September 13, 2016
Tea has hundreds of individual components, with many of them still unexplored and little being known about many of the remainder. Universally valid statements about the ingredients of tea are therefor quite difficult to make. They are subject to a long range of reservations. This particularly applies to alleged health effects of individual active substances. Whatever is evident in vitro, might not work the same way under reality conditions. Not only the large number of active substances in tea, but also their mutual interaction on different levels – in the tea leaf, in the infusion and in the human body – bestow a high degree of complexity on the topic.
In principle, we distinguish between volatile and solid plant compounds and between primary and secondary plant compounds. Volatile plant compounds are essential oils, whose presence becomes evident in both the dry tea leave and the infusion’s fragrance and aroma. The tea plant contains estimated 360 to 400 such essential oils.
1. Ingredients of Tea – Primary Plant Coupounds
As primary plant compounds we refer to those materials that are directly involved in the plant’s energy metabolism and cell construction. These are different types of carbons such as sugars, carbohydrates, fats, celluloses, mineral compunds and vitamins. For us humans, these substances serve as energy and nutrient suppliers.
The carbohydrates, mineral compounds and vitamins contained in the tea infusion are insignificant for the human nutrition, measured at our daily requirements. Exceptions are potassium and Vitamin C, which have been found in individual teas in adequate concentrations. As for the carbohydrates contained in tea, if we’d take in nothing but tea, we’d soon starve to death.
2. Ingredients of Tea – Secondary Plant Compounds
Because of their broad spectrum of flavor and health effects of much greater interest for us are the secondary plant compounds contained in tea. Secondary plant compounds are for example dyes and aroma stuffs whose exact function in the plant is widely unexplored. Recent insights show that these functions might mainly be about the plant’s interaction with ist environment. Examples for this would be enticement and defense mechanisms.
Tea contains several hundred individual secondary plant compounds, and more are being discovered on a regular basis. Only little is known about the individual substances‘ effects on the human being. Because of their suspected health effects, especially the Polyphenols – and among them most notably the catechins – have come into recent focus. We do know, though, that (L-) Theanin, the amino acid with the highest concentration in tea, has significant effects on a tea’s taste. And the caffeine, of course, owes its comparably comprehensive scientific exploration to its known stimulating effects.
3. Ingredients of Tea – Solids Extraction in the Tea Infusion and Bioavailability of Active Substances
Ca. 30% of active substances contained in tea are solved in the infusion. This is quite a high value, compared to many other plants that we need to eat in order to take in their active substances in significant amounts. Beside this, the active substances in the tea infusion are particularly well bioavailable for the human organism. For some active substances, their bioavailability is even higher than if we’d eat the tea leaves. However, there are also active substances contained in tea, for which the opposite applies. They show better bioavailibilty when eaten.
The above diagram shows the typical course of extraction of active substances in the tea infusion at the example of the polyphenols. For the corresponding experiment, a green tea and a black tea were infused in parallel at 100°C water temperature. So, the obtained values will probably not be applicable to your common cup of green tea at home. What becomes obvious, though, is that at least half the polyphenols are already extracted during the first 2 minutes. Likewise, it becomes obvious that after a 2 min infusion, ensuing infusions – whatever taste they still might bring – will inevitably show lower amounts of active ingredients.
Based on these insights, Matcha tea quasi offers the “best oft wo worlds”. Matcha tea is infused with hot water on the one hand. On the other hand, the whole leaf is taken in as fine powder with the infusion. Matcha drinkers thereby get to make use of all ingredients. Those with better bioavalibilty when infused and those with better bioavailability when eaten. Matcha tea therefor sticks out in some areas, especially with vitamins and mineral compounds, where the „normal“ tea rather draws a blank. All active substances are taken in with the Matcha and are optimally bioavailable.
4. Ingredients of Tea – State of Scientific Knowledge
The scientifically best-explored teas – or better: tea categories – are green tea and black tea. The latter owes the high level of attention awarded to it its proportional dominance on the consumer market (71%). Green tea, on the other hand, has mainly come into public focus due to its alleged health effects.
However, due to the complexity of the composition of ingredients in tea and their mutual interaction under individual cultivation, picking, processing and preparation conditions, the scientific state of knowledge leaves huge gaps even in these two areas. All too often, these gaps are filled with speculative contents. This especially applies to the innumerous claims about potential health effects of specific teas, for example for promotional purposes.
5. Ingredients of Tea – Influence Factors for Active Substances Contents in Tea
The factors determining the presence and concentration of individual active substances in the tea leaf are located on four main levels of influence:
5.1. The Tea Plant itself
On the level of the tea plant itself, the content of ingredients and active substances varies from variety to variety and/or from cultivar to cultivar. In addition, the composition and concentration of active substances in the tea plant depends of each location’s specific cultivation and environment conditions.
