Antioxidants in rooibos tea: Dihydrochalcones and flavonoids

One gram of unfermented rooibos tea (soluble dry matter) contains about 50 mg of the dihydrochalcone glucoside aspalathin; of flavonoids, it contains 0.1 mg aglycone, 2 mg C-O-linked flavonoid glycosides and 7 mg C-C-linked flavonoid glucosides. The concentration of these in fermented tea is reduced to about 1.2, 0.2, 1.7 and 2.4 mg/g, resp. In the fermentation process, the potent antioxidant aspalathin is nearly completely oxidized to dihydroisoorientin. The C-glucosyl flavonoids orientin, isoorientin, vitexin and isovitexin are partly degraded as well. Part of the O-glucosyl flavonoid, rutin, is converted to its aglycone, quercetin. Due to these changes, the total antioxidative activity of the aqueous extract of fermented rooibos tea is only half of that of the unfermented produce. Data about absorption, metabolism and protective effects against cardiovascular diseases and cancer are available for quercetin and luteolin including their glucosides, but not for aspalathin and nothofagin.