Ozlem Yesil-Celiktas

Ege University, Ismir, İzmir, Turkey

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Publications (26)61.84 Total impact

  • Deniz Senyay-Oncel, Aslihan Kazan, Ozlem Yesil-Celiktas
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    ABSTRACT: This study is related to altering the activity and stability of Bacillus sp. protease under SC-CO2 conditions.•The effects of various process parameters on the activity were evaluated.•Best conditions were identified as 300 bar, 54 °C, 6 g/min CO2 flow and 120 min.•An increase of 54.4% was achieved in comparison to the untreated enzyme.•NMR, SEM, FTIR, SDS-PAGE and XPS analyses were conducted.
    Biochemical Engineering Journal 11/2014; 92. · 2.37 Impact Factor
  • Aslihan Kazan, Halil Koyu, Irem Cemre Turu, Ozlem Yesil-Celiktas
    Journal of Supercritical Fluids The 08/2014; · 2.57 Impact Factor
  • Ece Yildiz, Dilan Karabulut, Ozlem Yesil-Celiktas
    Journal of Supercritical Fluids The 05/2014; · 2.57 Impact Factor
  • 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. · 3.21 Impact Factor
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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; · 2.36 Impact Factor
  • 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. · 2.57 Impact Factor
  • New Biotechnology 09/2012; 29:S18. · 2.11 Impact Factor
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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. · 2.57 Impact Factor
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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. · 2.57 Impact Factor
  • 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. · 5.04 Impact Factor
  • 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). · 1.39 Impact Factor
  • 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. · 2.57 Impact Factor
  • Deniz Senyay-Oncel, Ozlem Yesil-Celiktas
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    ABSTRACT: Various physical, chemical and genetic approaches have been applied in order to enhance enzyme stability and activity. In this study, the aim was to investigate the capability of sub- and supercritical carbon dioxide to alter the stability and activity of α-amylase as an alternative technique. The effects of operational parameters such as pressure (50-300 bar), temperature (28-80 °C), CO₂ flow (2-10 g min⁻¹) and time (60-180 min) were evaluated in regard to the activity and stability of fungal based α-amylase from Aspergillus oryzea. The activity of untreated enzyme was determined as 17,726 μmol/ml/min. While both sub- and supercritical conditions enhanced the activity, the increase in flow rate had an adverse effect and the activity was decreased by 28.9% at a flow rate of 10 g min⁻¹ under supercritical conditions. Nuclear magnetic resonance (NMR) spectra of untreated enzyme and treated samples exhibiting the lowest and the highest activities were almost identical except for the chemical shifts observed at the lowest activity sample from 4.0 to 4.4 ppm which were assigned to protons of hydrogen-bonded groups. Optimum conditions were determined as 240 bar, 41 °C, 4 g min⁻¹ CO₂ flow and 150 min of process duration yielding 67.7% (29,728 μmol/ml/min) higher activity than the untreated enzyme providing fundamental basis for enzymatic applications.
