Effects of Repeated Frying on the Composition of some Vegetable Oils

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Abuzaid Mohammed Abuzaid, Idris
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The refined groundnut, corn, sunflower and cottonseed oils were used for chips frying for one hour, the frying was repeated three times and physicochemical tests were done before and after each time to determine the changes that occurred in oils. The liquid chromatography, lovibond tintometer, viscometer, refractometer, and spectrophotometer devices were used to determine the type and ratios of constituents fatty acid of oils, to estimate the degree of colour, to measure the viscosity, refractive index and absorbance of carbonyl products, respectively. Moreover, the traditional method was used to determine the polymer content of oils. The results obtained from liquid chromatography showed a slight decrease and / or increase in percentage of saturated fatty acid after first use, with a significant decrease in saturated and unsaturated fatty acids ratios after second and third use of oil. The linoleic acid percent of groundnut, corn, sunflower and cottonseed oils decreased from 40.02, 60.8, 48.7 and 53.12% in fresh oils to 1.46, 5.15, 1.12 and 0.81 % after third fry time respectively. As a result of fatty acid oxidation the refractive index, viscosity, colour, carbonyl value and polymer content increased. When comparing the stability of oils towards oxidation, was found that the groundnut oil scored the best results compared to other oils. However, the refined corn oil that contained antioxidant additives, gave good results after first and somewhat after second use, but after third iv frying it showed significant changes. The results showed that the sunflower oil was better than cottonseed oil especially in polymer content, viscosity and colour.
Effects of Repeated Frying on the Composition of some Vegetable Oils