What are polyphenols?
Tea is a rich source of chemicals known as polyphenols. These are very strong antioxidants found in abundance in fruit and vegetables, but also in other foods such as chocolate and soy, and even in red wine or coffee.
Antioxidants are the army of bodyguards protecting our body against self-destruction caused by so-called “free radicals” which are unstable molecules in our body. Read more on antioxidants.
They can be divided into four main groups of compounds. These are:
1. Phenolic acids
The first group phenolic acids can be subdivided into four main classes: ferrulic acid, caffeic acid, condensed tannins, and hydrolysable tannins. The last two are responsible for the astringent taste of tea when brewed too strong.
Anyway, before plunging into a world of chemistry, the only thing important to know here is these phenolic acids (about one-third of the polyphenol content in our diets) are found in dietary fiber, fruits – e.g., mango fruit, blackberries, raspberries, strawberries -, vegetables and/or coffee.
A major food source of stilbenes – with resveratrol as its most important class – is red wine. Enterodiol are a class of lignans, found in flaxseed or flaxseed oil.
However, by far the most important group for us are the flavonoids.
An estimated two-thirds of the polyphenol content in our diets, thus the most abundant, are flavonoids, divided into seven main groups (again, I won’t bore you with the chemical definitions that determine these): flavones, flavonols, flavanols, flavanones, isoflavones, anthocyanins, and proanthocyanidins….
Yep, I admit, these chemical guys have not been extremely creative in coming up with new names…..
Each of these groups can be found primarily in the following major food sources:
- Flavones: sweet red pepper and celery
- Flavonols: tea, onions and apples
- Flavanols: tea, especially green tea, chocolate, cocoa
- Flavanones: oranges, citrus fruits
- Isoflavones: soybeans, soy protein-containing foods
- Anthocyanins (providing the red pigment of fruits): cherries, plums, strawberries, raspberries, blackberries, grapes, red and black currants
- Proanthocyanidins (providing the astringency of food): tea, apples, pears, grapes and red wine
Digging a little bit deeper again, we see that the major flavanols are catechins of which epigallocatechin-3-gallate (EGCG) is by far the most important one.
Black Tea or Green Tea?
Green tea is rich in phenolic acids (the tannins) and flavonoids (the catechins) where EGCG is the most abundant and the most researched due to its health effects as you can read here.
Black tea is rich in other polyphenol ingredients than green tea since they are processed differently. Read more on the differences between black tea and green tea here: black tea vs green tea.
Brannon C. Green Tea: new benefits from an old favorite? Nutrition Dimension, 2009.
Cabrera C, Artacho R, Ginemez R. Beneficial effects of green tea – a review. Journal of the American College for Nutrition 25(2): 79-99, 2006
Scalbert A, Johnson IT, Saltmarsh M. Polyphenols: antioxidants and beyond. American Journal of Clinical Nutrition 81(suppl):215S-217S, 2005.
Scalbert A and Williamson G. Dietary intake and bioavailability of polyphenols. Journal of Nutrition 130: 2073S-2085S, 2000.