Date

2006

Author

Oymak, Mert Mehmet

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Wheat germ, a nutritionally rich by product of wheat milling, has poor storage stability due to its content of essential fatty acids along with oxidative enzymes. A pilot scale conventional spouted bed was designed and constructed as a high temperature short time treatment unit to bring about drying and roasting effects. By facilitating the use of high temperature inlet air, yet maintaining the bed solids at a temperature below the degradation temperature, spouted bed dryers achieve thermal efficiencies unachievable by other dryers. The inlet diameter, diameter of the column and the angle of the cone were 6.2 cm, 16 cm and 65° respectively. Thermocouples were placed on the inlet, exit and discharge gate of the column. Temperature profiles were recorded during drying, roasting and cooling of wheat germ. The drying temperatures ranged between 201 and 243°C, operation times between 6.5 and 12 minutes, and air flow rate between 55 and 65 m3/h. It was seen that the degree of roasting was closely related to the exit temperature of the air. The exit air temperature range was determined as 155-160°C. Sensory evaluation tests were carried out. Wheat germ processed at 60 m3/h 209°C for 12 min and 55 m3/h 216°C for 7 min were selected as the samples for storage studies, on the basis of the results of sensory evaluation tests. Reproducibility runs were carried out for the selected conditions. The bed height increase study was carried out at 60 m3/h 240 to 243°C. The processed and raw wheat germ was stored in paper pouches at 40°C, to estimate the shelf life on the basis of earlier studies. Peroxide values of both raw and processed samples were followed during the storage period. The initial peroxide values of raw germ, processed samples, and reproducibility samples were 1.1 meq peroxide / kg oil. The peroxide value formation data were found to follow zero order rate kinetics. Comparison of the peroxide value changes in the processed and raw samples indicated that in the studied range of 55-60 m3/h 209-216°C 7-12 min, about 810 fold increase in the shelf life due to stabilization was achieved. The color parameters of each run were determined using the CIELAB (L*, a*, b*) system. Total color difference (E*) values due to processing were calculated using L*, a* and b* values, to be between 2.3 and 58.6.

Subject Keywords

Chemical Engineering.

URI

http://etd.lib.metu.edu.tr/upload/3/12607153/index.pdf
https://hdl.handle.net/11511/16572

Collections

Graduate School of Natural and Applied Sciences, Thesis