Nabil Souissi

Physical, structural, antioxidant and antimicrobial properties of gelatin-chitosan composite edible films.

Physico-chemical and mechanical properties of cuttlefish skin gelatin (G), chitosan (C) from shrimp (Penaeus kerathurus) and composite films (G75/C25, G50/C50, G25/C75) plasticized with glycerol were investigated. The results indicated that chitosan film had higher tensile strength and lower elongation at break when compared with the other films. Composite films show no significant difference in tensile strength (TS), thickness and transparency. The structural properties evaluated by FTIR and DSC showed total miscibility between both polymers. DSC scans showed that the increase of chitosan content in the composite films increases the transition temperature (Tg) and enthalpy (ΔHg) of films. The morphology study of gelatin, chitosan and composite films showed a compact and homogenous structure. In addition, gelatin and G75/C25 films demonstrated a high antioxidant activities monitored by β-carotene bleaching, DPPH radical-scavenging and reducing power activities, while films contained chitosan exhibited higher antimicrobial activity against Gram-positive than Gram-negative bacteria.

Comparative study of physico-mechanical and antioxidant properties of edible gelatin films from the skin of cuttlefish.

Physicochemical properties of edible films based on cuttlefish skin gelatin extracted without (G0) or with different concentrations of pepsins (5 (G5), 10 (G10) and 15 (G15) U/g of skin) were investigated. Edible films prepared with partially hydrolyzed gelatins had lower tensile strength (TS) and elongation at break (EAB), but higher water vapour permeability (WVP) and water solubility than the control film. FTIR spectra of obtained gelatin films revealed a significant loss of molecular order of the triple helix. In addition, differential scanning calorimetric (DSC) analysis indicated that partially hydrolyzed gelatine films exhibited lower transition temperature and enthalpy compared with those of control film. The properties of the films were related to their microstructure, which was observed by scanning electron microscopy. Films with G0 and G5 had a smooth surface and a more compact structure, while films prepared with G10 and G15 had coarser surface. Thus, the chain length of extracted gelatin directly affected the properties of corresponding films.

Characterization and Potential Use of Cuttlefish Skin Gelatin Hydrolysates Prepared by Different Microbial Proteases

Composition, functional properties, and in vitro antioxidant activities of gelatin hydrolysates prepared from cuttlefish skin were investigated. Cuttlefish skin gelatin hydrolysates (CSGHs) were obtained by treatment with crude enzyme preparations from Bacillus licheniformis NH1, Bacillus mojavensis A21, Bacillus subtilis A26, and commercial alcalase. All CSGHs had high protein contents, 74.3–78.3%, and showed excellent solubility (over 90%). CSGH obtained by alcalase demonstrated high antioxidant activities monitored by β-carotene bleaching, DPPH radical scavenging, lipid peroxidation inhibition, and reducing power activity. Its antioxidant activity remained stable or increased in a wide range of pH (1–9), during heating treatment (100°C for 240 min) and after gastrointestinal digestion simulation. In addition, alcalase-CSGH was incorporated into turkey meat sausage to determine its effect on lipid oxidation during 35 days of storage period. At 0.5 mg/g, alcalase-CSGH delayed lipid oxidation monitored by TBARS and conjugated diene up to 10 days compared to vitamin C. The results reveal that CSGHs could be used as food additives possessing both antioxidant activity and functional properties.

Biochemical properties of anionic trypsin acting at high concentration of NaCl purified from the intestine of a carnivorous fish: smooth hound (Mustelus mustelus).

