Ozlem Yesil-Celiktas

Ege University, Ismir, İzmir, Turkey

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Publications (34)81.31 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: In this study, the effect of binary and ternary systems, solvent/feed (S/F) ratio (20–100 w/w), time (2–3 h) and pressure (10–200 bar) were tested with subcritical and supercritical CO2 to produce valonea tannin from acorn cups. The best yield of phenolic contents (PCs) of the valonea tannin (34.73 ± 0.02 wt%) was obtained by H2O/CO2 binary system under the conditions of S/F = 100 (w/w) at 100 bar for 3 h with supercritical CO2. Phase equilibria of H2O/CH3OH/CO2 ternary system with different solvent fractions at different temperatures and pressures were also imaged in the high pressure view cell, where liquid–liquid–vapor phase behaviors were observed for all ratios of H2O and CH3OH from 60 to 100 °C and 60 to 250 bar. High tannin content isolated in a short time will decrease the waste load and provide great advantage in terms of reducing the cost of the tannin used in leather industry.
    Separation and Purification Technology 05/2015; 146. DOI:10.1016/j.seppur.2015.03.018
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    ABSTRACT: Olive pomace is a by-product of olive oil production and an important biomass for the Mediterranean countries. The aim of this study was to optimize the oil extraction from olive pomace by supercritical CO2 and utilize the remaining biomass by hydrolysis. A Box–Behnken statistical design was used to evaluate the effect of temperature (30–80 °C), pressure (120–300 bar) and CO2 flow rate (10–20 g/min) for 60 min. The most effective variable was pressure (p < 0.005) and optimum extraction conditions were elicited as 68 °C, 280 bar and 20 g/min flow rate yielding 4.8% of oil. Additionally, the effect of particle size was investigated on extraction efficiency. Indeed, the oil yield was increased to 13.8% by decreasing the particle size from 2000 to 850–500 μm. For utilization of remaining biomass, both supercritical CO2 (SC-CO2) and hexane de-oiled pomaces were subjected to acid and enzymatic hydrolyses. Hydrolyses with 2% of sulfuric acid for 90 min yielded 12.30 and 12.65 g/l reducing sugar from SC-CO2 and hexane treated biomasses, whereas the highest reducing sugar concentrations achieved with enzymatic hydrolysis with a substrate amount of 6 g, 20–27% Cellic CTec2/Novozyme 188 for 24 h were 12.72 g/l and 10.13 g/l, respectively. A holistic engineering approach is proposed where supercritical CO2 can be used as a main process to extract remaining oil in olive pomace and as a pretreatment loosen the structure in order to obtain liquor which can be converted to a biofuel.
    Journal of Supercritical Fluids The 02/2015; DOI:10.1016/j.supflu.2015.01.025
  • Deniz Senyay-Oncel, Aslihan Kazan, Ozlem Yesil-Celiktas
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    ABSTRACT: Enzymatic reactions with supercritical carbon dioxide (SC-CO2) have received increased attention during the last decade. The objective of this study was to alter the activity and stability of Bacillus sp. protease under SC-CO2 conditions. The activity and stability of protease were evaluated according to the effects of operational variables, temperature (28-80 degrees C), pressure (60-300 bar), CO2 flow (2-10 g/min) and process duration (60-180 min). Best conditions were identified as 300 bar, 54 degrees C, 6 g/min CO2 flow and 120 min of process time efficient 54.4% (417.50 mu mol/ml/min) as against to the untreated enzyme. Activity enhancement was observed with the raise of pressure while low flow rates decreased the activity by 5.1% with a flow rate of 2 g/min under supercritical conditions. Potential mechanisms for pressure stimulated activation and stabilization were investigated by NMR, SEM, FTIR, SOS-PAGE and XPS analyses. As a result, applications of SC-CO2 medium for enzymatic processes are expected to become sustainable and important with economical synthetic and environmentally friendly protocols.
