The effects of filtering through bleaching media on decrease of peroxide value (PV) of autoxidized soybean oil were investigated to improve its quality. Sixteen kinds of filtering and bleaching media were employed. The standard activated clay was the most effective in decreasing the peroxides in autoxidized soybean oil. The relations between the decrease of PV and the physical or the chemical properties of the media were examined. It was found that peroxides are reduced in proportion to the amount of acid at the highest acid strength range + 1.5--5.6 rather than amount of acid at the lower acid strength range, total amount of acid or specific surface area of medium.

Effects of filtration bleaching on thiobarbituric acid values (TAV) and carbonyl values (CV) of autoxidized soybean oil were investigated by using sixteen kinds of bleaching media in order to improve oil quality. The standard activated clay was the most effective in reducing the amounts of aldehydes and ketones in autoxidized soybean oil. From the decreases in TVA and CV and physical and chemical properties of media, it was concluded that decreases of TAV and CV are mainly dominated by the acidity over the highest range, +1.5∼−5.6, rather than the acidity over the lower acid strength ranges, total acidity or specific surface area of media. From the results of chemical composition and acidity over the highest range (+1.5∼−5.6) of the clays and TAV or CV reduction by using the heattreated clays, it was suggested that the acidity over the highest range originated from the water contained between layers and bound water in the clay.

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