Investigation of Trace Elements in Hydrogenated Vegetable Oils

Abstract

Previous workers have suggested that fats and oils may undergo some reactions in presence of trace metals. The present work applying atomic absorption spectrophotometry investigated the physicochemical effects of the presence of trace metal contaminants in two samples of hydrogenated vegetable oils, Aseel and Hanim, collected from the local market. The results obtained showed that metals have harmful effects on the stability of hydrogenated vegetable oils even if they are present at trace levels. These effects were studied by measuring peroxide values, acid values, iodine values, free fatty acids, changes of colours, densities and refractive indices. The results showed that copper contamination level in Aseel sample, 1.05 ppm, was higher than the standard level of 0.10 ppm.Consequently, the peroxide value increased to 2.1 millimeq oxygen/Kg oil, the free fatty acid increased to 0.14% and the iodine value decreased to 33.4 mg. The nickel contamination level of Aseel, 1.8 ppm, was also higher than the standard level of 0.20 ppm. On the other hand, the nickel contamination level of Hanim hyrdogenated vegetable oil sample, 0.28 ppm, was higher than the standard level of 0.20 ppm Consequently, the peroxide value increased to 2.5 mg/Kg, the free fatty acid increased to 0.21%, and the iodine value decreased to 41.73 mg/100g. The present work showed that vegetable oils are susceptible to oxidative rancidity due to trace metal contamination introduced to unsaturated vegetable oils as a result of metal catalytic hydrogenation.