الفهرس 
Acknowledgment
edible oils oxidationOnly 14 pages are availabe for public view
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Abstract
The study aimed to evaluate some physical and chemical properties of sunflower and corn oil in markets, detect the oxidative changes in sunflower and corn oils due to storage in different storage conditions, and detect the oxidative changes and changes in fatty acid composition in sunflower and corn oils due to repeated frying.
A total of 100 oil samples, representing corn and sunflower oil samples (50 samples each), were collected from different shops in Assiut city with different trademarks. The oil samples were examined for their sensory properties , density, viscosity, peroxide value (PV), anisidine value (AV) and totox value (TV) before and after storage.
The obtained results revealed that storage of oil lead to decrease in sensory scores and gave values of density as 0.912 g/mL for sunflower oil and 0.923 g/mL for corn oil , while values of 40.23 millipoise/sec and 45.57 millipoise/sec were obtained for viscosity. Peroxide value (PV), Anisidine value (AV) and totox value (TV) were 19.77 meq O2/kg, 3.40 and 42.94 respectively for sunflower oil and 3.63 meq O2/kg, 2.19 and 10.11 respectively for corn oil.
After storage there were no significant change in density and viscosity but there was a significant increase in peroxide value, anisidine value and totox value either after increase in storage period or storage conditions.
Oil samples were subjected to sensory, physical, chemical analyses and quantitative analysis using gas chromatography (GC) before and after frying.
Studying the effect of repeated frying on sunflower and corn oil revealed that the sensory properties of oils decreased significantly, While density and viscosity increased significantly with increasing the number of frying.
Peroxide value (PV) of the sunflower oil was 3.65 meq O2/kg when used for frying 10 times at a temperature 190°C, increased to 73.82 meq O2/kg, then began to decrease after 15 fryings to reach 39.37 meq O2/kg. As for corn oil the PV increased from 2.74 meq O2/kg to reach 31.31 after 10 fryings then began to decrease to reach 17.94 meq O2/kg after 15 fryings.
Each of anisidine and totox values increased significantly with increasing the number of fryings as anisidine value (AV) increased from 2.14 to reach 61.64 after 15 fryings for sunflower oil, and in corn oil it was 2.80 and reached 78 after 15 fryings. Likewise, totox value increased from 9.43 to 140.38 after 15 fryings of sunflower oil, and increased from 8.24 to 113.83 after 15 fryings of corn oil.
In addition, the results obtained from the gas chromatography showed a significant change in saturated and unsaturated fatty acid percentages, as after frying the saturated fatty acids increased and unsaturated fatty acids decreased with a significant increase in trans fatty acids.