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Structural and compositional characteristics of gelling galactan from the red alga Ahnfeltia tobuchiensis (Ahnfeltiales, the Sea of Japan)
Abstract
The composition and structure of a sulfated polysaccharide from Ahnfeltia tobuchiensis, a red seaweed of Kuril Islands and Japan, were investigated. Samples of the galactan were characterized by 13C NMR and FTIR spectroscopy and chemical analysis in comparison with well-known commercial agarose preparations. The main components of the polysaccharide from A. tobuchiensis were 3,6-anhydro-l-galactose (38±4.5%) and galactose. Methoxy groups (2.2%) of the galactan are located in the position 2 of the anhydrogalactose residues. The galactan proved to be a high-sulfated agarose. Sulfur content of this polysaccharide is 0.2–0.3%, and sulfate groups may be removed by alkali treatment to a limited extent only. The precision of quantification and possibilities of analytical methods used are discussed.
... species has its own chemical features which might be influenced by the growing conditions [100]: SGs from Ahnfeltia are also be ascribed to agaran-type polysaccharides by normal and second-derivative spectra from FTIR results at 931.8, 893.6, 790.9, 771.3, 741.0, 717.7, and 693.9 cm −1 [16], which composed of alternating 3-linked β-D-galactopyranosyl and 4-linked α-L-galactopyranosyl or 3,6-anhydro-α-L-galactopyranosyl residues. Methyl disaccharide units are present in position two of 3,6-anhydro-L-galactose (LA) residues and absent in D-galactose residues (G) [92] (Figure 6). ...
... Significantly, SGs from different species vary in the modification pattern and the SGs from Ahnfeltia are also be ascribed to agaran-type polysaccharides by normal and second-derivative spectra from FTIR results at 931.8, 893.6, 790.9, 771.3, 741.0, 717.7, and 693.9 cm −1 [16], which composed of alternating 3-linked β-D-galactopyranosyl and 4-linked α-L-galactopyranosyl or 3,6-anhydro-α-L-galactopyranosyl residues. Methyl disaccharide units are present in position two of 3,6-anhydro-L-galactose (LA) residues and absent in D-galactose residues (G) [92] (Figure 6). SGs from Ahnfeltia are also be ascribed to agaran-type polysaccharides by normal and second-derivative spectra from FTIR results at 931.8, 893.6, 790.9, 771.3, 741.0, 717.7, and 693.9 cm −1 [16], which composed of alternating 3-linked β-D-galactopyranosyl and 4-linked α-L-galactopyranosyl or 3,6-anhydro-α-L-galactopyranosyl residues. ...
... SGs from Ahnfeltia are also be ascribed to agaran-type polysaccharides by normal and second-derivative spectra from FTIR results at 931.8, 893.6, 790.9, 771.3, 741.0, 717.7, and 693.9 cm −1 [16], which composed of alternating 3-linked β-D-galactopyranosyl and 4-linked α-L-galactopyranosyl or 3,6-anhydro-α-L-galactopyranosyl residues. Methyl disaccharide units are present in position two of 3,6-anhydro-L-galactose (LA) residues and absent in D-galactose residues (G) [92] (Figure 6). ...
Agarophytes are important seaweeds of the Rhodophyta type, which have been highly exploited for industrial use as sources of a widely consumed polysaccharide of agar. In addition to that, sulfated galactans (SGs) from agarophytes, which consist of various functional sulfate groups, have attracted the attention of scientists in current studies. SGs possess various biological activities, such as anti-tumor, anticoagulant, anti-inflammatory, antioxidant, anti-obesity, anti-diabetic, anti-microbial, anti-diarrhea, and gut microbiota regulation properties. Meanwhile, the taxonomy, ecological factors, i.e., environmental factors, and harvest period, as well as preparation methods, i.e., the pretreatment, extraction, and purification conditions, have been found to influence the chemical compositions and fine structures of SGs, which have, further, been shown to have an impact on their biological activities. However, the gaps in the knowledge of the properties of SGs due to the above complex factors have hindered their industrial application. The aim of this paper is to collect and systematically review the scientific evidence about SGs and, thus, to pave the way for broader and otherwise valuable industrial applications of agarophytes for human enterprise. In the future, this harvested biomass could be sustainably used not only as a source of agar production but also as natural materials in functional food and pharmaceutical industries.
... Ahnfeltia, the subject of this study, is commercially important as it is a valuable agarophyte, known for high-quality agar production with a low sulfate ratio (Chapman and Chapman, 1980;Truus et al., 2006;Zhang et al., 2019). The sulfate ratio of agar from Ahnfeltia plicata is less than half of that of the wellknown agarophytes, Gelidium amansii and Gracilariopsis lemaneiformis (Zhang et al., 2019). ...
... Commercial production of agar from Ahnfeltia occurs in both Russia and Japan, and the agar is known as Itani agar in Japan and Sakhalin agar in Russia. In particular, 170,000-230,000 wet tons of Ahnfeltia are reported to be harvested annually in Russia (Titlyanov et al., 1999;Truus et al., 2006). ...
The agarophyte Ahnfeltia (Ahnfeltiales, Rhodophyta) is a globally widespread genus with 11 accepted species names. Two of the most widespread species in this genus, A. plicata and A. fastigiata, may have diverged genetically due to past geographic changes and subsequent geographic isolation. To investigate this genomic and genetic diversity, we generated new plastid (ptDNAs) and mitochondrial genomes (mtDNAs) of these Ahnfeltia species from four different regions (A. plicata - Chile and UK and A. fastigiata - Korea and Oregon). Two architecture variations were found in the Ahnfeltia genomes: in ptDNA of A. fastigiata Oregon, the hypothetical pseudogene region was translocated, likely due to recombination with palindromic repeats or a gene transfer from a red algal plasmid. In mtDNA of A. fastigiata Korea, the composition of the group II intronic ORFs was distinct from others suggesting different scenarios of gain and loss of group II intronic ORFs. These features resulted in genome size differences between the two species. Overall gene contents of organelle genomes of Ahnfeltia were conserved. Phylogenetic analysis using concatenated genes from ptDNAs and mtDNAs supported the monophyly of the Ahnfeltiophycidae. The most probable individual gene trees showed that the Ahnfeltia populations were genetically diversified. These trees, the cox1 haplotype network, and a dN/dS analysis all supported the theory that these Ahnfeltia populations have diversified genetically in accordance with geographic distribution.
