Master Degree / Yüksek Lisans Tezleri

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

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Subject: search.filters.subject.Phenols

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Now showing 1 - 4 of 4
  • Master Thesis
    Characterization of Antioxidant Properties for Dried Organic Fruits in Turkish Market and Development of Novel Strategies To Increase Their Potential Health Benefits
    (İzmir Institute of Technology, 2013) Dervişoğlu, Gökhan; Yemenicioğlu, Ahmet; Yemenicioğlu, Ahmet; 03.08. Department of Food Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    In this thesis antioxidant parameters including trolox equivalent antioxidant capacity (TEAC) and total phenolics (TPC) and flavonoid (TFC) contents of major organic dried fruits (raisins, figs, prunes and apricots) produced in Turkey have been determined to understand the bioactive potential of these products. Moreover, a novel method based on controlled rehydration of specified dried fruits in phenolic extracts has been developed to boost the phenolic content and antioxidant activity of dried fruits with low bioactivity and potential health benefits. The TEAC, TPC and TFC of sun dried fruits varied between 35.7 and 74.1 μmol trolox/g (d.w.), 1762 and 4062 μg gallic acid/g (d.w.) and 830 and 2559 μg catechin/g (d.w.), respectively. The TEAC and TPC of prunes were 1.7 to 2.3 fold higher than those for apricots, raisins and figs which showed quite similar TEAC and TPC values. On the other hand, the TFC of prunes and figs were similar and 1.7 to 3 fold higher than those of raisins and apricots. The rehydration studies with raisins conducted in different concentrations (0.5% or 1% (w/w)) of green tea extract (GTE) and walnut shell extract (WSE) at room temperature until reaching of final moisture content of 38.73 % (w/w) showed the possibility of increasing TEAC, TPF and TPC of raisins 1.6-1.8 fold. Similar rehydration strategy applied to figs, prunes and apricots in 1% GTE to bring their moisture content to 39.83, 36.97 and 43.81 % respectively, caused 1.1-1.6 fold increase in TEAC, TPC and TFC of these dried fruits. This work clearly showed the considerably higher bioactive potential of organic dried prunes than organic dried raisins, figs and apricots. However, the application of controlled rehydration process developed in this work enables increasing antioxidant potential and phenolic contents of figs, raisins and apricots to the level of prunes.
  • Master Thesis
    A Proteomic Analysis of the Response of Listeria Monocytogenes To the Stress Induced by O-Coumaric Acid and Ferulic Acid
    (Izmir Institute of Technology, 2013) Cerit, Ender Efe; Soyer, Ferda; Soyer Dönmez, Ferda; 04.03. Department of Molecular Biology and Genetics; 04. Faculty of Science; 01. Izmir Institute of Technology
    Phenolic acids are known for their potential antimicrobial action, however their mechanisms of action are still unraveled. In this study, effect of phenolic acid stress on Listeria monocytogenes, a dangerous foodborne pathogen, was studied with a proteomic approach. Two phenolic acids found in olive oil, namely o-coumaric acid and ferulic acid, were applied on this bacterium via microtiter plate assay. The concentrations of these phenolic acids that inhibit the bacterial growth by 50% were determined as 7.5 mM for o-coumaric acid, and 8 mM for ferulic acid. Besides, minimum bactericidal concentration of o-coumaric acid was also found as 12 mM. Cellular proteomes of phenolic acid-treated and untreated bacteria were analysed with nanoLC-ESI-MS/MS system, and identified with MaxQuant/Andromeda bioinformatic toolbox. According to the results, both phenolic acids induced oxidative stress in L. monocytogenes cells. In addition to this, DNA replication and repair enzymes, nutrient uptake proteins and several proteins directly related with the virulence of L. monocytogenes were among the targets of phenolic acid stress. Last but not least, proteins associated with biosynthetic pathways were found to be predominantly downregulated. Moreover, the morphology of phenolic acid-treated and untreated cells was visualized with scanning electron microscope to support these findings. The images showed that lengths of treated cells were either abnormally elongated or shortened when compared to untreated cells. A possible reason for these abnormalities is the unequal fission promoted by two factors; excessive production of cell envelope biosynthesis and fission regulatory proteins, and repression of aforementioned DNA replication and repair enzymes.
