Chemical characterization of polysaccharides from Gracilaria gracilis from Bizerte (Tunisia).

Polysaccharides were extracted from Gracilaria gracilis collected from Manzel Jemil Lake in Bizerte Tunisia, with two different solvents (water and NaOH 0.3 M). Different assays were performed on samples (total sugars, neutral sugars, uronic acids, anhydrogalactose, proteins, sulphates, pyruvates), followed by high performance anion-exchange chromatography (HPAEC) to observe the monosaccharide composition, high pressure size exclusion chromatography with multi-angle laser light scattering (HPSEC-MALS) to obtain the molecular mass, Fourier transform infrared spectroscopy (FTIR), and 1D and 2D nuclear magnetic resonance (NMR) to access to structural data. Results have shown that the polysaccharide extracted from Gracilaria gracilis collected from Manzel Jemil Lake in Bizerte Tunisia, is of agar type but with high molecular mass and some original structural features. Hence, the sample was found to contain 9 % of pyruvate groups and is partly sulphated at the C4 of ß-d-galactose and methylated on C2 of anhydro-α-l-galactose. The polymer from G. gracilis from Bizerte thus presents a never described structure that could be interesting for further rheological or biological activities applications.

Structural characterization and rheological properties of a galactomannan from Astragalus gombo Bunge seeds harvested in Algerian Sahara.

A water soluble polysaccharide (WSP) was extracted and purified from Astragalus gombo seeds (Fabaceae) harvested in Septentrional Sahara (Ouargla, Algeria) with a yield of 6.8% (w/w of the dry seed ground). It was characterized by gas chromatography coupled to the mass spectrometry (GC-MS), size exclusion chromatography with Multi-Angle Light Scattering analysis (SEC-MALLS), high-resolution 1H and 13C NMR, and rheological measurements. The structural characterization indicated that this WSP fraction is a galactomannan with a mannose/galactose ratio of 1.7 formed by a backbone of ß-(1,4)-d-mannopyranosyl residues (63%) substituted at O-6 position by a single α-galactopyranose residue (37%). SEC-MALLS analysis revealed that this galactomannan has an average molecular mass (Mw) of 1.1×106g/mol, an intrinsic viscosity of 860mL/g and, a random coil conformation structure. Rheological analysis in semi diluted regimes shown pseudo-plastic and viscoelastic behaviour.

Antioxidant activities of a polyglucuronic acid sodium salt obtained from TEMPO-mediated oxidation of xanthan.

A xanthouronic acid sodium salt called xanthouronan was produced from xanthan by regioselective oxidation with NaOCl/NaBr using 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) as catalyst. The efficiency of the one pot TEMPO-mediated oxidation was confirmed by HPAEC-PAD, (13)C NMR, and FT-IR. The oxidation degree was close to 98% and the mass yield of this new polyglucuronic acid was higher than 90% (w/w). The macromolecular characterization of xanthouronan using SEC-MALLS showed a molecular size reduced by a third due to the oxidation treatment and the degree of polymerization (DP) of the xanthouronan form was about 665. The evaluation of the enzymatic degradation of this C-6 carboxylated xanthan by various polysaccharide hydrolases and one polysaccharide lyase showed its high resistant to biodegradation. The antioxidant activity of xanthouronan was also tested by using the 2,2'-diphenyl-1-picrylhydrazyle (DPPH) and hydroxyl radical procedures. At 1 g/L, xanthouronan presented 75% of the ascorbic acid antioxidant activity.

A new method to screen polysaccharide cleavage enzymes.

The activity of polysaccharide cleavage enzymes has usually been evaluated by qualitative plate screening methods and quantitative colorimetric or chromatographic assays. The recent development of protein engineering has shown the limits of these techniques when applied to high throughput screening. Here we propose a microplate method to measure the activity of polysaccharide cleavage enzymes through small variations in viscosity. Polysaccharide solutions are co-incubated with magnetic particles in enzyme buffers. The cleavage action of polymer-degrading enzymes increases the mobility of the particles in a magnetic field, even at low levels of enzyme activities. This reproducible, sensitive technique was used to evaluate enzymatic specificity towards substrates. BioFilm indices (BFI) determined by associated software were used to follow enzyme kinetics and measure the usual variables.

A new tool to detect high viscous exopolymers from microalgae.

Microalgae are microorganisms often surrounded by a slime layer made of secreted polymeric substances sometimes including polysaccharides. These polysaccharides, weakly described in the literature, can constitute value-added molecules in several industrial areas. The aim of this article is to show that a new tool, the BioFilm Ring Test®, can be used to detect viscous microalgal exopolymers. Two red microalgal strains (Rhodella violacea and Porphyridium purpureum), one cyanobacterium (Arthrospira platensis) and their excreted polymeric fractions were studied. R. violacea and P. purpureum induced a positive response with the BioFilm Ring Test® contrary to A. platensis. Finally, the understanding of the fractions viscosity involvement in the BRT response was performed by a rheological study.

New method showing the influence of matrix components in Leuconostoc mesenteroides biofilm formation.

Studying biofilm formation and influence of the matrix composition was heavy because only old and long methods were employed up to now: confocal microscopy, fluorescent chemical markers, and/or dying techniques. In this context, an innovative tool, the BioFilm Ring Test, was here employed to explore the role of exopolysaccharides, proteins, and nucleic acids in the formation of biofilm by Leuconostoc mesenteroides. The principle is to add magnetic particles in the culture medium. When a biofilm is formed, particles are unable to migrate in the media to form a ring when a magnet is brought nearer to the well. Therefore, culture media supplemented with proteases, glycanases, and/or nucleases allowed us to identify the involvement of these substances in L. mesenteroides biofilm formation. The results permitted to demonstrate that dextran, proteins, and nucleic acids are implied in biofilm formation.