Master Degree / Yüksek Lisans Tezleri

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

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Subject: search.filters.subject.Fruit--Drying

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  • Master Thesis
    Determination of Effective Parameters for Drying of Apples
    (Izmir Institute of Technology, 2007) Dikbasan, Tarık; Gökçen Akkurt, Gülden; Gökçen Akkurt, Gülden; 03.06. Department of Energy Systems Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Drying is one of the oldest methods for the preservation of agricultural products such as fruits and vegetables. Apple has a significant share in fruit production both in the World and in Turkey. It is also an important raw material for many food products.Temperature, velocity and relative humidity of drying air are important parameters for hot air drying process. To determine the drying kinetic of agricultural products, drying and drying rate curves should be plotted.Experiments are conducted in a tunnel dryer using cubic shaped (10x10x10mm) red delicious (Malus Domestica) apple for various drying air temperature (40.1-65.3oC), velocity (1.1, 1.4, 1.9, 2.3 and 2.5 m/s) and relative humidity (4.6-20.5%) values. The temperature and relative humidity are measured and recorded every 1 min. at fan inlet, upstream and downstream of the tray, the velocity is measured only at the tunnel exit. The measured data is used to obtain drying and drying rate curves. The curves indicate that drying process takes place in the falling rate period except very short unsteady-state initial and constant rate periods. Thus, effective diffusion coefficients are calculated using the data collected during the falling rate period and the experimental data are fitted to fourteen thin layer drying models which are found in the literature. Rehydration time and colour are used as parameters for the dried apple quality.The effective diffusion coefficients are obtained within the range of 0.486x10-9 -5.63x10-9 m2/s Regarding with drying time, rehydration time and colour data, the best results are obtained at 2.5 m/s velocity, 20.5% relative humidity and a temperature range of 53.5-65.3oC under experimental conditions. Midilli and Kucuk model is the best fitted model with a minimum R2 of 0.9991 and a maximum RMSE of 0.0087976.
  • Master Thesis
    Control of Microbial and Enzymatic Changes in Intermediate Moisture Sun-Dried Figs by Mild Heating and Hydrogen Peroxide Disinfection
    (Izmir Institute of Technology, 2003) Demirbüker Kavak, Dilek; Yemenicioğlu, Ahmet; Demirbüker Kavak, Dilek; Yemenicioğlu, Ahmet; 03.08. Department of Food Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    During cold storage, the enzyme pectin methylesterase (PME) caused softening and lossof desired gummy texture in rehydrated intermediate moisture (IM) sun-dried figs. Heat inactivation studies indicated that the purified PME can be inactivated rapidly at 80 o and 90 oC. However, at or below 70 oC the enzyme showed activation by heating and inactivated very slowly. The in-situ activation of PME occurred much more extensively when sun-dried figs were rehydrated between 70o and 90 oC to produce IM figs with approximately 30 % moisture and this prevented the effective inactivation of enzyme even by rehydrations conducted at 80 o and 90 oC. The partial reduction of PME enzyme activity (almost 30 %) by rehydration of figs at 80 oC for 16 min may be used to delay undesirable textural changes in cold stored IM figs for 3 months. However, for longer storage periods hot reyhdration alone is not sufficient to prevent softening. No considerable yeast and mold growth was detected in IM figs cold stored 3-3.5 months.However, in some samples rehydrated in water at 80 oC, the total mesophilic aerobic counts and total yeast and mold counts showed a considerable increase when storage time exceeded 3-3.5 months. The rehydration of IM figs in 2.5 % H2O2 for 16 min at 80 oC reduced the total mesophilic aerobic microbial count of figs almost 90 %. Due to bleaching caused by H2O2, the brown fig color turned to a desirable and stable yellowlight brown as well. However, during cold storage the O2 gas released due to the decomposition of H2O2 by in situ fig catalase, accumulated within figs and caused some physical defects. Also, the residual level of H2O2 in the homogenates of disinfected figs was too much (300 ppm) and it seemed unlikely to eliminate this amount of H2O2 by physical or chemical means during processing. Pureeing IM figs eliminated residual H2O2 very rapidly. The application of rehydration first in 2.5 % H2O2 solution at 80 oC for 4 or 8 min and then in hot water at the same temperature for 12 or 8 min, respectively, also reduced the amount of residual H2O2 in IM figs considerably.Besides, these two-stage rehydration procedures eliminated the physical defects occurred in IM figs due to O2 gas release and gave firmer IM figs. To reduce the initial microbial load of IM figs, 4 and 8 min disinfections conducted in H2O2 solutions were less effective than 16 min disinfection in H2O2 solution. However, both 4 and 8 min disinfections effectively suppressed microbial load for at least 3.5 months and they may be used in the production of SO2 free light colored fig products.