reaction times were implemented (10−60 min). ...
Water polluted by phenolic compounds is a global threat to health and the environment; accordingly, we prepared a green novel sorbent biological system from a chitosan (CS), gelatin (GT), and Chlorella vulgaris freshwater microalgae (m-Alg) composite impregnated with zinc oxide nanoparticles (ZnO-NPs) for the remediation of bisphenol-A (BPA) from water. C. vulgaris was selected to be one of the constituents of the prepared composite because of its high capability in phytoremediation. The morphology and the structure of CS/GT*m-Alg/ZnO beads were characterized by SEM, FTIR, XRD, and TGA. Different monitoring experimental conditions, such as contact time, pH, BPA concentration, and sorbent dosage, were optimized. The optimum conditions for the adsorption process showed outstanding removal efficiency toward BPA at pH 4.0, contact time 40.0 min, and 40.0 mg L-1 BPA initial concentration. Langmuir, Freundlich, and Temkin isotherm models have been studied for adsorption equilibrium, and the best fit is described by the Langmuir adsorption isotherm. The adsorption kinetics has been studied using pseudo-first-order (PFO), pseudo-second-order (PSO), Elovich, and intraparticle diffusion (IPD) models. The pseudo-second-order kinetic model shows the optimum experimental fit. The monolayer adsorption capacity of the prepared CS/GT*m-Alg/ZnO for BPA was determined to be 38.24 mg g-1. The prepared CS/GT*m-Alg/ZnO beads show advantageous properties, such as their high surface area, high adsorption capacity, reusability, and cost-effectiveness.
... [4][5][6][7] Hence deacetylation should be of considerable interest in the food industry for regulating the required gel properties of KGM. κ-Carrageenan (CAR), composed of ⊎-1,3-galactopyranose and 3,6-anhydro-⊍-1,4-galactopyranose, 8 has been widely employed as a favorable food additive such as gelling agent. 9 Certain cations, such as potassium ion, could promote the formation of gel. 10 Nevertheless, the brittleness, low elasticity and poor water-holding capacity of CAR have severely limited its application in gel food. ...
BACKGROUND
Konjac glucomannan (KGM) showed a synergistic interaction with κ‐carrageenan (CAR), which led to the formation of a promising compound hydrocolloid gel in the food field (such as jelly). Nevertheless, the mixed gels formed by adding KGM to CAR still displayed defects in gel strength and syneresis, and would hardly meet the quality requirements of some gel foods. However, deacetylated KGM and maltodextrin (MD) have always been used in gel foods and affect their viscosity and rheological properties.
RESULTS
In our paper, different amounts of MD were first used to alter the textural properties, and the results showed that both tensile strength and elongation exhibited first an increasing and then a decreasing trend with the increasing MD proportion and achieved a maximum at a final maltodextrin proportion of 4 g kg⁻¹ in the KGM/CAR/MD system. Based on the above results, we further explored the effects of deacetylation degree of KGM on the gel properties of mixed gel system. The results revealed that, compared to the native KGM, the partial deacetylated KGM was capable of significantly improving the tensile strength and elongation of KGM/CAR mixed gel.
CONCLUSION
Our study found that the appropriate addition of MD (0.4%) and DKGM were able to alter the tensile properties of KGM/CAR mixed gel, with potential to meet the needs of consumers and further design innovative tensile gel products in the soft gel industry. © 2021 Society of Chemical Industry
... This renders iota carrageenan more stable compared to kappa carrageenan. The stability usually decreases in the order of iota carrageenan > lambda carrageenan > kappa carrageenan > furcellaran > agarose (Robal, Truus, Volobujeva, Mellikov, & Tuvikene, 2017). Susceptibility toward degradation is notably influenced by the presence of counterions and co-solutes which have a strong influence on the conformation of the polysaccharide chains. ...
Carrageenans represent a group of high-molecular-weight sulfated galactans found in the cell walls of red algae. The structural diversity of these polysaccharides gives rise to a wide range of rheological properties beneficial in various food and nonfood applications. This chapter provides an overview of the manufacturing process, chemical composition, and functional characteristics of different carrageenan types. The effects of co-solutes and counterions on texturizing properties of the commercially important kappa, iota, and lambda carrageenans are covered in detail. Furthermore, physicochemical properties of frequent hybrid carrageenans, including furcellaran, are summarized. Finally, the regulatory status and common applications of carrageenans are presented, along with the primary methods to test or analyze these biomolecules in commercial formulations.
... The presence of 3,6-anhydrogalactose in the galactan hydrolysis, a notable amount of 5-hydroxymethylfurfural (yield 0.7e21.8%) was formed during the decomposition in a soluble state [62]. ...
The study aimed to utilize the industrial spent seaweed biomass (SSB) for effective ethanol production using yeast as a fermenting microorganism. Pretreatment of SSB was optimized using different acids. The highest percentage of spent biomass was obtained from G. corticata (12.53 ± 2.66% DW). The proximate, ultimate and biochemical constituents of spent biomass were calculated. The total sugar (440 ± 40 mg/g DW), reducing sugar (129.85 ± 10.23 mg/g DW) and protein (11.08 ± 0.11 mg/g DW) content of SSB were analysed. Pretreatment was optimized using three different acids. The effect of different pH (4.5, 5.0, 5.5 and 6.0) and temperature (30 and 35 °C) on ethanol production using baker’s and MTCC yeast was studied. At 35 °C, the maximum (4.85% w/w) ethanol production was achieved in a fermentation process maintained at pH 4.5 and 5.0 at 24 h and 72 h, respectively. Substrate fermented with MTCC yeast recorded the maximum production of ethanol (4.98% w/w) at pH 4.5 within 48 h. The fermentation process was scaled up to 300 mL for ethanol production, and achieved 3.75% w/w ethanol (72 h, pH 5.5). To conclude, in future SSB would be a potential renewable novel substrate for bioethanol production when compared to other lignocellulosic substrates.
... The κ-carrageenan (CAR), a kind of sulphated polysaccharide, is composed of β (1 → 3) galactopyranose and 3, 6 anhydro α (1 → 4) galactopyranose (Robal, Truus, Volobujeva, Mellikov, & Tuvikene, 2017). CAR tends to form an elastic gel because of the varied conformation from a coil random to a double helix by cooling (Ikeda & Nishinari, 2001). ...
The rheological and textural properties of κ-carrageenan (CAR) and konjac glucomannan (KGM) with definite deacetylation degree (DD) mixed system in the presence of potassium chloride (KCl) were investigated to study the influence of deacetylation degree on KGM, CAR and KCl mixed system. The results revealed that the zero-shear viscosities of the mixed sol system increased firstly and then decreased with the gradual increase of DD. Besides, the sols had the capability of being transformed into irreversible gel by heating them at 80 °C for 30 min and then cooling to room temperature. The DD of KGM did have impacts on the characteristics of the ensuing hydrogels. That is, the mixed gels showed an initial increase and ensuing decrease in gel strength over DD, reaching the maximum with a DD of 21.07%. Overall, by controlling the deacetylation degree of KGM, the gel behaviors of the mixed system can be regulated.
