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Alginate

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Ki-jung Paeng – One of the best experts on this subject based on the ideXlab platform.

  • effect of calcium ion cross linker concentration on porosity surface morphology and thermal behavior of calcium Alginates prepared from algae undaria pinnatifida
    Carbohydrate Polymers, 2010
    Co-Authors: Tara Sankar Pathak, Ki-jung Paeng

    Abstract:

    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.

  • 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, 2009
    Co-Authors: Tara Sankar Pathak, Daejin Baek, Ki-jung Paeng

    Abstract:

    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.

  • New insights into Pseudomonas fluorescens Alginate biosynthesis relevant for the establishment of an efficient production process for microbial Alginates.
    New Biotechnology, 2016
    Co-Authors: Susan Maleki, Svein Valla, Mali Mærk, Radka Hrudikova, Helga Ertesvag

    Abstract:

    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.

  • New insights into Pseudomonas fluorescens Alginate biosynthesis relevant for the establishment of an efficient production process for microbial Alginates.
    New Biotechnology, 2016
    Co-Authors: Susan Maleki, Svein Valla, Mali Mærk, Radka Hrudikova, Helga Ertesvag

    Abstract:

    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.

  • Enzymatic Alginate Modification
    Alginates: Biology and Applications, 2009
    Co-Authors: Helga Ertesvag, Svein Valla, Gudmund Skjåk-bræk

    Abstract:

    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.

Thierry Benvegnu – One of the best experts on this subject based on the ideXlab platform.

  • extracted and depolymerized Alginates from brown algae sargassum vulgare of lebanese origin chemical rheological and antioxidant properties
    Journal of Applied Phycology, 2016
    Co-Authors: Nouha Sarichmayssem, Samir Taha, Hiba Mawlawi, Jeanpaul Guegan, Jelena Jeftic, Thierry Benvegnu

    Abstract:

    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.

  • Extracted and depolymerized Alginates from brown algae Sargassum vulgare of Lebanese origin: chemical, rheological, and antioxidant properties
    Journal of Applied Phycology, 2016
    Co-Authors: Nouha Sari-chmayssem, Samir Taha, Hiba Mawlawi, Jeanpaul Guegan, Jelena Jeftić, Thierry Benvegnu

    Abstract:

    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