Abstract
Bleaching is known to alter the composition of edible oils as it removes impurities and certain food nutrients. The characteristics of bleached oil are strongly related to type bleaching medium, temperature at which bleaching is done and other factors. In this study we compare peroxide, free fatty acid, acid and iodine values, copper and iron content of bleached and crude oils to establish the quality and characteristics of cotton and sunflower oils bleached using clays from Iliri. A known mass of bleached oil (0.2 g) digested in the perchloric-nitric-hydrofluoric acid mixture (3.0 mL) then with distilled water as aspirated to atomic absorption spectrophotometer Shimadzu-AA-6200 and absorbance of copper recorded at 324.8 nm. Similarly, another oil portion was treated, aspirated and absorbance of iron was determined at 478 nm when ammonium thiocyanate had been added. Oil dissolved in ethanoic acid-chloroform-water-potassium iodide-starch indicator was titrated with sodium thiosulphate to obtain peroxide value of oil. And oil dissolved in butan-1-ol was titrated with ethanolic potassium hydroxide solution to get acid and free fatty acid values. The percentage decrease in copper content was higher than for iron. The content of iron in cotton oil decreased by 66.4% when bleached with iliri clay leached in 30% hydrochloric or sulfuric acids yet that in sunflower fell by 62.9 and 60.0% when respectively bleached in 30% hydrochloric and sulfuric acid. The content of copper in cotton oil decreased by 82.5% when bleached with Iliri clay leached in 30% hydrochloric acid and 85.0% for 30% sulfuric acid leached clay. That in sunflower fell by 73.3% when bleached with clay leached 30% hydrochloric acid and 83.3% when bleached with 30% sulfuric acid. The acid values showed that the acidity in sunflower oils is largely due to oleic acid, cotton-seed oil corresponded to linoleic acid. The levels of free fatty acid were found to lie in range from 3.8–3.2 for all clays used showing no significant rise. The peroxide values of bleached oils lay between 1.2 and 0.8. The bleached oils were found to be fit for human use because the quality was high.
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