... Furthermore, the 2D 13 C/ 1 H HMBC NMR spectrum of the copolymer (Fig. 5) shows a correlation between carbon C-4 of β-galactopyranosyl residue and the methylene protons of polyacrylamide. Truus et al. (2006) reported that A. plicata produces agaran-or carrageenan-type polysaccharides depending on environmental conditions. In this work, analysis of normal and secondderivative FT-IR spectra of dried and milled A. plicata collected in the Magellan ecoregion allowed the assignments of signals ascribed to agaran, indicating the presence of an agarophyte. ...
... Furthermore, the full assignments of 1 H and 13 C NMR spectra of agarose were achieved with the aid of 2D NMR spectra as depicted in Table 2. The chemical shifts are very similar to those published in the literature for agarans and commercial agarose and confirm that the agaran obtained from A. plicata is a neutral agarose (Usov, et al. 1980;Truus et al. 2006;Maciel et al. 2008). This neutral agarose constitutes a very special polysaccharide for the preparation of new products with valuable biological properties. ...
Aqueous extraction of Ahnfeltia plicata collected in the Magellan ecoregion afforded agarose devoid of sulfate groups. This neutral agarose was subjected to sulfation with SO3-pyridine complex, giving an aqueous soluble derivative with 35.5 % sulfate groups. Analysis by Fourier transform infrared spectroscopy (FT-IR) and by H-1 and C-13 NMR spectroscopy indicated that this derivative was sulfated at positions C-6 of the beta-galactopyranosyl residue and C-2 of the alpha-3,6-anhydrogalactopyranosyl residue and partially sulfated at position C-2 of the beta residue. The antioxidant capacity of sulfated agarose was evaluated by the oxygen radical absorbance capacity (ORAC) method, ABTS radical cation, hydroxyl radicals, and chelating assays. This capacity of sulfated agarose toward peroxyl radicals was higher than that of commercial lambda-carrageenan, while native agarose presented good activity, with an ORAC value similar to that of commercial kappa-carrageenan. Sulfated agarose presented good antioxidant capacity toward other radicals. Copolymerization of sulfated agarose with acrylamide was achieved using ceric ammonium nitrate as initiator. NMR spectroscopy indicated grafting of polyacrylamide at position C-4 of beta-galactopyranosyl residues.
... Furcellaran was isolated (Tuvikene et al. 2006) from the red alga Furcellaria lumbricalis (Kassari Bay, the Baltic Sea, Estonia) by hot alkaline extraction in 0.02 M KOH solution (at 100°C, 4 h) and precipitated by isopropanol (four-fold volume per extract). Agarose from Ahnfeltia tobuchiensis (Truus et al. 2006) (various lots of commercial production) was obtained from the pilot production plant of the Institute of Chemistry, Estonian Academy of Sciences. According to the labelling, the Serva agarose sample contains 0.06% sulfur and less than 0.01% salts. ...
... The values are in accordance with literature data (Van de Velde et al. 2002). The shift values of two investigated agaroses of different origin coincide, which is typical of commercial high-quality agaroses (Truus et al. 2006). Thus the structural type and characteristics of the galactans to be studied were established. ...
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.
... In addition, as can be seen from the agarose gel electrophoresis diagram (Figure 3b-d), the separation effect of the desulfated agar is as good as that of commercially available agarose and it can be used as the agarose gel electrophoresis medium to separate DNA molecules. Sulfate is one of the main negatively charged groups in the agar molecule [37]. The reduction in the sulfate content of desulfated agar decreased electro-infiltration, and the electrophoresis band became clearer. ...
Agarose is a natural seaweed polysaccharide and widely used in the medicine, food, and biological fields because of its high gel strength, non-toxicity, and electrical neutrality. The sulfate group is one of the main charged groups that affect the performance of agarose. In the present study, a simple, eco-friendly, and efficient method was explored for agarose preparation. After desulfation with hydrogen peroxide (H2O2), the sulfate content of agar reached 0.21%. Together with gel strength, electroendosmosis, gelling and melting temperature, the indicators of desulfated agar met the standards of commercially available agarose. Notably, the desulfated agar can be used as an agarose gel electrophoresis medium to separate DNA molecules, and the separation effect is as good as that of commercially available agarose. Further, the H2O2 desulfation process was analyzed. The addition of a hydroxyl radical (HO•) scavenger remarkably decreased the H2O2 desulfation rate, indicating that HO• has a certain role in agar desulfation. Sulfate content detection indicated that sulfur was removed from agar molecules in the form of sulfate ions (SO42−) and metal sulfate. The band absence at 850 cm−1 indicated that the sulfate groups at C-4 of D-galactose in sulfated galactan were eliminated.
... The KC sample sulphur content was lower than expected, but this can be attributed to the presence of sucrose additive. Excluding the additive, the KC sulphur content was approximately one group per repeating disaccharide unit, a value that is in agreement with the data reported elsewhere [25,26]. ...
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.
