Sabrine Sellimi

Influence of acetylation degree and molecular weight of homogeneous chitosans on antibacterial and antifungal activities

The results given in the literature are conflicting when considering the relationship between antimicrobial activity and chitosan characteristics. To be able to clarify, we prepared fifteen homogeneous chitosans with different acetylation degrees (DA) and molecular weights (MW) by reacetylation of a fully deacetylated chitin under homogeneous conditions. They were tested at different pH values for their antimicrobial activities against four Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae and Salmonella typhi), four Gram-positive bacteria (Staphylococcus aureus, Bacillus cereus, Enterococcus faecalis and Micrococcus luteus) and three fungi (Aspergillus niger, Fusarium oxysporum and Alternaria solani). Chitosans markedly inhibited growth of most bacteria and fungi tested, although the inhibitory effect depends on the type of microorganism and on the chitosan characteristics (DA and MW) with minimum inhibitory concentrations in the range of 0.001 to 0.1 w%. Considering chitosan efficiency on bacteria, our series of data clearly show that the lower DA and the lower pH give the larger efficiency. Antibacterial activity was further enhanced for Gram-negative bacteria with decreasing MW, whereas, opposite effect was observed with the Gram-positive. Concerning the antifungal activity, the influence of chitosan characteristics was dependent on the particular type of fungus. Fungal growth decreased with increasing MW for F. oxysporum and decreasing DA for A. solani, but no MW or DA dependences were observed with A. niger.

Structural, physicochemical and antioxidant properties of sodium alginate isolated from a Tunisian brown seaweed

An original sodium alginate from Tunisian seaweed (Cystoseira barbata) was purified and characterized by circular dichroism (CD) and ATR-FTIR spectroscopies. ATR-FTIR spectrum of C. barbata sodium alginate (CBSA) showed the characteristic bands of mannuronic (M) and guluronic acids (G). The M/G ratio was estimated by CD (M/G = 0.59) indicating that CBSA was composed of 37% mannuronic acid and 63% guluronic acid. The analysis of viscosity of CBSA showed evidence of pseudoplastic fluid behaviour. The emulsifying capacity of CBSA was evaluated at different concentrations (0.25-3%), temperatures (25-100 °C) and pH (3.0-11.0). Compared to most commercial emulsifiers, the emulsion formulated by CBSA was found to be less sensitive to temperature changes and more stable at acidic pH. CBSA was examined for antioxidant properties using various antioxidant assays. CBSA exhibited important DPPH radical-scavenging activity (74% inhibition at a concentration of 0.5 mg/ml) and considerable ferric reducing potential. Effective hydroxyl-radical scavenging activity (82% at a concentration of 5 mg/ml) and potent protection activity against DNA breakage were also recorded for CBSA. However, in the linoleate-β-carotene system, CBSA exerted moderate antioxidant activity (60% at a concentration of 1.5 mg/ml). Therefore, CBSA can be used as a natural ingredient in food industry or in the pharmaceutical field.

Functional, antioxidant and film-forming properties of tuna-skin gelatin with a brown algae extract.

Characteristics and functional properties of gelatin from skin of Atlantic Bluefin tuna (Thunnus thynnus) were investigated. The gelatin was extracted by an acid-swelling process in the presence of different concentrations of commercial pepsin, followed by subsequent heating. The extraction yield was higher when increasing concentrations of pepsin were used during the swelling process. Emulsion activity index, foam formation ability and foam stability of gelatin increased with the increase of gelatin concentration. Antioxidant properties (ferric-reducing ability and DPPH-radical-scavenging capacity) of gelatin-based edible films containing aqueous or methanolic extracts of brown algae (Cystoseira barbata) were also assessed. For comparative purposes, tuna-skin gelatin edible film with BHA was studied. Antioxidant properties of the films were increased significantly when natural extracts were added. Extracts of brown algae could be useful additives to obtain edible films from tuna-skin gelatin with interesting functional and antioxidant properties.

