Phd Degree / Doktora

Permanent URI for this collectionhttps://hdl.handle.net/11147/2869

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Author: search.filters.author.Özen, Fatma BanuDepartment: search.filters.department.Thesis (Doctoral)--İzmir Institute of Technology, Food Engineering

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Now showing 1 - 5 of 5
  • Doctoral Thesis
    Application of Non-Targeted Analysis Methods in Adulteration Detection and Prediction of Process Parameters of Vinegars
    (01. Izmir Institute of Technology, 2023) Çavdaroğlu, Çağrı; Özen, Fatma Banu
    Vinegar plays a multifaceted role in human diet, encompassing nutritive, functional, and taste-enhancing aspects. Quality of vinegar is influenced by quality of raw materials and production methods employed. Spectroscopic techniques offer distinct advantages in terms of speed and environmental friendliness, making them valuable tools for monitoring and controlling food production processes. This study has two major parts. In the first part, traditional and commercial grape vinegar production were monitored using both chemical parameters (total acidity, pH, brix, ethanol etc.) and mid-infrared (mid-IR) and UV-visible (UV-vis) profiles. These measured chemical parameters were predicted from spectral profiles in combination with multivariate statistical analysis techniques. In the second part, mid-IR, UV-vis and fluorescence spectroscopic techniques were used in determination of adulteration of both grape and apple vinegar with acetic acid and spirit vinegar at various ratios. Capability of spectroscopic methods combined with chemometrics were tested for prediction of various chemical parameters of vinegar as well as detection of adulteration of vinegar with different adulterants. Those techniques have proven to be effective in estimating the overall quantities of sugars, phenolics, flavonoids, and organic acids. Utilizing chemometric models with UV–vis and mid-IR data yielded high rates of correct classification, sensitivity, and specificity, particularly for adulteration levels exceeding 5% in vinegar. The performance of mid-IR spectroscopy demonstrated success in detecting the presence of spirit vinegar and acetic acid in apple vinegar. Overall, with this thesis, the usefulness of spectroscopic methods was highlighted by emphasizing the importance of chemometric tools for the parameter prediction and detection of vinegar adulteration.
  • Doctoral Thesis
    Minor Components of Olive Oils as Indicators for the Authenticity of Virgin Olive Oils
    (Izmir Institute of Technology, 2021) Uncu, Oğuz; Özen, Fatma Banu
    Adulteration of olive oil is a major problem of olive oil industry and may result in health problems as well as unfair earnings. Especially after the update in EU regulations about the labelling of olive oils, a need is arisen to detect the mixtures of old and fresh olive oils. Improvements in detection methods could fall behind of the inventiveness of the fraudsters. Detecting and preventing adulteration could be a challenging task; therefore, new methods and solutions are always in demand to solve this problem. First purpose of this theses is to characterize Aegean region olive oils with respect to their quality parameters such as fatty acid alkyl esters, diacylglycerols, and pigment compositions and to investigate differentiation power of these parameters on harvest year and geographical origin in comparison with spectroscopic methods. It is also aimed to predict these quality parameters by the fast and environmentally friendly ultraviolet-visible (UV-vis) and mid-infrared (mid-IR) spectroscopic techniques in combination with multivariate statistical methods. Finally, the applicability of spectroscopic methods (UV-vis, mid-IR, fluorescent) to detect adulteration of fresh olive oil with old olive oil is investigated. Olive oils were successfully differentiated with respect to geographical location by spectroscopic methods, fatty acid alkyl esters and pigments. In general, prediction of investigated chemical parameters was achieved robustly with mid-IR spectral data except pigments which were estimated better with UV-vis spectral data. Fluorescence and mid-IR + UV-vis spectroscopies were successful in detecting old olive oils in fresh olive oils.
  • Doctoral Thesis
    Chemical and Enzymatic Interesterification of Tallow With Different Oils
    (Izmir Institute of Technology, 2019) Aktaş, Ayşe Burcu; Özen, Fatma Banu; Yemişçioğlu, Fahri
