Abstract
Rooibos flavonoids and tannin, as well as aqueous extracts and crude phenolic fractions of unfermented and fermented rooibos ( Aspalathus linearis) were evaluated for their capacity to scavenge α,α-diphenyl-β-picrylhydrazyl (DPPH ) and superoxide anion (O 2 − ) radicals. The relative potency of rooibos flavonoids towards DPPH decreased in the order: quercetin ⩾ procyanidin B3 ⩾ orientin ⩾ luteolin ⩾ aspalathin ≈ isoquercitrin > iso-orientin catechin > rutin ≫ vitexin ⩾ chrysoeriol. A different order was obtained for O 2 − : quercetin ≈ aspalathin > orientin ⩾ catechin ⩾ rutin ⩾ isoquercitrin > iso-orientin > luteolin > chrysoeriol > vitexin. Aspalathin was more effective than Trolox, the water-soluble analogue of α-tocopherol. Ethyl acetate solubles of the aqueous extract of unfermented rooibos and the crude aspalathin fraction, with the highest total polyphenol and aspalathin contents, had the greatest anti-radical capacity. Rooibos tannin, lowest in total polyphenol content, was the least effective radical scavenger. Fermentation decreased the anti-radical capacity of the aqueous extracts and crude phenolic fractions.
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