Fucans from a Tunisian brown seaweed Cystoseira barbata: Structural characteristics and antioxidant activity

Sulfated polysaccharides from brown seaweeds are known to be a topic of numerous studies, due to their beneficial biological properties including antioxidant activity. Fucans were isolated from the brown seaweed Cystoseira barbata harvested in Tunisia. ATR-FTIR and (1)H-NMR spectroscopies demonstrated that C. barbata sulfated polysaccharides (CBSPs) consisted mainly of 3-linked-α-l-fucopyranosyl backbone, acetylated and mostly sulfated at C-4. Molar degrees of sulfation and acetylation of CBSPs were 0.79 and 0.27, respectively. Neutral sugars analysis determined by gas chromatography-mass spectrometry (GC-MS) showed that CBSPs were mainly composed of fucose (44.6%) and galactose (34.32%) with few amounts of other sugars such as glucose (7.55%), rhamnose (6.41%), xylose (4.21%) and mannose (2.91%). CBSPs were examined for in vitro antioxidant properties using various antioxidant assays. CBSPs exhibited important DPPH radical-scavenging activity (100% inhibition at a concentration of 1.5mg/ml) and considerable ferric reducing potential (24.62 mg ascorbic acid equivalents). Effective chelating activity and significant protection activity against hydroxyl radical induced DNA breakage were also recorded for CBSPs. However, in the linoleate-β-carotene system, CBSPs exerted moderate antioxidant activity (62% inhibition at a concentration of 1.5mg/ml). Therefore, CBSPs can be used as a potent natural antioxidant in food industry or in the pharmaceutical field.

Polyphenolic-protein-polysaccharide ternary conjugates from Cystoseira barbata Tunisian seaweed as potential biopreservatives: Chemical, antioxidant and antimicrobial properties

The present study investigated the antioxidant and antimicrobial activities of naturally occurring Cystoseira barbata seaweed glyco-conjugates (CBGs), with a view to developing safer food preservatives. CBGs were successfully isolated, then chemically and structurally characterized. CBGs contained a high amount of polysaccharides (49.76%) that consisted mainly of neutral sugars (47.67%) and uronic acids (2.09%). The carbohydrate fraction was sulfated (13.81%) and conjugated with proteins (9.86%) and phenolic compounds (4.98%). Infrared spectroscopy of CBGs showed interactions between polyphenols, proteins and polysaccharides, which were characterized by α-type glycosidic bond and sulfate groups in the axial position of sugar residues. Neutral sugars analysis of CBGs by GC-MS revealed that conjugated polysaccharides were mainly composed of galactose (34.02%), fucose (26.25%) and mannitol (21.25%) with few amounts of other sugars such as glucose (5.78%), rhamnose (4.9%), xylose (3.22%) and mannose (2.22%). Analysis of the amino acid composition of CBGs showed a high level of essential amino acids (40.36%), in which threonine was the most relevant (10.28%). LC-QTOF-MS analysis of the phenolic fraction of CBGs showed a variety of phenolic compounds including flavonoids, phlorotannins and anthraquinone glycosides. CBGs exhibited potent antioxidant activities including radical scavenging activity, chelating ability and reducing power, and displayed noticeable antibacterial and antifungal activities, which may open the way to the development of a natural biopreservation strategy based on algae.

Enhancing colour and oxidative stabilities of reduced-nitrite turkey meat sausages during refrigerated storage using fucoxanthin purified from the Tunisian seaweed Cystoseira barbata

