Tell me more about tea!

Exploring some research into the antioxidant activities of different teas.

As you probably know very well, kombucha is made from a base of sugary tea.

In the articles I’ve already covered on this site we’ve discovered that the number and strength of antioxidants in kombucha is greater than what is found in the normal tea, and we also know that green tea kombucha has a higher level of antioxidant activity than black tea kombucha.

What I haven’t looked into on this website yet are any papers about the antioxidant activities of different types of tea.

There’s quite a bit of research done on this, so it was difficult to find a single study that would give a good overview of the current understanding, and there seem to be several factors involved in antioxidant level – it’s not as simple as saying “green tea is high, black tea is low.” Those things are generally true, but it’s possible for a high-quality, whole-leaf black tea that has been carefully handled to have a higher antioxidant level than a low-quality, green, tea-bag tea made with broken up tea leaf dust and kept in wildly fluctuating temperatures. I’ll try to cover some of the broader findings about antioxidants in tea that are from outside this paper once we get down to the “So What?” section.

I chose this particular paper because it was published relatively recently and also because it included roasted teas – a type of tea that I had not heard of, and was curious about.

Antioxidants

Because this research paper is all about antioxidants, lets do a quick and dirty recap of antioxidants first.

This infographic originally appeared in my article “Is Kombucha Healthy?” Click on the image to read that article.

I cover this subject pretty well in this article “Is Kombucha healthy?” But in short, we need antioxidants to help protect us from Reactive Oxygen Species. Reactive Oxygen Species (also known as free radicals) can damage molecules in your body. This damage is a factor in the aging process, and can contribute to cardiovascular damage and to various types of cancer.

The antioxidants known as polyphenols are found in plant-based foods such as berries and tea, and are particularly effective natural antioxidants.

In tea, the type of antioxidant, the amount, and its effectiveness all depend on which type of tea, how it is grown, and perhaps most importantly, how it is processed.

So let’s begin there, with tea types and processing, before getting into the research from this paper.

Tea types and processing

Now, I have to admit that I’m a total tea ignoramus. I really prefer to drink coffee if I’m having a hot drink, and here in New Zealand – which is a British colony – the only tea that is widely drunk here is dreadful generic black teabag tea. This tea is locally referred to as “gumboot tea”: a joke about suspecting that the teabags are filled with what is poured out of the workers’ gumboots at the end of the day.

A cup of “gumboot tea”. Mmmm. Appetizing.

The tea situation in New Zealand is not nearly as dire as it was when I was a child, and a huge variety of teas are now available, especially through specialty tea stores where great care is taken over tea origin and processing and very careful blending of teas to get the desired effect. But I myself haven’t got a clue.

So come with me as I explain my new-found knowledge about tea types and processing! Most of what I’m about to explain I gleaned from the excellent Tea Guardian website.

What I’ve come to discover is that there is no universally accepted way to categorize tea, and every region of the world has what they think of as ‘normal’ tea, with various sub-types and variations on normal, and then have categories for the ‘other’ teas – which they drink only rarely, or not at all.

Western tea

A silver English ‘tea service’ set

For instance, in the West, ‘normal’ tea is what we call black tea (usually referred to as ‘red’ tea in the East because that’s the color of the liquid). We have different sub-types and flavors of Black tea like English Breakfast, Orange Pekoe, and Lady Gray and Earl Gray for instance. Then we have the types that we don’t traditionally drink – “Green,” (any type of tea that is processed when the leaves are freshly picked) and maybe “Oolong” if we’re fancy and knowledgeable, although we might think that Oolong is a variant of black teas.

