Phd Degree / Doktora

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

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Now showing 1 - 10 of 30
  • 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
    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.
  • 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
    Assesment of the Efficiency of Uv Light Emitting Diodes (uv-Leds) for Fruit Juice Pasteurization
    (Izmir Institute of Technology, 2019) Akgün, Merve; Ünlütürk, Sevcan
    The objectives of this thesis are to evaluate the application of ultraviolet light emitting diodes (UV-LEDs) with various wavelengths for pasteurization of cloudy (CAJ) and clear apple juices (AJ), to assess the disinfection efficiency of combined UV-LED irradiation and mild heat (UV-LED+MH) treatments, to investigate the effect of individual and combined processes on the activity of enzyme, physicochemical and microbiological quality of AJ, to determine the shelf life of UV-LED irradiated juice during storage, to reveal the reactivation potential of target microorganism (E. coli K12) in juice medium with different optical properties, and to elucidate the mechanism of microbial inactivation by UV-LEDs. 280/365 nm UV-LED irradiation assisted by mild heat at 55ºC and 15 min exposure time enhanced the inactivation of E. coli K12 and polyphenoloxidase and satisfied the 5-log reduction pasteurization criterion in apple juice. UV-LED+MH treatment extended the shelf life of CAJ from 3 to 30 days and increased its total phenolic content. However, the color properties were slightly affected by ultraviolet treatment. Subsequent photoreactivation of E. coli K12 after inactivation by UV-LEDs was observed in both CAJ and AJ. Contrarily, dark repair was repressed at 4ºC and 22ºC, furthermore, a decrease in the survival ratio was recorded in both medium. It was revealed that the damage of DNA repair enzymes and the proteins that form the outer cellular membrane of bacteria was highly induced by UV-C light at 280 nm. Additionally, the bactericidal effect of 365 nm (UV-A) wavelength was attributed to enhanced production of reactive oxygen species (ROS) resulting in oxidative damage to cellular lipids, proteins and DNA. The combination of these two wavelengths provided more efficient disinfection than that of UV-C light used alone. UV-LED irradiation assisted by mild heat has a potential to be used as an alternative technique to traditional thermal pasteurization process for juice products. This study leads to useful information for the future design of UV-LED treatment systems.
  • Doctoral Thesis
    Exploring the Factors Modulating the Solubilization of Ss-Carotene in Dietary Mixed Micelles Through Computer Simulations
    (Izmir Institute of Technology, 2018) Tunçer, Esra; Bayramoğlu, Beste
    β-carotene is one of the major carotenoids beneficial to human health in the prevention of a variety of diseases. However, due to its hydrophobic nature, the bioavailability of β-carotene is very low. The solubilization of β-carotene in the duodenal mixed micelles is considered as a key step in their bioavailability. Therefore, understanding the factors and the molecular mechanisms behind their solubilization within the dietary mixed micelles are of great importance. Based on this motivation, the aim of this dissertation was to systematically investigate this phenomenon via extensive coarse-grained molecular dynamics simulations in three steps: (i) the characterization of the self-assembly and structure of the mixed micelles of bile salts and phospholipids at fasted and fed state conditions, (ii) determination of the effects of addition of the fatty acids with different chain lengths and degrees of unsaturation ,(iii) solubilization of different amounts of β-carotene in the selected mixed micelles. As it would be computationally too expensive to equilibrate the systems with full atomistic resolution, the MARTINI force field, which is a well-established model for lipid systems, was used. All the simulations were carried out using the GROMACS simulation package. Validations of results were made by comparison of the micellar properties with experimental data in the literature when available. The knowledge gained by this study provides important information to be utilized in the design of effective nutraceutical delivery systems that optimize the bioaccessibility of β-carotene.
  • Doctoral Thesis
    Preparation, Production and Industrial Application of Cheese Protective Cultures
    (Izmir Institute of Technology, 2018) Şatana, Elçin; Harsa, Hayriye Şebnem
    Cheese industry is always under the risk of microbiological contaminations. These contaminants can be either bacteria or fungal species; both affect the final product quality and acceptance. Globally, 20% of the cheese produced industrially is lost due to microbial contaminations. Fungal contaminations can be overcome by the usage of chemicals; sorbate, benzoate, natamycine, propionate, etc. or by natural biopreservatives such as protective cultures or some metabolites of antifungal cultures. Chemical preservatives have a legal limit for their usage and these limits are generally not effective to prevent the product from fungal growth. Also consumers demand goes toward the clean-labeled products and force the manufacturers to use bioprotectants if necessary. There are many types of bioprotectants commercially available with defined lactic acid bacteria combinations which are not so effective for some fungal species due to the species that they include. In this study, several lactic acid bacteria (LAB) strain has been selected to prepare efficient protective culture combinations e.g. Lactobacillus rhamnosus, Lactobacillus plantarum and Lactobacillus paracasei spp. paracasei. The maximum antifungal effect was determined by using mixed culture combination of lactic acid bacteria strains with equal volume. In cheese applications, 3x108 cfu/ml antifungal bacteria mixture including; Lactobacillus rhamnosus, Lactobacillus plantarum and Lactobacillus paracasei spp. paracasei, was inoculated into the curd before fermentation and found more effective than surface applications to the final products. In yoghurt production, same antifungal lactic acid bacteria mixture was found to be effective when applied before fermentation with 106 cfu/ml initial cell counts.