... Doped with metal-organic materials or binary transitionmetal oxides, agarose polymer electrolytes can be utilized for quasi-solid-state dye-sensitized solar cells [85]. Compared with other polysaccharides, such as furcellaran, funoran, or carrageenan, it shows the highest thermal stability in the dry state and the lowest thermal stability in the sol state [86]. Magnetic agarose bead based assays were produced for examination of the influence of natural products on C5 interaction [87]. ...
Carboxymethylcellulose (CMC) belongs to the biopolymers with interesting intrinsic physical and chemical properties which can be used for diverse medical, biotechnological and other applications. CMC has, e.g., been used for drug delivery of diclofenac or lidocaine. Blended with poly(vinyl alcohol), sodium carboxymethylcellulose has shown pH-responsive swelling behavior. CMC acetate butyrate, on the other hand, showed increased hydrophobicity. Although CMC is known to be electrospinnable with poly(ethylene glycol) (PEG), experiments to create such nanofiber mats are scarce. The chapter thus gives an overview of recent developments in electrospinning carboxymethylcellulose nanofiber mats and reports on the latest results of our group in needleless electrospinning CMC/PEG nanofibers as well as tests of CMC blended with other (bio)polymers. It shows that while electrospinning CMC in combination with PEG as a spinning agent can result in relatively homogeneous mats of fine nanofibers, blends of CMC with other (bio)polymers do not create spinnable polymer solutions, but partly at least solutions for electrospraying. In both cases, however, the polymer blend ratios are crucial and must be tailored carefully to enable electrospinning or electrospraying, respectively. Generally, it can be concluded that CMC does not only belong to the not electrospinnable polymers, but even prohibits electrospinning of usually spinnable polymers already for small amounts of carboxymethylcellulose.
... In addition, when some of the acetyl groups are removed from the molecular chain, the gel properties of KGM change, and the structure of the gel formed by deacetylated konjac glucomannan (Da-KGM) is irreversible at almost all temperatures [11]. κ-Carrageenan is a hydrophilic polysaccharide composed of β-D(1 → 3)-galactopyranose and 3,6-anhydro-α-D(1 → 4)-galactopyranose [12]. κ-Carrageenan has been widely used in the food industry as a food additive, and many of its properties are considered to be superior to those of other similar hydrocolloids for use as a thickener, gelling agent and stabilizer [13]. ...
The main aim of the current study was to research the effect of the degree of konjac deacetylation on the rheological and textural properties of konjac glucomannan (KGM) and κ-carrageenan blends. A series of deacetylated konjac glucomannan (Da-KGM) with different degrees of deacetylation (0, 20.35%, 35.62%, 57.19%, and 74.01%) was prepared by a heterogeneous deacetylation method. The rheological and textural properties of mixed sols and gels of Da-KGM with different degrees of deacetylation and κ-carrageenan were determined. The results showed that the viscosities of mixed sols of Da-KGM and κ-carrageenan decreased with increasing degree of deacetylation. The partial removal of acetyl groups from konjac glucomannan could significantly improve the hardness and springiness of mixed gels of KGM and κ-carrageenan. Meanwhile, decreasing the acetyl content could decrease the syneresis of mixed gels. By regulating the deacetylation degree of konjac, gels with high gel strength could be prepared, which provides a new idea for the production of high-strength gelatin food.
... L'effet des conditions acides (pH 3 - 4) ont ?t? d?crites comme ayant un effet sur la stabilit? des carragh?nanes entrainant d?gradations s?v?res de leur structure (Masson et al. 1954 ;Robal et al. 2017). De ce fait, il est possible que le traitement par le CO 2 supercritique, fluide pr?sentant un pH acide, entraine une d?polym?risation des carragh?nanes. ...
Ce projet de thèse a été réalisé au sein du Laboratoire de Biotechnologie et Chimie Marines. Ce travail est le fruit d’une collaboration au niveau régional avec deux entreprises morbihannaises Armen Instruments et Newonat et au niveau international avec l’institut de recherche CINVESTAV au Mexique. Solieria chordalis (Rhodophyta, Gigartinales) est une algue proliférante de la côte de Bretagne sud. Cette algue s’échoue chaque année sur la presqu’île de Rhuys dans le Morbihan, et représente une biomasse importante encore sous exploitée. Les objectifs de cette thèse portent sur l’application de différents procédés éco-responsables (CO2 supercritique, Extraction Assistée par Enzyme et Extraction Assistée par Microondes) utilisés pour l’extraction de molécules à partir de S. chordalis. Dans le cadre de la première partie, l’extraction assistée par microondes a permis la production d’extraits polysaccharidiques de faibles poids moléculaires non cytotoxiques dont l’efficacité antivirale est supérieure à celle observée pour les fractions obtenues après extraction aqueuse à haute température. La deuxième partie concerne le couplage de différents procédés : Extraction Assistée par Enzymes (EAE), CO2 supercritique et Extraction Assistée par Microondes (EAM). En fonction des procédés utilisés, différentes familles de molécules ont pu être caractérisées. Le couplage de procédés permet de proposer un schéma de bioraffinage. La dernière partie porte sur l’optimisation d’une méthode de fractionnement par Chromatographie de Partage Centrifuge (CPC). Ce système de purification innovant a conduit à l’isolement de composés naturels dont des Mycosporines-like Amino Acids ayant différentes propriétés valorisables dans le domaine de la cosmétique. Ces travaux enrichissent les connaissances sur l’algue S. chordalis et ouvrent la voie à la valorisation de cette biomasse proliférante sur les côtes bretonnes.
As a polysaccharide extracted from marine red algae, carrageenan has the advantages of biodegradability, nontoxicity and water solubility over petroleum‐based plastics for use as films and coatings for keeping food fresh. Aqueous solutions of carrageenan can be cast into films on plates and then made into food packaging bags, as well as coated directly onto food surfaces, all of which are referred to as ‘wraps’. To overcome the inherent limitations of carrageenan as a packaging material, physical and chemical modifications have been studied. The mechanical, thermal, barrier and antibacterial properties of modified carrageenan make it widely applicable for extending the shelf life of food products and monitoring its freshness. The research progress of carrageenan‐based wraps in recent years has been reviewed in terms of preparation methods, physicochemical properties, gelation mechanisms and applications, and the factors affecting the drying rate of them have been analysed. Finally, applications and future research directions of carrageenan are summarized and discussed to provide useful guidelines for further research.