... It is based on a polysaccharide with G-L and G-LA backbones. Taking into account the diversity of the substitution patterns in agarans, the following backbones are also included in this group: The G-LA repeating unit of agarose, is present in the orders Gelidiales (Pterocladiella capillaceae, Pterocladiaceae; Gelidium rex, Gelidium corneum (as G. sesquipedale), Gelidiaceae), Anhfeltiales (Anhfeltia plicata and A. tobuchiensis, Anhfeltiaceae), and Gracilariales (Gracilariopsis longissima (as Gracilaria verrucosa), G. cervicornis, G. blodgettii, Crassiphycus crassissimus (as Gracialaria crassissima), G. gracilis, Crassiphycus birdiae (as Gracilaria birdiae), Gracilariopsis hommersandii, Gracilariaceae) in major quantities (Matsuhiro and Urzua, 1990;Errea and Matulewicz, 1994;Murano, 1995;Errea and Matulewicz, 1996;Freile-Pelegrıń and Murano, 2005;Truus et al., 2006;Rodrıǵuez et al., 2009;Souza et al., 2012;Rodrıǵuez Sańchez et al., 2019;Zhang et al., 2019;Martıńez-Sanz et al., 2020). ...
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.
... The sulfate content was higher in WSPN than in the rest of the polysaccharide samples. In general, the sulfate content in the three polysaccharides analyzed were similar to those reported for a sulfated galactan from the red algae Ahnfeltia tobuchiensis (0.2%e 0.3% w/w) (Truus et al., 2006), but lower than the levels reported for Navicula species (6.3% and 8% w/w) (Lee et al., 2006;Staats et al., 1999). It is well known that the sulfate content in microalgae is highly variable and can range from 0 to 90% (P erez Loyola, Popowski Casaña, P erez Castillo, & Alonso Romero, 2003). ...
Sulfated polysaccharides were extracted from Navicula sp. cultivated at three wavelengths: white (WSPN), red (RSPN) and blue (BSPN) with yield rates of 3.4, 3.9 and 4.4 (% w/w dry biomass basis) respectively. Analysis of these polysaccharides using gas chromatography showed that they contain glucose, galactose, rhamnose, xylose and mannose as main neutral sugars. The amount of rhamnose was higher in WSPN. The molecular weight (Mw) value was 17, 107 and 108 kDa for WSPN, BSPN and RSPN, respectively. The sulfate content in WSPN was higher (0.40% w/w) than in the BSPN and RSPN. The polysaccharides recovered from Navicula sp. presented antioxidant activity, which could be related to the molecular structural characteristics such as Mw and sulfate content. The scavenging activity was higher in WSPN (DPPH 49% and ABTS⁺ 68 μmol Trolox/g), than in the BSPN and RSPN samples. The WSPN possess a high antioxidant capability, thus this sulfated polysaccharide might be a potential antioxidant for biotechnological applications.
... Gelidium yields the best quality of agar, but its cultivation is difficult to carry out; also, its natural resource is less abundant than Gracilaria, which is the genus cultivated in several countries and regions on commercial scale [13]. Pterocladia and Ahnfeltia grow in a limited zone and are currently utilized only in New Zealand and Russia, respectively [35,36]. ...
Marine organisms represent an enormous reservoir of compounds with many potential applications. Microbes, vegetals and animals from the sea have been exploited for numerous purposes. From seaweeds, in particular, many active compounds can be obtained, such as three important phycocolloids: agar, carrageenan and algin. In this report, an overview is given about biological characteristics, cultivation, agar and bioactive molecules content of the Rhodophyta Gracilaria gracilis; also, agar extraction processes and its traditional and innovative applications are discussed. Cultivation of G. gracilis is subject of several studies and experiments, because there is still much to understand for improving productivity and biomass yield. G. gracilis is one of the best candidates for cultivation and consequent agar extraction, thanks to: fast growth rate, ease of vegetative reproduction, good resistance to salinity and temperature oscillation, good agar qualities. The possibility of farming G. gracilis opens positive perspectives if some factors are taken into account: constant availability of raw material for agar extraction and preservation of ecological balances in natural environments. Agar extraction methods have been also reviewed in terms of improvement related to both agar yield and agar gel strength. As widely acknowledged, the main uses of agar are related to formation of thermoreversible gels at low concentrations in water. It exhibits also many beneficial biological activities including anticoagulant, antiviral, antioxidative, anticancer and immune- modulating activities. Newest applications of agar in pharmaceutical, medical, engineering and other fields are of great interest and are the topic of current and future studies.
... The 13 C NMR was used to study the structure of agarose and its related compounds, and major signals were unanimously assigned to the carbons of agarobiose units (Usov et al., 1980;Rochas, Lahaye, Yaphe, & Phan Viet, 1986;Murano et al., 1992;Truus et al., 2006;Meena et al., 2007;Maciel et al., 2008;Sousa et al., 2012;Gericke & Heinze, 2015). Data from the last five papers are shown in Table 3. Murano et al. (1992) did not find a significant difference in 13 C NMR signals before and after the alkali treatment of Gracilaria dura although the significant increase of 3,6-anhydro-L-galactose and the significant decrease of sulphate ester and some changes in 2-O-Me-L-galactose, 6-O-Me-L-galactose and pyruvate were detected by chemical analysis. ...
Since agar has been used for various applications such as gelling agents in food industry, culture medium in microbiology, gel elecrophoresis in biotechnology, pharmaceutical by virtue of its potential bioactivity, the relation between the structure and physico-chemical/physiological properties has been studied extensively. To develop further utilization, the relation between the structure and properties for agar materials from seaweeds not from chemical reagents sold by chemical industrial companies is discussed in the present paper. Reducing sulphate content and increasing 3,6-anhydro-L-galactose by alkali treatment led to the increase in gelling ability, however the optimum condition of alkali treatment (alkali concentration, temperature, time) was shown to depend on the species, the production place, and harvesting season of seaweeds. As the detailed study of agaropectin which does not form a gel by itself has not been done so much because of its complexity of the structure, its role in the gelation of agar is discussed. It was shown that agaropectin did not inhibit the gelation of agar but rather enhances the gelation.
