Comparison of the antioxidant activity of rooibos tea (Aspalathus linearis) with green, oolong and black tea

The antioxidant activity of aqueous extracts of rooibos tea (unfermented, semi-fermented and fermented) was compared with that of green, oolong and black teas. The α,α-diphenyl-β-picrylhydrazyl (DPPH) radical scavenging and β-carotene bleaching methods were used to determine the antioxidant activity of extracts prepared in a similar manner and diluted to the same amount of soluble solids. All the tea extracts were strong inhibitors of β-carotene bleaching as well as highly active hydrogen donors to the DPPH radical. Antioxidant activity as assessed with the β-carotene bleaching method decreased in the order: green > black > oolong > fermented rooibos > unfermented rooibos > semi-fermented rooibos. However, antioxidant activity as assessed by the DPPH radical scavenging method decreased in the order: green > unfermented rooibos > fermented rooibos > semi-fermented rooibos > black > oolong.