Bioavailability and antioxidant potential of rooibos flavonoids in humans following the consumption of different rooibos formulations

In a complete crossover design, a human study with twelve healthy male volunteers has been conducted using a placebo and different rooibos drinks (rooibos tea and an isolated active fraction) from unfermented rooibos (Aspalathus linearis). Blood and urine samples were collected before and up to 24 h after consumption of the drinks. C–MS/MS, seven metabolites of aspalathin and nothofagin were identified in urine samples, as well as intact aspalathin and nothofagin. Moreover, sulphated, glucuronidated, methylated, both glucuronidated and methylated aspalathin, and glucuronidates of the aglycones of aspalathin and nothofagin were detected. The main metabolite excreted was methylated aspalathin. Most of the metabolites were detected after administration of both rooibos formulations. In plasma samples characteristic unchanged flavonoids derived from unfermented rooibos (e.g. aspalathin) were detected in trace quantities this is due to the changes in Table 5 after ingestion of both rooibos formulations. On average a total of 0.76 nmol of flavonoids were detected during their peak concentration after intake of the rooibos tea, accounting for 0.26% compared to the total amount of flavonoids ingested. Despite the comparable intake of total flavonoids, only an overall 0.41 nmol of flavonoids could be detected after ingestion of the isolated active fraction. No significant increase in plasma antioxidant capacity was observed using the ORAC assay giving rise to the assumption that the effects of rooibos flavonoids have to be detected using other endpoints.