... However, a higher content of protein has been reported for polysaccharides from Chlorella pyrenoidosa at different ethanol concentrations (0.75%-11.21% w/w) [12]. The sulfate content found in the polysaccharide from Navicula sp. in this study (0.33%) ( Table 1) was in the range reported for a sulfated galactan from the red algae Ahnfeltia tobuchiensis (0.2%-0.3% w/w) [13] but lower than that in other reports for Navicula species (8% and 11% w/w) [3,11]. However, it is well known that the sulfate content in microalgae is highly variable and can range from 0 to approximately 90% [14]. ...
A sulfated polysaccharide extracted from Navicula sp. presented a yield of 4.4 (% w/w dry biomass basis). Analysis of the polysaccharide using gas chromatography showed that this polysaccharide contained glucose (29%), galactose (21%), rhamnose (10%), xylose (5%) and mannose (4%). This polysaccharide presented an average molecular weight of 107 kDa. Scanning electron microscopy (SEM) micrographs showed that the lyophilized Navicula sp. polysaccharide is an amorphous solid with particles of irregular shapes and sharp angles. The polysaccharide at 1% (w/v) solution in water formed gels in the presence of 0.4% (w/v) FeCl₃, showing elastic and viscous moduli of 1 and 0.7 Pa, respectively. SEM analysis performed on the lyophilized gel showed a compact pore structure, with a pore size of approximately 150 nm. Very few studies on the gelation of sulfated polysaccharides using trivalent ions exist in the literature, and, to the best of our knowledge, this study is the first to describe the gelation of sulfated polysaccharides extracted from Navicula sp.
... Earlier investigations from red algae extracts showed that this value slightly varies depending on raw material and differences in processing conditions, particularly on duration of washing of the final product. Prolonged water elution of the galactan preparations reduces sulfate content (high-charged fractions get faster detached), but this process is disadvantageous for practical applications [57]. ...
The red seaweed Melanothamnus somalensis was investigated as potential economic source of agar. The effect of different conditions of alkali pre-treatment on chemical properties of agar was evaluated. Agar was extracted by various concentrations of NaOH (4%, 6% and 8%) and heated at different temperatures (70 °C, 75 °C and 80 °C) for different durations (2 h, 2.75 h and 3.5 h). The yields—molecular weight (MW) and sulfate contents of extracted agar were analysed and characterized by FTIR spectroscopy. The yield was significantly increased at these treatments from 23.29% to 30.86%. MW studied by HPLC ranged from (12.45 ± 0.21) × 105 to (8.60 ± 2.40) × 105 Da. FTIR bands show sulfate groups in C4 and C6 of galactose and no sulfate group were found on both C2 of galactose and C2 of 3,6-anhydrogalactose. All treatments showed a high sulfate content that ranged from 5.4% to 10.1%. These properties were found to be significantly affected by the alkali pre-treatment concentration (p < 0.05). In conclusion, agar extracted in this study was considered acceptable for industrial application and the optimal conditions for extraction were found to be at 6% NaOH at 70 °C for 2 hours.
Key words: Seaweed, Melanothamnus somalensis, agarophytes, agar extraction, alkali pre-treatment, FTIR.
... The highest 3,6-AG levels were found in the fraction HF1b with a maximum value of 34.4% for the funoran from the gametophytic form of G. complanata. This value is close to those observed for some agaroses (Truus et al., 2006). ...
... Also the absence of signals of non-anomeric sugars carbons at a lower field than ı 82 in the 13 C NMR spectrum demonstrated the pyranoid form of all sugar residues (Bock & Pedersen, 1983). The signal assignments (Table 1) were made on the basis of comparison with spectra of model compounds, agarose and other related polysaccharides (Lahaye, Yaphe, Viet, & Rochas, 1989;Lai & Lii, 1998;Miller & Furneaux, 1997;Truus et al., 2006;Usov, Yarotsky, & Shashkov, 1980;Valiente, Fernandez, Perez, Marquina, & Velez, 1992). The anomeric region (ı 90-110) shows two main signals as C-1 of -d-galactose linked to 3,6-␣-l-anhydro galactose (agarose unit) at 102.2 and C-1 of 3,6-␣-l-anhydro galactopyranose at 98.2. ...
An agar polysaccharide has been isolated from the red seaweed Gracilariopsis persica collected from the Persian Gulf (Iran). Characterization of the structure by chemical and spectroscopic methods showed a basic repeating structure of alternating 3-linked β-d-galactopyranosyl and 4-linked 3,6-anhydro-α-l-galactopyranosyl units. The main polysaccharide components were 3,6-anhydrogalactose (31.8%), galactose (52.1%) and 6-O-methyl-galactose (10.9%). In addition, minor components such as glucose (4.1%) and xylose (1.1%) were detected. The degree of substitution (DS) of sulfate, calculated from S%, was 0.18%. Data from 13C NMR, FT-IR, methylation and desulfation–methylation provided evidence of sulfation at C-2 and C-6 of l-galactose and also C-4 of d-galactose. Gel permeation chromatography (GPC) indicated Mw = 2.22 × 105 g/mol for this polysaccharide.
... 13 C NMR spectroscopy 13 C NMR spectra of the agarose samples as well as their solid state spectra (CP-MAS) are presented in Figs. 3 and 4, respectively. The chemical shifts of the 12 carbon atoms (Fig. 3) of the disaccharide repeating units of agarose (Fig. 1) were comparable with those reported in the literature (Lahaye, Yaphe, Viet, & Rochas, 1989;Truus et al., 2006;Usov, Yarotsky, & Shashkov, 1980) (Table 4). The solid state spectra (CP-MAS) exhibited five peaks at (Fig. 4), which was similar to those reported by Rochas and Lahaye (1989). ...
