Rooibos – Plant Compounds and Phytochemistry
Why this South African plant produces distinctive polyphenols – and why scientists study them.
At a glance
What makes the compounds in rooibos so interesting? Rooibos contains various polyphenols, including aspalathin, which is particularly characteristic of the plant. Several of these compounds show antioxidant properties in laboratory tests. To understand why scientists are interested in them, it helps to start by looking at the roles such substances play in living organisms.
Understanding the connections
Why do plants produce antioxidant compounds?
Rooibos grows in the dry landscapes of South Africa. Intense sunlight, prolonged periods of drought and fluctuations in temperature are part of its natural environment. A plant cannot simply move away from these conditions. It has to adapt its metabolism and protect its cells.
Plants also produce reactive oxygen species during energy production and other metabolic processes. At controlled levels, many of these substances play an important part in cellular signalling. If they accumulate excessively under unfavourable conditions, they can damage components of cells. Plants therefore have their own enzyme-based defence systems and produce numerous other compounds, including certain polyphenols and flavonoids.
These plant compounds can serve different purposes: some participate in antioxidant reactions, others help plants adapt to strong UV radiation or contribute to their defences. Their functions go well beyond simply neutralising free radicals.
Of particular relevance to rooibos: Plants can respond to drought, intense sunlight and other environmental pressures by altering their polyphenol metabolism. There is also evidence that polyphenols contribute to protective responses to drought stress in rooibos. However, it has not yet been sufficiently established whether this specifically increases aspalathin production or which conditions determine its concentration.
What are free radicals – and what role do antioxidants play in the body?
Free radicals and other reactive oxygen species are also produced during normal metabolism in the human body. For example, they arise when cells generate energy. Certain immune cells even produce them deliberately to help defend against pathogens. At controlled levels, these substances also participate in signalling between cells.
What can increase their production? During infections and inflammation, activated immune cells may produce larger amounts. Intense UV radiation, air pollutants, tobacco smoke and persistently high blood glucose levels can also increase oxidative processes. Production may rise temporarily during strenuous physical activity too – this is part of the body’s normal adaptation to exercise and is not automatically harmful.
Our bodies have their own antioxidant defence systems. These include enzymes such as superoxide dismutase and catalase, as well as substances produced by the body, such as glutathione. They help regulate reactive oxygen species. Oxidative stress occurs when their production and the protective and repair mechanisms of cells become unbalanced. Oxidative reactions can then damage cell membranes, proteins and genetic material, for example.
Normal metabolism
Reactive oxygen species are produced continuously and also perform useful functions.
The body’s defences
The body regulates these substances using enzymes and other compounds it produces itself.
Oxidative stress
When production and protective mechanisms are out of balance, components of cells may be damaged.
Put simply: the aim is not to eliminate every free radical, but to maintain a functioning balance. This principle is relevant both to plant physiology and to research into human metabolism.
Research & sources
Why do scientists study antioxidants in rooibos?
Because some rooibos polyphenols can react with reactive substances in laboratory experiments, researchers investigate their chemical properties and behaviour in biological systems. The work is no longer limited to the direct neutralisation of free radicals. Researchers also explore whether plant compounds can influence cellular signalling pathways and the body’s regulatory processes.
Rooibos is of particular interest because its phytochemistry includes some distinctive compounds. The best-known example is aspalathin. It belongs to the flavonoids, and rooibos is currently the only known dietary source.
Research ranges from chemical analyses and cell- or animal-based models to small studies involving people. A systematic review published in 2024 identified eight human studies with a total of 175 participants. Some reported changes in the outcomes measured. Taken together, however, the available evidence is not yet sufficient to establish reliable health benefits from drinking rooibos.
The central research question: Which compounds measured in rooibos might influence biological processes, and under what conditions? Demonstrating antioxidant properties in a laboratory does not answer that question – but it does make the compounds scientifically interesting.
Which distinctive plant compounds does rooibos contain?
The term polyphenols covers a large group of plant compounds. Many are classified as secondary plant metabolites. Rooibos contains several flavonoids that differ chemically and do not all respond to processing in the same way.
| Plant compound | In simple terms | Why it matters |
|---|---|---|
| Aspalathin | A flavonoid belonging to the dihydrochalcone group that is particularly characteristic of the polyphenol profile of rooibos. | Rooibos is the only known dietary source so far. Aspalathin undergoes substantial changes during oxidation. |
| Nothofagin | A dihydrochalcone that is closely related chemically to aspalathin. | Also occurs in other plants; its concentration changes during rooibos processing. |
| Orientin and isoorientin | Other flavonoids, more specifically flavones. | They contribute to the diverse chemical profile of rooibos, and their relative amounts can vary with the plant material. |
| Rutin and other polyphenols | A range of additional plant compounds. | They show why rooibos phytochemistry cannot be reduced to aspalathin or to a single measurement. |
What makes aspalathin special?
