Sami Sayadi

Detrimental effects of high molecular-mass polyphenols on olive mill wastewater biotreatment

Research was undertaken to investigate whether low, medium or high molecular-mass polyphenolics were the most problematic compounds for olive mill wastewater (OMW) biotreatments. For this reason, three polyphenolic fractions were isolated by ultrafiltration of crude OMW and characterized by GC/MS and gel filtration analysis. When P. chrysosporium was cultivated in the presence of F1 polyphenolic fraction (F1 60 kDa) was observed. Lignin peroxidase (LiP) was detected as traces for the F1 fraction and undetected in the case of F3 one. Moreover, increasing the molecular-mass of aromatics led to decreases in levels of depolymerization and COD removal by P. chrysosporium cultures. The use of a lignin peroxidase induction medium has a positive effect on the high molecular-mass fraction decolorization and a high degree of decolorization paralleled the appearance of LiP activity in the extracellular fluid. By comparison to the synthetic medium used, LiP production was delayed in the presence of F1 fraction but strongly inhibited (80% loss) in the presence of F3 fraction. The F1 fraction was well degraded aerobically by P. putida DSM3932 (pWWO) and A. eutrophus DSM 4057 (pJP3) or an activated sludge consortium while F3 resisted degradation by the OMW-acclimated activated sludge. Moreover, continuous anaerobic biomethanization experiments conducted in parallel with the different fractions showed that at the same hydraulic retention time (26 days), the F1 fraction was bioconverted into methane at high yield while F3 fraction was poorly biodegraded.

Antidiabetic and Antioxidant Effects of Hydroxytyrosol and Oleuropein from Olive Leaves in Alloxan-Diabetic Rats

This study was designed to test the antidiabetic and antioxidative activities of olive leaf oleuropein and hydroxytyrosol. Diabetes in Wistar rats was induced by intraperitoneal injections of alloxan. The serum glucose and cholesterol, hepatic glycogen, the thiobarbituric acid-reactive substances (TBARS), and the components of hepatic and serum antioxidant system were examined. Diabetic rats showed hyperglycemia, hypercholesterolemia, increased lipid peroxidation, and depletion in the antioxidant enzymes activities. The administration, for 4 weeks, of oleuropein and hydroxytyrosol rich extracts, leading to 8 and 16 mg/kg body weight of each compound, significantly decreased the serum glucose and cholesterols levels and restored the antioxidant perturbations. These results suggested that the antidiabetic effect of oleuropein and hydroxytyrosol might be due to their antioxidant activities restraining the oxidative stress which is widely associated with diabetes pathologies and complications.

Low cost biosorbent "banana peel" for the removal of phenolic compounds from olive mill wastewater: Kinetic and equilibrium studies

The aim of this work is to determine the potential of application of banana peel as a biosorbent for removing phenolic compounds from olive mill wastewaters. The effect of adsorbent dosage, pH and contact time were investigated. The results showed that the increase in the banana peel dosage from 10 to 30 g/L significantly increased the phenolic compounds adsorption rates from 60 to 88%. Increase in the pH to above neutrality resulted in the increase in the phenolic compounds adsorption capacity. The adsorption process was fast, and it reached equilibrium in 3-h contact time. The Freundlich and Langmuir adsorption models were used for mathematical description of the adsorption equilibrium and it was found that experimental data fitted very well to both Freundlich and Langmuir models. Batch adsorption models, based on the assumption of the pseudo-first-order, pseudo-second-order and intraparticle diffusion mechanism, showed that kinetic data follow closely the pseudo-second-order than the pseudo-first-order and intraparticle diffusion. Desorption studies showed that low pH value was efficient for desorption of phenolic compounds. These results indicate clearly the efficiency of banana peel as a low-cost solution for olive mill wastewaters treatment and give some preliminary elements for the comprehension of the interactions between banana peel as a bioadsorbent and the very polluting compounds from the olive oil industry.