Agarose was prepared from a red alga Gracilaria dura occurring in the Arabian Sea at the west coast of India. The agarose has been characterized by studying its physicochemical properties as well as by FTIR, 13C NMR and CP-MAS spectra, inductively coupled plasma (ICP) spectrophotometric and rheological measurements. This agarose had gel strength 2200 g cm−2, gelling temperature ⩽ 35 °C, sulphate content ⩽ 0.25%, and Mw 1.25 × 105 g mol−1. These properties were benchmarked against those of the commercially available agarose products of Sigma (A0576) and Fluka, and were found to be comparable.
The present study was aimed at investigating the optimization of extraction variables for food grade quality agar from Gracilaria tenuistipitata, so far, the first study on Bangladeshi seaweed. Water (native)‐ and NaOH (alkali)‐pretreated agars were comparatively analyzed by several physicochemical parameters. All extraction variables significantly affected the agar yield in both extraction conditions. Alkali‐pretreated agar provided a better yield (12–13% w/w) and gel strength (201 g/cm2) in extraction conditions as followed by 2% NaOH pretreatment at 30°C for 3 h, seaweed to water ratio at 1:150, and extraction temperature at 100°C for 2 h. Gelling and melting temperatures, color, and pH values of both agars were found to be comparable with commercial agar. Significantly higher sulfate contents including organic and inorganic and total carotenoids were reported in native (3.14% and 1.29 μg/mL) than that in alkali‐pretreated agar (1.27% and 0.62 μg/mL). FTIR spectrum demonstrated the purity of the agar as characterized by the stronger relative intensity with higher degree of conversion of L‐galactose 6‐sulfate to 3,6‐anhydrogalactose in alkali pretreatment group than that of native ones. Moreover, antioxidant activity (% DPPH scavenging) was observed and confirmed by IC50 values of 5.42 and 9.02 mg/mL in water‐ and alkali‐pretreated agars, respectively. The results suggested that agar from G. tenuistipitata with optimized alkali extraction conditions could promote cost‐effective yield with improved physicochemical characteristics and biofunctional values upon consumption by the consumers as food materials. Extraction variables affect agar yield in both water‐ and NaOH‐pretreated groups. Among them, 2% NaOH pretreatment of Gracilaria tenuistipitata results cost‐effective agar yield with food grade quality having improved physicochemical characteristics.
Agar was dispersed fully in ethanol solution with certain mass fraction, and a series of modified agar were prepared with hydrogen peroxide treatment at different temperatures. Results indicated that the agars can be desulfated, oxidized and degraded by hydrogen peroxide. The modified agars exhibited lower sulfate content and ash content than raw agar because hydrogen peroxide had a good removing effect on alkali-stable sulfate. As the reaction temperature increased, the carbonyl content of modified agar increased which means raw agar can be oxidized by hydrogen peroxide. The molecule-chain breakage and molecular-weight reduction indicated that the agars can be degraded after hydrogen peroxide treatment. FT-IR spectrum of modified agars at 1156 and 1071 cm⁻¹ showed differences confirmed that the structure of modified agars had changed. Thermogravimetric analysis revealed that the modified agars had higher thermal stability than raw agar. Compared with raw agar, the modified agars showed novel physical properties including high gel strength, low viscosity and low ash content. All physicochemical properties changes were more conducive to the application of agar, which means the modified agar had better quality and wider application value than raw agar.
Agar and sulfated galactans were isolated from the red seaweeds Gracilariopsis lemaneiformis and Gelidium amansii. A previously purified arylsulfatase from Marinomonas sp. FW-1 was used to remove sulfate groups in agar and sulfated galactans. After enzymatic desulfation, the sulfate content decreased to about 0.16% and gel strength increased about two folds. Moreover, there was no difference between the DNA electrophoresis spectrum on the gel of the arylsulfatase-treated agar and that of the commercial agarose. In order to reveal the desulfation ratio and site, chemical and structural identification of sulfated galactan were carried out. G. amansii sulfated galactan with 7.4% sulfated content was composed of galactose and 3,6-anhydro-l-galactose. Meanwhile, G. lemaneiformis sulfated galactan with 8.5% sulfated content was composed of galactose, 3,6-anhydro-l-galactose, 2-O-methyl-3,6-anhydro-l-galactose and xylose. Data from 13C NMR, FT-IR, GC-MS provided evidence of sulfate groups at C-4 and C-6 of d-galactose and C-6 of l-galactose both in GRAP and GEAP. Data from GC-MS revealed that desulfation was carried out by the arylsulfatase at the sulfate bonds at C-4 and C-6 of d-galactose and C-6 of l-galactose, with a desulfation ratio of 83.4% and 86.0% against GEAP and GRAP, respectively.
Algae are a diverse group of photosynthetic organisms containing polysaccharides as the main components of biomass. Gelling algal polysaccharides (phycocolloids), such as agars, carrageenans and alginic acids, are produced on a large scale and have a wide range of applications in the food, pharmaceutical and cosmetic industries, while many related polysaccharides devoid of gelling ability are investigated as biologically active compounds. This chapter describes the present data on the chemical structures of polysaccharides obtained from the three groups of macrophytes (red, brown and green algae) and from several microalgae.
Since last decades, lot of biological and rheological properties of polysaccharides and oligosaccharides were described. Among them, galactans and more especially sulfated galactans from seaweeds have shown interesting and specific properties not only as texturing agents but also as biological active compounds on several organisms. This class of polysaccharides includes classical sulfated galactans extracted from seaweeds and classified as agar and carrageenans. However, some galactans are more complex and their specific structural features have been characterized after their extraction from terrestrial plants, seaweeds but also animals and microoragnisms. This review catalogues the origins, structural characteristics and potentialities of these polysaccharides and their oligosaccharides derivatives.
