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Ki-jung Paeng - One of the best experts on this subject based on the ideXlab platform.
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effect of calcium ion cross linker concentration on porosity surface morphology and thermal behavior of calcium Alginates prepared from algae undaria pinnatifida
Carbohydrate Polymers, 2010Co-Authors: Tara Sankar Pathak, Ki-jung PaengAbstract:Abstract Alginic acid and metal (sodium) Alginates was prepared from fresh algae using hot extraction method. Calcium Alginates are also prepared from sodium Alginate by varying calcium ion (calcium chloride) concentrations. FTIR spectra indicate that alginic acid is converted into metal Alginate. Surface morphology as well as total intrusion volume, porosity (%) and pore size distribution changes by changing calcium ion (cross-linker) concentrations. Thermal degradation of calcium Alginates showed a stepwise weight loss during thermal sweep, indicating different types of reactions during degradation. Calcium Alginate (Calg0.6) prepared at low calcium ion concentration is least stable whereas at highest calcium ion concentration, the Alginate sample (Calg20) is most stable at final degradation temperature (800 °C). Kinetic analysis was performed to fit with TGA data, where the entire degradation process has been considered as four consecutive 1st order reactions.
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effect of cross linker and cross linker concentration on porosity surface morphology and thermal behavior of metal Alginates prepared from algae undaria pinnatifida
Carbohydrate Polymers, 2009Co-Authors: Tara Sankar Pathak, Daejin Baek, Ki-jung PaengAbstract:Abstract Alginic acid and metal Alginates are prepared from fresh algae using extraction method. FTIR spectra indicate that alginic acid is converted into metal Alginate. Asymmetric stretching of free carboxyl group of zinc Alginate at 1596 cm −1 is shifted to 1582 cm −1 in cadmium Alginate, due to the change of charge density, radius and atomic weight of the cation. Surface morphology changes by changing the cross-linker and cross-linker concentration at same magnification. Total intrusion volume, porosity (%) and pore size distribution also changes by changing cross-linker and cross-linker concentration. Thermal degradation results reveals that zinc and cadmium Alginates started decomposing at 100 °C, but rapid degradation started around 300 °C and showed a stepwise weight loss during thermal sweep, indicating different types of reactions during degradation. Kinetic analysis was performed to fit with TGA data, where the entire degradation process has been considered as two or three consecutive 1st order reactions.
Svein Valla - One of the best experts on this subject based on the ideXlab platform.
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New insights into Pseudomonas fluorescens Alginate biosynthesis relevant for the establishment of an efficient production process for microbial Alginates.
New Biotechnology, 2016Co-Authors: Susan Maleki, Svein Valla, Mali Mærk, Radka Hrudikova, Helga ErtesvagAbstract:Abstract Alginate denotes a family of linear polysaccharides with a wide range of industrial and pharmaceutical applications. Presently, all commercially available Alginates are manufactured from brown algae. However, bacterial Alginates have advantages with regard to compositional homogeneity and reproducibility. In order to be able to design bacterial strains that are better suited for industrial Alginate production, defining limiting factors for Alginate biosynthesis is of vital importance. Our group has been studying Alginate biosynthesis in Pseudomonas fluorescens using several complementary approaches. Alginate is synthesised and transported out of the cell by a multiprotein complex spanning from the inner to the outer membrane. We have developed an immunogold labelling procedure in which the porin AlgE, as a part of this Alginate factory, could be detected by transmission electron microscopy. No time-dependent correlation between the number of such factories on the cell surface and Alginate production level was found in Alginate-producing strains. Alginate biosynthesis competes with the central carbon metabolism for the key metabolite fructose 6-phosphate. In P. fluorescens, glucose, fructose and glycerol, are metabolised via the Entner-Doudoroff and pentose phosphate pathways. Mutational analysis revealed that disruption of the glucose 6-phosphate dehydrogenase gene zwf-1 resulted in increased Alginate production when glycerol was used as carbon source. Furthermore, Alginate-producing P. fluorescens strains cultivated on glucose experience acid stress due to the simultaneous production of Alginate and gluconate. The combined results from our studies strongly indicate that the availability of fructose 6-phosphate and energy requires more attention in further research aimed at the development of an optimised Alginate production process.
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New insights into Pseudomonas fluorescens Alginate biosynthesis relevant for the establishment of an efficient production process for microbial Alginates.
