Abstract
The classical approach to the process of bleaching has been to treat it in terms of color reduction. However, barring the sporadic and infrequent occurrence of high chlorophyll levels, the color of soybean oil is normally not of great concern. Though, in soybean oil processing, color reduction occurs at each step: degumming, caustic refining, bleaching, hydrogenation, and deodorization, but bleaching improves the flavor of refined soybean oil. Modern approaches to bleaching now focus on both color reduction and the importance of an acid treatment of the oil, brought about either by moisture-containing acid-activated earths or by actual addition of moisture and acid in conjunction with weakly acid or neutral earths. Such considerations suggest that for soybean oil, adsorption treatment is a more appropriate term for the process than bleaching. The primary function of bleaching soybean oils is to reduce or change the oxidation products; remove trace amounts of soaps, phosphatides, and metals; and decolorize. Such treatment may be considered more as an acid/adsorptive treatment involving moisture, acid, and an adsorbent. When an acid-activated earth is used, this reaction is possible with no added acid or water if there is sufficient acidity and moisture in the earth.
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