Red algae (Rhodophyta) are known as the source of unique sulfated galactans, such as agar, agarose, and carrageenans. The wide practical uses of these polysaccharides are based on their ability to form strong gels in aqueous solutions. Gelling polysaccharides usually have molecules built up of repeating disaccharide units with a regular distribution of sulfate groups, but most of the red algal species contain more complex galactans devoid of gelling ability because of various deviations from the regular structure. Moreover, several red algae may contain sulfated mannans or neutral xylans instead of sulfated galactans as the main structural polysaccharides. This chapter is devoted to a description of the structural diversity of polysaccharides found in the red algae, with special emphasis on the methods of structural analysis of sulfated galactans. In addition to the structural information, some data on the possible use of red algal polysaccharides as biologically active polymers or as taxonomic markers are briefly discussed.
Orientadora: Maria Eugęnia Duarte Noseda Co-orientador: Miguel Daniel Noseda Tese (doutorado) - Universidade Federal do Paraná, Setor de Cięncias Biológicas, Programa de Pós-Graduaçăo em Bioquímica. Defesa: Curitiba, 2007 Inclui bibliografia e anexos
A nomenclature system for red algal galactans based on their chemical structures is proposed. The terms 'agaran' and 'carrageenan' are suggested as the generic names for two possible diastereoisometric extreme structures of carbohydrate backbone built of alternating 3-linked beta-D-galactopyranose and 4-linked alpha-galactopyranose residues and differing only in the absolute configuration of the 4-linked alpha-galactose residues (L- or D-, respectively). 'Agarose' and 'carrageenose' are the generic names for the corresponding backbones having 3,6-anhydro-alpha-galactopyranose (also L- and D-) as the 4-linked residue. All the other known regular structures may then be designated as substituted (methylated, sulfated, etc.) derivatives of agaran and agarose (agar group polysaccharides) or carrageenan and carrageenose (carrageenan group polysaccharides). A shortland notation system (uppercase letter code) is also proposed, which is especially useful for designation of hybrid (masked repeating) polysaccharide structures or their corresponding oligosaccharidic fragments and for interpretation of the NMR spectra.
Lipid compositions of five species of marine macro-phytes (marine algae Ahnfeltia tobuchiensis, Laminaria japonica, Sargassum pallidum, Ulva fenestrata and sea-grass Zostera marina), collected in spring at 2.9 or 5.58C, and in summer at 238C in the Sea of Japan were ana-lyzed, and major membrane lipids were determined. The relative content of neutral lipids was higher in summer for all species except A. tobuchiensis. Triacylglycerols reached 18–37% of total lipids. There were no correla-tions between the free sterol content and season. The quantity of individual phospholipids and glycolipids dif-fered between seasons in all macrophytes. Molar ratios of phosphatidylcholine/free sterols and diacylglyceryl-O-(N,N,N-trimethyl)homoserine/free sterols varied from 0.9 to 1.7 among species. The relative content of phospho-lipids was much higher in spring. The ratio of phospho-lipids to glycolipids was reduced in the majority of macrophytes in summer. The seasonal changes of lipid composition may be related to thermal adaptation of macrophytes, as well as to their developmental biology.
Many seaweeds produce phycocolloids, stored in the cell wall. Members of the Rhodophyceae produce polysaccharides the main components of which are galactose (galactans)-agar and carrageenan. In addition, alginic acid is extracted from members of the Phaeophyceae. This is a binary polyuronide made up of mannuronic acid and guluronic acid. The wide uses of these phycocolloids are based on their gelling, viscosifying and emulsifying properties, which generate an increasing commercial and scientific interest. In this work, the FTIR and FT-RAMAN spectra of carrageenan and agar, obtained by alkaline extraction from different seaweeds (e.g. Mastocarpus stellatus, Chondrus crispus, Calliblepharis jubata, Chondracanthus acicularis, Chondracanthus teedei and Gracilaria gracilis), were recorded in order to identify the type of phycocolloid produced. The spectra of commercial carrageenan, alginic acid and agar samples (SIGMA and TAAB laboratories) were used as references. Special emphasis was given to the 500-1500 cm(-1) region, which presents several vibrational modes, sensitive to the type of polysaccharide and to the type of glycosidic linkage. The FT-Raman spectra present a higher resolution than FTIR spectra, this allowing the identification of a larger number of characteristic bands. In some cases, phycocolloids can be identified by FT-Raman spectroscopy alone.
This chapter reviews algal polysaccharides. Fossil evidence indicates that many of the algae have changed very little in the hundreds of millions of years and it may be somewhat reckless to assume that the evolution of algal glycan structures has proceeded exactly in parallel with morphology. As new fossil evidence comes continually to light, ideas about the phylogenesis of algae are constantly being revised and there are inevitably areas of disagreement among authorities. There is unanimous agreement that the blue-green algae (Cyanophyta) are by far the oldest and there is reasonable evidence that the red algae (Rhodophyta) appeared next and the brown algae (Phaeophyta) last. In view of the very primitive morphology of algae, one might expect that the structures of the glycans would also be simple. In fact, the reverse seems to be true. Many algal glycans surpass even the gum exudates of terrestrial plants in apparent complexity. Some disorder might perhaps be expected in the glycans of organisms that are low on the evolutionary scale, because it implies that the biosynthetic enzymes are low in specificity rather than large in number. The apparent structural complexity of some algal glycans is increased by a special feature of the reproductive cycle of many algae, whereby the organism passes successively through gametophytic (haploid, male and female) and sporophytic (diploid) forms. There is growing evidence that many algal glycans exist in the native state, at least partly, as proteoglycans and that accepted procedures for isolation usually entail some degradation of these more complex macromolecules, with the liberation of the glycan moiety.
