Effect of extraction time and additional heating on the antioxidant activity of rooibos tea (Aspalathus linearis) extracts.

摘要

The effects of extraction time and additional exposure to heat on the antioxidant activity of aqueous extracts of rooibos tea (Aspalathus linearis) were determined. Two fractions of the aqueous extract, consisting of phenolic compounds soluble in ethyl acetate and, after removal of these substances, the remaining polymeric fraction only soluble in water, were analysed for antioxidant activity. The effect of concentration of the soluble solids of rooibos tea on the oxidation of lard and linoleic acid were assessed by the Rancimat and beta-carotene bleaching methods, respectively. Increasing extraction time increased (P=0.0001) the induction time for a fixed ratio of soluble solids to lard. Additional heat treatment of tea extracts also increased (P=0.05) antioxidant activity according to the Rancimat method, without exhibiting a prooxidative effect at high concentrations. Antioxidant activity of rooibos was demonstrated for the ethyl acetate soluble phenolic compounds and the highly polymerized polyphenols only soluble in water.