Rooibos and the Food Matrix
What happens to plant compounds when we consume rooibos as tea, an extract or a powder – and what our bodies can actually absorb.
At a glance
Can our bodies benefit from the polyphenols in rooibos? To explore this question, measuring the aspalathin content of a plant is not enough. We also need to know what passes into the water during brewing, what happens during digestion, which compounds are absorbed and metabolised, and which biological processes they may actually influence.
This brings us to a term that sounds technical but describes something quite familiar: the food matrix. Rooibos in a teabag, a soluble extract added to a drink and finely ground rooibos stirred into porridge are not simply three different ways of achieving the same result.
What does it contain?
Which plant compounds are present in the rooibos leaf, extract or finished food?
What becomes accessible?
What dissolves during preparation and is released during digestion?
What reaches the body?
Which compounds are absorbed, transformed or excreted?
Understanding the connections
What exactly is a food matrix?
A food matrix is the way a food's constituents are combined and arranged. It includes water, plant fibres, starch, proteins and fats, for example, as well as whether a compound is dissolved, enclosed within plant cells or bound to other components.
When we brew a cup of rooibos, we steep the plant material in water and then remove it. With rooibos powder, by contrast, the material also retains plant components that do not dissolve completely in water. Adding an extract to yoghurt or a smoothie introduces proteins, acids, dietary fibre and other ingredients.
The crucial distinction: The same starting amount of a plant compound can behave differently depending on the preparation method and the surrounding food matrix. This does not automatically mean that one form is absorbed more effectively by the body.
What happens to rooibos compounds on their way into the body?
Food science distinguishes several stages. They are connected, but each answers a different question. This matters particularly when packaging or a study refers to a product as containing “lots of antioxidants”.
| Stage | What does it mean? | Rooibos example |
|---|---|---|
| Compound content | How much of a compound is present in the starting material? | Aspalathin in a green rooibos leaf or dry extract. |
| Extraction | What is released from the plant material during preparation? | Water-soluble polyphenols pass into the tea infusion. |
| Bioaccessibility | Which compounds become available for possible absorption after digestion? | Rooibos compounds released during simulated digestion. |
| Bioavailability | Which compounds or their derivatives are actually absorbed and become available within the body? | Detection of certain rooibos compounds in the blood after consumption. |
| Metabolism and excretion | How does the body transform and eliminate absorbed compounds? | Metabolites of aspalathin detected in urine. |
| Bioactivity | Which biological processes can compounds interact with under particular conditions? | Studies involving cells, microorganisms or human participants. |
Compounds can also come into contact with the intestinal lining and microorganisms in the gut itself. They do not first have to appear in large quantities in the bloodstream. Whether such contact produces a meaningful effect in humans, however, is a separate research question.
How do rooibos tea, extracts and powder differ?
The form of a product helps determine which components are actually consumed. A conventional rooibos infusion mainly contains water-soluble constituents. With finely ground plant material, a larger proportion of the original plant can remain part of the food.
| Form | What does it contain? | What matters? |
|---|---|---|
| Traditional tea infusion | Water-soluble constituents; the leaves and shoots are normally removed. | Amount used, water temperature, brewing time and cut grade. |
| Cold infusion / cold brew | Constituents extracted from the plant material, but under different extraction conditions. | Temperature, steeping time and the particular rooibos used. |
| Concentrated infusion | Water-soluble compounds in a stronger preparation. | A higher concentration per millilitre tells us nothing on its own about the proportion absorbed. |
| HWS / CWS – soluble extracts | Concentrated constituents previously extracted from rooibos. | HWS/CWS indicate intended solubility in hot or cold water, not bioavailability. |
| Finely ground rooibos powder | Finely milled plant material, including components that are not fully water-soluble. | Particle size, distribution through the food and subsequent digestion. |
| Rooibos in yoghurt, a smoothie or porridge | Rooibos constituents alongside other ingredients. | Proteins, starch, fibre, acidity and processing, among other factors. |
A common misconception: An extract is not simply “more tea”, and a powder is not the same as a water-soluble extract. Nor does the product name tell us what proportion of a particular polyphenol reaches the body.
Why does the way rooibos is prepared already make a difference?
Brewing extracts only those compounds that leave the plant material under the particular conditions and remain in the drink. Hotter water, longer steeping or a finer cut can change the composition of an infusion. The effect is not the same for every compound, however, and steeping for longer does not necessarily produce a proportionate increase in content.
A concentrated tea can contain more dissolved constituents per cup than a weaker infusion. That does not tell us whether those compounds will remain stable during storage or be absorbed later.
This also illustrates the distinction between chemical analysis of the compounds in a product and a bioavailability study: the former can measure what is present in the drink; the latter follows what happens to compounds after consumption.
Does combining rooibos with yoghurt, milk or porridge change anything?
Such combinations can alter how plant compounds behave. A rooibos extract in water is in a different environment from the same extract in protein-rich yoghurt or warm porridge.
Proteins can interact with polyphenols, and these interactions may change again during digestion. Starch and dietary fibre influence the structure of a food and may therefore affect how individual constituents are released. Acidity, temperature and storage time can also matter.
These relationships are known from wider food and polyphenol research. They do not, however, allow us to make a firm claim about increased or reduced absorption from a particular rooibos yoghurt or porridge recipe. That specific combination would need to be studied.
Does milk make the antioxidants in rooibos ineffective?
