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Rheological characterization of exopolysaccharides from Porphyridium microalgae

2018; Frontiers Media; Volume: 5; Linguagem: Inglês

10.3389/conf.fmars.2018.06.00052

2296-7745

David W. Lemos, Luís Alves, Lília M.A. Santos,

Biocrusts and Microbial Ecology

Event Abstract Back to Event Rheological characterization of exopolysaccharides from Porphyridium microalgae David Lemos1, 2*, Luís Alves3 and Lília M.A. Santos2 1 Instituto Politécnico de Coimbra, ESAC, Portugal 2 Algoteca de Coimbra (ACOI), Departamento de Ciências da Vida, Universidade de Coimbra, Portugal 3 Centro de Química de Coimbra, Departamento de Química, Faculdade de Ciências e Tecnologia Universidade de Coimbra, Portugal The red microalga Porphyridium Nägeli has been extensively studied due to its metabolites interesting characteristics. Species of this genus are unicellular, spherical and encapsulated by a polysaccharide that dissolves in the extracellular medium as the cell grows (Geresh et al. 2002), making them mucilaginous. This exopolysaccharide is a copolymer, composed by several different monomers, with a high molecular weight (ca. 2-7 x 10^6 Da) and is negatively charged due to the presence of glucuronic acid and half-ester sulfate groups (Arad & Levy-Ontman, 2010; Geresh et al., 2009). The high molecular weight presented by these exopolysaccharides indicates thickening properties; this is confirmed by visual observation of the extracellular medium. The viscosity visually increases as the culture grows and the exopolysaccharides solubilize in the medium. Thickening properties are commercially and academically relevant, especially on hydrocolloids fields; polymers like xanthan and carrageenan, are used as thickening and gelling agents thanks to their ability to produce highly viscous aqueous solutions with relatively low polymer concentrations (Eteshola et al. 1998). In this study, aqueous solutions of the exopolysaccharides of three strains of Porphyridium (P. aerugineum, P. sordidum, and P. purpureum) were rheologically characterized, focusing on their viscosity profile. The obtained exopolysaccharides were compared with commercially available polymers, used for several applications, like k-carrageenan, agar, alginate, xanthan gum, guar gum and sodium carboxymethylcellulose. In order to obtain the exopolysaccharides, the applied methods were based on the works presented by Jones (1962), Geresh & Arad (1991), Geresh et al. (2002) and Patel et al. (2013) with minor modifications. The strains were cultivated for 15 days, with the biomass dry weight registered on t0 and t15 to obtain the total biomass produced. The culture was then centrifuged, the supernatant recovered and evaporated afterwards to concentrate the exopolysaccharides. Absolute ethanol was used to precipitate the exopolysaccharides; the precipitate was redissolved in water and dialyzed (for 7 days) to purify the samples; precipitation was done using around 94% of the supernatant volume as absolute ethanol. The rheological studies were performed on a stress-controlled rheometer at three different temperatures: 0°C, 20°C, and 50°C, set with a cone and plate geometry. Aqueous solutions at 2% (wt/wt) were prepared for all the studied polymers including the commercial polymers. Data were analyzed with the corresponding software. The results were consistent with the works of Geresh & Arad (1991), Geresh et al. (2002) and Patel et al. (2013); all polymer solutions showed a pseudoplastic behavior, i.e., the viscosity decreases as the applied stress increases, being the Newtonian viscosity value significantly different depending on the polymer in question. Among all of the polymers studied, the Porphyridium exopolysaccharides show considerable similarity to xanthan gum, agar, and k-carrageenan with similar Newtonian viscosity and yield stress values. As expected, the solutions viscosity decreased as the temperature was raised with the exceptions of xanthan gum and P. purpureum. The production yield of Porphyridium exopolysaccharides ranged from 3 to 8%; at first glance, it seems low when compared to current yields of commercially available polymers, that can reach yields superior to 50% (alginate for example) (Fertah et al. 2017). However, it should be noted that those yields are obtained with optimized culture conditions in order to maximize production, contrary, to the present results that were obtained under regular, non optimized culture conditions. In conclusion, the results of this study look promising, indicating a real potential of these exopolysaccharides to be used in many different applications such as thickeners, drug release agents and other pharmaceutical uses. Additionally, physicochemical characterization is ongoing to fully characterize the exopolysaccharides (detailed chemical monosaccharides composition, accurate molecular weight determination, solutions viscoelasticity). Also, the optimization of culture conditions to maximize the exopolysaccharides production is underway. These studies will certainly improve our knowledge about the polymer behavior in solution and expand the range of possible applications. Acknowledgements Special thanks to Mariana Assunção for review of this manuscript, to the remaining members of the ACOI team and to the UC Chemistry Center and Colling group teams for all the support throughout this work. References Arad, S., and Levy-Ontman, O. (2010). Red Microalgal Cell-Wall Polysaccharides: Biotechnological Aspects. Current Opinion in Biotechnology 21:358-364 Eteshola, E., Karpasas, M., Arad, S., and Gottlieb, M. (1998). Red Microalga Exopolysaccharides: 2. Study of the Rheology, Morphology and Thermal Gelation of Aqueous Preparations. Acta Polymerica 49:549–556 Fertah, M., Belfkira, A., Dahmane, E., Taourirte, M., and Brouillette, F. (2017). Extraction and Characterization of Sodium Alginate from Moroccan Laminaria Digitata Brown Seaweed. Arabian Journal of Chemistry 10:S3707–S3714 Geresh, S., Adin, I., Yarmolinsky, E., and Karpasas, M. (2002). Characterization of the Extracellular Polysaccharide of Porphyridium sp.: Molecular Weight Determination and Rheological Properties. Carbohydrate Polymers 50:183–189 Geresh, S., and Arad, S. (1991). The Extracellular Polysaccharides of the Red Microalgae: Chemistry and Rheology. Bioresource Technology 38:195–201 Geresh, S., Arad, S., Levy-Ontman, O., Zhang, W., Tekoah, Y., and Glaser, R. (2009). Isolation and Characterization of Poly- and Oligosaccharides from the Red Microalga Porphyridium sp.. Carbohydrate Research 344:343-349 Jones, R. (1962). Extracellular Mucilage of the Red Alga Porphyridium cruentum. Journal of Cellular Physiology 60:61–64 Patel, A., Laroche, C., Marcati, A., Ursu, A., Jubeau, S., Marchal, L., Petit, E., Djelveh, G., and Michaud, P. (2013). Separation and Fractionation of Exopolysaccharides from Porphyridium cruentum. Bioresource Technology 145:345-350 Keywords: Microalgae, Porphyridium, Exopolysaccharide, Rheology, Viscosity Conference: IMMR'18 | International Meeting on Marine Research 2018, Peniche, Portugal, 5 Jul - 6 Jul, 2018. Presentation Type: Oral Presentation Topic: Blue Biotech Citation: Lemos D, Alves L and Santos L (2019). Rheological characterization of exopolysaccharides from Porphyridium microalgae. Front. Mar. Sci. Conference Abstract: IMMR'18 | International Meeting on Marine Research 2018. doi: 10.3389/conf.FMARS.2018.06.00052 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 05 Apr 2018; Published Online: 07 Jan 2019. * Correspondence: Mr. David Lemos, Instituto Politécnico de Coimbra, ESAC, Coimbra, 3045-601, Portugal, davidlemos629@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers David Lemos Luís Alves Lília M.A. Santos Google David Lemos Luís Alves Lília M.A. Santos Google Scholar David Lemos Luís Alves Lília M.A. Santos PubMed David Lemos Luís Alves Lília M.A. Santos Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.