Browsing by Author "Gongi, Wejdene"
Now showing 1 - 5 of 5
Results Per Page
Sort Options
- Characterization of biodegradable films based on extracellular polymeric substances extracted from the thermophilic microalga Graesiella spPublication . Gongi, Wejdene; Pinchetti, Juan Luis Gómez; Cordeiro, Nereida; Sadok, Saloua; Ouada, Hatem BenIn this research, a new type of biodegradable film based on the extracellular polymeric substances (EPS) and isolated from the thermophilic microalga Graesiella sp., was formulated and characterized. The EPS film was 0.221 mm thick. Atomic force microscopy and scanning electron microscopy images revealed a homogeneous character with a lamellar microstructure. The EPS film displayed yellowish color, high transparency, high ul traviolet barrier properties, and low oxygen (0.008 SI), and water-vapor permeability (0.037 SI). Film tensile strength (16.24 MPa) and elongation at break (4.76%) were in the range of common biofilms and the thermal analyses showed high transition temperature (126 ◦C) and high thermal stability (up to 800 ◦C). Compared to ascorbic acid, results indicated that the EPS film shows a higher antioxidant activity, mainly as β-carotene anti bleaching (84%), DPPH- free radical scavenging ability (80%), and ferrous iron-chelating (55%). Graesiella sp., EPS film effects on beef meat packaging were studied during nine days of cold storage. Compared to polyvinylchloride-packed meat, EPS-packed meat samples showed higher stability of color (redness = 13.6) and pH (5.85) during storage and low proliferation of total viable counts (4.04 CFU⋅g− 1 ) and Pseudomonas bacteria (4.09 CFU⋅g− 1 ). They also exhibit lower drip loss (9%) and less metmyoglobin (32%), heme iron (4.87 μg⋅g− 1 ) total volatile basic nitrogen (TVB-N = 22.96 mg⋅kg− 1 ), and lipid oxidation (MDA = 0.025 mg⋅kg− 1 ). The obtained results highlight the potential for use of microalgae EPS as a new film forming material that could be applied in beef meat preservation.
- Extracellular polymeric substances produced by the Thermophilic Cyanobacterium Gloeocapsa gelatinosa: characterization and assessment of their antioxidant and metal-chelating activitiesPublication . Gongi, Wejdene; Gomez Pinchetti, Juan Luis; Cordeiro, Nereida; Ouada, Hatem BenCyanobacteria, particularly thermophilic strains, represent an important potential source of EPSs, harboring structural complexity that predicts diverse and specific bioactive potential. The ther mophilic cyanobacteria Gloeocapsa gelatinosa, isolated from a natural hot source in Ain Echfa (Tunisia), was cultivated in a cylindrical reactor, and the production of biomass and EPSs was investigated. Results revealed that the strain is amongst the most efficient EPSs producers (0.89 g L−1 ) and that EPSs production was not correlated with the growth phase. EPSs were sulfated heteropolysaccharides containing carbohydrates (70%) based on nine different monosaccharides, mainly mannose (22%), and with the presence of two uronic acids. EPSs were formed by two polymers moieties with a molecular weight of 598.3 ± 7.2 and 67.2 ± 4.4 kDa. They are thermostable in temperatures exceeding 100 ◦C and have an anionic nature (zeta potential of −40 ± 2 mV). Atomic force microscopy showed that EPSs formed multimodal lumps with 88 nm maximum height. EPSs presented high water holding capacity (70.29 ± 2.36%) and solubility index (97.43 ± 1.24%), and a strong bivalent metal sorption capacity especially for Cu2+ (91.20 ± 1.25%) and Fe2+ (75.51 ± 0.71%). The antioxidant activity of G. gelatinosa EPSs was investigated using four methods: the β-carotene-bleaching activity, DPPH assays, iron-reducing activity, and metal-chelating activity. EPS has shown high potential as free radicals’ scavenger, with an IC50 on DPPH (0.2 g L−1 ) three-fold lower than ascorbic acid (0.6 g L −1 ) and as a metal chelating activity (IC50 = 0.4 g L−1 ) significantly lower than EDTA. The obtained results allow further exploration of the thermophilic G. gelatinosa for several biotechnological and industrial applications.
