Tuesday, March 10, 2009

Vitamin C Protects Green Tea Catechins from Degradation

Ascorbic Acid Protects Green Tea Catechins from Degradation
Lemon juice might not have enough vitamin C to make a difference. (Photo by ^Vanessa^)

The main health benefits of green tea come from its catechin content. Catechins belong to the flavonoid family and are the most abundant polyphenols of green tea. The main catechin of green tea is epigallocatechin gallate (EGCG), which also has more positive health data behind it than the other catechins, though other catechins seem to be useful as well.

While catechins are not well absorbed by the human body, drinking a few cups of green or black tea will nonetheless significantly increase antioxidant levels in plasma. Still, finding ways to improve the bioavailability of catechins is a worthwhile effort, especially if you want to get all the health benefits but don't want to drink ten cups per day or take supplements.

It will also give us an idea of whether adding green tea catechins to various products will actually do anything. For example, you've probably seen or heard that even Coca-Cola has now jumped on the bandwagon and added green tea extract to Coke to make it seem healthier. But if the catechins will just degrade, what's the use?

Ascorbic vs. citric acid in green tea

Chen et al. compared the effects of citric acid and ascorbid acid (another name for vitamin C) on the stability of green tea catechins. They dissolved catechins in a sodium phosphate buffer and then added either citric acid or ascorbid acid to see how they affected the degradation of the catechins.

After two hours, half of the catechins had degraded. Adding citric acid to the buffer didn't protect them from being degraded in any significant way. However, ascorbic acid improved the stability of the catechins for up to 20 hours.

The pH of the control sample (catechins in sodium phosphate buffer) was 7.42, while the samples containing citric acid or ascorbid acid were 7.28 and and 7.38, respectively. Thus, the acidity of the samples increased only slightly as a result of adding citric acid or ascorbic acid, and since the increase was smaller from ascorbic acid than citric acid, the stabilizing effect was not due to a change in pH.


Vitamin C and degradation of green tea catechins
The protection from degradation increased with dosage. When 0.005 mg/mL of vitamin C was used, there was no effect. With 0.05 mg/mL there was a slight effect. Increasing the dose to 0.1-0.2 mg/mL improved the stability further, with 0.2 mg/mL being significantly more effective than 0.1 mg/mL.

Green tea and vitamin C: Practical applications

So what does all this mean in practice? First, we know that the solution the authors used contained 0.5 mg of green tea catechins per mL. An average cup of green tea is 2.5 dL (or 250 mL). The amount of catechins depends on several things, but if we assume a conservative estimate of 100 mg catechins per cup, we get 100 mg / 250 mL = 0.4 mg/mL of catechins, which is pretty close to what the study used.

Second, the amount of vitamin C that showed the most benefit was 0.2 mg/mL. In a 2.5 dL cup of green tea, this would translate to 50 mg of ascorbic acid. One teaspoon of pure ascorbic acid powder contains about 5 grams of ascorbic acid, so only 1/100th of a teaspoon would be needed to reach the levels used in the study.

If you don't happen to have jars of ascorbic acid powder in your kitchen cabinet, the next question is: What about lemon juice? Lemon juice only contains about 110 mg of vitamin C per cup, so squeezing lemons into your green tea is not really a viable route to reach the levels used in the study. While a slice of lemon with green tea won't affect the catechins negatively, the vitamin C content is also not enough to prevent their degradation (of course, lemon juice may have other properties that have a stabilizing effect).

All of this may not matter, however, because earlier studies have shown that the stability of catechins depends in part on the pH of the solution, with more acidic solutions having less degradation than alkaline solutions. Since green tea has a lower pH than the buffer solution used in the study and fermented tea products have less catechin degradation than unfermented tea products, perhaps green tea doesn't really need ascorbic acid.

On the other hand, once the green tea comes into contact with the intestines, it may be susceptible to degradation, since intestinal pH is neutral or slightly alkaline. Therefore, while adding ascorbic acid to green tea might not do much while in the cup, it might have a benefit after consuming it.

