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
- 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.)
- Substantial variation was observed in the individual content values of the phenolic compounds and total antioxidant capacity within production seasons and quality grades.
- Production season had no significant effect on the total polyphenol content.
- 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.
Results from a clinical trial showing that Rooibos significantly reduces the risk of heart disease were announced at a Rooibos Science Café at the MTN ScienCentre in Cape Town on 26 November 2008. About 150 members of the media, health sector and the Rooibos industry attended the event and were delighted about this new and conclusive evidence of the health promoting properties of Rooibos in humans.
Researchers traced the protective effect of Rooibos by looking at two important markers in the blood, as well as the oxidative status of the 40 adults who participated in the study. They found a significant decrease in conjugated dienes and malondialdehydes of 35% and 50% respectively – two blood markers that indicate oxidative damage – in the group that drank six cups of Rooibos per day for 6 weeks. “This means that Rooibos may help to slow down atherosclerosis, or the hardening of arteries,” explained Dr Jeanine Marnewick, who led the clinical trial at the Oxidative Stress Research Centre at the Cape Peninsula University of Technology. On top of this, Rooibos also increased the levels of the body’s own ‘super anti-oxidant’ called glutathione and helped to reduce the levels of “bad” LDL-cholesterol significantly.
“This is incredible news for Rooibos and the public,” said Mientjie Mouton, a director of the South African Rooibos Council. “We need scientific evidence to substantiate what we have always known – that Rooibos is good for you!”
Dr Marnewick also explained that they asked study participants for feedback on how they felt during the clinical trial. “Many of them reported feeling irritated during the washout period when they could not drink Rooibos, and much calmer once they were enjoying their six cups of Rooibos per day. That is why she will continue the clinical trial to look at the effect of Rooibos and stress.”
At the same science café Dr Carl Albrecht, head of Research at the Cancer Association of South Africa (CANSA) gave an overview of nearly a decade of research at South Africa’s Medical Research Council into the ability of Rooibos to prevent or slow down cancer. He also emphasised the importance of the ability of Rooibos to reduce oxidative stress in the body, as shown by the results of a study on rats, published in 2003. “I am elated that Dr Marnewick and her team were now able to prove that Rooibos also has this effect in the human body,” he added. Oxidative stress plays a role in the development of a whole range of diseases, including cancer, stroke, heart and liver disease, diabetes and Alzheimer’s. Another important milestone was the discovery, published in 2004, that Rooibos can prevent and slow down skin cancer in mice. “The next challenge is to prove that Rooibos can also prevent cancer in people, and I believe that there is a good chance that we’ll be able to prove this,” Dr Albrecht said.
This Rooibos Science Café was organised by the South African Rooibos Council who invests in Rooibos research, along with funding partners such as South Africa’s National Research Foundation as well as the Medical Research Council and CANSA.
A collaborative study by scientists at four international research facilities has found the first clinical evidence that drinking rooibos tea significantly increases the antioxidant capacity in human blood, thereby boosting the body’s natural defences.
The researchers in Rome and Glasgow found that the antioxidant capacity in the blood of 15 healthy volunteers peaked one hour after drinking 500ml ready-to-drink rooibos tea. Both traditional (fermented) and green (unfermented) rooibos tea had a significant effect.
“On the basis of the results of our study, we conclude that Rooibos tea is able to deliver antioxidant ingredients to the body, thereby stimulating the body’s internal redox network,” says Professor Mauro Serafini, leader of this research project and Head of the Antioxidant Research Laboratory at INRAN, a nutrition research insitute in Rome, Italy. “It is highly possible that, once absorbed in the circulatory stream, the unique ingredients of Rooibos may display other biological activities in the human body. That is why we are planning further intervention studies in humans to investigate the effect of Rooibos tea on the body’s strategy of defence to counteract the development of heart disease.”
“After an hour, the plasma antioxidant levels start to drop and that is why we recommend drinking up to six cups of rooibos spaced throughout the day for a sustained health benefit,” explains Professor Jeanine Marnewick from the Cape Peninsula University of Technology. She led a recent study that showed the beneficial effect of drinking six cups of rooibos a day to promote heart health.
Numerous studies over the past few decades have helped scientists to understand the complex and unique blend of antioxidants found in rooibos. They have also proved that the active compounds in rooibos are bioavailable and are metabolised (converted) in the body. The significance of the latest study is that it provides the first direct evidence that rooibos boosts antioxidant levels in the blood of healthy humans.
“This new research proves that the compounds in rooibos are potent enough to have a measurable effect on the antioxidant capacity of the blood,” says Professor Lizette Joubert, one of South Africa’s leading rooibos researchers, working on the quality and chemical composition of rooibos at South Africa’s Agricultural Research Council.
The most active antioxidant in rooibos – aspalathin – is unique to the plant species Aspalathus linearis. This fynbos plant thrives in the Western Cape’s Cedarberg region where it is commercially cultivated and wild-harvested for the production of rooibos tea.
“This study underlines the value of rooibos as a widely available and affordable source of dietary antioxidants,” comments Mientjie Mouton, chair of the Product Research Committee of the South African Rooibos Council. “It is very encouraging that leading research institutions around the world are working on rooibos and producing such promising results. There is also a great deal of work being done by local rooibos researchers and we will continue to invest in this research.”
The South African Rooibos Council invests some R1 million a year to fund research into rooibos’ health properties. This year the Council is supporting research projects at several local universities and science councils focusing on how rooibos can counter cancer and stress, as well as the link between rooibos and exercise. A project on rooibos and obesity has been approved for funding in 2011.
Summaries of the most recent rooibos studies published in top peer-reviewed scientific journals can be found on the website of the SA Rooibos Council at www.sarooibos.co.za
Notes to editors
The collaborative research was carried out at: Antioxidant Research Laboratory, Human Nutrition Unit, INRAN, Rome; Food and Nutrition Unit, IRCCS, Rome; Plant Products and Human Nutrition Group, University of Glasgow; Diabetes Unit, San Camillo Forlanini Hospital, Rome.
The study has been published in Food Chemistry: Villaño, D., et al. 2010. Unfermented and fermented rooibos teas (Aspalathus linearis) increase plasma total antioxidant capacity in healthy humans. Food Chemistry 123 (2016) 679-683.