New Biotechnology, 2016Co-Authors: Susan Maleki, Svein Valla, Mali Mærk, Radka Hrudikova, Helga ErtesvagAbstract:Abstract Alginate denotes a family of linear polysaccharides with a wide range of industrial and pharmaceutical applications. Presently, all commercially available Alginates are manufactured from brown algae. However, bacterial Alginates have advantages with regard to compositional homogeneity and reproducibility. In order to be able to design bacterial strains that are better suited for industrial Alginate production, defining limiting factors for Alginate biosynthesis is of vital importance. Our group has been studying Alginate biosynthesis in Pseudomonas fluorescens using several complementary approaches. Alginate is synthesised and transported out of the cell by a multiprotein complex spanning from the inner to the outer membrane. We have developed an immunogold labelling procedure in which the porin AlgE, as a part of this Alginate factory, could be detected by transmission electron microscopy. No time-dependent correlation between the number of such factories on the cell surface and Alginate production level was found in Alginate-producing strains. Alginate biosynthesis competes with the central carbon metabolism for the key metabolite fructose 6-phosphate. In P. fluorescens, glucose, fructose and glycerol, are metabolised via the Entner-Doudoroff and pentose phosphate pathways. Mutational analysis revealed that disruption of the glucose 6-phosphate dehydrogenase gene zwf-1 resulted in increased Alginate production when glycerol was used as carbon source. Furthermore, Alginate-producing P. fluorescens strains cultivated on glucose experience acid stress due to the simultaneous production of Alginate and gluconate. The combined results from our studies strongly indicate that the availability of fructose 6-phosphate and energy requires more attention in further research aimed at the development of an optimised Alginate production process.
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Enzymatic Alginate Modification
Alginates: Biology and Applications, 2009Co-Authors: Helga Ertesvag, Svein Valla, Gudmund Skjåk-brækAbstract:Alginate is a linear 1-4-linked copolymer of β-d-mannuronic acid and its C-5-epimer α-l-guluronic acid. The polymer is produced by some algae and bacteria, and is used for numerous purposes in industry. Alginate is initially synthesized as mannuronan, which is then modified at the polymer level by mannuronan C-5-epimerases, Alginate lyases, and O-acetylases. This generates a variety of heteropolymers where properties such as viscosity, chain stiffness, gel formation, water-binding potential, and immunogenicity are dependent on the action of the modifying enzymes. Both Alginate lyases and C-5-epimerases can be used in vitro to tailor Alginates for specific purposes. The lyases may also be used as tools to better define the sugar monomer sequences of an Alginate sample.
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ionic and acid gel formation of epimerised Alginates the effect of alge4
International Journal of Biological Macromolecules, 2000Co-Authors: Kurt Ingar Draget, Berit L Strand, Svein Valla, Martin Hartmann, Olav Smidsrød, Gudmund SkjakbraekAbstract:AlgE4 is a mannuronan C5 epimerase converting homopolymeric sequences of mannuronate residues in Alginates into mannuronate/guluronate alternating sequences. Treating Alginates of different biological origin with AlgE4 resulted in different amounts of alternating sequences. Both ionically cross-linked Alginate gels as well as alginic acid gels were prepared from the epimerised Alginates. Gelling kinetics and gel equilibrium properties were recorded and compared to results obtained with the original non-epimerised Alginates. An observed reduced elasticity of the alginic acid gels following epimerisation by AlgE4 seems to be explained by the generally increased acid solubility of the alternating sequences. Ionically (Ca2+) cross-linked gels made from epimerised Alginates expressed a higher degree of syneresis compared to the native samples. An increase in the modulus of elasticity was observed in calcium saturated (diffusion set) gels whereas calcium limited, internally set Alginate gels showed no change in elasticity. An increase in the sol–gel transitional rate of gels made from epimerised Alginates was also observed. These results suggest an increased possibility of creating new junction zones in the epimerised Alginate gel due to the increased mobility in the Alginate chain segments caused by the less extended alternating sequences.
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biosynthesis and applications of Alginates
Polymer Degradation and Stability, 1998Co-Authors: Helga Ertesvag, Svein VallaAbstract:Abstract Alginate is a family of linear polysaccharides composed of mannuronic acid (M) and guluronic acid (G). The polymer is used as a gel-former and viscosifier in a wide range of industrial applications. It is also used for encapsulation of cells and enzymes. The viscosity of Alginate is mainly dependent on the polymer length, while the gel-forming and water-binding properties and the degree of immunogenicity are determined by the fraction and distribution of G-residues. Alginates are currently manufactured by harvesting brown algae, but in nature the polymer is also produced by some bacteria belonging to the genera Azotobacter and Pseudomonas . The biosynthesis of Alginate has been mostly studied in Pseudomonas aeruginosa , where many of the involved proteins and genes have also been identified. In both algae and bacteria the polymer is first produced as mannuronan, which is then epimerized by the enzyme mannuronan C-5-epimerase. A gene encoding a periplasmic epimerase has been identified in the Alginate gene clusters of P. aeruginosa and Azotobacter vinelandii . The A. vinelandii genome also encodes a family of at least five secreted epimerases, each of which introduces different distributions of G in the Alginate. These enzymes can therefore be used to modify Alginates in vitro to obtain polysaccharides with the desired content and distribution pattern of G. Such Alginates may become useful in applications where reproducible and specific physical properties are required.
