Master Degree / Yüksek Lisans Tezleri

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

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Access Right: Embargoed AccessAuthor: search.filters.author.Ünlütürk, Sevcan

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  • Master Thesis
    Investigation of Applicability of Uv-Light Emitting Diodes (uv-Leds) as an Alternative Technology in Pasteurization of Cold-Pressed and Newly Formulated Mixed Beverage
    (Izmir Institute of Technology, 2022) Baykuş, Gökçen; Ünlütürk, Sevcan; Ünlütürk, Sevcan; 03.08. Department of Food Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    The aims of this thesis were to evaluate the cold pressing technique for juice extraction and to evaluate whether the cold pressed mixed beverage can be pasteurized with ultraviolet light emitting diodes (UV-LEDs) using E. coli K12 as the target microorganism. Initially, the physical, chemical and optical properties of cold pressed juice (CPJ) were compared with juice extracted by centrifugal juicer (CDJ). The CPJ was then exposed to UV-LEDs simultaneously and sequentially and the microbial inactivation was evaluated. Besides, barrier technologies have been tried to increase the UV-LED inactivation effect. It has been found that the juice yield performance of the cold pressing technique is better than the centrifuge method. The total phenolic content of the CDJ and CPJ was 922 ± 0.01 mg GAE/L, and 867.25 ± 0.01 mg GAE/L, respectively. However, DPPH radical scavenging activity of both beverages were not significantly different. The use of UV-LEDs in simultaneous or sequential mode could not achieve a 5-log reduction in pertinent microorganism required as part of HACCP mandated by US Federal regulations for juice issued by the Food and Drug Administration (FDA). However, filtration and addition of ginger juice revealed that the inactivation efficiency of UV-LEDs increased in highly turbid juice reaching to 3.65 ± 0.218 log10 CFU/ml. In conclusion, this study showed that UV-LEDs used simultaneously at different wavelengths may have the potential to be used in turbid cold press juice pasteurization when combined with different barrier technologies.
  • Master Thesis
    Investigation of the Usability of Radiochromic Films for Determination of Dose Uniformity of Food Surface in Uv-C Treatment
    (Izmir Institute of Technology, 2022) Ünlütürk, Sevcan; Ünlütürk, Sevcan; 03.08. Department of Food Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    The microbial inactivation efficiency of UV light is dependent on product shape and surface morphology on non-planar food surfaces. Since every point of the product is not exposed to the same level of UV light, the efficiency decreases. In addition, during UV light illumination, blind spots may occur, and sufficient inactivation cannot be achieved. So, it is essential to determine UV fluence (dose) applied to surfaces. Actinometry, biodosimetry and mathematical techniques are used to evaluate UV fluence on solid surfaces and in liquid foods. In this study, use of radiochromic films (RCFs) integrated with a computer vision system (CVS) based on image analysis is proposed as an alternative method to evaluate UV fluence on food surfaces. For this purpose, the color change of RCFs on non-planar surfaces exposed to different UV intensity and exposure time was correlated with UV fluence. The results were compared with actinometric and radiometric measurement techniques. Experimental results have been tested and verified on real food surfaces such as apples. It was revealed that there is a linear correlation between the color change of RCF and UV fluence. The maximum UV fluence that could be determined using RCF at 254 nm was approximately 60 mJ/cm2. It was found that films were stable up to 15 days at room and refrigerated conditions. The shape of the apples resulted in different UV fluence distribution profiles on the surface. As a result, it has been demonstrated that RCFs can be successfully used to determine UV fluence on sample surfaces.
  • Master Thesis
    Disinfection of White Grape Juice by Using Continuous Flow Uv Reactor
    (Izmir Institute of Technology, 2011) Kaya, Zehra; Ünlütürk, Sevcan; Ünlütürk, Sevcan; 03.08. Department of Food Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Although continuous flow UV irradiation process is applied to several kind of fruit juices as a non-thermal method, it hasnot treated to white grape juice before. The main objective was to study the effect of commercial UV disinfection system on the spoilage microorganisms in white grape juice. Physical, chemical and optical properties were measured after and before irradiation. Biodosimetric studies were performed by using Bench Top UV apparatus and continuous flow commercial UV reactor. Bench top UV study showed that 228.96 mJ/cm2 UV dose provided complete inactivation of S. cerevisiae in the pasteurized juice at 0.91 mW/cm2 UV intensity.. 3.00±0.16 log cfu/ml yeasts and 4.32±0.03 log cfu/ml lactic acid bacteria reduction were detected in naturally fermented juice after 282.24 mJ/cm2 UV dose. D(10) of yeasts (43.86 mJ/cm2) were higher than lactic acid bacteria (33.78 mJ/cm2) because of showing higher resistance to UV light. In the continuous flow UV reactor, the highest reduction of S. cerevisiae was achieved as 3.39±0.044 log cfu/ml at 56.06 mJ/cm2 UV dose and low flow rate (820 ml/min) in pasteurized juice. However, highest reduction was observed in yeast and lactic acid bacteria count as 1.70±0.028 log cfu/ml and 2.49±0.0031 log cfu/ml respectively at 19.96 mJ/cm2 UV dose in medium flow rate (1516 ml/min) of fresh squeezed juice. Absorbance, color, and titratable acidity were changed by irradiation. As a result of 13 days shelf life study, no significant increase was seen in spoilage microorganisms after irradiation.