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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 1 H and 13 C NMR spectroscopy. An alginate with a low content of protein (<0.62 %) 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  > 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.

Since the opening of the Suez Canal in 1869, a plethora of Red Sea fishes have entered the Mediterranean Sea (Lessepsian migration). The Comber Serranus cabrilla is considered to have moved in the opposite direction as anti-Lessepsian migrant and has an established population in the northern Red Sea. Mitochondrial (COI) and nuclear DNA from 49 individuals from Red Sea (Gulf of Suez) and Mediterranean populations (Cyprus, Egypt and Lebanon), as well as GenBank sequences from other Mediterranean and Atlantic populations were analyzed to study phylogenetic relationships. COI sequencing resulted in a phylogenetic tree that isolated the Red Sea population from all Mediterranean and Atlantic populations. Furthermore, sequence divergence within the Red Sea population was significantly lower than in Atlantic and Mediterranean populations. Moreover, none of the Mediterranean haplotypes were present in the Red Sea. SNPs and MIG-seq analyses of nuclear DNA confirmed that the Red Sea population is genetically different from the Mediterranean populations. A rough estimate of divergence time suggested that Mediterranean and Red Sea populations separated 194,055 years ago, at the latest. Serranus cabrilla must, therefore, have existed in the Red Sea prior to the opening of the Suez Canal and can no longer be considered as an anti-Lessepsian migrant.

Over the last years, different seaweeds have raised considerable interest as sources of valuable and biodegradable materials from renewable and environmental sources in order to limit the use of the traditional non-renewable petroleum/chemical-based ones. For instance, the exploitation of algae as a source of carbohydrate polymers has been the target of special attention and specifically research on the unexploited green algae, including their polysaccharide ulvan. In this study, a simple method for extraction of ulvan from the green alga Ulva linza of Lebanese origin is demonstrated successfully without enzymatic treatment. The isolated ulvan (yield = 21.7%) was characterized in terms of composition and structure by elemental analysis, turbidimetric method of barium sulfate, size exclusion chromatography, HPLC after acidic methanolysis of ulvan, FTIR, and NMR spectroscopy. An ulvan with a relatively low content of protein (2.56%), high amount of sulfate (17.2%), and a molecular weight of 565,100 g mol−1 was identified as a sole polysaccharide. This ulvan was rich in rhamnose (26.2%) and glucuronic acid (11.5%) while a low amount of iduronic acid (3.5%), xylose (5.8%), and glucose (1.2%) was detected. Rheological properties of ulvan revealed a shear-thinning pseudoplastic behavior for a concentration range between 0.5 and 3% in a solution of 7 mM CaCl2 and 7 mM H3BO3. Also, storage (G′) and loss (G″) moduli were studied for ulvan solution (1%). Besides, an original hydrophobically modified uronamide ulvan (HM-ulvan) was elaborated in aqueous medium using the coupling agent EDC-HCl in the presence of octylamine. The linkage between carboxylic groups of ulvan uronic acid and octylamine via amide functions was demonstrated chemically by FTIR and NMR (1D and 2D). In conclusion, the introduction of octyl fatty chains on the ulvan backbone increased the dynamic viscosity and improved the rheological properties by creating hydrophobic associations in the solution of HM-ulvan. The low degree of substitution (0.42) influenced dramatically the critical aggregation concentration (CAC) and no foam properties of HM-ulvan were detected.

Chlorophyta most abundant, Rhodophyta, taxonomy, paleoecology, intertidal and restricted shelf environment