Latest findings on polyphenols and antioxidants in Rooibos

Stellenbosch, 28 August 2012

In a three-year study supported by the SA Rooibos Council (2009 – 2011) Prof Lizette Joubert and her team at the Nietvoorbij Research Institute of Agricultural Research Council looked at the variation in phenolic content and antioxidant activity of fermented Rooibos tea, and how this is affected by different production seasons and quality grades.


The aim of this study was to generate representative content values for the principal monomeric phenolic compounds present in a ‘cup-of-tea’ rooibos infusion as normally consumed (regular, fermented Rooibos tea).

Samples were obtained from different geographical areas, and different producers, to capture as much potential variation in the phenolic composition and antioxidant activity as possible to create a representative data set suitable for inclusion in food composition databases. A total of 114 Rooibos samples were analysed over three productions seasons (2009, 2010 and 2011) and quality grades (A, B, C and D).

Their research article based on the outcomes of this study has been peer-reviewed and accepted for publication in the Journal of Agricultural Food Chemistry (published online on 24 Aug 2012 – see http://pubs.acs.org/doi/pdf/10.1021/jf302583r).

Key findings from the study

  1. The major phenolic constituents in fermented rooibos are isoorientin and orientin (> 10 mg/L), with quercetin-3-robinobioside, phenylpyruvic acid glucoside and aspalathin present at > 5 mg/L. Isovitexin, vitexin and hyperoside were present at < 3 mg/L, rutin, ferulic acid and isoquercitrin at < 2 mg/L and nothofagin at < 1 mg/L. Only traces of luteolin-7-O27 glucoside and the aglycones quercetin, luteolin, and chrysoeriol were present. (See Table 5 in research article.)
  2. Substantial variation was observed in the individual content values of the phenolic compounds and total antioxidant capacity within production seasons and quality grades.
  3. Production season had no significant effect on the total polyphenol content.
  4. The higher quality grade samples tend to be associated with higher levels of the phenolic compounds (Table 6). Grade A samples had the highest mean values for most phenolic compounds and also contained significantly higher levels of aspalathin, isoquercitrin, rutin, hyperoside and quercetin-3-O-robinobioside than the other grades.

Researchers optimistic about anti-diabetic potential of rooibos

Cape Town, South Africa – With World Diabetes Day in sight on 14 November, new evidence of the anti-diabetic potential of Rooibos has emerged …

Cape Town, South Africa – With World Diabetes Day in sight on 14 November, new evidence of the anti-diabetic potential of Rooibos has emerged from a study conducted jointly at the Diabetes Discovery Platform from South Africa’s Medical Research Council (MRC) and the Agricultural Research Council’s (ARC) Infruitec-Nietvoorbij Institute. Researchers found that an aspalathin-enriched extract of green Rooibos is able to lower raised glucose levels in the blood of diabetic rats. Aspalathin is a unique antioxidant found in nature only in the Rooibos plant (Aspalathus linearis). When combined with rutin, another key compound in Rooibos tea, the glucose-lowering action was further enhanced.

Working with diabetic rats, the researchers were able to show that the Rooibos extract could achieve a glucose lowering effect comparable to known diabetic drugs.

“Our work confirms the constituents present in Rooibos could prove beneficial in the fight against diabetes,” says Doctor Johan Louw of the MRC who led the study. “We believe that Rooibos can provide a basis to develop a standardised anti-diabetic product and in a country like South Africa, where a large section of the population relies on herbal medicines, such a product could be of huge value.”

“We have also confirmed that the polyphenols in complex mixtures, such as Rooibos tea, work synergistically to achieve favourable health effects,” Louw explains. “This points to the value of drinking the ‘whole’ tea containing the required amount of these beneficial constituents, rather than a tablet containing just one of the compounds.

“Our Rooibos research to date focused mostly on the antioxidant activity of Rooibos, but this evidence of its ability to lower blood glucose levels opens up new and exciting possibilities for this unique South African herb” says Prof Lizette Joubert of the ARC who collaborated on this project. “We now need to dig deeper to determine the optimal combination and ratio of the active compounds such as aspalathin and rutin in controlling blood glucose levels, and also to understand the exact mechanisms involved.” Follow-up studies indicated that other compounds are also important.

The study has been published online on 19 October 2012 in the Journal of Phytomedicine. (http://www.phytomedicinejournal.com/article/S0944-7113(12)00320-0/abstract)

This Rooibos and diabetes study was funded jointly by the National Research Foundation of South Africa, the Medical Research Council and the Agricultural Research Council, with contributions to post-doctoral fellowships from the Department of Science and Technology. Prof Stephen Fey from the University of Southern Denmark also collaborated on the study.

Notes for editors

The World Health Organization (WHO) estimates that 439 million people will have diabetes by 2030, with the major increase occurring in developing countries.