Konjac glucomannan (KGM) is commonly blended with κ-carrageenan to improve the gel properties of food, which are mostly influenced by KGM purification. Control of ethanol pH for KGM purification is an easy and simple option to modify the properties of KGM, that tends to alter the gel properties of κ-carrageenan/KGM blends. In this study, the effect of ethanol at different pH (ranging from 2.5 to 12.5) on KGM was investigated, and the gels of κ-carrageenan with KGM purified by ethanol at different pH were prepared with microwave heating. With KGM purified with ethanol between pH 5.5 and 9.5, κ-carrageenan/KGM blends exhibited higher gel strength, hardness and water holding capacity than those of gel with native KGM, which was much related with the removal of impurity, the increased viscosity and altered structure of KGM, enhancing the interaction between κ-carrageenan and KGM. Poor gel properties of the blends were observed with KGM purified with ethanol at pH between 2.5 and 4.5 caused by KGM degradation, or at pH 12.5 due to the removal of acetyl groups. Thus, control of ethanol pH during KGM purification can easily and simply optimize the gel characteristics of κ-carrageenan/KGM blends to meet desired application requirements.
We synthesized a designed monomer with azide and alkyne units that mimic α-d-galactose for topochemical azide-alkyne cycloaddition polymerization to produce a cross-linkable galactan-mimic. The monomer molecules pre-organize in the crystals in a linear head-to-tail fashion, with the reactive units properly aligned for topochemical reaction. When the monomer crystals are heated, they undergo regiospecific topochemical azide-alkyne cycloaddition polymerization, resulting in a galactan-mimic with two vicinal diol units per repeating unit. We covalently cross-linked this galactan-mimic using bis-dioxaborolane as the dynamic covalent cross-linker. When compared to the parent galactan-mimic, the mesoporous cross-linked polymer had a sevenfold increase in porosity, a 200-fold increase in particle size, and higher thermal stability. We demonstrated that by varying the temperature, the extent of cross-linking and thus particle size can be reversibly tuned. Our findings show that topochemical polymerization can be used to create polymers with improved properties from monomers derived from naturally available feedstock materials.
Sulfate polysaccharide is a kind of polyanionic linear macromolecular compound which contained sulfate groups. In vivo, most of them combine with proteins to form proteoglycans. The oligosaccharides obtained by degradation from polysaccharides would have different biological activities. Sulfate polysaccharides and oligosaccharides have immunomodulatory activity, which can be involved in activating immune cell recognition, controlling immune cell activity and reducing the side effects caused by inflammatory reactions. Polysaccharides treated with sulfate can act on multiple targets of the immune systems, affecting the occurrence and development of diseases and even cancer. In this article, polysaccharide and oligosaccharide containing sulfate groups were classified as endogenous and exogenous, and sulfated derivatives. And their biological activities in immune regulation were reviewed. Polysaccharides and oligosaccharides or the derivatives after sulfuric acid modification would have relatively unique biological activities due to the negative charge of the sulfate group and the change of their solubility.
Ultrasound-assisted extraction was used to recover gelling biopolymers and antioxidant compounds from Chondrus crispus with improved biological potential. The optimal processing conditions were evaluated using a Box-Behnken design, and the impact on the biological and thermo-rheological properties of the carrageenan fraction and on the bioactive features of the soluble extracts were studied. The optimum extraction parameters were defined by extraction time of ∼34.7 min; solid liquid ratio of ∼2.1 g/100 g and ultrasound amplitude of ∼79.0% with a maximum power of 1130 W. The dependent variables exhibited maximum carrageenan yields (44.3%) and viscoelastic modulus (925.9 Pa) with the lowest gelling temperatures (38.7°C) as well as maximum content of the extract in protein (22.4 mg/g), gallic acid (13.4 mg/g) and Trolox equivalents antioxidant capacity (182.4 mg TEAC/g). Tested hybrid carrageenans exhibited promising biological activities (% of growth inhibition around 91% for four human cancer cellular lines: A549; A2780; HeLa 229; HT-29).
The goal of this paper is the valorisation of the Chondrus crispus (Rhodophyta) wastes generated during the industrial extraction of hybrid carrageenan using microwave technology of a temperature range from 140 to 200 ºC, using water as a solvent. Mineral and phenolic content, antioxidant capacity and thermorheological features of the recovered hybrid carrageenans were determined. Results indicated the suitability for the recovery of high valuable compounds from these algae residues, after the optimization of the extraction conditions. At microwave processing conditions (160 °C, 5 min), it is still possible to recover around 10% of semi-refined hybrid carrageenan from the industrial raw material as well as to achieve the maximum value of total phenolic compounds of 12.8 mg GAE/g extract and antioxidant capacity of 51.70 mg Trolox/g extract. Extracted biopolymers exhibited thermomechanical features, in terms of viscoelastic moduli or gelling and melting temperatures, comparable to their commercial counterparts.
Marine polysaccharides are part of the huge seaweeds resources and present many applications for several industries. In order to widen their potential as additives or bioactive compounds, some structural modifications have been studied. Among them, simple hydrophobization reactions have been developed in order to yield to grafted polysaccharides bearing acyl-, aryl-, alkyl-, and alkenyl-groups or fatty acid chains. The resulting polymers are able to present modified physicochemical and/or biological properties of interest in the current pharmaceutical, cosmetics, or food fields. This review covers the chemical structures of the main marine polysaccharides, and then focuses on their structural modifications, and especially on hydrophobization reactions mainly esterification, acylation, alkylation, amidation, or even cross-linking reaction on native hydroxyl-, amine, or carboxylic acid functions. Finally, the question of the necessary requirement for more sustainable processes around these structural modulations of marine polysaccharides is addressed, considering the development of greener technologies applied to traditional polysaccharides.
Sugars appearing as structural units in softwood hemicelluloses (mannose, glucose, galactose, xylose and arabinose) were processed in media containing the ionic liquid 1 -butyl-3-methylimidazolium chloride ([Bmim]CI) and CrCI3 as a catalyst. Experiments were directed to the production of furans (hydroxymethylfurfural and furfural from hexoses and pentoses, respectively). Operation was performed at a fixed substrate loading (10 g /100 g [Bmim]CI) using a low catalyst charge (0.5 g CrCI3·6H2O/100 g [Bmim]CI). The effects of temperature and reaction time on the production of the target products were assessed. The optimal conditions for furan production were identified, and the furan yields were evaluated comparatively to the ones reported in related studies.
The stability of carrageenan to depolymerization has been studied both in batch experiments and under physiologically realistic conditions, namely in an artificial stomach. Degradation was characterized from on-line size exclusion chromatography and multiangle laser light scattering data. No hydrolysis of kappa-carrageenan occurs at pH 8 and even under the most drastic conditions (6 h at pH 1.2) the weight-average molecular weight remains >200 kDa only 20% has a molecular weight <100 kDa. This is in marked contrast to the previous findings of Ekström. It has been found that carrageenan in helical form (with potassium) is less susceptible to acid hydrolysis. Moreover iota-carrageenan is always more resistant than the kappa form. In simulated gastric juice the degradation of kappa-carrageenan is very limited; only 10% of the carrageenan exposed is reduced to a molecular weight <100 kDa. This is important since toxicological problems, if any, mainly concern poligeenan, a sulphated polysaccharide with molecular weight <100 kDa.