    The purpose of this study is to manufacture structured lipids by enzymatic and chemical interesterification of tallow with corn, canola and safflower oils individually and to investigate the effects of several process parameters on various chemical and physical properties of structured lipids. Moreover, collection of Fourier-transform mid infrared (FT-MIR) and near infrared (FT-NIR) spectra during interesterification process is also aimed in order to monitor the processes and to construct chemometric models for the prediction of chemical and physical properties of the interesterified products. Both enzymatic and chemical interesterification provided modification of the properties of tallow. The blend ratio is the most significant factor among the parameters investigated for both types of interesterification. Longer reaction time for enzymatic interesterification caused undesirable changes in physical properties of fats. Interesterified lipids have generally low trans fatty acids and they tend to have lower consistencies and solid fat contents compared to their physical blends and the tallow; as a result, they also acquired better spreadable and plastic behaviors. The structured lipids produced with chemical interesterification of tallow with corn oil have better physical properties, higher oxidative stability and lower free fatty acid content compared to structured lipids produced with other vegetable oils. Chemical and physical properties of interesterified fats could be predicted accurately with chemometric analysis of FT-NIR spectra.
  • Doctoral Thesis
    Effect of Harvest Time, Malaxation Tempetature and Olive Variety on the Chemical Characteristics of Olive Oils
    (Izmir Institute of Technology, 2016) Jolayemi, Olusola Samuel; Tokatlı, Figen; Özen, Fatma Banu
    Changes in chemical and quality characteristics of olive oils were evaluated with respect to pre and post-harvest factors such as: olive type, harvest time, malaxation temperature, and storage at room temperature. Additionally, discriminative and predictive capacities of UV-vis, near infrared (NIR), mid infrared (MIR) spectra and electronic nose data on olive oils by using multivariate statistical tools were studied. Varietal and harvest time differences were the most significant factors influencing the quality and chemical properties of Ayvalik and Memecik olive oils. Malaxation temperature was significant on a number of phenolic compounds such as tyrosol, hydroxytyrosol and pinoresinol, and peroxide value. Olive oils of early and mid-harvest were higher in phenolic alcohols, and pigments content, whereas peroxide values, linoleic and stearic acids characterized late harvest oils. Storage for 15 months at room temperature in dark facilitated evolution of some important phenols, while increasing the content of ethyl and methyl esters at varying degrees among varieties. There were no significant changes in fatty acids and acidity contents of the oils. However, total phenol content and oxidative stability declined and a significant depletion of colors and pigments contents occurred. Multivariate regression analysis indicated that lipid-based variables are the most consistent contributors (positive or negative) to olive oil oxidative stability. UV-vis, MIR, NIR spectroscopies and e-nose data were excellent varietal and harvest season discriminating tools. Pigments were well predicted by UV-vis, while MIR performs better in the prediction of fatty acids, alkyl esters, oxidative stability and free fatty acid.
  • Doctoral Thesis
    Applications of Mid-Ir Spectroscopy for Identification of Wine and Olive Yeasts and Characterization of Antimicrobial Activities of Phenolics on Yeasts
    (Izmir Institute of Technology, 2015) Canal, Canan; Özen, Fatma Banu; Baysal, Ayşe Handan
    The aim of this study was application of mid-IR spectroscopy in combination with multivariate statistical analysis for characterization of yeasts from two fermented products, wine and olive, in comparison with cultural and molecular tests and characterization of antimicrobial effects induced by olive phenolics on yeasts. Totally 19 wine yeasts were molecularly identified as M. pulcherrima (11%), P. membranifaciens (16%), H. uvarum (5%) and S. cerevisiae (68%). According to FTIR spectroscopic data of wine samples, S. cerevisiae isolates formed a cluster which were generally separated from all other yeasts. Totally 182 olive yeasts were identified from naturally debittered Hurma and a common olive variety and their leaves. The most common yeasts were Metschnikowia sp. (39%) and Aureobasidium sp (78%) in the first and the second harvest years, respectively. Since only Aureobasidium sp. was the common yeast isolated from Hurma during both years, any link between natural debittering of Hurma and the yeast population of this olive type might be related to Aureobasidium sp. Molecularly identified yeast types generally formed different clusters and showed spectral differences. For antimicrobial activity tests, all phenolic compounds were found effective on both S. cerevisiae and A. pullulans; however, A. pullulans was observed to be more sensitive. Antimicrobial activity was differentiated with respect to treatment time and phenol concentration with statistical treatment of FTIR data. As a complementary technique, FTIR could be successfully used for identification of yeasts and characterization of antimicrobial activity of phenolics against yeasts.