Primary structural features, physicochemical and biological properties of two water-soluble polysaccharides extracted from the brown Tunisian seaweed Halopteris scoparia.

Marine algae are the most abundant resource in the marine environment and are still a promising source of bioactive compounds including hydrocolloids. This study contributes to the evaluation of the biological and biotechnological potentials of two water soluble polysaccharides, namely alginates (AHS) and fucoidan (FHS), extracted and purified from Halopteris scoparia, an abundant Tunisian brown macroalgae collected in Tunisia (Tabarka region). The total sugars, neutral monosaccharides, uronic acids, proteins, polyphenols, and sulfate groups contents were quantified for both fractions, as well as their functional groups and primary structural features by Fourier transform infrared spectroscopy, ionic and/or gas chromatography and nuclear magnetic resonance analyses. AHS and FHS showed significant anti-inflammatory (IC50 ≈ 1 mg/mL), anticoagulant (e.g., 27-61.7 for the activated partial thromboplastin time), antihyperglycemic (0.1-40 µg/mL) and anti-trypsin (IC50 ≈ 0.3-0.4 mg/mL) effects. FHS and a hydrolyzed fraction showed a very promising potential against herpes viruses (HSV-1) (IC50 < 28 µg/mL). Besides, AHS and two hydrolyzed fractions were able to stimulate the natural defenses of tomato seedlings, assessing their elicitor capacity, by increasing the activity of phenylalanine ammonia-lyase (66-422 %) but also significantly changing the polyphenol content in the leaves (121-243 %) and roots (30-104 %) of tomato plants.

Elicitor Activity of Low-Molecular-Weight Alginates Obtained by Oxidative Degradation of Alginates Extracted from Sargassum muticum and Cystoseira myriophylloides.

Alginates extracted from two Moroccan brown seaweeds and their derivatives were investigated for their ability to induce phenolic metabolism in the roots and leaves of tomato seedlings. Sodium alginates (ALSM and ALCM) were extracted from the brown seaweeds Sargassum muticum and Cystoseira myriophylloides, respectively. Low-molecular-weight alginates (OASM and OACM) were obtained after radical hydrolysis of the native alginates. Elicitation was carried out by foliar spraying 20 mL of aqueous solutions (1 g/L) on 45-day-old tomato seedlings. Elicitor capacities were evaluated by monitoring phenylalanine ammonia-lyase (PAL) activity, polyphenols, and lignin production in the roots and leaves after 0, 12, 24, 48, and 72 h of treatment. The molecular weights (Mw) of the different fractions were 202 kDa for ALSM, 76 kDa for ALCM, 19 kDa for OACM, and 3 kDa for OASM. FTIR analysis revealed that the structures of OACM and OASM did not change after oxidative degradation of the native alginates. These molecules showed their differential capacity to induce natural defenses in tomato seedlings by increasing PAL activity and through the accumulation of polyphenol and lignin content in the leaves and roots. The oxidative alginates (OASM and OACM) exhibited an effective induction of the key enzyme of phenolic metabolism (PAL) compared to the alginate polymers (ALSM and ALCM). These results suggest that low-molecular-weight alginates may be good candidates for stimulating the natural defenses of plants.

Assessment of the antioxidant, antimicrobial and antibiofilm activities of essential oils for potential application of active chitosan films in food preservation.

In the food industry, the development of microbial biofilms is a serious problem that leads to the contamination and deterioration of food products. To overcome that, our aim consists of searching for natural antimicrobial and non-toxic compounds (essential oils EOs), which might be used alone or adsorbed on natural biopolymer films (chitosan). In this work, the antioxidant activity of eight EOs was evaluated by DPPH radical-scavenging method while their antibacterial activity was determined by diffusion on agar and microdilution methods. Among all tested EOs, Eugenia caryophyllus, Cinnamomum zeylanicum Blume and Thymus satureioides Cosson showed high antioxidant activities at the concentration of 25.6 mg/mL, with respective values of (86.26%, 81.75%, and 76%), and strong antibacterial activity against Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, and Enterococcus hirae, with (MIC) values ≤ 4 µL/mL. At the concentration of 1 µL/mL, these EOs tested alone, showed values of antibiofilm-forming activity ranging from 79.43 to 99.33% and from 44.18 to 94.17%, when they are adsorbed onto chitosan film. These promising results confirm that these three EOs have a good potential for an eventual application in the food industry, as antimicrobial and antioxidant agents, or as active biodegradable food packaging, if combined with chitosan.

Influence of the sulfate content of the exopolysaccharides from Porphyridium sordidum on their elicitor activities on date palm vitroplants.

