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Solutions of food colorants were tested with insoluble drugs (kaolin, active carbon, talc, natural aluminum silicate) for their adsorption phenomena in purified water, gastric and intestinal fluid test solutions, respectively. The adsorption isotherms of kaolin with Red 2 in purified water, and active carbon with Red 2, 3, 40 in the three media, with Yellow 4 in purified water, gastric fluid, with Yellow 5 in intestinal fluid and natural aluminum silicate with Red 3 in purified water, intestinal fluid, with Yellow 4, 5 in purified water followed the Freundlich equation, and those of talc with Red 2, 3, Yellow 5 in the three media, with Red 40 in purified water, gastric fluid, with Yellow 4 in intestinal fluid fitted the Langmuir equation. With decrease of the alcohol content of aqueous solutions, the adsorption of coloring food additives is increased, but it decreased in high temperature. Also the activation energy of adsorption of coloring food additives by active carbon was determined.
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