Date: Tue, 22 Aug 1995 15:16:53 +0000
From: jonathan treasure <jtreasure.JONNO.DEMON.CO.UK>
Subject: Re Tannins
>The use of the general term, tannins, is on the wane as I understand. The so-called tannins in tea, for instance, have been redefined as --polyphenols--, and attributed a range of medicinal benefits.
No, not really Paul,
tannins are tannins are tannins, a subclass of polyphenols. Tannins astringe. (ie combine with protein - that's why they turn animal hide into leather)
Polyphenols include tannins, coumarins, anthraquinones, napthaquinones, flavones, anthocyanadins etc etc. And the glycosides of the same. All with different effects.
Some polyphenols are more fashionable than others, and even subject to the attentions of desperado MLM ers, etc,but no-one has redfined a subset as a superset yet.
Bit like saying the term apple is on the wane, they are being called fruit nowadays.
The tannins in tea are condensed tannins, sometimes called proanthocyanidins, and because catechins are involved in their biosynthesis, they are related to flavonoid pigments (the fashionable ones). Green tea is very strong in catechin and epicatechin, whereas black tea has all trace of nice catechins roasted into nasty condensed tannins. One could go on blah blah ----- best to stick to East Asian wotsits if your pharmacognosy is as suspect as your comment suggests. At least you are an authority on that subject (since no one else is).
From: Paul Iannone <p_iannone.POP.COM>
: One could go on blah blah ----- best to stick to East Asian wotsits if your pharmacognosy is as suspect as your comment suggests. At least you are an authority on that subject (since no one else is).
A biting little comment, jonathan, that is rankly inaccurate. Just because I chose the term East-Asian Traditional Healing instead of the poorly-chosen Traditional Chinese Medicine, to represent my practice, is no reason for you to snidely rip me over it every time you can.
The source of my rather garbled comment was 'All the Tea in China.' Not that I disagree with you, since you sound definitive (and I make no claim of being a biochemist), but here is the section I was using as the basis of my comments:
Tea polyphenols, though popularly known as tannins, are not, as widely believed, the tannic acid used in leather preparation. In fact, they are not tannins at all. With some chemical and functional similarity, they became known by this name long before modern methods of chemical analysis made it possible to distinguish the two.
Here we have run into another of the name confusions that seem to haunt tea. There's more. Three-fourths of the tea polyphenols are catechins which are part of the chemical group flavanols (they do indeed have something to do with flavor, as distinct from either aroma or astringency). At least six catechins have been isolated.
We might make a summary outline like this:
Polyphenols (compounds with two or more phenolic hydroxyl groups)
Flavonols (one kind of polyphenol)
Catechins (the name for flavanols in tea)
Reports on the health benefits of these substances may use any of the three. Often no distinction is made between the terms 'catechins' and 'polyphenols,' and in many cases the two are used interchangeably.
On the previous page is found this information:
The polyphenols, about thirty altogether, account for nearly a third of the
soluble matter in the fresh tea leaf. During the fermentation process about a third (some say half) of the total amount is oxidized into more complicated oxidized products such as theaflavin. Therefore, after this process the tea contains two kinds of polyphenols, oxidized and unoxidized (natural polyphenols). The latter, released in the beverage, create the astringent, 'puckery' feeling in the mouth when you drink tea. This stimulates the salivary glands, which is why tea is a thirst quencher.
The unoxidized polyphenols provide the pungency, while the oxidized ones give the tea its color and flavor. The higher the degree of oxidation, the more color and less pungency a tea has. Green tea, which does not undergo oxidation, has more natural unoxidized polyphenols, and also more astringency. Black tea has more color but less astringency. Both oxidized and unoxidized polyphenols may be beneficial.
Now let's see what happens in the polyphenol oxidation process. At the tea factory, the freshly picked leaves sit until they have become soft and limp as a result of water evaporation. Then they are rolled to break down the membranes and bring the juices containing polyphenols in contact with the enzyme polyphenolase (polyphenol oxidase) which catalyzes the oxidation of the polyphenols by oxygen in the atmosphere. The product resulting from this process, together with other constituents, accounts for the unique flavor and rich, deeper color of black and oolong teas.
The action of the enzyme, and therefore the oxidation process, is eventually stopped through heating, but these compounds remain in the dried prepared leaves waiting for boiling water to dissolve them.
The word "tannins" is shorter than the word "polyphenols" and is therefore easier to say. And with the Earth's population rapidly swelling, we need to save our breath, so 2 syllables are better than 4??? What am I saying???
I posted something here a couple of weeks ago, I think, but it was so soundly ignored that I'm posting this, too. Maybe I have at last found a conference where I can safely post and no one will ever read anything I write. Yuck???
David Roland Strong