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Browsing by Author "Kaya, Zehra"

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    Doctoral Thesis
    Development of different koruk (Unripe grape) products by using several processing techniques
    (Izmir Institute of Technology, 2018-07) 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.
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    Master Thesis
    Disinfection of white grape juice by using continuous flow uv reactor
    (Izmir Institute of Technology, 2011) Kaya, Zehra; Ünlütürk, Sevcan
    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.