Tannins: Chemical Properties and Uses

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Questions and Answers

What is the primary origin of the name 'tannin'?

From a Latin word for leather processing

From a botanical term describing complex polyphenols

From the French term 'tanin', referring to tanning substances. (correct)

From a Greek word describing plant extracts.

Which test is used to assess the tanning properties of a compound?

The Goldbeater's skin test (correct)

The Fehling's test

The Ninhydrin test

The Benedict's test

What is the main difference between true tannins and pseudotannins, based on the Goldbeater's skin test?

True tannins fail the goldbeater's skin test, while pseudotannins pass it.

True tannins give a positive tanning test and are mostly retained by hide powder, while pseudotannins fail to give the test and are only partially retained. (correct)

Both true tannins and pseudotannins show the same results in the goldbeater's skin test, the only difference is their molecular weights.

True tannins are not retained by hide powder, while pseudotannins are.

How are complex polyphenolics, commonly found in true tannins, formed?

By the polymerization of simple polyphenols. Signup and view all the answers

What kind of chemical reaction characterizes hydrolysable tannins?

Hydrolysis by acid, alkali, enzymes, or hot water. Signup and view all the answers

Which of the following best describes condensed tannins?

They are also known as proanthocyanins and are resistant to hydrolysis. Signup and view all the answers

What is a common example of a pseudotannin?

Gallic acid in rhubarb Signup and view all the answers

Which of the following is NOT a described medicinal use of tannins?

Antidiabetic. Signup and view all the answers

What is the primary mechanism by which tannins exhibit astringency?

By binding with carbohydrates and proteins, rendering them insoluble. Signup and view all the answers

Which statement accurately describes the prooxidant behavior of tannins?

Tannins can act as prooxidants, potentially carcinogenic at high levels Signup and view all the answers

How does the processing of green tea differ from black tea, based on their tannin content?

Black tea is rolled and exposed to air to heighten flavor, green tea's process inhibits oxidation to retain its color. Signup and view all the answers

What effect do tannins have on iron absorption in the body?

They bind specific non-heme iron, found in plant-based foods, impairing its absorption. Signup and view all the answers

Which statement is correct about the impact of proanthocyanidins on the brain?

Proanthocyanidins from blueberry act on striatum of the brain helping to keep the memory function while ageing. Signup and view all the answers

How does the consumption of cranberries aid in the prevention of urinary tract infections?

Proanthocyanidins from Cranberry have a protective effect against urinary track infections by reducing the ability of E.coli bacteria to adhere to the cells lining the urinary tract. Signup and view all the answers

Which of the following is NOT a mentioned use of witch hazel tannins?

As a weight loss supplement. Signup and view all the answers

What is the main difference between heme and non-heme iron?

Heme iron is found in animal proteins; non-heme iron is obtained from plant-based foods. Signup and view all the answers

Study Notes

Tannins

Tannins are complex organic compounds with high molecular weight.
They are derived from the French word "tanin" (tanning substances).
They combine with proteins in animal hides, preventing decomposition and turning them into leather.
Tannins are astringent due to their ability to precipitate proteins, making them resistant to enzymatic breakdown.

Sources of Tannins

Beverages: Red wine, green tea
Grains: Barley, chickpeas, beans, legumes
Fruits: Strawberry, blueberry, pomegranate, grapes, apple, jamun, guava, orange
Herbs and spices: Clove, cinnamon, cumin, catechu, vanilla, mint, basil
Nuts: Walnut, almond, cashew, apricot
Tannins are generated through the shikimic acid pathway, phenylpropanoid pathway, and flavonoid pathway.

Classification of Tannins

True Tannins: High molecular weight compounds, positive Goldbeater's skin test
- Hydrolysable Tannins: (Pyrogallol) hydrolyzed by acid, alkali, enzymes, and hot water. Produce gallic or ellagic acid.
- Condensed Tannins: (Catechol) Polymerized flavan-3-ols, resistant to hydrolysis.
- Complex Tannins: A combination of both.
Pseudo Tannins: Low molecular weight compounds, do not give a strong positive reaction to the Goldbeater's skin test.
- Includes: Gallic acid in rhubarb, catechins in catechu.

Uses of Tannins

Antioxidant: Free-radical scavengers, prevent oxidation, but at high levels can be prooxidants/carcinogens.
Antidiarrheal: Astringent, helps with heavy metal poisoning.
Treatment of burns: Contract body tissue and precipitate proteins.
Stop bleeding: Astringent use in hemorrhoids.
Anti-inflammatory
Anti-viral
Mouthwashes, eyewashes, and bowel conditions

Tannins in Berries

Proanthocyanidins in blueberries affect the striatum (memory), and Ellagitannins in strawberries reduce hippocampus aging effects on spatial orientations.
Cranberry tannins prevent urinary tract infections by inhibiting E. coli adhesion and preventing kidney stones.
Cranberries are a source of proanthocyanidins which have a protective effect against urinary tract infections.

Tannins in Herbal Teas

Tannins can inhibit the absorption of iron in plants, particularly non-heme iron.
Some herbal teas, notably higher-tannin ones, are believed to contain tannins which may inhibit iron absorption.

Green Tea vs Black Tea

Both are from Camellia sinensis plant.
Black tea leaves are rolled and exposed to air to cause oxidation (darker colour), enhancing flavours.
Green tea isn't exposed to air to prevent oxidation (lighter colour).
Black tea generally has a higher tannin level than green tea. More oxidisation means more tannins and polyphenols.

Witch Hazel (Hamamelis Virginiana)

A source of tannin used in skin care, treating bee stings and abrasions.
Used in mouthwashes, eyewashes, and some bowel conditions.

Tannin Facts

Unripe fruits contain high levels of tannins, discouraging animal consumption until the seeds mature.
Tannins are present in coffee, tea, red wine, and beer.
Tannins contribute to the colours of flowers and autumn leaves.

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Description

This quiz explores the origins, characteristics, and applications of tannins. Delve into the differences between true tannins and pseudotannins, as well as their chemical reactions and medicinal uses. Test your knowledge on these fascinating compounds and their significance in chemistry.