Hybrid κ-/μ-carrageenan, water-extracted from Kappaphycus alvarezzi, was incubated with Pseudoalteromonas carrageenovora κ-carrageenase. The five most abundant hybrid κ-/μ-carrageenan oligosaccharides were purified and their structure was determined by NMR and mass spectrometry. Since the enzyme-resistant fraction was small, these five oligosaccharides were representative of the distribution of the μ-carrabiose moieties along the carrageenan chain. Three main distributions of μ-carrabiose were found: -μ-, -μ-μ- and -μ-μ-μ-. Interestingly, the chemical shifts of the anomeric proton and carbon were strongly influenced by the identity of the adjacent carrabiose, which explains the asymmetrical D6S-H1 NMR signal that we observed. Although μ-carrabiose chemical shifts are usually attributed to blocks of μ-carrabiose as expected in ideal μ-carrageenan, we demonstrate that they are in fact due to μ-carrabiose units positioned between κ-carrabiose units. Using NMR and chromatography to monitor the alkaline conversion of μ- to κ-carrabiose, we found that the μ-carrabiose distribution (-μ-, -μ-μ-, -μ-μ-μ-) did not influence the conversion rate.
The structure and composition of galactan from Furcellaria lumbricalis (furcellaran) were investigated in connection with rheological specificities, gel structure, and extraction conditions. The
polysaccharide was characterized by 13C nuclear magnetic resonance (13C-NMR) and Fourier transform infrared spectroscopy, inductively coupled plasma-optical emission spectrometry, electrothermal
atomization atomic absorption spectrometry, and gel permeation chromatography methods. The microstructure of polymer gels
was studied using a cryofixation method in combination with freeze-drying and scanning electron microscopy (SEM) techniques.
The undersulfated furcellaran backbone consists mainly of 3,6-anhydro-d-galactose (28.5–30.1%) and galactose residues, the latter being partly sulfated in positions 4 and 6, which give rise to
some specific properties of the gel. Also, residues of 6-O-methyl-d-galactose as a minor component are found to be present. The water-extracted furcellaran with the average molecular weight
about 290kDa is rich in nitrogen, calcium, magnesium, and potassium, while the sodium content is rather low. The low sulfur
content (5.3%) and 13C-NMR spectra refer to an undersulfated nature of this galactan. The extraction of seaweeds in low concentration alkaline
solutions (instead of water) leads to a significant increase of the minimum size of the galactan particles and the value of
gel strength (more than 12 times for Rb-containing gels). The properties of the gel are dependent on specific tentacle-like
structure units present in furcellaran gels established by a high-resolution SEM.
Hybrid κ/ι-carrageeans extracted from Gigartina skottsbergii, Chondracanthus chamissoï, and Chondrus crispus were incubated with Pseudoalteromonas carrageenoVora κ-carrageenase and Alteromonas fortis ι-carrageenase. The degradation products as well as the resistant fraction were fully characterized by chromatography, NMR, and mass spectrometry. The low percentage of degradation observed after treatment by the ι-carrageenase suggests that long segments of ι-carrabiose or block of ι-carrageenan are low in abundance. The degradation products of the κ-carrageenase allow discriminating three modes of κ-carrabiose distribution: blocks of κ-carrabiose, κ-carrabiose rich fraction containing ι-carrabiose units probably randomly distributed, and ι-carrabiose rich fraction which corresponds to the resistant fraction. The proportions of each fraction were related to the botanical origin as well as the place of growth of the seaweed.
Carrageenan is not a single polysaccharide but a group of sulfated galactans extracted from a number of red seaweeds. The carrageenans constitute the principal structural polysaccharides of certain seaweeds. The carrageenan content of commercial seaweeds is normally 30–60% of dry weight but can be as much as 70–80%. Carrageenan is located in the cell wall and the intercellular matrix of the plant tissue, whereas the scarce cellulosic material constitutes the core of the microfibrils, located circumferentially in the outer cell wall, presumably for reinforcement. Carrageenan synthesis varies within some important red algal families according to the reproductive phase of the plant. This chapter describes the life cycle of carrageenan seaweeds. Carrageenan manufacture consists of extraction, purification, concentration, precipitation, and drying. Carrageenan is that group of linear galactan polysaccharides extracted from red seaweeds of the Gigartinaceae, Hypneaceae, Solieriaceae, Phyllophoraceae, and Furcellariaceae families that have an ester sulfate content of 15–40% and contain alternately (1 → 3)-α-D- and (1 → 4)-β-D-glycosidic linkages. The carrageenan market is dominated by food applications, the dairy sector representing the largest part.
The thermal depolymerisation kinetics of agarose and κ-carrageenan in water were investigated by measurement of intrinsic viscosity ([η]). An isokinetic relationship (IKR) revealing a kinetic compensation effect in polysaccharide depolymerisation was then discovered from the obtained kinetic data and those reported in the literature. Generally, the Arrhenius frequency factor, k0, and activation energy, Ea, of depolymerisation of agarose, κ/λ-carrageenan, κ-carrageenan and schizophyllan, under commonly used thermal conditions (high temperature, in water or pH-7 solvents, without deaeration and in disordered conformation), were in the ranges of 1.8×107–7.8×1010 s−1 and 97–126 kJ mol−1, respectively. These two variables showed parallel increases when using solvents of lower pH values (especially in k0) or with deaeration, and polysaccharides in ordered conformation or at lower concentrations. The IKR for the polysaccharide depolymerisation was: ln k0/s−1=0.379.Ea/kJ mol−1–18.5 (R2=0.906), giving an isokinetic temperature (Tiso) of 317 K. Conclusively, the depolymerisation mechanism was the same for all polysaccharide systems examined.
κ-/β-Carrageenans extracted from Furcellaria lumbricalis and Tichocarpus crinitus are hybrid polysaccharides that have roughly similar κ- and β-carrabiose contents. The distributions of these carrabiose moieties were compared using gel permeation chromatography to analyse the end-products obtained after degradation with Pseudoalteromonas carrageenovora κ-carrageenase. Three fractions were obtained: standard oligo-κ-carrageenans, hybrid oligo-κ-/β-carrageenans and an enzyme-resistant fraction. The structure of the most abundant hybrid oligo-κ-/β-carrageenans and the composition of the κ-/β-fractions resistant to degradation were determined by 1H NMR. Altogether, the results suggest that the κ- and β-carrabiose moieties in F. lumbricalis are more randomly distributed than in T. crinitus carrageenan, which has a more regular block-type distribution.
