The antioxidant activity of aspalathin, the major flavonoid of unfermented rooibos tea, was compared with that of other polyphenols present in rooibos tea, α-tocopherol, BHT, and BHA using the β-carotene bleaching, α,α-diphenyl-β-picrylhydrazyl (DPPH) radical scavenging, and automated Rancimat methods. The phenolic compounds include the flavonoids vitexin, rutin, quercetin, luteolin, isoquercitrin, (+)-catechin, and the phenolic acids protocatechuic acid, caffeic acid, p-hydroxybenzoic acid, p-coumaric acid, ferulic acid, syringic acid, and vanillic acid. (+)-Catechin had the longest induction period according to the Rancimat method, while BHT was the most effective inhibitor of β-carotene bleaching. Compounds with the highest degree of DPPH radical scavenging and highest rate of scavenging were caffeic acid and aspalathin, respectively. Aspalathin offered less protection against lipid oxidation than BHT and α-tocopherol according to the Rancimat and β-carotene methods, but it displayed a higher ability to scavenge the DPPH radical.