Chinese tea

In China, in contrast, ‘normal’ tea is Green tea, and exactly which Green tea will depend on where you are in China. Chinese Green tea is commonly processed by toasting or roasting the leaves shortly after they are picked, and they (in general) seem to dislike the seaweedy flavor that steam-processing can produce. They also drink Oolong and Pu-er teas, which have the leaves naturally fermenting and oxidising over a matter of weeks before processing and produce a dark tea. European-style Black tea is not commonly drunk at all, and is considered to be vastly inferior to their traditional brews. The manufacture of black tea was only invented after Britain developed an insatiable appetite for a weak type of Oolong tea, and a fast industrial process was needed that could mimic Oolong well enough to satisfy the large (and fairly undiscriminating) British market.

japanese tea

And then in Japan, which is where this research was done, the story is different again. Green tea is the normal tea, as in China, but a very different type of Green tea. The Japanese prefer their Green tea to be processed by steaming the leaves shortly after picking them. They also drink Oolong tea, and are familiar with European black tea (although they don’t drink it), and also have a tea which they call Hōjicha. Hōjicha is a green tea that has been processed by roasting in a porcelain pot over a charcoal fire. In this it is closer in character to the ‘normal’ Chinese green tea, which is traditionally hand-toasted in a wok.

Tea in Morocco

There are other tea stories and preferences in Korea, the Indian subcontinent, North Africa, and everywhere else too!

So. In addition to these broad categories of ‘green’ and ‘black’ turning out to not be very descriptive or useful, individual types of tea can be categorized based on its processing style, its region of origin, the time of year it is harvested, the part of the bush that the leaf is plucked from, whether it is just leaves that are plucked or if there are buds as well, whether the bush is grown in the shade or the sun, the exact cultivar of bush…

In short, there is no universally agreed upon way to group different teas together, and there are thousands of individual teas. It is likely that each of these variations will produce a different profile of polyphenols that are present, just as they produce a different flavor. And then of course, there’s the way that the handling and storage conditions of the tea will affect its antioxidants.

Investigating antioxidant levels in tea is not at all as straightforward as I thought it would be!

In general, though, the more oxidised a leaf becomes during processing, the darker it becomes. And, as we will see in this research paper, the more oxidised the leaf, the lower its antioxidant powers.

In general, though, the more oxidised a leaf becomes during processing, the darker it becomes. And, as we will see in this research paper, the more oxidised the leaf, the lower its antioxidant powers.

So, with that general overview of the confusing world of tea types, lets have a closer look at this research paper.

The research paper

Comparison of the antioxidant activity of roasted tea with green oolong, and black teas. Satoh et al.; (2005); International Journal of Food Sciences and Nutrition, 56(8): 551 – 559

As I’ve said above, this research group is based in Japan, which means that their ‘normal’ tea is steam-processed green tea, and their ‘other’ teas are roast-processed green tea, oolong tea, and European-style black tea.

Also, do forgive me, but the full text of this article is behind a paywall, and the text and figures are subject to copyright so I can neither link you to them nor reproduce them here. I’ll summarize as best as I can.

What they already knew:

Research had already been done into antioxidant levels in green, oolong and black teas, but no research had been done on the Japanese roasted tea Hōjicha.

The antioxidant content and properties of each tea type depend on how oxidated the tea leaves are during their processing. (see this research paper)

What they wanted to know:

They wanted to fill in a gap in the knowledge about antioxidants in tea. They saw that research hadn’t been done on Hōjicha and they wanted to see where it fitted alongside the other types of tea.

What they did and what they found out:

The team prepared tea samples and then used them to perform a few different tests of antioxidant activity and to measure the amount of polyphenols in each tea. Antioxidant activity can be measured in a number of different ways, so they chose three tests to get a more rounded view of each tea’s antioxidant powers.

Preparation of tea samples

The research team prepared water extracts from each of the four tea types. A water extract is not quite the same as just brewing a pot of tea. It involved boiling the tea in water for one hour, then filtering the brew to remove any trace of tea leaves, and then freeze-drying the brew to produce a powder.

These tea extract powders are what they did their experiments on – diluting the powders to various concentrations for the different tests.

Total phenolic content
Total phenolic contents of different teas. Based on data given in the research paper

The antioxidant activity in tea mostly comes from its polyphenols, and this test measures the quantity of phenolic compounds in each tea sample.

This is because it is helpful to know just how many molecules are doing the work.

For example, if you were conducting an experiment into how loudly different school choirs sing, it’s helpful to know not just the decibel level of the noise (the antioxidant power in this case), but the number of children in each choir (the total phenolic content).

The results were: 

Green tea > Black tea > Oolong tea > Roasted tea

So Green tea (Japanese-style steam-processed) has more antioxidant molecules than Black tea, which in turn has more than Oolong tea, and Hōjicha tea has the least.