κ- and ι-carrageenan that were partially hydrolyzed in dilute acid while being in the ordered conformation (induced by LiI or LiCl, respectively) gave rise to bimodal molecular weight distributions (MWDs) as shown by size-exclusion chromatography (SEC) and gel filtration. Optical rotation measurements showed that the high molecular weight (MW) fraction remained conformationally ordered, whereas the low-MW fraction was in the disordered state. The relative amount of the low-MW fraction increased with degradation time. By inducing the disordered conformation (in 0.01 M LiCl) the weight average molecular weight (Mw) of the partially hydrolyzed samples decreased 1.5−3 times. These results are interpreted in favor of a double-stranded ordered conformation. Partial hydrolysis of this structure yields a metastable, partially double-stranded structure containing chain breaks that are “unexposed” due to partial overlap of the individual chain fragments. When the degree of polymerization (DP) of such fragments decrease below the critical value (DPc) for duplex stabilization the fragments are released and appear as a separate low-MW fraction in the SEC chromatograms. DPc was estimated to be approximately 100 residues in both cases. After induction of the disordered conformation in partially hydrolyzed samples the molecular weight distribution remained bimodal. For κ-carrageenan this is attributed to the higher rate of hydrolysis in the disordered fragments than in the parent ordered chains, which also leads to a rapid accumulation of dialyzable oligomers (DP 1−4). For ι-carrageenan, where the rate of hydrolysis ideally is independent of the conformational state, the bimodality is tentatively attributed to the presence of κ-units (partially formed by desulfation), which are hydrolyzed more rapidly in the disordered state than in the ordered state.
Thermal stability, by means of air drying a furcellaran powder, and its impact on gel strength and cation mobility were studied. Halogen heating in the temperature range 90–115°C for 15 min resulted in loss on drying (LD, %). These results can be described by polynom LD=−9.583+2.989τ−0.249τ2+0.00729τ3+0.1034t (R2=0.9976), indicating a gradual decomposition of carbohydrates. Air-drying induced a decrease in gel strength and the partial removal of potassium, calcium and sodium ions from the matrix. Air drying above 115°C yielded a remarkable destruction of polysaccharides with a total collapse in gelling power.
κ- And τ-carrageenan were hydrolysed in 0.1 M HCl in the presence of Lil (κ-) or LiCl (τ-). The rate constant for the hydrolysis determined from the decrease in the specific viscosity [k′ = Δ(c/ηsp)/Δt] increased by a factor 200 and 10 for κ- and τ-carrageenan, respectively, when passing above the conformational transition temperature (Tm). The rate constant determined from the increase in the number of reducing end-groups (k) increased by a factor 10 for κ-carrageenan, whereas no increase was observed for τ-carrageenan. The activation energy (Ea) for κ-carrageenan increased from 120 to 190 kJ/mol upon conformational ordering, whereas for τ-carrageenan the activation energy was 135 kJ/mol in both conformational states. The activation energies were virtually independent of the ionic strength. The results indicate that the stability properties of κ- and τ-carrageenan as reflected by viscosity or molecular weight decay is determined by differences in the nature of the ordered and disordered conformation, respectively, rather than differences in the hydrolytic stability of glycosidic linkages. The results are best described in terms of a multiple-stranded structure of the ordered conformations of both κ- and τ-carrageenan.
A further study has been made of the degradation of carrageenin in aqueous solution. An 80 °C. extract of Chondrus crispus degraded more rapidly than a preparation from which a 30 °C. extract had been first removed. The latter preparation could be degraded to a lower limiting intrinsic viscosity under suitable conditions. Degradation was mainly random, but a more rapid initial degradation was observed under all conditions studied. The presence of dissolved oxygen accelerated the reaction above 60 °C. Maximum stability was observed in an inert atmosphere at pH 9 in the presence of salts. Hydroxymethylfurfural and formic acid were identified as products, the yield of the former being higher than from D-galactose alone. The results have been discussed in the light of recent work on the constitution of the polysaccharide.
The degradation of carrageenin in buffered aqueous solution at pH 7.0 has been studied over the temperature range 60° to 101 °C. by following the change in viscosity and reducing properties. Kinetic analysis indicates the occurrence of two reactions: (a) an initial rapid degradation representing only about 0.3% of the complete hydrolysis, followed by (b) a first-order random degradation having k = 2.75 × 1013 e−29,200,/RT hr−1. The latter reaction becomes important at temperatures above 60 °C. The results indicate that carrageenin is more unstable than would be expected of a simple 1–3 galactan, and that two types of weak linkage are involved in the structure of the polysaccharide.
Studies on the effect of heat on carbohydrates are reviewed. Attention is centered on thermal degradation of mono-, di-, and polysaccharides in dry systems. Mechanisms leading to the formation of both volatile and nonvolatile products are discussed. The possible relation between products of thermal degradation of simple carbohydrates and compounds identified in several foodstuffs is pointed out.
Furcellaran formed complexes with transition metal ions. The amount of bound metal ions decreased in the following order: Fe(III) > Mn(II) > Cu(II) > Cr(III) > Zn > Ni(II), thus the hardness of these Lewis acids seemed to be the most essential factor controlling their ligation with the polysaccharide. Resulting complexes decomposed thermally at lower temperature than plain furcellaran. Neither furcellaran bound coumarin selected as the model molecule for mycotoxins nor this oxacompound coordinated to furcellaran metal salts.
We present a general view of κ-carrageenan gelation and some new experimental results concerning their behavior in the presence of Na+, K+, or Rb+ counterions in semidilute concentration. The gelation mechanism is based on the aggregation of helical dimers.
The kinetics and mechanisms of depolymerization of aqueous chitosan and alginate solutions at elevated temperatures have been investigated. Chitosan salts of different degree of acetylation (FA), type of counterions (-glutamate, -chloride) and degree of purity were studied. One commercially available highly purified sodium alginate sample with high content of guluronic acid (G) was also studied. Furthermore, the influence of oxygen, H(+) and OH(-) ions on the initial depolymerization rates was investigated. Depolymerization kinetics was followed by measuring the time courses of the apparent viscosity and the intrinsic viscosity. The initial rate constants for depolymerization were determined from the intrinsic viscosity data converted to a quantity proportional to the fraction of bonds broken. The activation energies of the chitosan chloride and chitosan glutamate solutions with pH close to 5 and the same degree of acetylation, FA=0.14, were determined from the initial rate constants to be 76±13kJ/mol and 80±11kJ/mol, respectively. The results reported herein suggest that the stability of aqueous chitosan and alginate solutions at pH values 5-8 will be influenced by oxidative-reductive depolymerization (ORD) as the primary mechanism as long as transition metal ions are presented in the samples. Acid - and alkaline depolymerization will be the primary mechanisms for highly purified samples.
