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.
A recent study at the Oxidative Stress Research Centre, Cape Peninsula University of Technology (CPUT), has proven the ability of rooibos to improve liver function and protect the liver against oxidative damage.
Photo: Dr Wale Ajuwon preparing a dried green rooibos extract.
6 June 2013
In this 10-week study, 80 male rats were treated with a liver-damaging chemical known as t-BHP (Tert-butyl hydroperoxide). The study showed that giving these rats access to rooibos (instead of water) helped to protect the liver against structural, enzymatic and biochemical damage, and could even reverse some of the damage already present in the liver. The findings of the study have been published in the journal “Evidence-Based Complementary and Alternative Medicine”. The full scientific paper is available online at http://dx.doi.org/10.1155/2013/984273.
“These findings provide biological evidence that Rooibos can protect the liver and that it has potential to be used as a supporting treatment for liver disorders,” says Dr Wale Ajuwon, researcher at CPUT, who led this investigation as part of his doctoral study.
“Liver diseases and drug-induced liver injuries are a leading cause of death around the world, and synthetic drugs used to treat liver disorders often cause further damage to the liver,” Dr Ajuwon points out. “That is why it is so exciting to present this evidence that rooibos can be used as a liver protector and an adjuvant therapy for the treatment and management of liver disorders.”
“Although this study was done in animals, they give us insight into mechanisms of what might be taking place in the human body and I believe that they are useful to make recommendations to people.”
Dr Ajuwon came to South Africa in 2010 to study at CPUT. Three years later he is an avid rooibos fan and is now also encouraging his friends and family in Nigeria to have at least six cups of rooibos every day. “I encourage them to drink rooibos, because it is safe and contains a plethora of polyphenolic antioxidants that have been shown scientifically to have beneficial effects,” he says.
Dr Ajuwon studied at CPUT under the leadership of Prof Jeanine Marnewick, one of South Africa’s foremost researchers in the field of rooibos and oxidative stress.
This study was funded by CPUT.
Issued by Meropa, on behalf of the SA Rooibos Council.
Researchers at Stellenbosch University have found scientific evidence in support of the ability of Rooibos extracts to counter the negative side effects of stress.
Think about how often you hear people say “I’m stressed” – a phrase that has become one of the most common clichés in modern life. With the current recession affecting most households, stress levels seem to be escalating at a galloping pace. The importance of relaxation and finding remedies to soothe away the ailments associated with stress is a no-brainer, but with the busy lives we lead these days, finding time for this is often a challenge. The good news from Rooibos? Sipping a cup of relaxing, caffeine-free Rooibos tea can do just this.
Researchers at Stellenbosch University have found scientific evidence in support of the ability of Rooibos extracts to counter the negative side effects of stress. “We have found that Rooibos extracts inhibit the biosynthesis of the stress hormone, cortisol,” says Dr Amanda Swart, senior lecturer and natural plant products researcher at the Biochemistry Department. “This is good news, as the stress we experience chronically on a daily basis leads to abnormally high cortisol levels. High cortisol levels are associated with increased anxiety, high blood pressure, suppressed immunity and diabetes.”
People don’t realise the extent to which stress plays havoc with the Central Nervous System, which links to our health, emotions, well being and the overall functioning of our body on a day to day basis. According to studies conducted in South Africa and Japan, Rooibos has shown to have a remarkable calming and soothing effect on the Central Nervous System and can play a role in relieving health problems such as insomnia, irritability, headaches, nervous tension, hypertension and stress.
It’s so ironic that when people feel stressed they often have a caffeine containing drink, but studies show that caffeine only worsens a sensitive Central Nervous System, having the opposite effect to Rooibos, which is naturally caffeine free. So, next time you’re feeling stressed, brew some Rooibos tea, savour the taste, and relax as the tea goes about doing its job – healing your body and mind.
Chrysoeriol, an antioxidant in Rooibos, can prevent and treat vascular disease in people. This is the latest findings from scientists in Japan where Rooibos has been extensively researched in the past 20 years.
Chrysoeriol, an antioxidant in Rooibos, can prevent and treat vascular disease in people. This is the latest findings from scientists in Japan where Rooibos has been extensively researched in the past 20 years.
Chrysoeriol is able to inhibit the migration of smooth muscle cells inside the aorta, a key cause of atherosclerosis (narrowing or hardening of the arteries), according to new findings published in the Journal of Pharmacological Science . The research was done on human aorta cells. They recommend the use of chrysoeriol to prevent and treat the repeated narrowing of blood vessels following coronary angioplasty. During angioplasty a small balloon is used to open up a blocked or narrowed heart artery.
The characteristics and bioactivity of the complex mix of compounds in Rooibos are being studied by several research groups around the world. Chrysoeriol is already known for its antioxidant, cancer-fighting and anti-inflammatory properties.