5.2. The Picking
The second elementary factor are the picking conditions. Which parts of the plant are picked? The concentration of active substances increases with the picking standard. Accordingly, we find the highest concentrations in the best picking standard, i. e. in the bud and youngest leaves. When are the leaves picked? Also the picking season and exact time influence the picked tea leaves’ active substances content. As a rule of thumb, concentration levels will peak with the first picking in spring. After that, they will continuously drop across summer. Autumn then promotes some special activities in the plant, once again creating an active substances profile of its own. The autumn pickings of specific varieties – though strongly deviating from the same plant’s spring picking’s flavor profile – are therefore even considered as particularly tasty.
5.3. The Processing
In processing, the tea leaves are exposed to high temperatures as well as in particular oxidation processes. Further, their water content is extracted. All these process influence the composition and the content of active ingredients in the ready processed dry tea leaf. Consequently, teas of the different processing categories – black tea, green tea, white tea, Oolong tea, Pu Erh tea, yellow tea – will show different active ingredients profiles. Accordingly, differences in the active substances contents between Japanese Green Teas and Chinese Green Teas can be explained with the principle difference between steam fixation and roast fixation.
5.4. The Preparation
Besides the concentration of active substances in the ready processed tea leaf, the conditions of preparation are crucial role for the contents in the resulting tea beverage. The amount of extracted solids in the infusion, and hence the content of active ingredients in the tea, depends on a range of factors, the so-called “extraction conditions”:
- Tea / water ratio: of course, the more tea in the water, the higher the concentration of active ingredients in the infusion.
- Hardness of the used water: as a rule of thumb applies “the softer, the better”.
- Infusion temperature: as a rule of thumb applies “the hotter, the more”, whereas this applies to the individual substances groups in varying degree. The recommended infusion temperature for green tea is therefore at 70°C only. With higher temperatures, more polyphenols are extracted, so the tea gets more bitter.
- Infusion period: as a rule of thumb applies “the longer, the more”.
6. Ingredients of Tea – Generalizability of Measured Values
Because of the large number of influence factors, drawing conclusions from specific tea samples on other teas is very problematic. The obtained results are ultimately only valid for the measured sample. Tea leaves from the same bush can show significantly different results only weeks later. Another cultivar will show different results. The same cultivar in another place will show different results.
And if our analysis targets the processed tea leaf instead of the freshly picked one, then results will only apply for that processing type. This means the same tea leaves will show different ingredient contents if processed as a green tea vs. processed as a black tea. Or as a lightly oxidized Oolong tea… or as a strongly oxidized Oolong tea… or… or… or… Thus, published analysis values – whether averages or based on a specific tea – are suitable for general illustration purposes only. Conclusions on the tea that you might just have in your cup have only very limited validity.
Ingredients of Tea – Ingredients of the Green Tea Leaf
The following table shows averaged figures for the composition of ingredients in the green tea leaf:
When studying the table, it becomes obvious that the primary plant compounds in the tea leaf are mainly rather “trivial substances”, such as carbohydrates, sugars, fats and proteins, which can just as well – or even better – take in through other foods. Ingredients that are of greater interest for us because of their special properties – mostly secondary plant compounds – are referred to as “active ingredients”.
8. Ingredients of Tea – Active Ingredient Groups in Tea
Let us now throw a closer look at the individual active substances groups represented in tea:
The main category of polyphenols is chemically defined as compounds with more than 2 phenol groups at the aromatic ring. It consists of a whole range of subgroups. Polyphenols represented in tea are the:
- Flavanols – ca. 70% of them catechinse, in partcular:
- Epicatechingallat EPG,
- Epigallocatechin EGC,
- Catechin C,
- Epicatechin EC, and
- Epigallocatechingallat EGCG
AND, in black tea, the
- Theaflavins and
The polyphenols are considered the “bitter agents” in tea. This means the more of them is contained in the infusion, the more bitter the tea will taste. In regard to possible health effects, they have entered the focus of exploration mainly because of their alleged antioxidant properties.
Antioxidants eliminate free radicals, this way preventing the forming of cancer cells. The polyphenols in tea are said to possess particularly strong antioxidant properties. This applies in particular to the catechins and of these especially to the EGCG. However, to which extent exactly drinking tea now really prevents or counteracts cancer, in which dosage or frequency of consumtion could not yet be definitely established. Antioxidant properties are also attributed to the Theaflavins contained in black tea (also in Oolong tea, Pu Erh tea).