Hypolipidimic and antioxidant activities of oleuropein and its hydrolysis derivative-rich extracts from Chemlali olive leaves.

Oleuropein-rich extracts from olive leaves and their enzymatic and acid hydrolysates, respectively rich in oleuropein aglycone and hydroxytyrosol, were prepared under optimal conditions. The antioxidant activities of these extracts were examined by a series of models in vitro. In this study the lipid-lowering and the antioxidative activities of oleuropein, oleuropein aglycone and hydroxytyrosol-rich extracts in rats fed a cholesterol-rich diet were tested. Wistar rats fed a standard laboratory diet or cholesterol-rich diets for 16 weeks were used. The serum lipid levels, the thiobarbituric acid reactive substances (TBARS) level, as indicator of lipid peroxidation, and the activities of liver antioxidant enzymes (superoxide dismutase (SOD) and catalase (CAT)) were examined. The cholesterol-rich diet induced hyperlipidemia resulting in the elevation of total cholesterol (TC), triglycerides (TG) and low-density lipoprotein cholesterol (LDL-C). Administration of polyphenol-rich olive leaf extracts significantly lowered the serum levels of TC, TG and LDL-C and increased the serum level of high-density lipoprotein cholesterol (HDL-C). Furthermore, the content of TBARS in liver, heart, kidneys and aorta decreased significantly after oral administration of polyphenol-rich olive leaf extracts compared with those of rats fed a cholesterol-rich diet. In addition, these extracts increased the serum antioxidant potential and the hepatic CAT and SOD activities. These results suggested that the hypocholesterolemic effect of oleuropein, oleuropein aglycone and hydroxytyrosol-rich extracts might be due to their abilities to lower serum TC, TG and LDL-C levels as well as slowing the lipid peroxidation process and enhancing antioxidant enzyme activity.

Decolourization and detoxification of textile industry wastewater by the laccase-mediator system

Decolourization and detoxification of a textile industry effluent by laccase from Trametes trogii in the presence and the absence of laccase mediators was investigated. Laccase alone was not able to decolourize the effluent efficiently even at the highest enzyme concentration tested: less than 10% decolourization was obtained with 9 U/mL reaction mixture. To enhance effluent decolourization, several potential laccase mediators were tested at concentrations ranging from 0 to 1mM. Most potential mediators enhanced decolourization of the effluent, with 1-hydroxybenzotriazol (HBT) being the most effective. The effect of several physico-chemical parameters that could influence enzyme activity, such as pH, temperature and dye concentration was tested. Optimal decolourization occurred with 20% effluent at pH 5, a temperature of 50 degrees C, and in the presence of 1mM HBT. The toxicities of crude, laccase-HBT treated and laccase-acetosyringone treated effluent were evaluated using the Microtox assay. Only laccase-acetosyringone treated effluent was not toxic; crude and laccase-HBT treated effluent retained toxicity.

Isolation and characterization of Halomonas sp. strain C2SS100, a hydrocarbon-degrading bacterium under hypersaline conditions

Aims:  To isolate and characterize an efficient hydrocarbon‐degrading bacterium under hypersaline conditions, from a Tunisian off‐shore oil field.

Antibacterial activity of Thymus maroccanus and Thymus broussonetii essential oils against nosocomial infection - bacteria and their synergistic potential with antibiotics.