  • Master Thesis
    Inhibition of Catechol-0 (comt) Enzyme Activity by Some Plant-Derived Alkaloids and Phenols
    (Izmir Institute of Technology, 2009) Yalçın, Dilek; Bayraktar, Oğuz; Bayraktar, Oğuz; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    In this study, inhibition potentials of harmal seed alkaloids and olive leaf polyphenols were investigated on COMT catalyzed methylation reaction. Inhibition performances of natural alkaloids and polyphenolics whose purities were attempted to be increased by extraction and fractionation were compared with standards of these compounds and the best known COMT inhibitor, 3,5-dinitrocatechol. COMT enzyme inhibition experiments were performed with sentitive fluorometric method. In this method, Km values for SAM and aesculetin substrates were found as 3.5 + 0.3 uM and 6.4 + 0.4 uM, respectively. As a result of the inhibition study, the highest inhibitory effect is observed for harmine and harmaline rich fractions among harmal seed alkaloids. Inhibition constants indicating degree of competitiveness and noncompetitiveness (Ki and aKi) of the harmine fraction which has the highest inhibition performance were calculated as 0.15±0.07 ug/ml and 1.28±0.06 ug/ml, respectively.In the studies performed with standards of olive leaf polyphenols, while it was observed that rutin has inhibitory effect, oleuropein was found less effective. However, oleuropein rich fraction of olive leaf extract showed higher inhibitory effect than crude extract and rutin. It was also observed that polyphenolic extracts obtained from vitex, terebinth and mastic leaves showed high inhibition capacities, it was thought that fractionation should be performed for these plants. As a more general conclusion, it was revealed that harmal seed alkaloids and olive leaf fractions with high purity are promising natural COMT inhibitors. By performing this study, the kinetic inhibition constants of extracts, their fractions and standards could be determined and they could be reported into literature.
  • Master Thesis
    Classification of Turkish Virgin Olive Oils Based on Their Phenolic Profiles
    (Izmir Institute of Technology, 2008) Ocakoğlu, Derya; Tokatlı, Figen; Tokatlı, Figen; 03.08. Department of Food Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Virgin olive oil is different from other plant oils with its high phenolic content. The resistance to oxidation and the protection against some diseases has been linked to these components of olive oil. The sensorial characteristic of extra virgin olive oil is also related to its phenolic compounds.In this work, it is aimed to determine the phenolic profiles of Turkish olive oils, which have high economic value for Turkey. Phenolic profiles of monovarietal extra virgin olive oil samples extracted from six dominant and economically important Turkish olive cultivars (memecik, erkence, domat, nizip-yaglik, gemlik, ayvalik) and commercial extra virgin olive oil samples from two different areas (south and north) of the Aegean coast were determined for 2005 and 2006 harvest years. Total phenol contents, oxidative stabilities and chromatic ordinates as colour parameters were also measured. The effect of cultivar, geographical area and harvest year on phenolic profiles of olive oils was investigated. Multivariate data were subjected to principal component and partial least square-discriminant analyses.Typical phenolic substances of extra virgin olive oils from different variety and regions are; p-coumaric acid, cinnamic acid & apigenin for memecik, erkence oils and also for oils of south Aegean; vanillin & syringic acid for ayvalik, gemlik and also for oils of north Aegean. Domat oils were characterized by their relatively high content of oleuropein aglycon. Nizip oils were separated by their 4-hydroxyphenyl acetic acid content, which was determined in very low amounts or none in other olive oils. It was observed that harvest year strongly affected the phenolic profiles of olive oils. In addition, phenolic composition was found to be useful in discriminating the olive oils from different variety and geographical area.