Trypsin from the intestine of smooth hound (Mustelus mustelus) was purified by fractionation with ammonium sulfate, Sephadex G-75 gel filtration, and DEAE-cellulose ion exchange chromatography, with a 65-fold increase in specific activity and 15% recovery. The molecular weight of the purified trypsin was estimated to be 24 kDa using size exclusion chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The purified enzyme showed esterase-specific activity on N(alpha)-p-tosyl-L-arginine methyl ester hydrochloride (TAME) that was four times greater than its amidase-specific activity on Nalpha-benzoyl-DL-arginine-p-nitroanilide (BAPNA). The optimum pH and temperature for the trypsin activity were pH 8.5 and 50 degrees C, respectively, using TAME as a substrate. The enzyme was extremely stable in the pH range of 7.0-9.0 and highly stable up to 40 degrees C after 1 h of incubation. The purified enzyme was strongly inhibited by soybean trypsin inhibitor (SBTI) and N-p-tosyl-1-lysine chloromethyl ketone (TLCK), specific inhibitors for trypsin. In addition, smooth hound trypsin showed higher proteolytic activity at high NaCl concentration, demonstrating its potential for protein hydrolysis at high salt content. The N-terminal amino acid sequence of the first 12 amino acids of the purified trypsin was IVGGYECKPHSQ. This sequence showed high homology with trypsins from marine vertebrates and invertebrates. Purified trypsin had a Michaelis-Menten constant (K(m)) and catalytic constant (K(cat)) of 0.387 +/- 0.02 mM and 2.62 +/- 0.11 s(-1), respectively, when BAPNA was used as a substrate. For the hydrolysis of TAME, K(m) and K(cat) were 0.156 +/- 0.01 mM and 59.15 +/- 2.2 s(-1), respectively.

Microstructure, rheological and wound healing properties of collagen-based gel from cuttlefish skin

Collagen-based biomaterials are of the utmost importance for tissue engineering and regenerative medicine. The aims of the present investigation were to evaluate structural and rheological properties of collagen-based gel obtained from cuttlefish skin, and to investigate its ability to enhance wound healing. Scanning electron microscopy of resulted gel showed a dense fibrillar microstructure with high interconnection network with a smaller pore size. In addition, the rheological characterization of collagen gel showed an excellent reversibility, when subjected to a temperature variation. Moreover, in the wound-healing study, topical application of collagen based gel increased significantly the percentage of wound closure over a period of 12 days, when compared to the untreated and CICAFLORA(®)-treated groups. Wound-healing activity of collagen gel was confirmed by histopathology study. Thus, cuttlefish collagen based gel might be useful as a wound healing agent.

Sulfated polysaccharides from common smooth hound: Extraction and assessment of anti-ACE, antioxidant and antibacterial activities.

The present study investigates biological activities of sulfated polysaccharides (SPs) isolated from smooth hound by precipitation with cetylpyridinium chloride (SP1) or ethanol (SP2). SP1 showed the highest amounts of sulfated groups (10.2%) and proteins (7.84%) and high molecular weight sugars. Infrared spectroscopic analysis showed typical peaks of sulfated polysaccharides, particularly for the SP1 that was characterized by the presence of O=S=O groups and acetyl groups. Interestingly, SPs displayed important angiotensin I converting enzyme (ACE) inhibitory (IC50=1.04 and 0.75mg/ml for SP1 and SP2, respectively), antibacterial (Gram+ and Gram-) and antioxidant activities (reducing power, metal chelating activity, β-carotene bleaching inhibition and DNA nicking assay). Moreover, SPs fractionation by DEAE-cellulose column chromatography showed one peak during the buffer elution phase and three major fractions during the linear gradient of NaCl. The overall data suggested that SPs could be used as natural antioxidant, antimicrobial and anti-ACE ingredient to formulate functional foods.

Protein hydrolysates from Bluefin Tuna (Thunnus thynnus) heads as influenced by the extent of enzymatic hydrolysis