In addition, both the catechins and the flavonols allegedly have cardioprotective effects. The catechins, again especailly the EGCG, are also said to prevent caries.
8.2. Amino Acids
The most important and with a ratio of 70% the strongest presence among the amino acids in tea is L-Theanin. As a “sweet agent”, its content has great influence on a tea’s taste. However, Theanine is even better known for its proven interaction with another active ingredient of tea, the caffeine.
Theanine blocks our body’s caffeine receptors. The more theanine is contained in the infusion, the more the effects of the caffeine are delayed. In the infusion, caffeine is mainly extracted during the first 2 minutes. Theanine, however, will still be extracted in greater amounts beyond that time. Consequently, the theanine content in in the infusion will increase compared to the caffeine content beyond 2 minutes. This is why tea is perceived as less stimulating – or even wrongly as “calming” – beyond 2 minutes infusion time.
With exposure to sunlight, amino acids are transformed to catechins. Japanese “shaded teas” (Kabusecha Teas oder Gyokuro Teas, also: Matcha Tea) therefore show a particularly high content in amino acids. However, their average content in catechins will be lower accordingly.
8.3. Purine Alkaloids (Xanthins), in particular Caffeine
In fact, the “theine“, how the caffeine in tea once used to be called, is chemically identical with the caffeine in coffee. The classic delimitation of the caffeine in tea to that in coffee goes back to perceived difference in effect. This, however, is based on the above described special interaction of caffeine in tea with the amino acid theanine as well as that with polyphenols.
In average, Tea contains about half the amount of caffeine contained in coffee. However, the caffeine content in different teas varies within a very broad range. The spectrum reaches from teas, whose caffeine content can well keep up with hat of coffee, to the so-called “evening or baby teas” that contain nearly no caffeine at all.
In average, a cup of black tea (125ml) contains about 20 to 50 mg caffeine. The caffeine content in a cup of coffee of the same size reaches values of 50-130 mg. Other purine alkaloids (xanthins) contained in tea are theobromine and theophylline.
8.4. Mineral compounds
Contained in tea and extracted in the infusion in amounts that are significant for us are basically only potassium und fluoride. In minor concentrations, Fluoride contributes to the prevention of caries. In greater amounts, it becomes toxic Other mineral compounds in tea are calcium, potassium copper, zinc and nickel. However, their concentration in the tea infusion is so low that they don’t significantly contribute to the human daily requirement. An exception at this is Matcha tea. When drinking Matcha tea, all active substances contained in the green tea leaf are taken in.
For the vitamins contained in tea applies basically the same than to minerals. There are quite some vitamins contained in the green tea leaf, mostly the vitamins A, B and C. However, only vitamin C is extracted in the infusion in amounts that are significant for the human nutrition. Matcha tea, which is considered comparably rich in vitamins, is an exception also here.
9. Ingredients of Black Tea
The processing of the green tea leaf to black tea doesn’t remain without effects on the composition and content of active ingredients in tea. This applies in particular to the oxidation process involved in black tea processing. So, the polyphenol content in black tea is generally lower than in green tea. Established is especially the conversion of part of the catechins contained in the green tea leaf to theaflavins and thearubigins. Both substances are – among other functions – responsible for the dark red color of black tea. The catechin content of green tea is therefore generally higher than in black tea. Other polyphenols are subject to similar transformation processes with the processing of black tea from green tea leaves, though to a lesser extent.
Further, in the course of the oxidation process, fats and carotinoids are transformed into aromatic substances. chlorophyll degenerates, green becomes black. Black tea shows higher concentrations in fluoride, compared to green tea.
10. Ingredients of Oolong Tea
With the processing of Oolong tea, the tea leaves are principally subjected to the same type of oxidation as when processing black. The composition of an Oolong tea’s active ingredients therefore reflects that of black and/or green tea in accordance with the applied degree oxidation. Just like with black tea processing, catechins are transformed to theaflavins and thearubigins when processing Oolong tea.
11. Ingredients of Pu Erh Tea
The oxidation type involved in the processing of Pu Erh Tea is that of a fermentation. It differs in principle from the oxidation types occurring in black tea or Oolong tea processing. The latter consist in reactions of the leaf enzymes with external oxygen. The fermentation process of Pu Erh Tea, on the other hand is defined by enzymatical reactions within the tea leaf. However, there are also processes involved that are comparable to black tea processing. For example, the presence of theaflavins and thearubigins is also evident in Pu Erh tea.
12. Ingredients of White Tea and Yellow Tea
The oxidation processes involved in white tea and yellow tea processing are also partly deviant from those occurring in black tea processing. This is responsible for these teas’ individual active ingredients profile.