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λ-Carrageenan from Chondrus ocellatus was degraded by microwave. The changes in intrinsic viscosity [η] during degradation were investigated. Based on the concept that the random scission of glycosidic linkage basically obeys first-order kinetics, [η] for each short-term microwave process could be obtained. The degradation rate coefficient (kn) of kinetics equation describing the microwave degradation of λ-carrageenan on different conditions was determined. The results demonstrated that changes of external pressure play a most important role in degradation of λ-carrageenan for same short-term microwave process. The susceptibility to degradation is also related to molecular size and concentration of λ-carrageenan. But at higher stress, the relationship between kn and [η]n deviates first-order kinetics.
The mechanism of thermal depolymerization of alginate in the solid state has been investigated. Depolymerization at elevated temperatures of two commercial highly purified alginates, one with high content of guluronic acid (G) and another with high content of mannuronic acid (M) was followed by measuring the apparent viscosity and the intrinsic viscosity. The initial rate constants were determined from the intrinsic viscosity data, and no significant difference between the G-rich (FG=0.63) and M-rich (FG=0.43) alginate was found. The activation energies of the G-rich alginate and the M-rich alginate were determined from the initial rate constants to be 114±6 kJ/mol and 126±12 kJ/mol, respectively.
The thermal depolymerization of chitosan chloride in solid state has been examined. Depolymerization was followed by measuring the apparent viscosity and intrinsic viscosity. The initial rate constants were determined from the intrinsic viscosity data and were found to increase markedly with increasing degree of acetylation, FA, showing that the FA is an important parameter for the rate of thermal degradation. The activation energies of the three chitosan chlorides with degrees of acetylation, FA=0.02, FA=0.16 and FA=0.35 were determined to be 114±11 kJ/mol, 112±5 kJ/mol and 109±5 kJ/mol, respectively.The rate of degradation was found not to be dependent on the presence of oxygen. On the other hand, the initial rate constant for chitosan chloride prepared by freeze-drying of a solution at pH 4 was about 30 times greater than that of a sample freeze-dried at pH 6, showing that the pH of the chitosan is important for its ability to degrade. 1H and 13C NMR spectroscopy of the thermally degraded chitosan with FA=0.35 was used to identify the specificity in the reaction. The rate of acid hydrolysis of the glycosidic bond in chitosan solutions was recently (Proceedings of the 1st International Conference on Chitin and Chitosan (1997), 168) found to be in the order A–A≈A–D≫D–A≈D–D, which appeared also to be valid for thermal depolymerization of chitosan. The NMR spectra also indicated that hydrolysis of the N-acetyl bond (de-N-acetylation) at the new reducing ends occurs in addition to the cleavage of the glycosidic bond.The results reported herein show that acid hydrolysis is the primary mechanism involved in the thermal depolymerization of chitosan chlorides in the solid state and that cleavage of the A–A and A–D linkages is mainly responsible for the degradation in the range of acetyl content investigated here.
Sol-gel transition processes of algal galactans were studied using cryofixation method in combination with freeze-drying and scanning electron microscopy (SEM) techniques. The structures formed in successive stages of gelling process upon cooling were rapidly frozen at defined temperature points and viewed by SEM. It was established that in the case of both types of gelling galactans investigated, a fine honeycomb-like network exists for a wide range of solution temperatures. The formation and structure of this network depends on the structural type, gelling stage, and concentration of the galactan in solution. The honeycomb suprastructures exist also in carrageenan and agarose sols (at temperatures considerably exceeding the gelling temperatures). An additional helical network formed showed different behaviour in the case of carrageenan and agar-type polysaccharides. In the gel-formation process, tightening of the network takes place in both types of galactan gels; the honeycomb structures persist in carrageenan (furcellaran) but not in agarose gels.
The radiation degradation yield (Gd) of kappa, iota and lambda carrageenans was compared in solid and in 1% aqueous solution in air at ambient temperature. Gds obtained in solid and aqueous form did not vary with the different types of carrageenan.The chemical structural changes of carrageenans were accompanied by appearance of UV absorbance peak at 260 nm and a characteristic FT-IR band at 1728 cm−1. Changes in the FT-IR finger print regions were observed at high doses of the aqueous solution.Radiation-induced desulfation increased the acidity of the carrageenans. The number of reducing end groups increased with dose with greater susceptibility in κ-carrageenan.
The functionality of sulphated polysaccharides is directly related to the degree of sulphation of these polymers. Acid hydrolysis is often carried out to study the kinetics of hydrolysis/chain scission of these polymers and the effect on molecular mass. However, measurement of molecular mass by size-exclusion chromatography (SEC) can be artefactual if the hydrolysis step also leads to desulphation of the polymer. A new and sensitive method based on a combination of size-exclusion and ion-repulsion principles has therefore been developed to enable the rapid measurement of free sulphate (and chloride if needed) levels in polymer solutions without any sample separation/preparation step. This and an SEC–refractive index method have been used to follow the desulphation and depolymerization of five sulphated polysaccharides (κ-, ι-, λ-carrageenan, dextran sulphate, heparin) during acid (pH 2) hydrolysis at 35 and 55°C. Dextran sulphate was found to be the most sensitive to desulphation, probably due to its high chain flexibility. Heparin and the carrageenans were stable to desulphation during the time period examined here, confirming the suitability and applicability of SEC-based methods for molecular mass determination of these polymers. The molecular mass of all but heparin was, however, found to be rapidly lowered by the (chain scission) hydrolysis. Kinetic parameters for depolymerization have been recovered for these polymers.
Lambda-, kappa-, and iota-carrageenan were depolymerized in the presence of ferrous ions or ferrous ions plus ascorbic acid at room temperature. Tetrabutyl-ammonium salts of lambda-, kappa- and iota-carrageenan were dissolved in N,N-dimethylformamide and sulfated by the addition of pyridine-sulfur trioxide in N,N-dimethylformamide. Then, the sulfated carrageenans were depolymerized by the incubation with ferrous ions and ascorbic acid. The anti-HIV activities of the various preparations were determined in a system in which MT-4 cells were infected with HTLV-IIIB. The activity of lambda-carrageenan was similar to that of dextran sulfate and the depolymerized lambda-carrageenan retained high activity. The activities of kappa- and iota-carrageenan and their depolymerized forms were about 6% of that of lambda-carrageenan. The sulfation of kappa-and iota-carrageenan increased the activities of these compounds to the same level as that of lambda-carrageenan. However, the sulfation of lambda-carrageenan did not affect its activity. Depolymerized sulfated kappa- and iota-carrageenan with mean molecular weights of 50,000 (81,000-46,000) had higher anti-HIV activity than dextran sulfate and all other preparations of carrageenan tested.