Thierry Benvegnu - One of the best experts on this subject based on the ideXlab platform.
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extracted and depolymerized Alginates from brown algae sargassum vulgare of lebanese origin chemical rheological and antioxidant properties
Journal of Applied Phycology, 2016Co-Authors: Nouha Sarichmayssem, Samir Taha, Hiba Mawlawi, Jeanpaul Guegan, Jelena Jeftic, Thierry BenvegnuAbstract:Purified sodium Alginate (PS Alginate) was isolated from the brown seaweed Sargassum vulgare collected from the Lebanese Mediterranean coast and then depolymerized into homopolymeric polyguluronate (PolyG) and polymannuronate (PolyM) blocks by controlled acid hydrolysis. These fractions of PS Alginate issued from S. vulgare were characterized in terms of composition and structure by SEC, elemental analysis, FTIR and 1H and 13C NMR spectroscopy. An Alginate with a low content of protein ( 0.5) instead of the M blocks, and it showed more similarity to the composition of some Alginates extracted from other species of Sargassum. High G or M contents (≥80 %) were measured from PolyG and PolyM blocks, respectively. The viscosity of the PS Alginate and its fractions PolyG and PolyM was determined. PS Alginate from S. vulgare of Lebanese origin showed a Newtonian flow behavior for concentration lower than 0.5 % in 0.1 M NaCl solution, while a shear-thinning pseudoplastic behavior is observed for concentration range between 0.75 and 10 %. Also, storage (G′) and loss (G″) moduli were studied for two concentrations of PS Alginate solutions (5 and 10 %). Antioxidant properties of the non-depolymerized and depolymerized Alginates were evaluated by determining the scavenging ability of the stable radical DPPH (2,2-diphenyl-1 picrylhydrazyl). Clearly, the results demonstrated differences in radical scavenging efficacy between PolyG and PolyM fractions. The higher hydroxyl radical scavenging activity was observed for the PolyG fractions (~92 % at 2 mg mL-1) and this activity was comparable with those of standard antioxidants. These PolyG fractions could be valuable in foods or pharmaceutical products as alternatives to synthetic antioxidants.
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Extracted and depolymerized Alginates from brown algae Sargassum vulgare of Lebanese origin: chemical, rheological, and antioxidant properties
Journal of Applied Phycology, 2016Co-Authors: Nouha Sari-chmayssem, Samir Taha, Hiba Mawlawi, Jeanpaul Guegan, Jelena Jeftić, Thierry BenvegnuAbstract:Purified sodium Alginate (PS Alginate) was isolated from the brown seaweed Sargassum vulgare collected from the Lebanese Mediterranean coast and then depolymerized into homopolymeric polyguluronate (PolyG) and polymannuronate (PolyM) blocks by controlled acid hydrolysis. These fractions of PS Alginate issued from S. vulgare were characterized in terms of composition and structure by SEC, elemental analysis, FTIR and 1H and 13C NMR spectroscopy. An Alginate with a low content of protein (\textless0.62 %) and a molecular weight of 110 200 g mol-1 was identified as sole polysaccharide. Depolymerized PS Alginate fractions, PolyG (32.6 %) and PolyM (22.3 %), were found to have close molecular weights, of 7500 and 6900 g mol-1, respectively. From NMR analysis, values of F G, F M, M/G ratio, F GG, F MM, and F GM (or F MG) blocks were determined and compared with those of Alginates from S. vulgare of Brazilian origin and other Sargassum species. Our PS Alginate appeared different from the Brazilian S. vulgare Alginate, with a lower M/G ratio (0.785 instead of 1.27), a predominance of the G blocks (F G and F GG \textgreater 0.5) instead of the M blocks, and it showed more similarity to the composition of some Alginates extracted from other species of Sargassum. High G or M contents (≥80 %) were measured from PolyG and PolyM blocks, respectively. The viscosity of the PS Alginate and its fractions PolyG and PolyM was determined. PS Alginate from S. vulgare of Lebanese origin showed a Newtonian flow behavior for concentration lower than 0.5 % in 0.1 M NaCl solution, while a shear-thinning pseudoplastic behavior is observed for concentration range between 0.75 and 10 %. Also, storage (G′) and loss (G″) moduli were studied for two concentrations of PS Alginate solutions (5 and 10 %). Antioxidant properties of the non-depolymerized and depolymerized Alginates were evaluated by determining the scavenging ability of the stable radical DPPH (2,2-diphenyl-1 picrylhydrazyl). Clearly, the results demonstrated differences in radical scavenging efficacy between PolyG and PolyM fractions. The higher hydroxyl radical scavenging activity was observed for the PolyG fractions (~92 % at 2 mg mL-1) and this activity was comparable with those of standard antioxidants. These PolyG fractions could be valuable in foods or pharmaceutical products as alternatives to synthetic antioxidants
Anne S Meyer - One of the best experts on this subject based on the ideXlab platform.