The aim of this study was to evaluate the antibacterial effect of the association between conventional antibiotics and essential oils (EOs) of endemic Moroccan thyme species, Thymus maroccanus and T. broussonetii, on antibiotic-resistant bacteria involved in nosocomial infections. Synergistic interactions between antibiotics (ciprofloxacin, gentamicin, pristinamycin, and cefixime) and EOs, and between T. maroccanus and T. Broussonetii EOs were determined by the checkerboard test. Serial dilutions of two antimicrobial agents were mixed together so that each row (and column) contained a fixed amount of the first agent and increasing amounts of the second one. The results indicate that the oils had a high inhibitory activity against tested bacteria, except for Pseudomonas aeruginosa. In parallel with the increase of cellular killing, the release of 260nm-absorbing materials from bacterial cells, treated with EOs, increased in response to oil concentration. Out of 80 combinations tested between EOs and antibiotics, 71% showed total synergism, 20% had partial synergistic interaction and 9% showed no effect. Combination with carvacrol, the major constituent of T. maroccanus and T. broussonetii, showed also an interesting synergistic effect in combination with ciprofloxacin. The effect on Gram-positive bacteria was more important than on Gram-negative bacteria. These findings are very promising since the use of these combinations for nosocomial infections treatment is likely to reduce the minimum effective dose of the antibiotics, thus minimizing their possible toxic side effects and treatment cost. However, further investigations are needed to assess the potential for therapeutic application.

Hydroxytyrosol rich extract from olive leaves modulates cell cycle progression in MCF-7 human breast cancer cells.

Throughout the history, olive (Olea europea L.) leaves have been heavily exploited for the prevention or the treatment of hypertension, carcinogenesis, diabetes, atherosclerosis and so many other traditional therapeutic uses. These activities are thought to be the output of olive micronutrients especially polyphenols. Hydroxytyrosol and oleuropein are considered as major polyphenolic compounds in olive leaf. In this work, a hydroxytyrosol rich olive leaves extract was investigated for potential anti-tumoral activities. In vitro cytotoxic effects against MCF-7 breast cancer cells were examined using MTT and neutral red tests. The anti-tumor activities were further investigated by flow cytometry and western blotting. Cytotoxicity assays resulted in a dose dependent growth inhibition of MCF-7 cells. This inhibition was due to the cell cycle arrest in the G0/G1 phase. The understanding of the molecular mechanism by which olive leaves extract arrested cell growth showed a down-expression of the peptidyl-prolyl cis-trans isomerase Pin1 which in turn decreased the level of a G1 key protein; Cyclin D1. Additionally, olive leaves extract treatment up-regulated the AP1 transcription factor member, c-jun. Therefore, olive leaves extract will necessitate further deep investigation for a probable use as a cancer preventive food additive.

Simultaneous hydrocarbon biodegradation and biosurfactant production by oilfield-selected bacteria

Aims:  To study the bacterial diversity associated with hydrocarbon biodegradation potentiality and biosurfactant production of Tunisian oilfields bacteria.

Phenolic composition, sugar contents and antioxidant activity of Tunisian sweet olive cultivar with regard to fruit ripening.

Dhokar olive cultivar growing in the south of Tunisia is an unusual olive tree which is characterized by the sweet taste of its fruit. We were particularly interested in the phenolic compounds of this cultivar in comparison to Chemlali cv. During the different maturation stages of olive fruits, the phenolic composition, sugar content, antioxidant activity and enzymatic change were examined. The phenolic composition was studied by using reverse-phase high-performance liquid chromatography followed by LC-MS and GC-MS analysis. Oleuropein, the major olive fruit biophenolic compound, decreased significantly during all the ripeness stages, and its level decreased from 3.29 g/kg fresh olive (July) to 0.16 g/kg (October) in Dhokar cv. and from 5.7 g/kg (July) to 3.75 g/kg (October) in Chemlali cv. This decrease inversely correlated with hydroxytyrosol concentrations until September. DPPH and ABTS assays show that the more important antioxidant capacity of olive extracts was found at the last stage of maturation. beta-Glucosidase and esterase activities were evaluated during the ripening stage. The data obtained during the ripening indicate that polyphenol content and composition, in particular the oleuropein concentration, were in correlation with the measured enzymatic activities. Glucosidase and esterase showed their maximum values in September reaching 179.75 and 39.03 U/g of olive pulp, respectively. In addition, sugar content was quantified using colorimetric and chromatographic methods and was compared to its concentration in Chemlali olive fruit cultivar. Glucose and mannitol were the main sugars; they reached their highest level at the last stage of ripening: 8.3 and 79.8 g/kg respectively.