Phd Degree / Doktora

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Department: search.filters.department.Thesis (Doctoral)--İzmir Institute of Technology, Food Engineering

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  • Doctoral Thesis
    Investigations on the Prebiotic Activity of Xylan and Xylooligosaccharides Using in Vitro Mouse Fecal Culture and Ex Vivo Mouse Colon Model
    (01. Izmir Institute of Technology, 2024) Sabancı, Kevser; Büyükkileci, Ali Oğuz; Güleç, Şükrü
    Ksilan (KS) ve onun hidroliz ürünü olan ksilooligosakkaritler (KOS), prebiyotik özellikleriyle tanınmaktadır. KS'nin, KOS ve inüline (INU) göre daha yavaş bir şekilde kullanıldığı ve bağırsak mikrobiyotası üzerinde farklı etkiler gösterdiği gözlemlenmiştir. Ancak, KS'nin fizyolojik etkilerine yönelik araştırmalar hâlâ sınırlıdır. Bu çalışma, KS'nin kolondaki kullanımını ve mikrobiyota üzerindeki etkilerini, fare tabanlı in vitro ve ex vivo modeller kullanarak araştırmayı amaçlamıştır. In vitro çalışmalar, BALB/c fare dışkı inokulumu kullanılarak KOS, KS, INU ve KOS+KS ile INU+KS kombinasyonlarının etkilerini değerlendirmiştir. İyi bilinen bir prebiyotik olan INU, karşılaştırma amacıyla çalışmaya dahil edilmiştir. Sonuçlar, test edilen tüm prebiyotiklerin Bifidobacteria ve Lactobacillus popülasyonlarını önemli ölçüde artırırken, Enterococcus, Staphylococcus ve Clostridium sensu stricto popülasyonlarını çeşitli oranlarda azalttığını göstermiştir. Oligomerik KOS, özellikle Bifidobacteria ve Lactobacillus popülasyonlarını artırırken, polimerik KS daha çok Bacteroides türlerinin büyümesini desteklemiştir. Ex vivo modelde ise farelerin sekum, proksimal ve distal kolon bölümlerinde KS ve KOS'un lokalize etkileri incelenmiştir. Bulgular, her iki prebiyotiğin tüm bağırsak segmentlerinde metabolize edilerek kısa zincirli yağ asidi üretimine yol açtığını ve Bacteroides ile Bifidobacteria popülasyonlarını desteklediğini ortaya koymuştur. KS, tüm bağırsak bölümlerinde daha yüksek Bacteroides büyümesi ile ilişkilendirilmiş olup, sekumda yavaş fermantasyon göstererek prebiyotik aktivitenin distal kolona kadar uzanabileceğine işaret etmektedir. Bu bulgular, prebiyotiklerin bağırsak sağlığında potansiyel uygulamaları ile prebiyotik dinamiklerinin anlaşılmasına önemli katkılar sunmaktadır.