“Although chrysoeriol is not the most abundant antioxidant in Rooibos, we are now beginning to understand its other properties that may contribute to the overall health benefits of Rooibos,” Professor Jeanine Marnewick, specialist researcher at the Cape Peninsula University of Technology commented after reviewing these latest findings from Japan. “As scientists unravel the health contributions of the complex mix of compounds in Rooibos, we are finding more and more evidence to substantiate the traditional uses of Rooibos as a remedy for a variety of ailments.”
These latest findings follow on earlier work done at the Aga Khan University Medical College in Pakistan where researchers first found that the chrysoeriol in Rooibos has a bronchodilatory effect. They found that it helps to decrease muscle spasms in blood vessels and lung airways and recommended its use as a remedy for congestive airway disorders such as asthma. Their findings and recommendations were published in the European Journal of Nutrition in 2006.
NOTE: Cardiovascular disease is a leading killer worldwide and in South Africa. According to data from the Medical Research Council close to 200 people die in South Africa every day as a result of some form of heart or blood vessel disease. About half of these people are younger than 65 years.
South African researchers have developed a flavour and mouthfeel wheel that provides 27 descriptive attributes for Rooibos tea as a tool to facilitate communication among producers, processors, grading experts, marketers, flavour houses, importers and consumers.
Many of us have taken a sip of tea and immediately been able to distinguish the taste as either good or bland, without being able to say why. In order to go beyond simplistic distinctions and to properly discern the great many tastes and aromas that give rooibos tea its flavoured nuances, South African researchers have developed a flavour and mouthfeel wheel for the unique homegrown brew.
The novel wheel provides 27 descriptive attributes for rooibos – 20 flavour and seven taste and mouthfeel descriptors – and will be a practical tool to facilitate communication among rooibos producers, processors, grading experts, marketers, flavour houses, importers and consumers.
The wheel is the work of a team including Ilona Koch, a Masters student at Stellenbosch University. Under the leadership of Professor Elizabeth Joubert of the Agricultural Research Council, (who designed the project proposal together with Stellenbosch University lecturer Ms Nina Muller), Koch and a team of researchers have spent over a year compiling data through numerous experiments with rooibos tea.
“This study was conducted to characterise and quantify the sensory attributes associated with rooibos flavour (taste and aroma) and mouth-feel to paint a more comprehensive picture of what is frequently referred to as ‘typical’ or ‘characteristic’ rooibos flavour,” said Koch.
The researchers studied 69 different rooibos samples originating from 64 different plantations in various production areas. These samples had been graded from A to D, representing the highest to the lowest tea quality respectively.
A strict protocol was followed when brewing the tea – 300g of boiling, deionised water was poured onto 5.8 g of dry tea leaves, which was infused for five minutes. The tea was strained and stored in a stainless steel thermos flask to keep the temperature constant, and 100 ml of tea was served to each taster in a white porcelain cup covered with a plastic lid to prevent evaporation and loss of volatiles. The tea cups were preheated in an oven set to 70°C, and kept in water baths with the temperature regulator set at 65°C throughout the sensory analysis session.
Nine judges took part in the study, selected on availability and interest. “Most of them had extensive experience with descriptive analysis of a wide range of products. None of them, however, had previous experience with sensory analysis of rooibos,” said Koch.
During the first training stage the panellists were exposed to a number of rooibos samples to become familiar with the product and the evaluation protocol. During 22 one hour sessions, the 69 samples were analysed and compared to one another, and the panel generated aroma, taste and mouth-feel terminology.
Some 85 aroma and 38 taste and mouthfeel descriptors were generated at this stage, but this proved to be too large a field of data for the efficiency necessary to produce the wheel. The number of descriptors was subsequently reduced to eight aroma descriptors and nine taste and mouth-feel descriptors. A score card was developed which showed each of these 17 descriptors together with a 10cm unstructured line scale ranging from “none” to “prominent”.
After training was over, the panel used the score card to rate the intensity of the 17 attributes for each of the 69 samples during 40 sessions spread out over eight weeks.
Through the research, it was uncovered that the positive sensory characteristics such as floral, woody, honey and sweet could be separated from the negative attributes such as green plant, hay-like, dusty and sour. In light of this, the descriptors were grouped according to the positive or negative impact on the quality of the sensory experience.
While the research delved into a number of experiments to deduce specific data including the effect of steam pasteurisation, the effect of particle size and the oxygen radical absorbance capacity of rooibos (ORAC), the flavour and mouthfeel wheel represents the attributes of unpasteurised rooibos infusions.
The wheel will be further updated and refined with samples from another season during the three-year project, which will run until March 2012. It is being funded by the SA Rooibos Council and the Technology and Human Resources for Industry Programme (THRIP) that aims to boost South African industry by supporting research and technology development.
Now drinking tea will no longer be about whether it’s simply good or average, but a sensory experience akin to the tasting of wine where you will be able to indulge in the subtle tannins and fine distinctions in taste and aroma that rooibos infuses into each of its products.
Professor Elizabeth Joubert
Agricultural Research Council
Phone: +27 21 809 3444 – Fax: +27 21 809 3430