Master Degree / Yüksek Lisans Tezleri

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  • Master Thesis
    Physical and Spectroscopic Characterization of Bakery Products Made From Different Flour Mixtures
    (01. Izmir Institute of Technology, 2023) Tuna, Ayça; Tokatlı, Figen
    In this study, it was aimed to show the effect of legume and nut flours in bread formulations in order to improve the nutritional quality and also sensorial appeal of gluten-free bakery products. Breads with and without yeast were prepared according to mixture designs, in which white bean and hazelnut flours were incorporated in rice flour-corn starch based recipes. Flour and bread samples were described by their chemical, technological properties and mid-infrared Fourier transform spectroscopic profiles. Analyses were finalized by starch digestion of the best bread formulations. White bean flour was characterized by its high protein and water retention capacity, whereas hazelnut flour came forward for its highest fat and crude fiber content. Their spectroscopic profiles magnified the differences and confirmed the information gathered with chemical and physical analysis. Seven bread samples with and without yeast were prepared with flour mixtures containing bean and hazelnut flours between 0 and 30%. Doughs and breads were analyzed for their physical properties, and multivariate models were generated to differentiate samples of different gluten-free flour mixtures. Yeast bread containing 15% hazelnut flour was found to have the closest physical properties to standard bread and the capacity to increase nutritional values. The best formulation for yeast-free bread was found to have 15% bean and 15% hazelnut flours w.r.t. criteria of softness, taste, and volume. Starch digestion showed that the inclusion of bean and hazelnut flours in the formulation reduced the rapidly digested starch content of breads.
  • Master Thesis
    Effect of Storage Time on Olive Oil Quality
    (Izmir Institute of Technology, 2009) Yıldırım, Gaye; Tokatlı, Figen
    This work reports changes in the major quality parameters of Turkish extra virgin olive oils stored at room and refrigerator temperatures in dark and monitored for 14 months. Peroxide values, specific absorbance values, total phenol content, free fatty acidity, fatty acid and phenolic profiles of extracted (Erkence and Ayvalık-Edremit) and commercial extra virgin olive oil samples (Altınoluk, Ezine, Bayındır and Ortaklar) from South and North of the Aegean were determined. The acidity and K232 values of samples were within the acceptable limits, the peroxide and K270 values exceeded the limits after 7 and 9 months storage. Hydroxytyrosol, tyrosol, caffeic acid, vanillic acid, vanilin, p-coumaric acid, ferulic acid, m-coumaric acid, cinnamic acid, luteolin, and apigenin were determined as the major phenolics in Turkish extra virgin olive oils. The concentration of hydroxytyrosol and tyrosol increased, while a decrease was observed in the amounts of other phenolics during storage.The highly unsaturated flaxseed oil was mixed with olive oil at 5-15 % levels and stored at room and refrigerator temperature to examine the effect of olive oil on the oxidative stability of flaxseed oil. 15% olive oil addition to flaxseed oil increased its oxidative stability. Fourier Transform (FT-IR) spectral data were used to predict the oxidative quality parameters, total phenol content and the fatty acid compositions by partial least square analysis (PLS). FT-IR spectra of samples subjected to accelerated oxidation were examined to determine the bandwidths, which can be considered as the finger-prints of the oxidation phenomenon (2924, 2852, 1746-1743, 1163 and 967-976 cm-1).
  • Master Thesis
    Use of Multivariate Statistical Techniques in Haccp Programs
    (Izmir Institute of Technology, 2003) Balıklı, Umut Başak; Tokatlı, Figen
    Food safety is the major concern for the food industry and Hazard Analysis and Critical Control Points (HACCP) is an effective safety management system. Data analysis is an important ingredient of this system. The use of Statistical Process Monitoring (SPM) methods in critical control point monitoring step can further improve a HACCP system,since SPM and HACCP have a common goal which is to prevent failures before they occur.Food production processes include many variables and generally they are not independent of each other. The use of multivariate statistical methods is more appropriate than that of univariate statistical methods for food processes and provides comprehensive analysis of the data. The aim of this study was to display the benefits of the use of multivariate SPM techniques in HACCP system.In this study, data were taken from a food processing plant, which uses HACCP program in the production. They were collected in a frozen vegetable production line and composed of raw material properties, process conditions, microbiological counts and end product analyses. The data were analyzed by using multivariate statistical techniques such as Principal Component Analysis (PCA), Multiple Linear Regression (MLR), Principle Component Regression (PCR) and Partial Least Square Regression (PLSR). In the monitoring step, multivariate statistical tools such as Hotelling's T2, Squared Prediction Error (SPE) and contribution plots were utilized. Cause and effect diagrams were also employed as a problem analysis tool to improve the process.Uncorrelated score variables of PCA of process data and quality data successfully analyzed out of control observations on time basis in T2 and SPE plots. Contribution plots displayed the responsible variables, which alarmed at particular time instant. Contribution percentages of variables obtained from these out of control points displayed that blanching temperature and microbial counts are very important contributing factors. Blanching temperature is a variable of the first critical control point (CCP-1) and microbial counts are the verification of that CCP. This result indicates that CCP-1 is the point which extra care should be taken.PCR and PLSR techniques were successful in analyzing the process and product data individually. T2 and SPE plots of these models were nearly the same with the PCA of process data and product data. The regression models (MLR, PCR and PLSR) were not able to explain the correlation structure between process and product data, completely. The in-control data set used in this study was insufficient to construct regression models since it failed to explain the normal operating conditions exactly.It was stated that the proper data collection in the production line would cause an enhancement in the application of multivariate statistical techniques, in both monitoring and prediction of critical control point measurements.
