The antioxidant activity of natural products can be observed by their ability to prevent the discoloration of B-carotene, induced by the oxidative degradation products of linoleic acid. B-carotene bears a long unsaturated chain resulting in an intense orange color, which disappears after reaction with linoleic acid. Because of the disruption of conjugation .For this purpose, developed and dried TLC plates are sprayed with an emulsion of 0.03% B-carotene in chloroform and 0.01% linoleic acid in ethanol (1:2 v/v). After 2- to 3-h exposure to daylight, the yellow-orange background progressively bleaches, whereas the coloration remains in zones containing antioxidant products. Bleaching of B-carotene can also occur without linoleic acid, by simple exposure to daylight, although the reaction will proceed more slowly. In this case, TLC plates are sprayed with a solution of B-carotene only, and left in sunlight for at least 12 h until bleaching of the background occurs.