Lambda carrageenan was extracted from hand-sorted tetrasporophytes of Gigartina skottsbergii. Theta carrageenan was prepared from it by treatment with alkaline borohydride. Infrared spectroscopy showed complete, or essentially complete, conversion of 4-linked residues to the 3,6-anhydride ring form, and no detectable contamination with gelling carrageenans (iota or kappa). Optical rotation and differential scanning calorimetry (DSC) showed no evidence of conformational transitions on cooling and heating. Solutions of theta carrageenan at 2.0 wt.% in water and in 0.1 M KCl were Newtonian at 20 °C, and substantially less viscous than a 1.0 wt.% solution of the lambda carrageenan precursor. Close Cox–Merz superposition was observed between steady-shear (rotational) viscosity (η) and complex dynamic viscosity (η∗) at equivalent values of shear rate (/s−1) and frequency (ω/rad s−1), and the variation of log G″ with log ω was linear, with a slope of 1.0, strongly indicating a solution of disordered coils. The absence of double-helix formation, and associated gelation, is explained by sulfation at O(2) of 3-linked residues. A previous report of gel formation by theta carrageenan is attributed to the presence of some gelling carrageenan in the lambda sample from which it was prepared.
κ-, ι- and λ-Carrageenans were degraded by irradiation with gamma rays in the solid state, gel state or solution with various doses in air at ambient temperature. The molecular weights obtained were in the range of 10.5 × 104 to 0.8 × 104 of narrow molecular weight distribution. The chemical structural changes of carrageenans were accompanied by appearance of UV absorbance peak at 260 nm and a characteristic FT-IR band at 1728 cm−1. Due to radiation-induced desulfation, carrageenan oligomer has lower sulfate content. From comparison of radiation degradation yield (Gd), susceptibility to degradation of the three types of carrageenans in aqueous form follows the order of λ > ι > κ which could have been influenced by their conformational state. The oligomer obtained from κ-carrageenan with molecular weight of 1.0 × 104 showed a strong growth promotion effect on potato in tissue culture. Degradation of κ-carrageenan solution using vessel-type low energy electron beam accelerator (LEEB) (250 kV, 10 mA) was investigated. LEEB irradiation reduced the molecular weight of carrageenan though the electron beams have a depth penetration range of less than 3 mm in distilled water.
This review is concerned with the progress in the methods of structural analysis of sulfated galactans isolated from the red seaweeds, including determination of monosaccharide constituents and partial depolymerization by reductive hydrolysis, identification of disaccharide repeating units by NMR spectroscopy, and sequence analysis by enzymatic degradation. Examples of elucidation of primary structures for several complex sulfated galactans and xylogalactans are given.
The changes in intrinsic viscosity ([η]) during ultrasonic degradation of agarose, κ- and ι-carrageenans in water were investigated. Based on the concept that the random scission of glycosidic linkage basically obeys first-order kinetics, the degradation rate (k) for each short-term ultrasonication process could be obtained. The resultant k values for 0.5 wt% polysaccharide systems appeared to decrease quite linearly with reduced [η], in contrast to those for 1.5 wt% systems. Both k value and its [η]-dependence of diluted and concentrated systems were in the order of agarose>κ-carr>ι-carr, depending on the concentration of polysaccharides.
Sulfated polysaccharides from 11 species of tropical marine algae (one edible specie of Rhodophyta, six species of Phaeophyta and four species of Chlorophyta) collected from Natal city coast (Northeast of Brazil) were evaluated for their anticoagulant, antioxidant and antiproliverative in vitro activities. In the activated partial thromboplastin time (APTT) test, which evaluates the intrinsic coagulation pathway, seven seaweeds presented anticoagulant activity. Dictyota cervicornis showed the highest activity, prolonging the coagulation time to double the baseline value in the APTT with only 0.01 mg/100 microl of plasma, 1.4-fold lesser than Clexane, a low molecular weight heparin. In the protrombin time (PT) test, which evaluates the extrinsic coagulation pathway, only Caulerpa cupresoides showed anticoagulant activity. All species collected showed antioxidant activities. This screening emphasized the great antioxidant potential (total capacity antioxidant, power reducing and ferrous chelating) of four species: C. sertularioide; Dictyota cervicornis; Sargassum filipendula and Dictyopteris delicatula. After 72 h incubation, HeLa cell proliferation was inhibited (p<0.05) between 33.0 and 67.5% by S. filipendula; 31.4 and 65.7% by D. delicatula; 36.3 and 58.4% by Caulerpa prolifera and 40.2 and 61.0% by Dictyota menstrualis at 0.01-2mg/mL algal polysaccharides. The antiproliferative efficacy of these algal polysaccharides were positively correlated with the sulfate content (r=0.934). Several polysaccharides demonstrated promising antioxidant, antiproliferative an/or anticoagulant potential and have been selected for further studies on bioguided fractionation, isolation and characterization of pure polysaccharides from these species as well as in vivo experiments are needed and are already in progress.
Enzymatic degradation of standard κ-carrageenan and the low-gelling hybrid κ-/μ-carrageenan were conducted using recombinant Pseudoalteromonas carrageenovora κ-carrageenase. The initial velocity of the enzyme was determined as a function of varying Tris or NaI concentrations and at constant 200 mM cosolutes concentration, adjusting NaI and Tris concentrations accordingly. In both cases, we observed strong inhibition of the enzyme with increasing amounts of iodide. The characterization of the κ- and κ-/μ-carrageenan ordering by optical rotation and the visualization of iodide binding on carrageenan by (127)I NMR revealed that inhibition was not caused by the disordered-ordered transition of carrageenan in NaI, but by iodide binding. These results were confirmed by analysis of the degradation products by gel permeation chromatography. Degradation of carrageenan in the disordered state led to a rapid decrease in molecular mass and the production of all possible neo-κ-carrabiose oligomers. In the ordered conformation, the degradation kinetics, the decrease of average molecular weight, and the chain population distribution of degradation products varied with iodide concentration. These observations were interpreted to be the result of increasing amounts of bound iodide on carrageenan helices that, in turn, impede enzyme catalysis. Based on these results, we propose a single-helix ordered conformation state for κ-carrageenan and reject the previously advocated double-helix model.
The composition, structure, and thermal stability of carrageenans from unattached Coccotylus truncatus (the Baltic Sea, Estonia) were investigated. The complex polysaccharide was characterized by (13)C NMR and FTIR spectroscopy, ICP-OES and gel permeation chromatography methods. The main components of C. truncatus galactan are 3,6-anhydro-alpha-D-galactose-2-sulfate (30+/-1.5%) and beta-D-galactose-4-sulfate (45.3%), indicating a iota-carrageenan backbone. As the minor components, alpha-D-galactose-2,6-disulfate (12+/-2%) from nu-carrageenan and 4',6'-pyruvated beta-D-galactopyranosyl residues (1.4%) from pyruvated alpha-carrageenan are found to be present, latter being responsible for the undersulfated nature of the galactan. The native polysaccharide with the average molecular weight of about 1500 kDa is highly susceptible to thermal degradation. The high-temperature treatment of this galactan gives products with 3,6-anhydro-alpha-D-galactose units predominantly at the reducing end. The carrageenan extraction from C. truncatus gives characteristically low yields (12-17%); weak gelling ability of the polysaccharides from this seaweed species (gel strength 30-40 g/cm(2)) does not depend significantly on extraction conditions.