Reducing Power:
Reducing powers of different teas. Based on data in the research paper.

The reducing power of a molecule is its ability to donate an electron to another molecule. This is an important chemical step in neutralizing some types of free radical (the types with not enough electrons to be stable).

In this study they measured the ability of the tea extracts to donate electrons to ferric irons (which results in a color change that can be measured).

The results:

green tea > roasted tea > oolong tea > black tea

Given that the roasted tea has the lowest amount of total polyphenols, but is the second highest reducing activity, it would seem that, for some reason, Hoicha tea is punching above its weight when we use this measurement of antioxidant ability. To continue our children’s choir analogy, when we use these particular headphones to measure how loud they are singing, the Hojicha choir is singing the second-loudest, despite having the smallest number of children in it.

DPPH-scavenging
DPPH scavenging of different teas. Based on data in the research paper.

Another way to measure antioxidant activity is to see how well the tea extracts ‘mop up’ the DPPH free-radical. This test is widely used to measure antioxidant activity of foods and plant extracts.

Results:

Green tea > Roasted tea > Oolong tea > Black tea

These results are the same as the previous test, and similar conclusions can be drawn.

Erythrocyte hemolysis
Inhibition of erythrocyte hemolysis by different teas. Based on data from research paper.

One of the things that happen to cells when they get oxidised is that fatty acids in their membranes break down and the cells can break open. When a blood cell breaks open it is called hemolysis, and the particular blood cells they were looking at are called erythrocytes, hence ‘erythrocyte hemolysis’.

In this test they added the tea extracts to some blood cells taken from a horse and then added a known free radical (AAPH) and measured how many of the blood cells broke open.

They found that all of the extracts helped prevent the blood cells from being broken open by the AAPH. Green tea was the most effective, with the extracts from the other three teas being equally effective as each other, and only slightly less effective than the green tea.

So What?

So what does this mean? What did they conclude?

As far as this research paper is concerned, the researchers were happy to conclude that Hōjicha tea has definite antioxidant properties, and can inhibit oxidative damage to lipids in cellular membranes.

And what does this mean for us, as home kombucha brewers?

What I found interesting was that roasted tea had such a different antioxidant profile to Japanese green tea.

Remember that in this study, ‘green tea’ means steam-processed green tea, in contrast to standard Chinese green tea which is actually dry-processed (traditionally, toasted by hand in a wok).

It makes me wonder which ‘green tea’ is being used in other studies into antioxidant properties of tea, and into studies of kombucha, too.

I now wish that every study of tea and kombucha used a named specific variety of tea, sourced from an identified plantation. The data hound in me is dismayed that the European category of ‘green tea’ is too waffly and not at all informative.

I also note that on the Tea Guardian website that there’s a great discussion of other factors that effect the antioxidant properties of your tea (Start here, and then read this one, then explore all the articles under the Tea Health section – fascinating stuff). There’s the part of the plant that it is picked from, the age of the leaf, and of course the storage conditions of the tea once packed and shipped.

Some of these pure, whole-leaf, carefully handled green teas have very high levels of antioxidants in them indeed, such as Matcha tea.

And of course we know that starting with a base tea and then using it to brew kombucha results in an increase in the type and effectiveness of the antioxidants in the brew.

My take?

My take on it? If you go to the trouble to source high grade, organic, fair-trade pure-origin tea, then drink it as tea. It seems like a sacrilege to turn it into kombucha – like taking the finest of red wines and making a pot of mulled wine with it.

There’s also the slight chance that you’ll overload your system with too many antioxidants. It’s a long shot, but there is such a thing as too much of a good thing (as evidenced by this poor woman who poisoned herself by drinking too much Matcha tea a couple of years ago).

I’ve really enjoyed my journey into the amazing world of tea origins and varieties. The next time in a cafe that stocks real tea I’m going to branch out from my usual espresso order and try some properly brewed and carefully blended real tea!

Gorgeous tea leaves ready to brew.

Author: stacey

Stacey lives and works in the South Island of New Zealand with her husband, their 4 children, 4 hens, and a rabbit that they secretly think must have watched Monty Python's Holy Grail movie.

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