    Journal of Bioscience and Bioengineering 08/2011; 112(5):435-40. · 1.74 Impact Factor
  • Deniz Senyay-Oncel, Hasan Ertas, Ozlem Yesil-Celiktas
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    ABSTRACT: Utilization of renewable resources and development of new processes aimed at converting these materials into value added bio-products are gaining more emphasis. The scope of this study was to optimize supercritical CO2 extraction (SFE) parameters such as pressure, temperature and flow rate for the yields of unsaturated fatty acids from Pistacia terebinthus berries by a Box-Behnken statistical design. All samples were analyzed for fatty acids by GC-FID. The most effective variables were pressure (P<0.005) and flow rate (P≤0.005). Maximizing the evaluative criteria for dependent variables (oleic acid, linoleic acid and linolenic acid), optimal conditions were determined to be 240bar, 60°C and a flow rate of 16g/min yielding 51.2% oleic acid, 26.5% linoleic acid and 1.0% linolenic acid. The amounts of unsaturated fatty acids in SFE samples (81.3%) were higher than the hexane (74.3%) and were similar to that of cold press samples (80.1%). High concentrations of unsaturated fatty acids can indicate the utilization of the berries as a major dietary source and demonstrate challenges for industrial application of SFE as a green technology. KeywordsBox-Behnken–GC analysis–Linoleic acid–Oleic acid–Optimization–Supercritical fluid extraction
    Journal of Oil & Fat Industries 07/2011; 88(7):1061-1069. · 1.62 Impact Factor
  • Seref Akay, Ilknur Alpak, Ozlem Yesil-Celiktas
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    ABSTRACT: The aim of this work was to optimize total phenolic yield of Arbutus unedo fruits using supercritical fluid extraction. A Box-Behnken statistical design was used to evaluate the effect of various values of pressure (50-300 bar), temperature (30-80°C) and concentration of ethanol as co-solvent (0-20%) by CO(2) flow rate of 15 g/min for 60 min. The most effective variable was co-solvent ratio (p<0.005). Evaluative criteria for both dependent variables (total phenols and radical scavenging activity) in the model were assigned maximum. Optimum extraction conditions were elicited as 60 bar, 48°C and 19.7% yielding 25.72 mg gallic acid equivalent (GAE) total phenols/g extract and 99.9% radical scavenging capacity, which were higher than the values obtained by conventional water (24.89 mg/g; 83.8%) and ethanol (15.12 mg/g; 95.8%) extractions demonstrating challenges as a green separation process with improved product properties for industrial applications.
    Journal of Separation Science 06/2011; · 2.59 Impact Factor
  • I.H. Akgun, A. Erkucuk, M. Pilavtepe, O. Yesil-Celiktas
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    ABSTRACT: The effects of supercritical carbondioxide extraction was investigated to compare previously validated extraction methods on total alkannin yield with Alkanna tinctoria collected form Antalya, Turkey. A two-step process was used; extraction of alkannin derivatives with supercritical CO2 followed by alkaline hydrolysis of alkannin derivatives. A Box-Behnken exprerimental design was used to evaluate the effect of three variables, pressure (50–350 bar), temperature (30–80 °C) and CO2 flow (5–20 g min−1) at 1:30 ratio of alkanna root:CO2 amount. Response surface analysis revealed that the data were adequately fitted to a second-order polynomial model with R2 0.9665 and the most effective variable was pressure (P ≤ 0.05). Optimum conditions were determined as 80 °C, 175 bar, 5 g min−1 CO2 flow yielding the highest total alkannins (1.47%) which was higher than conventional hexane extraction (1.24%) providing a solvent-free alternative for industrial production.Graphical abstractResearch highlights► A two-step process was used to optimize extraction of alkannin derivatives with supercritical CO2 followed by alkaline hydrolysis of alkannin derivatives. ► The most effective variable was pressure (P ≤ 0.05). ► Optimum conditions were determined as 80 °C, 175 bar, 5 g min−1 CO2 flow yielding the highest total alkannins (1.47%) which was higher than conventional hexane extraction (1.24%). ► Providing a solvent-free alternative for industrial production.
    Journal of Supercritical Fluids The 05/2011; 57(1):31-37. · 2.57 Impact Factor
  • Ozlem Yesil-Celiktas, Deniz Senyay
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    ABSTRACT: The drawbacks of the conventional mechanical treatments for particle micronization often resulting in product damage or performance degradation have highlighted the need for alternative particle formation processes. The aim of this study was to shed light on the trends of the scientific studies and innovations in the field of particle formation using supercritical fluids (SCF) in order to observe the progress of science and technology and to satisfy the need for a global view of research activities. The publications in the ISI Web and the patents in a patent database were screened using nine different keywords in title or topics. A total of 939 journal publication and 206 patent disclosures between 1980−2009, with the contributions of 3588 authors and 604 innovators, were found to focus on particle formation using SCF. The results showed that the majority of the publication (59.2%) and patent (40.3%) disclosures were related to antisolvent precipitation and rapid expansion of SCF (18.3, 16%). Patents originating from United States (56.8%) were dominating, followed by those from the European Union (30.1%) and Japan (9.2%). The analysis revealed the appetite of the companies for commercialization (73.8%), which can be interpreted as an indicator of upcoming industrial applications.