  • 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
    Potential of Lactic Acid Bacteria To Produce Functional Fermented Whey With Putative Antihypertensive Properties : Enrichment Ofangiotensin–i Converting Enzyme (ace)– Inhibitory Peptides and Gamma–aminobutyric Acid (gaba)
    (Izmir Institute of Technology, 2023) Ağırbaşlı, Zeynep; Harsa, Hayri̇ye Şebnem; Sezgi̇n, Efe
    Bu tez Laktik Asit Bakterileri koleksiyonunun (LAB) antihipertansif yetenek potensiyallerinin değerlendirilmesine ve fermente peynir altı suyu içecek bazlarının geliştirişmesine odaklanmıştır. Bu amaçla, 400 adetten fazla LAB proteolitik aktiviteleri açısından farklı yağsız süt ortamlarında taranmıştır. LAB'lar arasında 39 adedi yüksek proteolitik olarak tespit edilmiştir. Fermente sütleri üretmek için suşlar seçilmiştir, 34 en yüksek ACE inhibitor aktiviteli LAB'dan 13 tanesi Lactobacillus brevis D9 and Lactococcus lactis ssp. lactis C24 ile ikili kültürlü fermente peynir altı suyu bazı oluşturmak üzere kullanılmıştır. Fermente sütlerdeki proteolitik aktivite ve ACE inhibitor aktivite of 4.11-1.8 mg/L Lösin ve %49–86 aktivite olarak sırasıyla tespit edilmiştir. İkili kültür fermente peynier altı suyu bazlarında ACE inhibitör aktiviteler %80-97 aralığında bulunmuştur. Seçilen 11 LAB'ın fermentasyon surasındaki proteolitik aktiviteleri HPLC ve SDS-PAGE analizi ile peynir altı suyu proteinlerinin degredasyon profilleri ile değerlendirilmiştir. 300 LAB arasından modifiye sıvı besiyerinde 37 veya 42 C'de 48 saat inkübasyon sonrası 33 suş GABA üretim kapasitesi gösterdiği ince tabaka kromatografisi (TLC) ile gözlemlenmiştir. Fermente whey içeceği bazı feliştirmek için 10 LAB türü, örneğin Lactiplantibacillus plantarum, Latilactobacillus curvatus and Levilactobacillus brevis, modifiye sıvı besiyerinde 50–367 mg/L konsantrasyonlarında verim göstermesi nedeniyle seçilmiştir. Buna göre, fermente peynir altı suyu bazlarında 24 saat 37 °C sonrası GABA konsantrasyonları 11–21mg/L aralığında hesaplanmıştır.
  • Doctoral Thesis
    Production of Pectin From Wastes and Low-Grade Products of Sun-Dried Fig Processing: Optimization of Pectin Extraction and Characterization of Its Major Properties
    (01. Izmir Institute of Technology, 2023) Çavdaroğlu, Elif; Yemenicioğlu, Ahmet
    This thesis aimed extraction and characterization of pectin from processing wastes as stalks and low-grade fruits of sun-dried figs as an alternative pectin source. The extraction performed with three techniques (hot acidic, ultrasonic, enzymatic extraction) was optimized for key parameters. The hot acidic extraction, the most feasible method, yielded 11.7% crude fig stalk pectin (CSP) and 9.4% crude low-grade fig pectin (CFP) at optimal extraction conditions. The CSP had higher galacturonic acid content (GA: 34.2%) and degree of esterification (DE: 45%) than CFP (GA: 32.2% and DE: 36.7%). Purification of CSP gave pectin (PSP) with the highest GA (63%) and DE (65.9%). Despite differences in sugar compositions (D-glucose, L-rhamnose, D-galactose and L-arabinose), fig and citrus pectins displayed similar molecular weights and FT-IR profiles. The fig pectins were characterized for their gelation, antioxidant activity, water/oil absorption, emulsification/foaming capacities and stabilities, and viscosity. The properties of edible fig pectin films obtained with or without CaCl2 crosslinking were also investigated. PSP films showed greater mechanical strength (15.6-19.1 MPa), but lower water vapor permeability (6.28-12.85 g.mm/m2.day.kPa) than other films. The crosslinked CFP film exhibited the lowest solubility (32.8%) and degree of swelling. The emulsion films of CFP with eugenol (EUG) characterized and applied as a coating on whole melons effectively inhibited Listeria innocua (-2.2 log reduction) within 1 weeks at 10 °C. Fig pectins exhibited comparable or superior functional properties than commercial pectins, thus, utilization of low-quality figs and fig stalks into pectin could provide huge economic benefits to Turkish dried-fruit industry.