  • Doctoral Thesis
    Development of Different Koruk (unripe Grape) Products by Using Several Processing Techniques
    (Izmir Institute of Technology, 2018) Kaya, Zehra; Ünlütürk, Sevcan
    Verjuice, obtained by pressing unripe grapes, is mostly used as an alternative to lemon juice and vinegar in salads and traditional meals due to its unique sour taste and flavour. It has a short shelf life due to growth of yeasts and molds when produced at household conditions. Verjuice products in the market are not meeting desirable quality characteristics. The high quality verjuice and its derivatives required to be produced by considering several processing techniques. The objectives of this Ph.D. thesis are to (i) produce long shelf life verjuice with minimum change in its “fresh like” properties by using the combination of UV-C irradiation or Pulsed-UV light (PUV) with mild heating, (ii) produce verjuice powder with a good storage stability by using freeze drying, (iii) produce concentrated verjuice with minimal quality loss by using vacuum evaporation. Verjuice was successfully pasteurized without loosing its desirable quality by a combined UV-C and mild heating (78.0 mJ/mL, 6.2 min, 51.2°C) and PUV assisted with mild heating (6.12 J/cm2, 8.5 min, 47°C) and mild thermal (72°C, 18 s) treatments. 5-log reduction of target S. cerevisiae (NRRL Y-139) was aimed for the pasteurization of verjuice. No microorganism was developed in pasteurized verjuice during 12 and 6 weeks of refrigerated storage after UV+MH and PUV+MH treatments, respectively. Freezedried verjuice powder containing maltodextrin (FD 48h, 20% MD), was highly stable under the accelerated storage conditions (40°C, 90%RH) for 70 days. Concentrated verjuice obtained under vacuum conditions of 45°C/913 mbar, showed minimal quality change and was consumable up to 12 weeks at refrigerated storage.
  • Doctoral Thesis
    Development of Novel Antimicrobial, Antioxidant and Bioactive Edible Gels Intended for Food Preservation and Promotion of Human Health
    (Izmir Institute of Technology, 2017) Boyacı, Derya; Yemenicioğlu, Ahmet
    The aim of this thesis was the development of edible gelatin (GEL) based composite gels with antimicrobial, antioxidant, and bioactive properties. For this purpose, composite gels of gelatin with rice starch (RS), candelilla wax (CW) and soy protein isolate (SPI) were incorporated with lysozyme (LYS) and green tea extract (GTE). LYS and GTE release profiles of GEL and its composites were tested in aqueous media and cold-smoked salmon selected as a model food. GEL, GEL/RS and GEL/CW gels did not show considerably different LYS and GTE release profiles in aqueous media, but their release profiles in the model food system were different. GEL/SPI gels bound LYS and prevented its release from the gels, but they released GTE. GEL showed the most rapid LYS delivery onto smoked salmon, while GEL/RS and GEL/CW caused sustained LYS delivery profiles. The total LYS delivered from GEL and GEL/RS gels onto smoked salmon were similar while GEL/CW gels caused almost 30% lower LYS delivery onto food samples. On the other hand, GEL/CW gels caused the highest amounts of GTE delivery onto model food. In broth media at 4°C, all LYS containing gels (with or without GTE) showed antimicrobial activity with a minimum 1.5 decimal reduction in L. innocua that was used as a target bacterium. In smoked salmon samples, the LYS containing gels inhibited the growth of L. innocua, but they did not cause a significant reduction in its counts. Antioxidant capacity, antihypertensive and antidiabetic activity, and cytotoxicity tests against human colon carcinoma cells (Caco-2) conducted with released GTE proved the bioactive potential of developed gels. The gels were also tested for their water binding capacity, and physical (textural properties) and morphological (SEM images) properties. This work clearly showed the possibility of using active gels as multifunctional delivery tools (as coating material, pad or pre-cast film) to prevent microbial and oxidative changes in food and to enhance their bioactive properties.