    Biochemical Engineering Journal 11/2014; 92. DOI:10.1016/j.bej.2014.06.021
  • Aslihan Kazan, Halil Koyu, Irem Cemre Turu, Ozlem Yesil-Celiktas
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    ABSTRACT: Mediterranean countries contribute highly on world peach production and tonnes of waste leaves are released due to pruning. The aim of this study was to investigate the utilization possibilities of the leaves by supercritical fluid extraction. A statistical design was used to evaluate the effect of temperature (40-80 degrees C), pressure (150-300 bar) and concentration of ethanol as co-solvent (6-20%) at a flow rate of 15 g/min and for a duration of 60 min. The most effective variables were found as pressure and co-solvent ratio (p < 0.005). Optimum extraction conditions were elicited as 60 degrees C, 150 bar and 6% co-solvent yielding a total phenol content of 79.92 mg GAE/g extract, EC50 value of 232.20 mu g/ml and a radical scavenging activity of 53.25% which was higher than the value obtained by conventional solvent extraction method (32.23%). Consequently, Prunus persica L. leaves were found as a potential phenolic source for industrial applications.
    Journal of Supercritical Fluids The 08/2014; 92. DOI:10.1016/j.supflu.2014.05.006
  • Ozlem Yesil-Celiktas
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    ABSTRACT: The miniaturization of continuous processes has been of interest in the academia and industry which is reflected by the increase in scientific publications and patent disclosures in the last decade. The aim of this study was to evaluate the patenting trends regarding enzyme related microfluidic applications in order to observe the progress of science and technology. The mapped patents have been classified as "immobilization method", "biomolecule screening systems", "integrated process development" and "microreactor design". Half of the patent disclosures were filed by academia, whereas the other half was from industrial research which complies with the shift in microfluidics from academic and industrial research to commercial applications. Immobilization procedures carried out at room temperatures such as formulation of silica matrices using sol-gel technique, incorporation of novel hybrid materials, the integration of supercritical fluids and microfluidics, employing ionic liquids as wall-less microreactors, designing low cost, high performance microfluidic devices were the highlights which can pose challenges in various life science applications. The increasing trend is expected to continue and the presented state-of-the-art in enzyme related microfluidic applications have the potential to enhance industry's capabilities for designing innovative systems which would demonstrate significant economic, societal and environmental benefits.
    Biochemical Engineering Journal 06/2014; 92. DOI:10.1016/j.bej.2014.06.017
  • Ece Yildiz, Dilan Karabulut, Ozlem Yesil-Celiktas
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    ABSTRACT: Echinacea species is provided as dietary supplements for various infectious and immune related disorders and has a potential role in cancer prevention. The aim of this study was to optimize the extraction of total flavonoids using different extraction methods and investigate the cytotoxic effects on various cancer cell lines (CaCo-2, MCF-7, A549, U87MG, and HeLa) and VERO (African green monkey) as a non-cancerous cell line. Box-Behnken statistical design was used to evaluate the effect of pressure (100-200 bar), temperature (40-80 degrees C) and ethanol as co-solvent (6-20 wt%) at a flow rate of 15 g/min for 60 min in supercritical CO2 extraction and the effect of temperature (60-100 degrees C), time (5-15 min) and power (300-900W) in microwave-assisted extraction. Optimum extraction conditions were elicited as 300 bar, 80 degrees C and 13% co-solvent yielding 0.472 mg rutin equivalent total flavonoids/g extract in SC-CO2 extraction, whereas 60 degrees C, 10 min and 300W yielded the highest (0.202 mg rutin equivalent) total flavonoids in microwave-assisted extraction. Additional trials with subcritical water (0.022 mg/g) and Soxhlet extraction with methanol (0.238 mg/g) yielded lower flavonoid contents. The exposures upto 50 mu g/ml of extracts revealed no significant inhibition on the proliferation of both tested cancer cells and healthy VERO cells.