  • Doctoral Thesis
    Innovative Food Applications of Novel Multifunctional Active Edible Gel Fillings and Coatings
    (01. Izmir Institute of Technology, 2022) Barış Kavur, Pelin; Yemenicioğlu, Ahmet
    This thesis organized as two chapters aimed to develop and test multifunctional novel gel filling and coating. In Chapter 1, the thesis focuses on developing antimicrobial and antibrowning gelatin based gel filling to produce safe caramel apples. For this purpose, water holding capacity and mechanical stability of gelatin (GEL) gels were improved by the incorporation of soy proteins (SP) and inulin (IN), respectively. The water activity (aw) of gels was also reduced to < 0.9 by the addition of sucrose (SUC). The apples were cored and the void cores were filled with GEL-SP-IN-SUC blend gel solution containing synergetic antimicrobials, nisin and lysozyme, and antibrowning agent ascorbic acid (each at 1% in gel). Candy sticks were then placed into gel-filled void cores, and apples were kept at 4oC for 20 h for gelation of filling before caramel dipcoating. The caramel apples with antimicrobial GEL-SP-IN-SUC filling showed 2.4 – 2.9 D lower Listeria count than traditional caramel apples during 7-day cold storage. The active blend gel-filling also prevented discoloration of apple core. In Chapter 2, the thesis focuses on controlling postharvest sprouting and microbial risks associated with shallot bulbs by active chitosan based coating loaded with eugenol (EUG). The sustained release of EUG was achieved by applying ultrasonic homogenization (US) to prepare a composite of chitosan (CHI) with chickpea proteins (CP) (CHI:CP ratio of films = 2). The CHI-CPEUG coating successfully reduced the sprouting and inhibited the inoculated E. coli and L. innocua in shallot bulbs by 2.3 log and 1.7 log, respectively.
  • Doctoral Thesis
    Development of Sensor Systems for Food Quality Monitoring
    (01. Izmir Institute of Technology, 2022) Büyüktaş, Duygu; Farris, Stefano; Korel, Figen
    The main objective of this thesis is to fabricate electrochemical sensors for the detection of 2,4-diaminotoluene (2,4 TDA), 2,6-diaminotoluene (2,6 TDA), and 4,4´-methylene diphenyl diamine (MDA), possibly carcinogenic primary aromatic amines (PAAs) that poses a serious health risk because they can transfer from multilayer food packages including adhesives based on aromatic polyurethane (PU) systems, to the food. The thesis is based on the following three chapters: (1) Development of a nano-modified glassy carbon electrode for the determination of 2,6-diaminotoluene (2) A screen-printed electrode modified with gold nanoparticles/cellulose nanocrystals for electrochemical detection of 4,4´-methylene diphenyl diamine (3) Development of a nano-modified screen-printed electrode for the determination of 2,4-diaminotoluene. In this work, full electrochemical characterization of the nano-modified electrodes was carried out, and the electrochemical properties were described. Migration tests were also conducted to modified sensors in order to investigate their potential application in real food systems. The results of this work clearly showed that modified electrochemical sensors allow reliable quantification of the most important primary aromatic amines migrating from packaging materials to food and can be used as an alternative to the commonly used conventional analytical techniques for the detection of these toxic compounds.
  • Doctoral Thesis
    Physiologic Effects of the Golden Thistle (scolymus Hispanicus L.) Hydromethanolic Extracts: Outcomes of Phytochemical Health Benefits
    (01. Izmir Institute of Technology, 2022) Özel Taşcı, Cansu; Güleç, Şükrü; Büyükkileci, Ali Oğuz; Güleç, Şükrü; Büyükkileci, Ali Oğuz
    This dissertation aimed to screen the beneficial health effects of a hydromethanolic extract (GTE) obtained from the golden thistle (S. hispanicus L.) on different health conditions, including type 2 diabetes, inflammation, cancer, and wound healing. First, 1 mg/mL GTE resulted in 6.94% chlorogenic acid (CGA) bioavailability with (1.82±0.07)x10-6 cm/s apparent permeability on differentiated CaCo-2 cells. Then, 1 mg/mL GTE prompted 39.4-42.6% less glucose efflux and 49-66% less GLUT2 mRNA expressions on CaCo-2 cells. In the systemic inflammation model, pre-treatments of 50-500 μg/mL GTE reduced some inflammatory markers after 0.5 μg/mL lipopolysaccharide (LPS) inflammation induction for 12 h on RAW 264.7 cells. Reductions in 30-53%, 32-45% and 16-36% ranges for nitric oxide, tumor necrosis factor-α, and interleukin-6 (IL-6) were determined, respectively. Additionally, same GTE concentrations were pre-treated with the CaCo-2 cells in the colonic inflammation model. 15.5-19.5% and 8.7-17.3% less IL-6 and IL-8 cytokine releases were detected from CaCo-2 cells, respectively. The wound healing model of 3T3-L1 mouse fibroblasts revealed that 40-80 μg/mL root bark extract resulted in enhanced wound closures with significant differences in the cell cycle distributions. As the most significant result, G2 phase distributions were 1.8% and 12.5% in the negative and positive control samples, respectively. The root bark extract treatments of 10, 40, and 80 μg/mL resulted in 6.6%, 7.1%, and 9.1% in increasing concentrations. Finally, 4 mg/mL GTE application to CaCo-2 human adenocarcinoma cells caused 78.4% reduced cell viability, a cell cycle arrest, and increased early and late apoptotic properties. Overall results suggest that S. hispanicus L. has functional molecules that influence cellular regulations and have potential beneficial health effects.
