Tannins

Tannin Definition

Tannin is any polyphenolic compound that forms strong complexes with proteins and other large molecules [4]. The word tannin originates from “tanning”, a leather production by soaking animal skins in plant extracts containing tannins [4]. Tannins are polyphenols that give bitter taste and mouth-drying effect to the plant foods.

Tannins Types

  • Hydrolyzable tannins are esters of gallic acid (gallotannins) or ellagic acid (ellagitannins) and sugars.
  • Non-hydrolyzable or condensed tannins or proanthocyanidins consist of flavan-3-ols. They include procyanidins, and prodelphinidins.
  • Derived tannins formed during food processing such as theaflavins and thearubigins in black tea or oolong tea.
  • Tannic acid extracted from nutgalls.
  • Oligostilbenoids
  • Reference: [4,7]

Foods High in Tannins

  • Red wine
  • Green tea, black tea, oolong tea
  • Chocolate, cocoa
  • Acorns
  • Unripe fruits: pomegranate, persimmon
  • Berries: strawberries, cranberries, blueberries
  • Apples with skin
  • Grapes, especially grape seeds and skins
  • Nuts: hazelnuts, walnuts, pecans
  • Spices: cloves, thyme, cumin, vanilla, cinnamon
  • Beans: red beans, acacia
  • Coffee
  • Beer
  • Sorghum
  • Smoked fish and meat
  • Reference: [4]

Tannins as Food Additives

Tannic acid is used as a clarifying agent or dye in fruit juices, soft drinks and alcoholic drinks.

Tannin Supplements

Various non prescription (over-the-counter) oral tannin supplements are available.

Tannins Health Benefits

There is INSUFFICIENT EVIDENCE about the effectiveness of tannins in the prevention or treatment of cancer [1] or high blood pressure [2] and hemochromatosis [3].

Tannins Safety: Side Effects, Toxicity

Side effects may include nausea, vomiting, diarrhea.

Tannins ingested in large amounts may reduce the absorption of the non-heme iron from plant sources, not iron from animal foods [5]. Tannins may reduce the absorption of certain medications.

  1. Li H et al, 2003, Review in the studies on tannins activity of cancer prevention and anticancer  PubMed
  2. Aviram M et al, 2001, Pomegranate juice consumption inhibits serum angiotensin converting enzyme activity and reduces systolic blood pressure  PubMed
  3. Kaltwasser JP et al, 1998, Clinical trial on the effect of regular tea drinking on iron accumulation in genetic haemochromatosis  PubMed
  4. Tannins: fascinating but sometimes dangerous molecules  Cornell University
  5. Iron  Linus Pauling Institute
  6. Brune M et al, 1989, Iron absorption and phenolic compounds: importance of different phenolic structures  PubMed
  7. Beecher GR, 2003, Overview of Dietary Flavonoids: Nomenclature, Occurrence and Intake  The Journal of Nutrition

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