    Journal of Supercritical Fluids The 05/2014; 89. DOI:10.1016/j.supflu.2014.02.005
  • Ersin Onem, Gurbuz Gulumser, Seref Akay, Ozlem Yesil-Celiktas
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    ABSTRACT: The aim of this work was to optimize the extraction parameters of tannins from the acorns and the tanning properties. Experiments were planned to evaluate the effect of solvent/feed ratio (20–100 ml/g), time (2–10 h) and solvent mixture ratio (methanol–water) (0–100%) on extraction yields, tannin contents and total tannin amounts. Valonea tannin obtained under optimum conditions was applied to leather tanning process where filling coefficient (%) and shrinkage temperature (Ts) of the leathers were examined. Optimum extraction parameters were elicited as 100 ml/g for solvent/feed ratio, 6 h of process duration and solvent mixture ratio of 62% methanol–38% water. The filling coefficient of the leathers tanned with extracted valonea (57.81%) and the shrinkage temperature (75.5 °C) was superior to the commercial valonea (52.83%, 73 °C) implying the significant impact of process optimization. The tanning properties of the extracted valonea were satisfactory for the vegetable tanning in leather industry.
    Industrial Crops and Products 02/2014; 53:16–22. DOI:10.1016/j.indcrop.2013.12.014
  • Ozlem Yesil-Celiktas, Sucre Cumana, Irina Smirnova
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    ABSTRACT: An efficient on-chip enzyme immobilized monolith microreactor for glucose 6-phosphate dehydrogenase and its extension to cellulase catalyzed reactions is reported. The monoliths were fabricated using the sol-gel technique, where two different silica precursors were investigated, tetraethoxysilane (TEOS) and ethylene glycol modified silane (EGMS) by determining the activity and aging of the enzymes in the gels. Subsequently catalytic reactions were conducted in continuous flow microreactors and the performance of the system was evaluated by applying various flow rates (5, 10, 15, 20 mu l/min). The addition of polyethylene oxide (PEO) reduced shrinkage of the gels during a period of 4 days after gel preparation suggesting a strengthened gel skeleton leading to a reduced channeling within the porous structure. In the microfluidic systems, the highest conversion rates achieved were 20.0% and 28.8% at a flow rate of 5 mu l/min with TEOS-PEO and EGMS-PEO gels. Continuous reaction exhibited better yield than batch-wise operation using same volume/enzyme ratios which can be attributed to favorable enzyme substrate affinities. However, increase in the flow rate resulted in reduced conversion rates due to lower residence times. Consequently, the applied technique not only provided shorter preparation times but also sustained the stability of immobilized enzymes.
    Chemical Engineering Journal 12/2013; 234:166-172. DOI:10.1016/j.cej.2013.08.065
  • Muge Pilavtepe, Ozlem Yesil-Celiktas
    Journal of Supercritical Fluids The 10/2013; 82:244-250. DOI:10.1016/j.supflu.2013.07.020
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    ABSTRACT: Black carrots contain anthocyanins possessing enhanced physiological activities. Explants of young black carrot shoots were cultured in Murashige and Skoog (MS) medium for callus initiation and were transferred to new MS medium supplemented with four different combinations of 2,4-dichlorophenoxyacetic acid and kinetin. Subsequently, the lyophilized calli and black carrot harvested from fields were subjected to ultrasound extraction with ethanol at a ratio of 1:15 (w:v). Obtained extracts were applied to various human cancer cell lines including MCF-7 SK-BR-3 and MDA-MB-231 (human breast adenocarcinomas), HT-29 (human colon adenocarcinoma), PC-3 (human prostate adenocarcinoma), Neuro 2A (Musmusculus neuroblastoma) cancer cell lines and VERO (African green monkey kidney) normal cell line by MTT assay. The highest cytotoxic activity was achieved against Neuro-2A cell lines exhibiting viability of 38-46 % at 6.25 μg/ml concentration for all calli and natural extracts. However, a significantly high IC50 value of 170.13 μg/ml was attained in normal cell line VERO indicating that its natural counterpart is an ideal candidate for treatment of brain cancer without causing negative effects to normal healthy cells.