  • Master Thesis
    Effect of Co2 Concentration and Temperature on Growth Rate and Lipid Content of Isochrysis Galbana
    (Izmir Institute of Technology, 2012) Umdu, Sabrettin; Tokatlı, Figen
    The lipid production and biomass growth of microalgae Isochrysis galbana was investigated under the effects of different medium temperature and carbon dioxide levels. Algae production was studied in ten-liter, open-air, aerated bioreactors and sampling was done daily to monitor the cell growth. At the end of each fermentation, the dry mass, lipid amount and fatty acid profiles were determined. The algae were grown according to designed experiments (central composite design (CCD)) at 15, 22.5 and 30 °C medium and aerated with air containing 5, 10 and 15% v/v CO2. It was observed that in 15 °C experiments, the fatty acid profile was formed mainly by unsaturated fatty acid (both mono and poly unsaturated) and the amount of saturated fatty acids increased by increased CO2 levels. The saturated fatty acid content increased with increasing growth temperature. Dominantly observed fatty acids are Pentadecanoic Acid (C15:0), Pentadecanoic Acid (C15:0), Palmitic Acid (C16:0), Linolenic Acid (C18:3), Oleic Acid (C18:1). In the algal productions performed at 22.5 °C and 30 °C medium conditions, the fatty acid content was mainly formed by saturated fatty acids. However, the amount of lipid produced increased with increasing temperatures. The highest cell growth was seen at 15 °C experiments. The lowest growth rate was observed at 30° C experiments. It was observed that the medium temperature had the largest effect for the production of saturated and unsaturated fatty acids. The carbon dioxide was found effective linearly on the fatty acid production.
  • Master Thesis
    Kinetic Modelling of Lactic Acid Production From Whey
    (Izmir Institute of Technology, 2004) Altıok, Duygu; Tokatlı, Figen
    Lactic acid is a natural organic acid, which is used in pharmaceuticals, chemical, textile and food industries. Since only L(+) lactic acid is found in normal human metabolism, the microbial production of L(+) lactic acid has great interest in recent years. Use of whey lactose to produce lactic acid by fermentation process is favourable due to the low cost of whey and its high organic matter content. Whey is suitable medium for some fermentations. However, its high lactose content makes it a potential environmental pollutant. The disposal problem of this pollutant could be overcome by utilization of whey lactose in the lactic acid production.The aim of this study was to develop a kinetic model for lactic acid productionfrom whey by Lactobacillus casei, which is a homofermentative lactic acid bacteria andcapable of producing L(+) lactic acid. Within this context, several batch fermentationexperiments in fermenter were performed at 37 C and pH 5.5. Seed culture that was produced in shake flask fermentations was used as the inoculum for the fermenter.Before the fermentation experiments, some of the proteins in whey were denatured by heat treatment and separated by centrifugation. This treatment decreased the protein amount from 11.15 % to 5.2 % in whey powder. The lactic acid production was associated with the biomass growth up to a certain time, but then a non-growth associated lactic acid production was observed in most of the fermentations except for the 9.0 g l-1 initial substrate fermentation run, where all the substrate was utilized when the stationary phase was attained. The maximum theoretical productivity was obtained as 2.4 g lactic acid l-1 h-1 in the fermentation with S0 equals to 35.5 g l-1. The kinetic parameters were obtained from different fermentation runs. mmax and KS were found as 0.265 h-1 and 0.72 g l-1, respectively. The average product yield coefficient, YPS, was determined as 0.682 g lactic acid (g lactose)-1.The modified form of logistic equation with product inhibition term for biomassThe modified form of logistic equation with product inhibition term for biomass growth, Luedeking and Piret equation for product formation and substrate utilization considering the consumption of substrate for product formation and maintenance, described most of the fermentation experiments in this study with high accuracy (SSE range was 0.0804-0.1531). The toxic powers in these inhibition terms, h and f, made the model applicable for the fermentation experiments with low and high initial substrate concentrations. In case of high initial substrate concentration fermentation (S0. 95.7 g l-1), the same model explains only the exponential phase of biomass and its product formation eventhough the substrate consumption is predicted very well.product formation eventhough the substrate consumption is predicted very well.