Current research identifies rooibos as the only known dietary source of aspalathin. This is a distinctive feature of the plant, but it does not demonstrate any particular effect of rooibos tea in humans. Nothofagin, by contrast, is not exclusive to rooibos: it has also been detected in other plants.
Why do green and red rooibos differ in their plant compounds?
Both are made from Aspalathus linearis. The crucial difference is how the harvested material is processed: pronounced oxidation is restricted when making green rooibos, whereas it is deliberately allowed to proceed when making red rooibos. This changes not only the colour but also the polyphenol profile.
| Characteristic | Green rooibos | Red rooibos |
|---|---|---|
| Oxidation | Restricted during processing. | Deliberately allowed during processing. |
| Aspalathin | Typically retained in higher amounts. | Usually greatly reduced through oxidation. |
| Other polyphenols | The profile remains closer to the minimally oxidised starting material. | Has its own distinct profile, altered by oxidation. |
| Caffeine | Naturally caffeine-free. | Naturally caffeine-free. |
More aspalathin initially means only one thing: more of that particular plant compound. It does not in itself demonstrate better overall tea quality or greater health benefits. We explore the taste and aroma profiles of the two varieties in more detail on our page “Green Rooibos – Aroma, Taste and Quality”.
Does wild-growing rooibos contain more antioxidants than cultivated rooibos?
Not necessarily. Research has established that plants can respond to strong sunlight, water shortages and other stresses partly by changing their polyphenol metabolism. But this does not justify a general rule that wild-growing rooibos is richer in polyphenols. Cultivated rooibos also grows in South Africa’s demanding conditions.
Wild-growing forms of rooibos can also differ considerably in their genetics and chemical composition. A study by van Heerden and colleagues (2003) found substantial differences between wild populations. In some, aspalathin could not be detected; other flavonoids, such as orientin, isoorientin or rutin, predominated.
This is a particularly interesting finding: plants may use different chemical strategies to adapt to their environment. The polyphenols present in rooibos therefore depend not only on how harsh the growing conditions appear, but also on the particular plant type, its origin and subsequent processing.
What does the “antioxidant power” of rooibos mean in laboratory tests?
Information about rooibos often refers to its antioxidant activity or an ORAC value. ORAC stands for Oxygen Radical Absorbance Capacity. Such tests measure how a sample responds to specific oxidative reactions under defined laboratory conditions.
This can help compare rooibos samples processed in different ways, provided the samples, preparation methods and testing procedures are comparable. A high laboratory value initially describes a property of the sample being tested – not necessarily an effect after drinking it.
What actually ends up in a cup of rooibos?
When rooibos is prepared with water, some compounds are extracted from the dried leaves and young shoots. The quantities entering the infusion depend on factors including the amount of rooibos used, water temperature, brewing time and cut grade.
Pure rooibos is naturally caffeine-free. For an unsweetened infusion, the South African Rooibos Council’s typical nutritional information gives 0 g sugar and 0 kJ per 200 ml. This refers to the prepared drink, not the full chemical composition of the dried plant. Minerals can be detected in rooibos, but the amounts in a typical infusion are small.
A rooibos infusion, finely ground rooibos powder and a concentrated extract are therefore not interchangeable: they differ in composition and in which compounds might ultimately be taken up by the body.
The next question: What happens to these plant compounds after we drink rooibos? Which become accessible during digestion, and which are actually absorbed? Our dedicated article explains the difference between extraction, bioaccessibility and bioavailability and explores the role of the food matrix.
Why rooibos phytochemistry tells us more than a list of compounds
The compounds found in rooibos connect several stories: how a plant adapts to its environment, the diversity of wild-growing forms, the work of producers and the chemical changes that occur during processing. Aspalathin also makes rooibos particularly interesting to researchers.
The question of what benefits people might gain from these substances has not yet been answered. But we now understand why they are studied – and why it matters to distinguish between a living plant, a tea infusion and the processes that take place in the human body.
Scientific sources
- Sies and Jones (2020): Reactive oxygen species as physiological signalling agents – on the normal functions of reactive oxygen species in the human body.
- The Role of Polyphenols in Abiotic Stress Tolerance (2025) – on plant polyphenols and environmental stress.
- MacAlister et al. (2020): Stress tolerant traits and root proliferation of Aspalathus linearis grown under differing moisture regimes and exposed to drought – on drought stress and protective responses in rooibos.
- New Insights into the Efficacy of Aspalathin and Other Related Phytochemicals (2022) – on aspalathin, nothofagin and processing.
- Van Heerden et al. (2003): Phenolic variation in wild populations of Aspalathus linearis – on variation among wild-growing rooibos populations.
- The Effect of Rooibos Tea Consumption on Human Health Outcomes (2024) – a systematic review of eight human studies.
- South African Rooibos Council: Typical Nutritional Information – typical nutritional information for pure rooibos infusion.