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characterization of Alginates from ghanaian brown seaweeds sargassum spp and padina spp
Food Hydrocolloids, 2017Co-Authors: Nanna Rheinknudsen, Fatemeh Ajalloueian, Anne S MeyerAbstract:Alginates of four locally harvested Ghanaian brown seaweeds from the Sargassum and Padina genus were assessed for their rheological and chemical characteristics. The seaweeds contained 16–30% by weight of Alginate assessed as the sum of d-mannuronic acid (M) and l-guluronic acid (G). In comparison, Alginate samples from Laminaria digitata and Macrocystis pyrifera, used commercially for Alginate extraction, contained 29% and 27% by weight of the two constituent uronic acids (M + G), respectively. Alginate extraction yields of the Ghanaian seaweeds ranged from 17 to 23% by weight of dry material; the corresponding yields from L. digitata and M. pyrifera were 26–29% by weight; these yields were equivalent to ∼49–99% of the theoretical yields, but the purity of the extracted Alginates varied, and were lowest for the Ghanaian seaweed Alginates. 1H NMR analysis of the uronic acid block-structure in the Alginates gave M/G ratios of 0.47 and 0.70 for the Alginates extracted from Sargassum natans and Sargassum vulgare, while Alginates from Padina gymnospora and Padina antillarum had M/G ratios of 1.75 and 1.85, respectively. The Alginates from the two Ghanaian Sargassum spp. had high contents of dimeric and trimeric homoguluronate elements: FGG and FGGG values were 0.61 and 0.58 for S. natans and 0.49 and 0.44 for S. vulgare. The Alginates from the two Padina spp. had gel strengths estimated as G′ surpassing those from the commercial Alginates with G′ values after 4 h of rheological oscillation of 340 Pa (P. gymnospora) and 376 Pa (P. antillarum), whereas the gelling properties of the Sargassum spp. Alginates were poor. The degree of polymerization of the acid tolerant Alginate backbone fragments, but not M/G ratio or homoguluronate dimer and trimer element contents, appeared to correlate to the Alginate gel strength. The study shows that notably Ghanaian Padina spp. hold Alginate having desirable properties for high gel-strength applications.
Helga Ertesvag - One of the best experts on this subject based on the ideXlab platform.
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New insights into Pseudomonas fluorescens Alginate biosynthesis relevant for the establishment of an efficient production process for microbial Alginates.
New Biotechnology, 2016Co-Authors: Susan Maleki, Svein Valla, Mali Mærk, Radka Hrudikova, Helga ErtesvagAbstract:Abstract Alginate denotes a family of linear polysaccharides with a wide range of industrial and pharmaceutical applications. Presently, all commercially available Alginates are manufactured from brown algae. However, bacterial Alginates have advantages with regard to compositional homogeneity and reproducibility. In order to be able to design bacterial strains that are better suited for industrial Alginate production, defining limiting factors for Alginate biosynthesis is of vital importance. Our group has been studying Alginate biosynthesis in Pseudomonas fluorescens using several complementary approaches. Alginate is synthesised and transported out of the cell by a multiprotein complex spanning from the inner to the outer membrane. We have developed an immunogold labelling procedure in which the porin AlgE, as a part of this Alginate factory, could be detected by transmission electron microscopy. No time-dependent correlation between the number of such factories on the cell surface and Alginate production level was found in Alginate-producing strains. Alginate biosynthesis competes with the central carbon metabolism for the key metabolite fructose 6-phosphate. In P. fluorescens, glucose, fructose and glycerol, are metabolised via the Entner-Doudoroff and pentose phosphate pathways. Mutational analysis revealed that disruption of the glucose 6-phosphate dehydrogenase gene zwf-1 resulted in increased Alginate production when glycerol was used as carbon source. Furthermore, Alginate-producing P. fluorescens strains cultivated on glucose experience acid stress due to the simultaneous production of Alginate and gluconate. The combined results from our studies strongly indicate that the availability of fructose 6-phosphate and energy requires more attention in further research aimed at the development of an optimised Alginate production process.