  • Doctoral Thesis
    Investigation of Compensatory Effect of Copper Mineral and Iron-Protein Complexes on Iron Deficiency Anemia in Human Enterocyte Cell Culture Model
    (Izmir Institute of Technology, 2021) Hoşer, Ezgi; Güleç, Şükrü; Yemenicioğlu, Ahmet
    Iron deficiency is the most encountered worldwide nutritional disease, affecting women, babies, and children. When dietary iron absorption is insufficient to fulfill physiological demands, nutritional iron insufficiency arises. Legumes are a low-cost source of protein that are also beneficial for human health. From a nutritional standpoint, the iron-chelating ability of legume proteins is of importance since they may have high iron mineral stability against in vitro digestion because they are bound to proteins. Legume proteins extracts are commonly utilized as functional components; however, their functionality must be proved in a cell culture system by assessing their physiological activity. Furthermore, during iron deprivation disturbances in copper homeostasis have been observed repeatedly in the literature. And this pointed out that copper might have a compensatory effect on anemia caused by iron deficiency dependant cellular signaling mechanisms. Within this context, the main objectives of this Ph.D. thesis were (i) to develop highly bioavailable, edible protein-iron complex hydrolysates from legumes that can be used as an additive in food products and investigate their functional properties against iron deficiency anemia. Also, (ii) investigating the compensatory effects of copper mineral on iron deficiency anemia and, (iii) its main application for functional food development were other driving forces for the experiments. It was revealed that protein (peptide)-iron complexes derived from lentil (10:1 ratio) and soybean (20:1 and 40:1 ratios) significantly influenced the iron-dependent gene regulation in enterocyte cells compared to the anemic group. Moreover, intracellular gene regulation was mainly affected by copper treatment in the basolateral side of enterocyte cells during IDA, indicating that blood copper level might have the ability to control the enterocyte iron metabolism at molecular and genetic levels during iron deficiency anemia.
  • 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
    Exploring Lysozyme-Nisin Antimicrobial Synergy at Different Conditions for Novel Food Applications
    (Izmir Institute of Technology, 2019) Sözbilen, Gözde Seval; Yemenicioğlu, Ahmet
    The main objective of this thesis is to explore lysozyme-nisin antimicrobial synergy in combination with refrigeration, mild heating or edible packaging for novel food applications. The thesis is based on the following four chapters: (1) Characterization of biochemical properties of lysozyme at different conditions; (2) Lysozyme-nisin synergy in combination with mild heating against Listeria innocua: test of findings in inoculated raw-milk (3) Lysozyme-nisin synergy in combination with chitosan coating against Listeria innocua: test of findings on coated inoculated sprouting seeds; (4) Lysozyme-nisin synergy in combination with refrigeration against lactic acid bacteria (LAB): test of findings in boza, a traditional fermented beverage. The results of this thesis clearly showed that the use of lysozyme-nisin synergy in combination with mild heating at 50 ºC or in combination with edible chitosan coating could be employed to reduce risk of listeriosis from raw-milk and sprouted seeds, respectively. It is also clearly demonstrated that the lysozyme-nisin synergy in combination with refrigeration could be used to delay acidic spoilage of boza without reducing LAB below 106 CFU/mL. This thesis clearly showed the high potential of using lysozyme-nisin synergy against pathogenic or spoilage bacteria as an effective hurdle.