If you're drinking products with added green tea extract (like the Coca-Cola one), it makes sense to see if the ingredient list also contains ascorbic acid. If it doesn't, you might be not be getting the health benefits you think you are. Whether the acidity of the drink is enough to prevent catechin degradation is unclear from this study.

Conclusion

Ascorbic acid protects green tea catechins from degradation in an alkaline solution for up to 20 hours. This stabilizing effect is dose-dependent and unrelated to changes in the pH status of the solution. Citric acid did not have a similar effect.

For more information on green tea, see these posts:

How Black Pepper Increases the Bioavailability of the Healthiest Green Tea Catechin
Green Tea Extract Enhances Abdominal Fat Loss from Exercise
Peak Increase in Antioxidant Activity Occurs 20-40 Minutes after Drinking Green Tea
Caffeine and Polyphenol Contents of Green Tea, Black Tea, Oolong Tea & Pu-erh Tea



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12 kommenttia:

Alex Perrone January 27, 2010 at 3:40 PM  
This comment has been removed by the author.
Alex Perrone January 27, 2010 at 3:41 PM  

Would eating a whole orange provide the 500 mg ascorbic acid needed for a cup of green tea? Would eating an orange provide the benefit, or does the green tea have to be mixed in or dissolved along with the ascorbic acid in a solution, in this case in the tea?
[previous deleted post was same, just wanted to get email followups]

JLL January 29, 2010 at 11:27 AM  

@Alex,

One orange only has about 45 mg vitamin C, so you'd have to eat a lot of them to get 500 mg.

I would imagine that if you're drinking green tea, the ascorbic acid doesn't have to be dissolved in the tea, because the problem is then degradation in the intestines, not while in the tea cup.

Still, the authors are only speculating here -- this study was more about the degradation of catechins in products with added green tea catechins and less about maximizing the potential of green tea's health benefits.

If you just want to be healthy in general, I think drinking 2-10 cups of green tea is the simplest way to go at this point. But of course, if you're using catechins to fight cancer, for example, I'd look further into the catechins + vitamin C issue and see what other authors have found.

- JLL

Alex Perrone January 29, 2010 at 1:37 PM  

JLL, this has really been a burning question for me: does 2-10 cups per day mean fresh cups?

I use the methods for Sencha that I read online, so I brew 2-3 min for the first infusion, then almost instantly for 2 more infusions (most sites seem to recommend this). So I drink "3" cups but only one serving size of tea leaves. Is this 3 cups or really 1? I'm not asking philosophically, just with respect to the recommended advice! Because of caffeine sensitivity, I prefer not to use more than one serving.

Similarly, I'd really like to know: does one get anything out of the cups of tea from the second and third infusions, specifically additional catechins?

JLL January 29, 2010 at 2:49 PM  

@Alex,

That's a good question. I think the answer depends on which kinds of studies you're looking at.

If it's an association study in humans where they just ask people how much green tea they drink, I assume it means the number of total cups and not the number of freshly brewed cups. In Asian countries, it's customary to re-use the leaves 3-4 times, which means that when these studies mention "the people who drank 10 cups of green tea were the healthiest", it most likely doesn't mean 10 cups of water + 10 servings of tea leaves. Still, I think it's not 10 cups of water + 1 serving of tea either -- probably something like 10 cups of water + 2-3 servings of tea.

On the contrary, if it's a rodent study where they give rats or mice a certain amount of tea in their feed, and extrapolate that to humans, then 10 cups really means 10 cups.

As for your second question, that depends on how long the infusion times are and how hot the water is. If the first one is 3 minutes @ 90 degrees Celsius, then yes, the second brewing will still have catechins. If it's 20 minutes @ 90 degrees, it might not.

Also, different catechins are released at different temperatures and brewing times (see this patent claim for a more detailed description), so your first and second cups will probably have different catechin compositions. Based on this, it seems to me like the Asian way of re-using the leaves is good for health.

- JLL

Anonymous February 20, 2010 at 9:17 AM  

[quote]Alex Perrone said: Would eating a whole orange provide the 500 mg ascorbic acid needed for a cup of green tea? [/quote]
There is arithmetic error in the text:
"the amount of vitamin C that showed the most benefit was 0.2 mg/mL. In a 2.5 dL cup of green tea, this would translate to 50 (not 500!) mg of ascorbic acid".