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New insights into Pseudomonas fluorescens Alginate biosynthesis relevant for the establishment of an efficient production process for microbial Alginates.
New Biotechnology, 2016Co-Authors: Susan Maleki, Svein Valla, Mali Mærk, Radka Hrudikova, Helga ErtesvagAbstract:Abstract Alginate denotes a family of linear polysaccharides with a wide range of industrial and pharmaceutical applications. Presently, all commercially available Alginates are manufactured from brown algae. However, bacterial Alginates have advantages with regard to compositional homogeneity and reproducibility. In order to be able to design bacterial strains that are better suited for industrial Alginate production, defining limiting factors for Alginate biosynthesis is of vital importance. Our group has been studying Alginate biosynthesis in Pseudomonas fluorescens using several complementary approaches. Alginate is synthesised and transported out of the cell by a multiprotein complex spanning from the inner to the outer membrane. We have developed an immunogold labelling procedure in which the porin AlgE, as a part of this Alginate factory, could be detected by transmission electron microscopy. No time-dependent correlation between the number of such factories on the cell surface and Alginate production level was found in Alginate-producing strains. Alginate biosynthesis competes with the central carbon metabolism for the key metabolite fructose 6-phosphate. In P. fluorescens, glucose, fructose and glycerol, are metabolised via the Entner-Doudoroff and pentose phosphate pathways. Mutational analysis revealed that disruption of the glucose 6-phosphate dehydrogenase gene zwf-1 resulted in increased Alginate production when glycerol was used as carbon source. Furthermore, Alginate-producing P. fluorescens strains cultivated on glucose experience acid stress due to the simultaneous production of Alginate and gluconate. The combined results from our studies strongly indicate that the availability of fructose 6-phosphate and energy requires more attention in further research aimed at the development of an optimised Alginate production process.
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Enzymatic Alginate Modification
Alginates: Biology and Applications, 2009Co-Authors: Helga Ertesvag, Svein Valla, Gudmund Skjåk-brækAbstract:Alginate is a linear 1-4-linked copolymer of β-d-mannuronic acid and its C-5-epimer α-l-guluronic acid. The polymer is produced by some algae and bacteria, and is used for numerous purposes in industry. Alginate is initially synthesized as mannuronan, which is then modified at the polymer level by mannuronan C-5-epimerases, Alginate lyases, and O-acetylases. This generates a variety of heteropolymers where properties such as viscosity, chain stiffness, gel formation, water-binding potential, and immunogenicity are dependent on the action of the modifying enzymes. Both Alginate lyases and C-5-epimerases can be used in vitro to tailor Alginates for specific purposes. The lyases may also be used as tools to better define the sugar monomer sequences of an Alginate sample.
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biosynthesis and applications of Alginates
Polymer Degradation and Stability, 1998Co-Authors: Helga Ertesvag, Svein VallaAbstract:Abstract Alginate is a family of linear polysaccharides composed of mannuronic acid (M) and guluronic acid (G). The polymer is used as a gel-former and viscosifier in a wide range of industrial applications. It is also used for encapsulation of cells and enzymes. The viscosity of Alginate is mainly dependent on the polymer length, while the gel-forming and water-binding properties and the degree of immunogenicity are determined by the fraction and distribution of G-residues. Alginates are currently manufactured by harvesting brown algae, but in nature the polymer is also produced by some bacteria belonging to the genera Azotobacter and Pseudomonas . The biosynthesis of Alginate has been mostly studied in Pseudomonas aeruginosa , where many of the involved proteins and genes have also been identified. In both algae and bacteria the polymer is first produced as mannuronan, which is then epimerized by the enzyme mannuronan C-5-epimerase. A gene encoding a periplasmic epimerase has been identified in the Alginate gene clusters of P. aeruginosa and Azotobacter vinelandii . The A. vinelandii genome also encodes a family of at least five secreted epimerases, each of which introduces different distributions of G in the Alginate. These enzymes can therefore be used to modify Alginates in vitro to obtain polysaccharides with the desired content and distribution pattern of G. Such Alginates may become useful in applications where reproducible and specific physical properties are required.