The present study investigated the angiotensin-I converting enzyme (ACE) inhibitory activity and the antioxidant properties, inxa0vitro and in cured meat sausages containing reduced levels of sodium nitrite, of fucoxanthin extracted from the Tunisian brown seaweed Cystoseira barbata (CBFX). Results revealed that CBFX exhibited great scavenging activities against DPPH free radicals (EC50xa0=xa0136xa0μg/ml), peroxyl radicals in the linoleate-β-carotene system (EC50xa0=xa043xa0μg/ml) and hydroxyl radicals generated by Fenton reaction (DNA nicking assay). A considerable ferric reducing potential was also recorded for CBFX (EC50xa0=xa034xa0μg/ml). It is interesting to note that CBFX was found to modulate the ACE activity, which is the key enzyme involved in the blood pressure regulation, with an EC50 of 5xa0μg/ml. When fucoxanthin was supplemented, the concentration of sodium nitrite added to cured turkey meat sausages was reduced from 150 to 80xa0ppm, coupled with the enhancement of colour and oxidative stabilities. Thus, CBFX, with noticeable antioxidant and antihyertensive effects, could be used as a natural additive in functional foods to alleviate potential human health hazards caused by carcinogenic nitrosamines formation.

Safer and healthier reduced nitrites turkey meat sausages using lyophilized Cystoseira barbata seaweed extract

Abstract Background Nitrite salts are still common additives in the meat industry. The present study provides a first approach on the employment of the lyophilized aqueous extract (WE) of the Tunisian seaweed Cystoseira barbata for the quality enhancement of turkey meat sausage. Methods WE was supplemented as a natural antioxidant agent to investigate its effectiveness in delaying lipid oxidation turkey meat sausages containing reduced amounts of sodium nitrites. Results On storage day 5, all concentrations of WE (0.01–0.4u2006%) reduced the meat lipid oxidation by approximately 36u2006%, as compared to the negative control containing only 80 mg/kg of meat of sodium nitrites as antioxidant. It was noted that within 15 days of refrigerated storage, a meat system containing 80 mg/kg of meat of sodium nitrites and 0.02u2006% and 0.04u2006% of WE had similar Thiobarbituric Acid Reactive Substances (TBARS) levels (19±1.32 and 17±1.12 µmol/kg of meat, respectively), which were comparable to the positive control containing sodium nitrites (150 mg/kg of meat) and 0.045u2006% vitamin C (18.46±1.27 µmol/kg of meat). In-depth, the metabolomic profiling using gas chromatography–mass spectrometry (GC/MS) and liquid chromatography–quadripole–time–of–flight–mass spectrometry (LC-QTOF-MS) analyses of the Tunisian seaweed C. barbata solvent extracts showed that the main active compounds were phenolic compounds, fatty acids and sterols. Conclusions Overall, the cold medium containing C. barbata lyophilized aqueous extrac, with strong antioxidant activity and antihypertensive properties, may open the way to the development of a natural quality enhancement strategy for new functional and ever healthier reduced nitrites meat sausages based on algae.

Antioxidant, antibacterial and in vivo wound healing properties of laminaran purified from Cystoseira barbata seaweed

Laminaran, a polysaccharide extracted from marine algae, exhibits attractive properties being non-toxic, hydrophilic and biodegradable. The aim of this study was to investigate the effectiveness of a cream based on the brown seaweed Cystoseira barbata laminaran (CBL) for healing full thickness wounds induced on rats. The antibacterial activity of CBL was evaluated against Gram positive and Gram negative bacteria and the antioxidant properties were assessed using five different assays. To highlight the healing effectiveness of CBL-based cream, the response to treatment was assessed by macroscopic, histologic and biochemical parameters and was compared to controls. CBL, recovered (7.27%) by ultrafiltration (1-10u202fkDa) and predominantly consisted of (1u202f→u202f3)-linked β-d-glucopyranose residues with a small level of (1u202f→u202f6)-glycosidic bonds, showed noticeable antioxidant and antibacterial properties. The cream containing CBL as an active ingredient exerted a promoting healing effect. The wound contraction reached 98.57u202f±u202f1.31% after thirteen days of treatment. The derma in CBL treated group is properly arranged and revealed an improved collagen deposition and an increased fibroblast and vascular densities compared with the control groups. Overall, these results established, for the first time, a scientific in vivo evidence of the efficiency of CBL as a wound healing agent of interest in modern medicine.