    Plant Foods for Human Nutrition 07/2013; DOI:10.1007/s11130-013-0371-z
  • Deniz Senyay-Oncel, Ozlem Yesil-Celiktas
    Journal of Molecular Catalysis B Enzymatic 07/2013; 91:72-76. DOI:10.1016/j.molcatb.2013.03.003
  • Elif Ozdemir, Aylin Sendemir-Urkmez, Ozlem Yesil-Celiktas
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    ABSTRACT: The effects of fabrication techniques were investigated for preparation of a chitosan based scaffold. A two-step process was used: fabrication of hydrogel which was subsequently processed either with supercritical CO2 (SC-CO2) or lyophilization. Various pressures from subcritical to supercritical (70, 160, 250 bar), temperatures (35, 45, 55 °C) and durations (2–3 h) were applied in order to elicit the optimum process parameters yielding the highest porosity which were determined as 250 bar, 45 °C, 2 h of processing at 5 g/min CO2 flow rate yielding a porosity of 87.03% which was similar to lyophilization (88.68%) achieved at 55 °C for 48 h. When osteosarcoma cells possessing cellular features of osteoblasts were seeded, SC-CO2 dried scaffold proved to be a more ideal support for cell attachment owing to the presence of both nano and micropores, thereby providing a more efficient and rapid alternative for tissue engineering applications.
    Journal of Supercritical Fluids The 03/2013; 75:120–127. DOI:10.1016/j.supflu.2012.12.031
  • Pharmazie 01/2013; 68:75-80.
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    ABSTRACT: The present study was designed to identify and compare the in vivo wound healing capacity of a bark extract from Pinus brutia and Pycnogenol in an incision wound model in rats. O/W cream formulations were prepared incorporating 2% Pycnogenol and P. brutia bark extract. The rats were divided into three groups (n = 8). Subsequently placebo and test formulations were applied to animals once a day from day "0" until the 9th day. Malondialdehyde (MDA), superoxide dismutase (SOD) and catalase (CAT) were studied in addition to histopathological examinations. Treatment with F. brutia extract containing cream inhibited lipid peroxidation by a 35% decrease in MDA and 46.8% increase in SOD activity, whereas 19.3% decrease in MDA and 34.7% increase in SOD activity were attained with Pynogenol compared to control. The histological data revealed a better performance of P. brutia extract enriched formulation in terms of degeneration of hair roots, increased vascularization and a decrease in necrotic area. Consequently, a high wound healing activity was observed in animals treated with P. brutia extract significantly accelerating the wound healing process.
    Pharmazie 01/2013; 68(1):75-80. DOI:10.1691/ph.2013.2089
  • New Biotechnology 09/2012; 29:S18. DOI:10.1016/j.nbt.2012.08.042
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    ABSTRACT: Supercritical CO2 extraction of phenolic compounds from Zostera marina residues was optimized by developing a mathematical model based on mass transfer balances. A linear driving force model was applied considering model parameters such as solute concentration on the surface of the solid (Cs) and in the supercritical fluid phase (Cf), film mass transfer coefficient (kf) and molecular diffusivity (DAB) and axial dispersion (Dax) coefficients. Henry's law was used to describe the equilibrium state of solid and fluid phases. The results of the proposed model were compared to that of the experimental data in terms of transport properties and extraction yield at various temperatures (303.15, 323.15, 353.15 K), pressures (15, 25, 35 MPa) and co-solvent mass ratios (0, 10, 20%). The optimum parameters were elicited as 25 MPa, 353.15 K and a co-solvent ratio of 20% yielding 77.22 μg g−1 dry feed. The model satisfactorily described the extraction yield which can be used for scale-up purposes.
    Journal of Supercritical Fluids The 08/2012; 68:87–93. DOI:10.1016/j.supflu.2012.04.013
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    ABSTRACT: Zostera marina is an aquatic plant forming wide grasslands and considered as the lungs of the marine ecosystems. However, the residues reaching the coastlines create nuisance and high costs are required for their disposal. The objective was to investigate the potential of Z. marina residues as a source of secondary metabolites and feedstock in order to propose alternative solutions to the landfill. The supercritical CO2 extract had a total phenol value of 55.4 mg GAE/g extract and a radical scavenging capacity of 71.4%. Considering the raffinate phase, 3% higher hemicellulose content was reached after supercritical CO2 treatment. Enzymatic hydrolysis revealed 31.45% and the yield of simultaneous saccharification and fermentation was 8.72% corresponding to a productivity of 0.273 kg/(m3 h). An integrated process is proposed, where supercritical fluid extraction can act both as the main process to obtain solvent-free pharmaceutical compounds and a pretreatment method in order to loosen the lignin structure, thereby liberating some of the hemicellulose in the matrix.