Given the increasing interest that is being paid to polysaccharides derived from algae as plant natural defense stimulators, the degree of sulfation of exopolysaccharides produced by P. sordidum for inducing defense responses in date palm vitroplants was investigated. Firstly, the culture parameters of P. sordidum were optimized to maximize the amount of sulfate in EPS using a Box-Behnken experimental design and the elicitor effects of two EPS which differ in the sulfation degrees were compared. Results demonstrated that the concentrations of NaCl, NaNO3 and MgSO4 set at 28, 0.54 and 16.31 g/L, respectively yielded the best sulfate contents. To elucidate defense-inducing activities in date palm vitroplants, EPS with the highest sulfate content (EPS1) were prepared for comparison with those obtained under standard conditions (EPS0). A fucoidan extracted from Cystoseira compressa was used as positive control and MgSO4 as negative control. Both EPS and the fucoidan displayed H2O2 accumulation and expression of PR1, SOD, PAL and WRKY genes. Interestingly, EPS1 was significantly more bioactive than EPS0 and the fucoidan suggesting that the elicitor activity is positively correlated with the sulfate groups content of this polysaccharide.

Induction of Natural Defenses in Tomato Seedlings by Using Alginate and Oligoalginates Derivatives Extracted from Moroccan Brown Algae.

Polysaccharides extracted from marine algae have attracted much attention due to their biotechnological applications, including therapeutics, cosmetics, and mainly in agriculture and horticulture as biostimulants, biofertilizers, and stimulators of the natural defenses of plants. This study aimed to evaluate the ability of alginate isolated from Bifurcaria bifurcata from the Moroccan coast and oligoalginates derivatives to stimulate the natural defenses of tomato seedlings. Elicitation was carried out by the internodal injection of bioelicitor solutions. The elicitor capacities were evaluated by monitoring the activity of phenylalanine ammonia-lyase (PAL) as well as polyphenols content in the leaves located above the elicitation site for 5 days. Alginate and oligoalginates treatments triggered plant defense responses, which showed their capacity to significantly induce the PAL activity and phenolic compounds accumulation in the leaves of tomato seedlings. Elicitation by alginates and oligoalginates showed an intensive induction of PAL activity, increasing from 12 h of treatment and remaining at high levels throughout the period of treatment. The amount of polyphenols in the leaves was increased rapidly and strongly from 12 h of elicitation by both saccharide solutions, representing peaks value after 24 h of application. Oligoalginates exhibited an effective elicitor capacity in polyphenols accumulation compared to alginate polymers. The alginate and oligosaccharides derivatives revealed a similar elicitor capacity in PAL activity whereas the accumulation of phenolic compounds showed a differential effect. Polysaccharides extracted from the brown seaweed Bifurcaria bifurcate and oligosaccharides derivatives induced significantly the phenylpropanoid metabolism in tomato seedlings. These results contribute to the valorization of marine biomass as a potential bioresource for plant protection against phytopathogens in the context of eco-sustainable green technology.

Use of Alginate Extracted from Moroccan Brown Algae to Stimulate Natural Defense in Date Palm Roots.

Our study aimed to search for seaweed polysaccharides able to stimulate date palm defense mechanisms. Extraction, purification, characterization, and elicitor activity of sodium alginate (FSSA and BBSA) from Moroccan brown seaweeds Fucus spiralis and Bifurcaria bifurcata were investigated. FSSA and BBSA were characterized by proton nuclear magnetic resonance spectroscopy (1H-NMR) and size exclusion chromatography (HPLC-SEC). The mannuronic acid/guluronic acid (M/G) ratio of FSSA was M/G= 0.92 indicating that FSSA contained 48% and 52% of mannuronic and guluronic acids respectively, and the M/G ratio of BBSA was 0.47 indicating that BBSA contained 32% and 68% of mannuronic and guluronic acids respectively. Elicitor activity of FSSA and BBSA was carried out by developing an innovative study model on the date palm. The elicitor capacities were evaluated by investigating phenolic metabolism including phenylalanine ammonia-lyase (PAL) activity and total polyphenol content in seedling roots of date palm maintained in alginates solution (FSSA and BBSA) at different concentrations. The results obtained show that the PAL activity and the phenolic compound content were significantly stimulated with 1 mg.mL-1 of FSSA and BBSA; after 1 day of treatment with FSSA, and after 12 hours of treatment with BBSA. These results show clearly those alginates extracted from Moroccan brown algae induced in date palm roots the stimulation of natural defense mechanisms.