Functional properties and antioxidant activities of protein hydrolysates from tuna (Thunnus thynnus) heads (THPHs), with different degrees of hydrolysis, obtained by treatment with Bacillus mojavensis A21 alkaline proteases and Alcalase, were investigated. Protein content of all freeze-dried THPHs ranged from 73.74 ± 0.5 to 78.56 ± 1.2%. The THPHs had excellent solubility, compared to untreated tuna head proteins and possessed interfacial properties, which were governed by their concentrations. Similarly, at a degree of hydrolysis (DH) of 12 and 15%, > 90% nitrogen solubility was observed at all experimental pH values tested. The emulsifying activity index (EAI) and emulsion stability index (ESI) of both hydrolysates at different DHs decreased (p < 0.05) with increasing DH. At low DH (5%), hydrolysates exhibited strong emulsifying properties. All THPHs produced by the A21 proteases generally showed higher antioxidative activity than that of the Alcalase protein hydrolysates. The highest DPPH radical-scavenging activity (78 ± 2.1% at 3 mg/mL) was obtained with a DH of 15%. The IC50 value for the β-carotene bleaching assay was 0.5 ± 0.03 mg/mL. Alcalase (DH = 12%) and A21 (DH = 15%) protein hydrolysates contained glutamic acid/glutamine and arginine as the major amino acids, followed by lysine, aspartic acid/ asparagine, histidine, valine, phenylalanine, and leucine. In addition, the THPHs had a high percentage of essential amino acids, which made up 50.52 and 50.47%, of the protein hydrolysates obtained by the Alcalase and A21 proteases, respectively. Therefore, THPHs can be used as a promising source of functional peptides with antioxidant properties.

Tunisian date (Phoenix dactylifera L.) by-products: Characterization and potential effects on sensory, textural and antioxidant properties of dairy desserts.

Three Tunisian date varieties, Deglet Nour, Kentichi and Allig, served to produce syrups and powders, which were then examined for their physico-chemical composition and antioxidant properties. Different proportions of these sweetening-like agents were incorporated to produce nine different formulations of dairy desserts, with lower amount of added sugars to avoid any artificial flavoring or coloring agents. Sensory and color evaluation data revealed that incorporating Deglet Nour and Kentichi syrup offers the most desirable formulation. Furthermore, syrup polysaccharides and fibers contribute to better maintain the final product texture. In addition, date by-products create a good source of natural thickening agents, involved in enhancing apparent viscosity and spontaneous exudation. Thanks to their high content in phenolic compounds, date by-products considerably improve antioxidant activities of the formulated desserts. Therefore, they could be valued as natural ingredients in the formulation of novel dairy products with high nutritional-properties.

Bioactive potential and structural characterization of sulfated polysaccharides from Bullet tuna (Auxis Rochei) by-products

The present study deals with the isolation of sulfated polysaccharides (Ps) from the Bullet tuna by-products (head, skin and bones). Results of chemical characterization revealed that Ps-bones showed the highest total sugar, uronic acid and sulfate group contents. Tuna extracted-Ps contained a mixture of neutral sugars, with high amounts of glucuronic and galacturonic acids and presented different molecular weights. The presence of sulfate groups in different Ps was confirmed by FTIR analysis. Interestingly, Ps-bones showed the highest antioxidant activity among all the extracted Ps. Moreover, results revealed that all polysaccharides displayed varying degrees of antibacterial activity. Ps-bones exhibited high and wide spectrum of activities, inhibiting the growth of all bacteria tested. Ps-bones incorporated during fillet cooking offered an excellent protection of fish fillet by avoiding pH change, color loss, lipid oxidation and spoilage. Overall, the results demonstrated that Ps could be potentially used as natural antioxidant and antibacterial agents.

Gelatin based bio-films prepared from grey triggerfish’ skin influenced by enzymatic pretreatment

Gelatins from grey triggerfish skin were extracted with different methods. The treatment by pepsin (PG) improved the yield of extraction when compared with untreated gelatin (UG) and acidic gelatin (AG). The outputs of gelatins AG, UG and PG, obtained respectively, with acitic acid, glycine buffer and glycine buffer added with 5U of pepsin/g of the skin beforehand treated by alkali, were 6.9%, 7.9% and 9.7%, respectively. The enzymatic treatment of the alkali-pretreated skin of grey triggerfish altered the electrophoresis profile, biophysical, gellification, rheological and thermal properties of the prepared gelatins extracted under acidic condition. However, the untreated gelatin obtained without pepsin exhibited the highest transition and enthaply temperatures. In addition, the properties of the prepared films were interconnected to their microstructure as demonstrated by scanning electron microscopy. Furthermore, films with PG and UG had a regular surface and a more condensed structure, whereas films prepared with AG had rougher surface.