    Journal of Supercritical Fluids The 08/2012; 68:117–122. DOI:10.1016/j.supflu.2012.04.019
  • Isik Coban, Sayit Sargin, Melih Soner Celiktas, Ozlem Yesil-Celiktas
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    ABSTRACT: The extracts of Stevia rebaudiana are marketed as dietary supplements and utilized as natural sweetening agent in food products. Subsequent to extraction on industrial scale, large quantities of solid wastes are produced. The aim of this study was to investigate the bioconversion efficiency of supercritical CO(2) extracted S. rebaudiana residues. Therefore, leaves were extracted with supercritical CO(2) and ethanol mixture in order to obtain glycosides, then the raffinate phase was hydrolyzed by both dilute acid and various concentrations of cellulase and β-glucosidase cocktail. The maximum yield of reducing sugars reached 25.67 g/L under the optimal conditions of enzyme pretreatment, whereas 32.00 g/L was reached by consecutive enzymatic and acid hydrolyses. Bioethanol yield (20 g/L, 2.0% inoculum, 2 days) based on the sugar consumed was 45.55% corresponding to a productivity of 0.19 kg/m(3)h which demonstrates challenges to be utilized as a potential feedstock for the production of bioethanol.
    Bioresource Technology 06/2012; 120:52-9. DOI:10.1016/j.biortech.2012.06.057
  • Muge Pilavtepe, Aysen Erkucuk, Ismail H. Akgun, Ozlem Yesil-Celiktas
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    ABSTRACT: Alkannin is a potent pharmaceutical substance with a wide spectrum of biological activities. In the scope of this study, supercritical CO2 extraction and sonication with hexane were applied to various Alkanna species, which were then subjected to hydrolysis. Total alkannins were quantified by HPLC/DAD and incorporated into yoghurt. Viscosities, pH values and microbial analyses were reported at 7 days of intervals for 21 days of storage. A. tinctoria possessed the highest amounts of alkannins and total phenols (686.3 mg GAE/g extract). The results revealed no significant changes in pH values (4.1–4.0), viable counts of Streptococcus salivarius ssp. thermophilus (80–150 × 106 cfu g−1) and slightly lower viscosities of enriched yoghurts (8,250–6,750 cPs) compared with the control (4.15–4.0; 110–105 × 106 cfu g−1; 12,600–11,310 cPs) during storage. However, viable counts of Lactobacillus delbrueckii ssp. bulgaricus of enriched yoghurts (87 × 103 cfu g−1) were much better than the control (191 × 103 cfu g−1), indicating a significant decrease in post acidification and generation of bitter peptides. Among the species investigated, A. tinctoria is the most promising source, obtained at higher yields via supercritical fluid extraction technology as a green alternative to solvent extraction and thus can be utilized at industrial scale in order to develop yoghurt products with improved health benefits.
    European Food Research and Technology 05/2012; 234(5). DOI:10.1007/s00217-012-1690-2
  • Ozlem Yesil-Celiktas, Emel Oyku Cetin-Uyanikgil
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    ABSTRACT: Polymer microspheres are becoming attractive drug delivery systems due to their biodegradability, nontoxicity and easy administration. In this study, a rosemary extract exhibiting anti-proliferative activity against various human cancer cell lines was encapsulated by polycaprolactone using gas anti-solvent process and solvent evaporation method. The particles were characterized by X-ray diffraction, differential scanning calorimeters analyses and scanning electron microscopy, whereas in vitro release kinetics was determined by the dialysis cell method. Although the fabrication methods seemed not to play an important role in the diffusion rate and release profiles of both loaded samples in aqueous medium, fabricated rosemary extract with gas antisolvent process at 300 bar, 40 °C and a flow rate of 20 g/min exhibited a narrow particle size distribution, a lower mean particle size and higher encapsulation efficiency (254.5 nm, 82.8%) compared to the traditional fabrication method (617.5 nm, 62.2%).
    Journal of Supercritical Fluids The 02/2012; 62:219–225. DOI:10.1016/j.supflu.2011.11.005