JLL February 20, 2010 at 5:35 PM  

@Anonymous,

Thank you for pointing that out! I seem to be making a lot of this kind of mistakes. I'm glad people take the time to correct them.

Of course, this means that the answer to Alex's question is yes, an orange would contain enough vitamin C.

- JLL

angus appleseed March 22, 2010 at 4:28 PM  

When I brew green tea in a container that minimizes the liquid/air contact, the tea tastes and looks fresh, even after many hours. Do you think reducing the oxidization of the infused tea increases its antioxidant content?
Also, "the amount of vitamin C that showed the most benefit was 0.2 mg/mL": does this mean that adding more than 0.2mg of vitamin C is less beneficial?

JLL March 23, 2010 at 9:40 PM  

@angus appleseed,

Possibly it does, but I don't know for sure. Given that the pH of green tea is slightly acidic, and catechins survive well in acidic conditions, I don't think catechin degradation in green tea is a huge problem.

- JLL

Anonymous October 11, 2010 at 7:36 AM  

btw, one lemon (3 table spoons of lemon juice) contains about 55 mg of vitamin C... a cup of lemon juice is probably around 6 lemon or 330 mg of vitamin C. Seems like the conclusions on this article are all wrong-- why not take it down?

JLL October 12, 2010 at 8:41 PM  

@Anonymous,

What's wrong in the conclusions? There are many estimates of the vitamin C content of citrus fruits. There are too many variables -- ripeness, size, etc. -- to know the exact amounts. The numbers I quoted are from here:

http://www.whfoods.com/genpage.php?tname=foodspice&dbid=27

"a cup of lemon juice is probably around 6 lemon or 330 mg of vitamin C."

Right...

- JLL

Ryan January 22, 2011 at 4:05 AM  

Hey JLL,

First of all thanks for all this information. I went to that link you gave above (http://www.freepatentsonline.com/7510736.html) and I have some questions...

1st- Is the amount of all the solids (EGCG, caffeine, etc) so dependent on the amount of water it's being dispersed into? If so, wouldn't that mean that the contents would vary considerably depending on the size of the vessel brewing the green tea? Some brew in mugs and others in kettles so this matters considerably I would think?

2- I'm looking at the bottom of the study where it shows in mg/g of tea leaves that that first step reveals 66mg of caffeine whereas the 2nd step extract revealed 105mg for a total of 171mg. That seems like a lot from green tea but then it seems to be that caffeine concentration is almost entirely dependent on brewing time. There was even more caffeine in the 2nd brew so are we left to assume that the 3rd brew will contain even more? Do we have any idea just how much caffeine a gram of average green tea could potentially yield? Given this information how could it be that anyone could comfortably have any more than 3 green teas in their day without too much caffeine. Assuming one has 4 cups using the 2 step brewing method twice then that would be 342mg and possibly even more if they re-brew the same leaves a 3rd or 4th time.

3rd and final for now.. ;-) -I'm trying to imagine how the solid molecules of EGCG and EGC disperse from the tea leaf into the water and I'm confused by it. Why does something like EGC have more in the first batch and lower in the 2nd where EGCG has only around 10% in the 1st with a huge increase in the 2nd. Going back to what I was saying about the amount of water affecting the amount of solids, could it be possible that EGC and others quickly disperse in the water thus 'preventing' room for further dispersal of the EGCG molecules, hence why the EGCG only starts coming in at bigger numbers in the 2nd brew when the water is pure? I guess what I'm getting at here is... if one brewed for 20 minutes straight without separating into two 10 minute steps would roughly the same amount of nutrients be in there as doing it in 2 steps? If not, why could this be? Is it the reheating of the once-brewed tea leaves? This is all so complicated I'm astonished.

I know this is a lot of questions but I see that you're very knowledgeable on this topic and I may not have another opportunity to ask said questions and get correct answers from anyone else. =)

Thanks so much!

~Ryan

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