Phenolic content and antioxidant activity of rooibos food ingredient extracts

Hot water extracts of the herbal tea, rooibos, are increasingly used as an ingredient in ready-to-drink beverages and a variety of food products. The quantity of extract solids used in the product is occasionally related to the equivalent number of one-cup-servings, yet to date no comprehensive data have been available to serve as guideline. The extent of variation in total polyphenol, aspalathin, orientin and isoorientin contents, as well as total antioxidant capacity (TAC) of hot water extract of fermented rooibos was determined and compared with that of the hot water soluble solids of infusions, prepared similar to a cup of tea. Extract preparation from a large number of individual rooibos production batches (n = 74) partly simulated industrial processing, while infusions were prepared from a sub-set of samples (n = 20). Based on the total polyphenol and aspalathin contents, rooibos extract and infusion were equivalent when compared on a soluble solids basis. The isoorientin and orientin contents of the soluble solids of the infusion were slightly higher than those of the extract. The TAC of the soluble solids of the infusion, measured with the oxygen radical absorbance (ORAC) assay, was slightly higher than that of the extract, while the opposite was observed for the TAC, measured with the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay.