Screening Bolivian plants for antioxidant activity

The aerial parts of 17 Bolivian plants were screened to determine antioxidant activity. A methanol extract of each plant was prepared and partitioned sequentially with hexane, chloroform, and ethyl acetate, leaving an aqueous solution. All extracts and their 5 fractions, for a total of 102 samples, were evaluated using two techniques: an adaptation of the beta-carotene bleaching technique using an emulsion of linoleic acid in water as the oxidizable substrate, and the DPPH free radical trapping technique. The results with the beta-carotene bleaching technique were more discriminating and better related to the rancidity process under normal conditions; with this assay, 11 species provided at least one fraction with highly promising antioxidant activity. All species gave good results under the DPPH technique, and in most cases they performed better than BHA, which was used as a reference antioxidant. We advocate the simultaneous use of these two techniques for screening purposes.