Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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2006 - 200932010 - 20111

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Author: search.filters.author.Bayraktar, OğuzSubject: search.filters.subject.Antioxidants

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Now showing 1 - 4 of 4
  • Master Thesis
    Development of Biosensors for Determination of the Total Antioxidant Capacity
    (Izmir Institute of Technology, 2008) Çoban, Seçil; Bayraktar, Oğuz
    In this study, an amperometric laccase biosensor was developed for determination of the oleuropein concentration that is the biological active component of olive leaf and contributes dominantly to the total antioxidant capacity. The biosensor was prepared by immobilization of laccase from Trametes versicolor by addition of cross-linking agent, glutaraldehyde, into the carbon paste electrode. Different biosensors were prepared by changing the amount of crosslinking agent and concentration of the enzyme solution. So, effect of these parameters on biosensor performance was investigated. The best biosensor performance was determined for the biosensor having glutaraldehyde amount of 12.03 % vol. of the biosensor bottom part and 5 mg/ml of laccase enzyme. The effect of scan rate and temperature on the biosensor performance was also investigated in this study. The scan rate of 10 mV/s was decided to be the optimum for the amperometric detection of oleuropein considering the fastest response and maximum reduction current. 250C was chosen as an optimum temperature value due to the maximum laccase activity and capability of oleuropein acting as an antioxidant. Extraction of phenolics from olive leaf was also an important part of this study. The extract was divided into fractions varying in their oleuropein amounts such as polar fractions and relatively less polar fractions. Therefore, biosensor performance was investigated for fractions containing different type of phenolics. HPLC analyses of the fractions were also performed in this study. In addition total phenol content and antioxidant capacity of the fractions were determined by conventional methods.
  • Master Thesis
    Screening of Some Plant Species for Their Total Antioxidant and Antimicrobial Activities
    (Izmir Institute of Technology, 2008) Kaçar, Diren; Bayraktar, Oğuz
    In this study aqueous/ethanol extracts of 42 plant species collected from same geographic region (Karaburun/İzmir) were screened for their relative total phenol contents, total antioxidant and antibacterial activities. In the first part of the study, Folin- ciocalteu assay and PCL (Photochemiluminescence) method were performed to detect the total phenol contents and total antioxidant activities of extracts, respectively.It was detected that the Hypericum empetrifolium had the highest activities for both water soluble and lipid soluble antioxidants and Sarcopterium spinosum has the highest result for total phenol assay as 635.26 GAEqmg/g sample.In order to detect the antibacterial activities of extracts a preliminary screening study was performed by using disc diffusion method. Out of the 42 plant species tested, 26 species exhibited antibacterial activities by inhibiting one or more microorganisms.Microdilution assays by 96 well plates were applied for the most active species to find out their minimum inhibition concentrations (MICs). The most promising plant species in the study, having the antibacterial activities were determined as H. empetrifolium, P.terebinthus, Arbutus unedo, and C. parviflorus.In this study there is a clear relationship between the analysis results and S.spinosum is one of the most noteworthy species in this study showing the highest total phenol content and important biological activities which has never been examined scientifically before. In that manner this study also presents new potential species that can be used as natural raw materials in some related industries.
  • Master Thesis
    Adsorption of Olive Leaf Antioxidants on Silk Fibroin
    (Izmir Institute of Technology, 2006) Bayçın Hızal, Deniz; Bayraktar, Oğuz
    This study focused on producing protein based functional food with antioxidative and antimicrobial properties by adsorption of olive leaf antioxidants on silk fibroin. In accordance with this aim, extraction and adsorption of two most abundant polyphenols in olive leaves, oleuropein and rutin were studied. Furthermore, desorption studies were performed to increase the purity of polyphenols.In this study, effect of various parameters on extraction and adsorption were investigated by HPLC and antioxidant analyses. The adsorption isotherms of oleuropein and rutin were plotted at different temperatures, pH values and solid-liquid ratios. After adsorption, the adsorbed polyphenols on silk fibroin was subjected to SEM, FTIR, color, antioxidant and antimicrobial analyses to observe the changes in the silk fibroin.The experimental data of adsorption isotherms were well-fitted to Langmuir model. The maximum adsorption capacity was determined as 108 mg oleuropein/g silk fibroin and 21 mg rutin/g silk fibroin. In desorption process, 81% of rutin and 85 % of oleuropein were removed from the adsorbent surface in 70 % aqueous ethanol solution.After adsorption of oleuropein and rutin, the antioxidant capacity of silk fibroin increased from 1.93 mmol TEAC/g to 3.61 mmol TEAC/g. Silk fibroin also gained antimicrobial activity against Staphylococcus aureus and Klebsiella pneumoniae after adsorption of olive leaf antioxidants. Desorbed polyphenols exhibited higher antioxidant capacity than the same amount of olive leaf extract due to the increase in the purity of oleuropein and rutin after desorption.Consequently, silk fibroin is a promising protein for the production of functional food or dietary supplements and for the purification of oleuropein and rutin.
  • Master Thesis
    Purification of Polyphenolic Compounds From Crude Olive Leaf Extract
    (Izmir Institute of Technology, 2011) Karakaya, Alihan; Bayraktar, Oğuz
    Study was carried out to investigate the adsorption characteristics of olive leaf extract on the macroporous adsorption resins and the efficiency of the adsorption column for the separation and purification of oleuropein and rutin from the crude plant extract. Both static and dynamic experiments were performed. In static studies, the performances of three macroporous Amberlite resins namely XAD4, XAD 16 and XAD7HP for the adsorption of polyphenols were evaluated. XAD7HP was chosen as an adsorbent for further adsorption study. XAD7HP was selected for the studies of isotherms, kinetics of adsorption. In conventional alcohol extraction, crude feedstock is mixed with solvent which is alcohol for most cases, and then extract is distilled to remove ethanol. This process ends with a certain amount of residual ethanol because of complication in separation process for ethanol and water makes an azeotropic binary system. The results showed that adsorption capacity of an alcoholic solution with 10 % ethanol content is better than aqueous solution which contained no ethanol. In dynamic studies, the adsorption and desorption experiments were carried out on a glass column packed with XAD7HP resin. The flow velocity 122 cm/h operated as a fixed bed while operation was in an expanded bed mode at 367 cm/h and 611 cm/h, respectively. The effectiveness of the packed bed adsorption and the fluidized bed adsorption were compared. The results show the breakthrough occurred earlier when the feed flow velocity increased. In the elution step, elution program with 2,000 ml for 0 %, 4,000 ml for 40 % and 3,000 ml for 90 % aqueous ethanol was used to achieve an efficient separation. Total phenol content and antioxidant capacity of olive leaf crude extract and effluent fractions were analyzed in order to find the difference between before and after separation. Consequently, fluidized bed adsorption is a promising alternative for the packed bed adsorption in order to isolate oleuropein and rutin from the olive leaf extract.