There is no basis for such a sweeping claim. Research on other types of tea shows that interactions between milk constituents and polyphenols can have different outcomes depending on the substance, drink and measurement method. Those findings cannot simply be transferred to aspalathin in rooibos.
For consumers, this means that choosing rooibos plain, with milk or in porridge is primarily a matter of taste and intended use. Claims of improved or reduced bioavailability require appropriate measurements.
Further reading: Günal-Köroğlu et al. (2023): Protein–polyphenol interactions in food matrices; Review of milk addition and antioxidant measurements in tea (not specific to rooibos).
Research & sources
What has research actually found after people drink green rooibos?
Certain rooibos compounds and their metabolites can be detected in humans – though not in the same forms or quantities as those originally consumed. A study by Breiter and colleagues (2011) illustrates this.
In a crossover study, twelve healthy men consumed different green rooibos preparations, including a tea infusion and an isolated fraction of plant compounds. The researchers then analysed blood and urine samples. They identified several metabolites of aspalathin and nothofagin in urine, particularly methylated aspalathin. Only trace amounts of unchanged rooibos flavonoids were detected in the blood.
The comparison between preparations is particularly interesting: despite similar total flavonoid intakes, the quantities measured in the blood differed. The study therefore suggests that the formulation can matter, without establishing which individual component was responsible.
What does this tell us? The aspalathin content of a drink is not the same as its systemic bioavailability. The detected metabolites also show that the body processes absorbed rooibos compounds. This finding alone does not establish any specific health benefit.
In this study, the antioxidant capacity of blood plasma measured using the ORAC method did not increase significantly either. That is a finding for this particular measurement under the conditions studied – neither proof of a health benefit nor a comprehensive verdict on every possible biological process.
What happens to aspalathin before we even drink it?
The composition of a finished food does not necessarily remain unchanged. Researchers have investigated how sensitive aspalathin is to conditions in drinks and powders, particularly those containing green rooibos extracts.
de Beer and colleagues (2012) compared rooibos iced-tea formulations containing different extracts and ingredients during storage. The formulation and acidity, among other factors, influenced the stability of the flavonoids studied. Further investigations of green rooibos iced-tea powders found substantial effects of heat, moisture uptake and packaging.
This highlights an important distinction: a manufacturer may measure the content of a plant compound immediately after production. Whether the same amount remains until the product is consumed is another question. That is why formulation, packaging and storage also form part of any examination of the food matrix.
Why this does not justify a general rule about adding lemon juice: Acids can affect the stability of individual rooibos compounds, but results vary depending on the extract and formulation. Neither these storage experiments nor human studies establish that “simply adding lemon helps the body absorb more aspalathin”.
Sources: de Beer et al. (2012): Aspalathin stability in ready-to-drink rooibos iced tea; de Beer et al. (2021): Storage stability of green rooibos iced-tea powder.
Must plant compounds enter the bloodstream to be of interest to researchers?
Not necessarily. Compounds from rooibos may first come into direct contact with the intestinal surface and the microorganisms living there. Researchers therefore also investigate interactions within the gut, regardless of whether large amounts of unchanged aspalathin appear in the blood.
For example, studies have examined responses to rooibos extracts in intestinal tissue from zebrafish models and in selected microbial cultures. These are interesting lines of investigation, but they are not clinical evidence that rooibos tea improves gut health in humans.
The food matrix can therefore influence both the release of compounds during digestion and their contact with the digestive tract. Appropriate studies are needed to establish whether this leads to any meaningful health effect.
How can researchers study what happens to rooibos during digestion?
Standardised laboratory methods are available for this purpose. The international research network INFOGEST developed a model that reproduces important stages of digestion in the mouth, stomach and small intestine under defined conditions.
For example, this model could be used to study how a particular rooibos extract changes during simulated digestion when mixed with water, yoghurt or porridge. The released compounds could then be measured using chemical analytical methods. Such a comparison would need to account for the initial quantities of the compounds examined and the individual formulations.
An INFOGEST experiment does not automatically measure bioavailability in humans. It initially helps researchers examine changes and bioaccessibility under controlled conditions. Suitable cell, animal or human studies are additionally required to investigate actual absorption.
Source: Brodkorb et al. (2019), Nature Protocols: INFOGEST 2.0.
What does the food matrix mean for how we understand rooibos?
Rooibos can be consumed as a conventional tea, a concentrated infusion, a soluble extract or finely ground plant material. Depending on the product form and added ingredients, different constituents enter the finished food, change during preparation and become accessible to differing degrees during digestion.
More aspalathin in the starting material, more dissolved polyphenols in the drink and greater absorption by the body are three different claims. Even confirmed absorption does not in itself establish a particular health benefit.
The fascinating point is that the rooibos plant is only the starting point. Its journey through harvesting, processing, formulation, preparation and digestion reveals the questions that science still needs to answer.
Scientific sources
- Breiter et al. (2011), Food Chemistry – human study involving twelve participants that compared different green rooibos formulations and identified metabolites.
- Brodkorb et al. (2019), Nature Protocols – standardised INFOGEST model for simulated digestion.
- Günal-Köroğlu et al. (2023), Food Research International – review of protein–polyphenol interactions in food matrices.
- Review (2017): Milk and tea – mixed findings for antioxidant measurements; not a rooibos-specific investigation.
- de Beer et al. (2012), Journal of the Science of Food and Agriculture – stability of aspalathin in ready-to-drink rooibos beverages.
- de Beer et al. (2021), Molecules – stability and storage of green rooibos iced-tea powder.