Treatment of L-fucose with an excess pf pyridine-sulphur trioxide gave an equilibrium mixture of mono-, di-, and tri-sulphates. L-Fucose was sulphated under optimal conditions for monosulphate formation, and the monoester fraction was isolated by chromatography on DEAE-cellulose. The isomeric L-fucose 2-, 3-, and 4-sulphates (1-3) were separated on a DEAE-cellulose column by elution with borate buffer. The structures of 1-3 were established by electrophoresis, colour tests, periodate oxidation, and, for the 2-isomer, by comparison with a specimen of 1 that had been definitively synthesised via methyl 3,4-O-isopropylidene-alpha-L-fucopyranoside (6) and methyl alpha-L-fucopyranoside 2-(barium sulphate) (5). The latter was rapidly hydrolysed in hot, dilute acetic acid to 1 and methyl alpha-L-fucopyranoside (4).
lambda-Carrageenan is a sulfated galactan isolated from some red algae and have been reported to have many kinds of biological activities. lambda-Carrageenan from Chondrus ocellatus, an important economic alga in China and many other parts of the world, was degraded by microwave, and obtained five products that have different molecular weight: 650, 240, 140, 15, 9.3 kDa. Analytical results confirmed that microwave degradation might not change the chemical components and structure of polysaccharides under certain condition. In this study, tumor-inhibiting activities, weight of immune organ, nature killer cells activity, lymphocyte proliferation ratio and pathological slice of spleen and tumor cells from the control group and lambda-carrageenan-treated mice of transplanted S180 and H22 tumor were investigated. The results indicated that the five lambda-carrageenan samples all showed antitumor and immunomodulation activities in different degree. Molecular weight of polysaccharides had notable effect on the activities. In addition, their antitumor and immunomodulation have some relevance and the five lambda-carrageenans probably inhibited tumor by means of activating the immunocompetence of the body. Among all the experiment results, samples with the highest activities are PC4 and PC5 whose molecular weight are 15 and 9.3 kDa.
A desulfation method using chlorotrimethylsilane for treatment of pyridinium salts of sulfated galactans was developed. It proved to be appropriate for desulfation of polysaccharides of both agar and carrageenan families. In order to evaluate its efficiency in presence of the maximum content of 3,6-anhydrogalactose, it was applied to commercial kappa-carrageenan, leading to obtention of a product mainly composed by beta-carrageenan. Best experimental conditions for achieving desulfation of kappa-carrageenan--in terms of low sulfate content, high recovery and low degradation of the product--were found. In addition, the complete assignment of the 1H NMR spectrum of beta-carrageenan was achieved by means of 1D and 2D NMR techniques.
Aqueous extraction of gametophytic Schizymenia binderi afforded a polysaccharide composed of galactose and sulfate groups in a molar ratio of 1.0:0.89 together with uronic acids (6.8 wt%) and minor amounts of other neutral sugars. Alkali-treatment of the polysaccharide afforded a polysaccharide devoid of 3,6-anhydrogalactose. 13C NMR spectroscopy of the desulfated alkali-treated polysaccharide showed a backbone structure of alternating 3-linked beta-D-galactopyranosyl and 4-linked alpha-galactopyranosyl units that are predominantly of the D-configuration and partly of the L-configuration. Methylation, ethylation and NMR spectroscopic studies of the alkali-treated polysaccharide indicated that the sulfate groups are located mainly at positions O-2 of 3-linked beta-D-galactopyranosyl residue and at position O-3 of 4-linked-alpha-galactopyranosyl residues, the latter is partially glycosylated at position O-2. The sulfated galactan from S. binderi exhibited highly selective antiviral activity against Herpes simplex virus types 1 and 2, with selectivity indices (ratio cytotoxicity/antiviral activity) >1000 for all assayed virus strains. This compound was shown to interfere with the initial adsorption of viruses to cells.
Polysaccharide from Porphyra yezoensis (PYPS) was degraded by ultrasound in this study. The changes of intrinsic viscosity with various conditions, such as ultrasonic power, irradiation time, reaction temperature, initial pH value of solution, and its concentration, were investigated by using Ubbleholde viscometry. It was found that the ultrasonic degradation rate of PYPS solution increases with the increase of ultrasonic power and reaction temperature and the decrease of the initial pH value of the solution. The order of the susceptibility of initial PYPS concentrations on degradation is 0.75 > 0.5 > 1.00 > 2.00 g/dL. The mechanism about the ultrasonic degradation of PYPS may be explained by more for mechanical and less for radical effects. Relationships between degradation rate and ultrasound time are exponential functions. The activation energy of ultrasonic degradation of PYPS solution is 52.13 kJ/mol, which was calculated by the logarithmic form of the Arrhenius equation, and is lower than one for the acid or enzyme catalyzing degradation of similar glycosidic bonds.
Recently there has been some debate regarding the presence and associated health risk of low molecular weight carrageenan in foodstuffs. Unfortunately measurement of the low molecular weight tail (LMT) of food-grade carrageenans (defined here as the carrageenan having relative molecular mass (Mr) below 50,000) is not trivial, largely due to its low abundance. So far methods employing light scattering have been unsuccessful in producing reproducible results, probably due to the poor detector response at low masses. In this work a method based on high performance size exclusion chromatography coupled to a refractive index detector (HPSEC-RI) has been used for the measurement of the LMT in food-grade carrageenan ingredients and in a carrageenan-containing finished product (a jelly). Over the course of half a year, 19 measurements were made on a reference carrageenan; the results demonstrated that the method had excellent reproducibility. Applied to a number of different carrageenan ingredients, it was found that, in general, the LMT represents less than 8% of the total carrageenan in ingredients, and under the correct conditions increases little during food processing. The data also indicated that pH appears to be a critical factor during food processing and pH levels below 4.0 should be avoided.
Physico-chemical properties of the gelling galactans from the red alga Chondrus elatus, Gums and Stabilisers for the Food Industry 18: Hydrocolloid Functionality for Affordable and Sustainable Global Food Solutions
- M Saluri
- D Fujita
- R Tuvikene
M. Saluri, D. Fujita, R. Tuvikene, Physico-chemical properties of the gelling
galactans from the red alga Chondrus elatus, Gums and Stabilisers for the Food
Industry 18: Hydrocolloid Functionality for Affordable and Sustainable Global
Food Solutions, R. Soc. Chem. (2016) 37-46.