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During the bleaching of edible oil, the color and many oil impurities are removed through the adsorbent which is usually the bleaching earth.  Although adsorbents containing silica have high bleaching capacity, the purpose of this study was to investigate the role of aluminium and magnesium oxides along with silica as the main component of adsorbent. The process was carried out with 1 and 2% of adsorbents consisting of different ratios of silica, aluminium and magnesium oxides. The amount of peroxide and acid values, chlorophyll, carotenoid, red and yellow colors, amounts of copper and iron of the bleached samples were determined. The results indicated that the effect of 2% of adsorbents was more effective than 1%  in reducing all of the investigated factors. The amount of 2% of the adsorbent containing 90% silica and 10% magnesium oxide reduced the peroxide value by 74.82% and the adsorbent containing 70% silica and 30% aluminium oxide reduced the acid value up to 50% (p˂0.05).  Combined adsorbents containing aluminium and magnesium oxides, especially those with 10 or 15% magnesium oxide reduced chlorophyll content significantly.  Adsorbents consisting of higher amounts of aluminium oxide were more effective to reduce carotenoids. Addition of aluminium and magnesium oxides had significant effect on reducing the amount of red color compared to the blank sample. The amount of copper decreased by about 50% compared to the blank sample (p˂0.05). The highest reduction in iron content was obtained using the adsorbent containing 70% silica, 10% aluminium oxide and 20% magnesium oxide. The results of this study showed that the adsorbents had a good performance during the bleaching process of soybean oil and the difference in bleaching depends on the consumed amount, the compounds of the adsorbent, especially aluminium and magnesium oxides, and the type of impurity.

Keywords: Aluminium, Bleaching, Magnesium, Oil, Oxide.

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