The 13C-n.m.r. signals of agarose oligomers with various substituted repeating units have been assigned. Enzymic hydrolysis of agaroses gave 21-O-methylagarobiose, 62-O-methylagarobiose, the agarobiose biological precursor, agarobiose 42-sulfate, 21-O-methylagarobiose 42-sulfate, and pyruvylated agarobiose. The chemical shift data of the oligomers and the parent polymers were compared, and indicated the distribution of the substituents in hybrid polymers.
Light-dependent transformations of carotenoids in 11 species of marine macroalgae have been studied in laboratory conditions. Beta-carotene and zeaxanthin were found in Gracilaria verrucosa, G. lichenoides, Ahnfeltia tobuchiensis, and beta-carotene and lutein in Phyllophora nervosa (Rhodophyta). Laminaria cichorioides, Coccophora langsdorfii, Cystoseira crassipes and Sargassum pallidum (Phaeophyceae, Chromophyta) possess beta- carotene, fucoxanthin and violaxanthin. Carotenoids typical for higher plants are present in Ulva fenestrata (Chlorophyta), alpha-carotene, neoxanthin, violaxanthin, siphonaxanthin and its 2 esters identified as siphonein A and siphonein B were found in Codium fragile and Cladophora opaca. The violaxanthin cycle was shown in Ulva fenestrata. No light-dependent transformations of carotenoids were observed in red and brown algae. A new phenomenon of the reversible light-induced de-esterification of siphonein B, in which siphonaxanthin is accumulated in high light and siphonein B in low light, was found in Codium fragile and Cladophora opaca. These data taken in the context of algal ecology are consistent with the understanding of the xanthophyll cycle as a protection for photosynthetic structures under stress conditions such as high light.
Regularities of distribution and primary production of an Ahnfeltia tobuchiensis (Kanno et Matsubara) Mak. population, an agar-containing red alga, were studied in the Bay ot Izmena. Experiments were conducted in a flow-through system under conditions similar to algal habitats. The population of A. tobuchiensis unattached to the ground may be from a few centimeters to as much as 1 m thick. It has been shown that only the upper part of a stratum 15–20 cm thick receives a sufficient amount ot light to realize its production potential. While 15–20% of photosynthetically active radiation (PAR) of that falling on the water surface reaches the stratum surface, only 0.1% of PAR from that falling on the water surface penetrates through stratum 15 cm thick. It has been shown for A. tobuchiensis that its photosynthetic rate curve during the daytime mainly follows the PAR intensity curve. The highest values of photosynthetic rate have been measured in the afternoon when PAR reaches its maximum. It is noted that a stratum 15–20 cm thick has peak values ot net primary production (NPP) which averages 3.2 g C m−2 day−1. The total area of A. tobuchiensis population was 23.4 km2, and its biomass was 125 000 tons in this area. On average, the NPP of the A. tobuchiensis population made up in summer and in autumn was 46.8 and 25.0% of its biomass, respectively.
Carrageenans represent one of the major texturising ingredients in the food industry. They are natural ingredients, which are used for decades in food applications. Carrageenan is a generic name for a family of linear, sulfated galactans, obtained by extraction from certain species of red seaweeds (Rhodophyta). Since natural carrageenans are mixtures of different sulfated polysaccharides, their composition differs from batch to batch. Therefore, the quantitative analysis of carrageenan batches is of greatest importance for both ingredient suppliers and food industries to deliver a constant consumer product and to develop new applications based on their unique intrinsic properties. Nowadays NMR spectroscopy is one of the standard tools for the determination of the chemical structure of carrageenan samples. This review gives an overview of NMR-spectroscopy (both 1H- and 13C-NMR) as a powerful tool for the qualitative and quantitative analysis of carrageenan samples. In addition to tables containing chemical shift data for both 1H- and 13C-spectra, details about sample preparation, selective degradation and fractionation techniques are included.
An improved, highly sensitive resorcinol reagent is described for the colorimetric determination of fructose, and of 3,6-anhydrogalactose in agar, carrageenan, and other algal polysaccharides.
Structures of the ‘masked repeating’ type seem to occur generally in κ-carrageenans from Chondrus crispus and Gigartina species and will account for the analytical variation between one sample and another. Most—possibly all—of the variation is in the 4-linked units which occur as 3,6-anhydrogalactose, 3,6-anhydrogalactose 2-sulphate, galactose 6-sulphate, and galactose 2,6-disulphate. In κ-carrageenan from G. stellata, as from C. crispus, all galactose units are believed to have the D-configuration. Samples from Chondrus were similar to each other and had a lower content of both types of 2-sulphate than those from Gigartina. The separation of a Chondrus sample into a series of subfractions which differed in the relative proportions of the various 4-linked units, suggests that κ-carrageenan might normally contain a mixture of related molecules. Evidence is given that absorption bands shown by sulphated 3,6-anhydrogalactose units in the 800–850 cm.–1 region of the infrared spectrum cannot be interpreted in the simple stereochemical terms used previously. However, many carrageenans show a band at about 805 cm.–1 which is characteristic of 3,6-anhydrogalactose sulphate and potentially useful because it is easily recognised, even in the presence of other sulphate esters. Gel formation by κ-carrageenan is enhanced by removal of 6-sulphate with conversion into 3,6-anhydrogalactose, but is much less sensitive to an excess of 2-sulphate. The variation of gel strength with polysaccharide structure provides some evidence on the molecular basis of gel formation.
13C-nmr spectra of red seaweed galactans, belonging to the agar and carrageenan groups or having the “intermediate” type of structure, were interpreted on the basis of 13C-nmr spectra of model compounds. Signal assignments have been made for most of the known extreme structures of such galactans. 13C-nmr spectroscopy was shown to be a rapid and convenient method of structural analysis, which permits one to determine the type of galactan structure, the absolute configurations of its constituents (galactose and 3,6-anhydrogalactose), and the positions of the sulfate and O-methyl groups in a polysaccharide molecule.
