Abstract:
This research was conducted to study the effect of repeated use of frying oil on physicochemical properties of cottonseed oil and sunflower oil as common edible oils used for food frying (tammiya , chips and fish ) . Samples were collected randomly from different restaurants in Khartoum state for three days in the morning and evening , then the following tests were carried out (viscosity , refractive index , colour ,smoking point , free fatty acid , polymer content , peroxide value ,iodine value ) .
The physical properties of collected cottonseed oil used for frying tammiya and potato chips . Viscosity of oil before frying tammiya and chips were 65.8 and 66.07 respectively, these results were changed significantly after frying to 72.42 ,70.00 respectively .Smoking point changed significantly after frying in collected samples from 217 to 190 ْC in tammiya and 217 to 191ْC in chips frying , but refractive index insignificantly changed after frying in all collected samples . also physical properties of collected sunflower oil used for frying fish were significantly changed after frying , viscosity of sunflower oil changed significantly after frying fish from 75 to 61.4 , and smoking point changed significantly from 215 to 195 ْC . The chemical properties of collected cottonseed oil used for frying in some restaurants in Khartoum area (iodine value , polymer content , peroxide value and free fatty acids ) were significantly changed after frying in all collected samples of different foods (tammiya and potato chips) . peroxide value changed significantly in tammiya and chips frying from 8 and 9 before frying to 10 and 11 respectively after frying . Polymer content of cottonseed oil changed significantly in tammiya and chips frying from 0.73 and 0.82 to 6.7 and 5.3 respectively . Iodine value of cottonseed oil changed significantly in tammiya and chips frying from 119 and 120 to 109 and 110 respectively .The chemical properties of collected sunflower oil used for frying fish in some restaurants in Khartoum area , iodine value changed significantly from 117 to 112 , and peroxide value changed significantly from 7 to 12 , polymer content changed significantly from 0.73 to 4.3 . Hence the used fried oil in restaurants should be discarded when peroxide value more than 10 m.Eq/kgand free fatty acids exceed 0.8mg KOH/g .