- Extracellular polymeric substances with high radical scavenging ability produced in outdoor cultivation of the thermotolerant chlorophyte Graesiella spPublication . Gongi, Wejdene; Cordeiro, Nereida; Pinchetti, Juan Luis Gomez; Sadok, Saloua; Ben Ouada, HatemThe present study developed a two-step strategy to enhance the production of extracellular polymeric substances (EPSs) by a thermotolerant chlorophyte, Graesiella sp., in view to their industrial valorisation. In the first step, Graesiella sp. was grown in outdoor conditions in pilot-scale photobioreactors of 100 L culture volumes. In the second step, the biomass collected in the exponential growth phase was submitted to heat stress (50 °C). A joint production of biomass reaching 0.50 gdw L−1 day−1 and of EPS production reaching 1.30 gdw L−1 in 2 days was obtained. EPSs mainly contained polysaccharides (80%) and proteins (14%). FTIR and 1HNMR revealed the presence of primary amine and sulfated groups. The EPSs contained antioxidant enzymes (SOD, CAT, and APX) maintained in an active state by the microenvironment offered by the EPSs. The EPSs were found to have a potent antioxidant activity via directly scavenging free radicals when compared to L-ascorbic acid.
- Functional, rheological, and antioxidant properties of extracellular polymeric substances produced by a thermophilic cyanobacterium Leptolyngbya spPublication . Gongi, Wejdene; Cordeiro, Nereida; Pinchetti, Juan Luis Gomez; Ouada, Hatem BenExtracellular polymeric substances (EPSs) produced by the flamentous cyanobacterium identifed as Leptolyngbya sp. IkmLPT16 were isolated and characterized chemically, and their antioxidant, functional, and rheological properties were studied. The strain produces a signifcant amount of EPSs (2.15 g L−1) conjointly with a biomass production achieved at a maximum of 1.35 g L−1 after nine production days. Chemical analysis of EPSs revealed the presence of mannose (35%), arabinose (24%), glucose (15%), rhamnose (2%), and one uronic acid (8%). Fourier transformed infrared spectrum of EPSs further revealed the presence of νC-N groups indicating the presence of peptide moieties. Elemental analysis of EPSs showed the presence of sulfate groups (S=0.59%) as inorganic substituents. Functional properties of Leptolyngbya EPSs were determined based on water holding capacity, oil holding capacity, foaming ability, and metal sorption ability. Experimental results showed high water holding capacity (119%), water solubility index (97.43%), and oil holding ability (87.52%), with a strong metal sorption ability and consequent foam stability (22%). The rheological properties of EPSs were comparable with commercial xanthan gum with higher resistance to Temperature. Leptolyngbya sp. EPSs displayed an efective antioxidant activity via directly scavenging free radicals particularly DDPH• (IC50=4 mg. mL−1 against 10 mg. mL−1 for l-ascorbic acid) and •OH (IC50=10 mg. mL−1 against 20 mg. mL−1 for l-ascorbic acid) and as an iron-chelating agent (IC50=40 mg. mL−1 against 60 mg.mL−1 for EDTA). The outcomes of this study demonstrate the potential use of Leptolyngbya sp. EPSs in several food and pharmaceutical applications.
- Production of exopolymer substances from the thermophilic chlorophyte Graesiella: industrial and ecological applicationsPublication . Gongi, Wejdene; Cordeiro, Nereida; Pinchetti, Juan Luis Gómez; Ben Ouada, HatemMicroalgal extracellular polymeric substances (EPSs) are heteropolysaccharides that have characteristics suitable for industrial and biotechnological applications. Notably, they have strong anionic nature and high hydrophobicity. Nevertheless, systematic studies to demonstrate the viability of the production of EPSs on an industrial scale are still crucial. In this research, the chlorophyte Graesiella was grown on a raceway pond to view its EPS valorization. The biomass production achieved a maximum of 1.98 g L−1 and an EPS production of 1.6 g L−1 after six production days. The Graesiella EPSs with a molecular weight above 100 kDa are sulfated exopolymers containing mainly polysaccharide (70%) and protein (16%). The EPSs produced more stable emulsions with hydrocarbons and oils than Tween-20. The emulsification indices with n-hexane (88%) and maize oil (28%) indicate the EPSs’ strong emulsion-stabilizing capacity. The EPSs showed a peak flocculating percentage of 95% to kaolin suspension, with better flocculation performance than Al2(SO4)3 and alginate. Moreover, Graesiella EPSs had a significant effect on antimicrobial activity, significantly inhibiting fungal growth (71% for Botytis cinerea and 87% for Fusarium oxysporum), spore germination (100% of inhibition at a concentration of 1.8 g L−1), and mycelium growth (68% of inhibition). Also, Graesiella EPSs acted as a bactericide against Vibrio anguilaruim and Listonella anguilaruim (100% inhibition). EPSs were also found to have potent antioxidant activity compared with L-ascorbic acid. The obtained results open new perspectives to the further exploration of Graesiella sp. as a potential EPS producer, making it a promising candidate for numerous industrial applications.