The composition, structure and rheological properties of a soluble sulfated polysaccharide from Gracilaria cornea (Brazilian red marine alga) were investigated. Agarocolloid yield, intrinsic viscosity, monosaccharide composition, sulfate and cation content as well as molecular weight were determined. The main polysaccharide components were 3,6-anhydrogalactose (24.7%) and galactose (64.6%). In addition, minor components such as 6-O-methyl-galactose (8.5%), glucose (1.5%), xylose (0.7%) and sulfated groups (4.8%) were detected. Comparison between sulfate contents determined by Fourier transform IR (FT-IR) spectroscopy and microelemental analysis was made. Data from 13C NMR and FT-IR provided evidence of sulfation in C-4 and C-6 of galactose. Sodium, calcium, magnesium and potassium cations were detected in the agarocolloid. The intrinsic viscosities were lower than typical values for agar in the same experimental conditions. No gelation in 1.5, 2.0 and 3.0% (w/v) aqueous solution was observed, even by cooling up to 4 °C. Gel permeation chromatography indicated two major polysaccharide fractions of Mpk 7.4×104 and 1.8×104 g/mol and a minor fraction of Mpk 2.1×106 g/mol, probably a protein–polysaccharide complex.
Information from classical infrared spectroscopy studies has been of significance for characterizing seaweed galactans. The development of Fourier transform infrared spectroscopy and of Fourier transform laser Raman spectroscopy has produced great advances in the application of vibrational spectroscopy to the structural study of polysaccharides. Computational facilities in the spectrometers allow the arithmetic manipulations of the spectra. The second-derivative mode in the FT IR spectrocopy provided more information by increasing the number and resolution of the bands in the spectra as compared to the parent ones. A review of literature data on vibrational spectroscopy of sulfated polysaccharides and new results are presented. Agar-type polymers showed two diagnostic bands in the second-derivative mode in the region 800–700 cm–1. Carrageenans exhibited a number of bands in the region 1600–1000 cm–1. Fourier transform laser Raman spectroscopy in the solid state gave well-defined characteristic spectra of agar and carrageenans. Both techniques can be applied to small samples in the solid state and allow differentiation in a few minutes between agar and carrageenan-type seaweed galactans. The second-derivative mode of the FT IR spectra can be applied to distinguish agar-producing from carrageenan-producing seaweeds. The spectra on KBr pellets of dried, ground agarophyte and carrageenophyte seaweed samples showed the same bands as the corresponding polysaccharides.
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.
Simple sugars, oligosaccharides, polysaccharides, and their derivatives, including the methyl ethers with free or potentially free reducing groups, give an orange-yellow color when treated with phenol and concentrated sulfuric acid. The reaction is sensitive and the color is stable. By use of this phenol-sulfuric acid reaction, a method has been developed to determine submicro amounts of sugars and related substances. In conjunction with paper partition chromatography the method is useful for the determination of the composition of polysaccharides and their methyl derivatives.
Alkali-treatment of agarose was found to be a very simple method to produce charge-free agarose from commercially available agarose in high yield (about 90%) with highly reduced content of sulphate groups and very low electroendosmotic flow. Applications of the agarose in immunoelectrophoretic experiments are also described.
A logical method for the preparation of agarose was developed based on the knowledge that agar consists of a spectrum of charged polysaccharides. The highly charged polysaccharides were removed by a two-stage washing procedure and agaroses of varying purity were prepared by fractionation of the purified agar. An agarose (0.6% sulfate and 0.05% pyruvic acid) equivalent to commercial agaroses was obtained by a modified polyethylene glycol procedure. Fractionation of the purified agar on DEAE-Sephadex A-50 yielded an agarose with 0.05% sulfate and less than 0.01% pyruvic acid. An essentially neutral agarose with 0.02% sulfate and no detectable pyruvic acid was obtained by fractionation of the polyethylene glycol agarose on DEAE-Sephadex A-50. The distribution, concentration, and type of charged polysaccharides in agars and agaroses may explain the anomalies reported when these preparations are used in various biological techniques.
This chapter presents the sulfates of simple sugars. In the plant kingdom, sugar sulfates are found combined in many polysaccharides of the algae, although they are rarely found in land plants. In the animal kingdom, these esters occur in mucopolysaccharides, such as heparin, chondroitins, and mucoitin sulfate; they are also found in the cerebron sulfate of the brain. A detailed examination of the molecular structure of a sulfated polysaccharide requires that the positions of attachment of the sulfate groups in the polysaccharide be known and that the chemical reactivity of these groups be understood. Chlorosulfonic acid has certain disadvantages as a sulfating agent; it is unpleasant to handle and generates chloride ions in the reaction mixture, but it is claimed to give mixtures of sulfates less complex than those afforded by the pyridine–sulfur trioxide complex.
A simple and inexpensive procedure of agar and agarose production from the red alga Ahnfeltia tobuchiensis was developed, which needs no additional chromatographic purification.
Infrared spectra have been recorded for sulphate esters of d-glucose, d-galactose and N-acetyl-d-glucosamine prepared by definitive and direct esterification. By comparing the spectra of the authentic 6-O-sulphate esters and the corresponding monosulphate esters prepared by direct esterification, evidence has been obtained supporting the location of the sulphate group on position 6 of the pyranose ring in the latter compounds. A similar spatial position for the sulphate group in N-acetyl-d-galactosamine monosulphate is suggested by the infrared spectrum of this ester. Infrared spectroscopic examination also supports the assignment of the sulphate group to position 6 of the d-galactose moiety of cerebron sulphate.
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.
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