    Industrial & Engineering Chemistry Research 07/2010; 49(15). · 2.24 Impact Factor
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    ABSTRACT: The leaves of Rosmarinus officinalis harvested from three different locations of Turkey were extracted by both methanolic and supercritical CO(2) extraction. Subsequently, six extracts and the active compounds, carnosic acid, and rosmarinic acid were applied to various human cancer cell lines including NCI-H82 (human, small cell lung, carcinoma), DU-145 (human, prostate, carcinoma), Hep-3B (human, black, liver, carcinoma, hepatocellular), K-562 (human chronic myeloid leukemia), MCF-7 (human, breast, adenocarcinoma), PC-3 (human, prostate, adenocarcinoma) and MDA-MB-231 (human, breast, adenocarcinoma) by MTT assay. Supercritical CO(2) extracts had superior antiproliferative effect compared to the soxhlet extracts. Although the extracts exhibited various cytotoxic effects against different cell lines, comparatively low IC(50) values ranging between 12.50 and 47.55 microg/ml were attained against K-562, being the most sensitive cell line. Moreover, carnosic acid caused the lowest cell viability with values ranging from 13 to 30 % at a concentration of 19 muM after 48 h of treatments, resulting in superior antiproliferative effect. Rosemary extract is a potential candidate to be included in the anti-cancer diet with pre-determined doses avoiding toxicity.
    Plant Foods for Human Nutrition 06/2010; 65(2):158-63. · 2.36 Impact Factor
  • A. Erkucuk, I. H. Akgun, O. Yesil-Celiktas
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    ABSTRACT: The aim of this work was to optimize the glycoside composition of Stevia rebaudiana leaves using supercritical fluid extraction (SFE). A Box-Behnken statistical design was used to evaluate the effect of various values of pressure (150–350bar), temperature (40–80°C) and concentration of ethanol-water mixture (70:30) as co-solvent (0–20%) by CO2 flow rate of 15gmin−1 for 60min. The most effective variables were co-solvent concentration (P
    Journal of Supercritical Fluids The 11/2009; 51(1):29-35. · 2.57 Impact Factor
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    ABSTRACT: Both supercritical CO2 and methanolic extracts from the leaves of rosemary (Rosmarinus officinalis) harvested from three different locations of Turkey at four different times of the year were added at a concentration of 100 mg/kg to wheat germ oil. Wheat germ oil samples were stored in an incubator for 10 days at 50C in order to promote oxidation and for the efficacy of the extracts for stabilization purposes to be examined. Degree of oxidation was determined by peroxide and p-anisidine values, which were performed every 2 days. Extracts from Mersin and Canakkale regions performed better results. Additionally, June and September harvests had lower peroxide values. According to the descriptive sensory analysis, both locations and extraction methods were found to effect flavor. Some flavor attributes, such as wheatlike/starchy, fishy and rubbery/metallic changed during storage regardless of locations and extraction methods. Supercritical CO2 extracts performed better results in terms of both oxidation and sensory properties.PRACTICAL APPLICATIONSFrom the perspective of the food industry, wheat germ oil stabilized with a natural antioxidant such as rosemary can be marketed as a functional product that can create a niche. Rosemary extracts containing higher amounts of rosmarinic acid and carnosic acid should be preferred in order to provide a better shelf life of an edible oil such as wheat germ oil.
    Journal of Food Quality 09/2009; 32(6):709 - 724. · 0.76 Impact Factor