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.