Goldbeater Skin Test: Identify Tannins with Quiz and Flashcards

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Questions and Answers

What is the term used to denote substances present in plant extract which react with protein of animal hide, prevent their putrefaction and convert hide and skin into leather?

Tannins

What are tannins?

Polyhydroxy phenolic compounds.

Which color are tannins typically?

Dark brown or reddish brown

What is the taste of tannins?

Puckering taste Signup and view all the answers

In what states are tannins found?

Non-crystalline Signup and view all the answers

What are tannins soluble in?

Water, alcohol, dilute alkalis, glycerols, and acetone Signup and view all the answers

What are the red colored complexes formed when flavonoid catechins are heated with acids?

Phlobaphenes Signup and view all the answers

Which plant examples fall under the category of complex tannins?

Tea, Quercus, Castanea Signup and view all the answers

What is the Gold beater’s skin test used to qualitatively detect?

Tannins Signup and view all the answers

What are the two types of tannins based on their ability to convert animal hide to leather?

True tannins and pseudo tannins Signup and view all the answers

What is the molecular weight range of true tannins?

1000-5000 Signup and view all the answers

What color reaction do tannins exhibit with iron in identification tests?

Color reaction Signup and view all the answers

What is the purpose of the Phenazone test in the identification of tannins?

The Phenazone test is used to precipitate tannins from an aqueous extract of the drug, forming bulky and colored precipitates. Signup and view all the answers

Explain the principle behind the Gold beater's skin test for tannins.

The Gold beater's skin test relies on the ability of tannins to tan or color the untanned skin. Tannins present in the solution will cause the Gold beater's skin to turn black or brown when treated with a solution of ferrous sulfate. Signup and view all the answers

What is the purpose of the Catechin test, and what is the principle behind it?

The Catechin test is used to detect the presence of catechin, a type of tannin. When catechin is heated with acid, it produces phloroglucinol, which can be detected by a matchstick test. Signup and view all the answers

How is the test for chlorogenic acid performed, and what is the expected result?

To test for chlorogenic acid, the extract containing chlorogenic acid is treated with aqueous ammonia and exposed to air. The presence of chlorogenic acid is indicated by the gradual appearance of a green color. Signup and view all the answers

What is the botanical origin and family of Hamamelis, and which part of the plant is used?

Hamamelis is obtained from the dried leaves of Hamamelis virginiana, which belongs to the family Hamamelidaceae. Signup and view all the answers

Describe the process of collecting and drying Hamamelis leaves.

Hamamelis leaves are collected throughout the summer. The drying process involves open-air drying, preferably under shade, to preserve the green color of the leaves. Signup and view all the answers

Study Notes

Tannins

The term "tannin" was first coined by Seguin in 1796 to describe substances in plant extracts that react with animal hide proteins, preventing putrefaction and converting hide and skin into leather.

Definition and Properties

Tannins are complex substances that occur as mixtures of polyphenols, which are difficult to separate and don't crystallize.
They can also be defined as polyhydroxy phenolic compounds.
Physical properties: dark brown or reddish brown color, puckering taste, non-crystalline state, and solubility in water, alcohol, dilute alkalis, glycerols, and acetone.
Chemical properties include precipitation, anti-oxidizing properties, astringency, carcinogenicity, and reaction with salts and potassium ferricyanide and ammonia.

Precipitation

Tannins can precipitate solutions of gelatin, alkaloids, glycosides, heavy metals, and proteins.

Anti-Oxidizing Properties

Tannins have anti-oxidant properties due to the accumulation of OH groups on a small nucleus.

Astringent Properties

Tannins can react with protein of mucous membrane, causing precipitation.

Carcinogenicity

Prolonged use of tannin-containing plant materials can cause cancer, such as oral and esophageal cancer from habitual use of Areca catechu.

Classification

Tannins can be classified into two types: true tannins and pseudo tannins.
True tannins are polyhydroxy phenolic compounds that convert animal hide to leather, precipitating proteins, and giving a positive Gold beater's skin test.
Pseudo tannins are phenolic compounds of plant origin that don't convert animal hide to leather but give a positive Gold beater's skin test.

Identification Tests

Color reaction: Tannins give a color reaction with iron.
Matchstick test: A pink or red color appears on a matchstick dipped in plant extract, dried, moistened with hydrochloric acid, and warmed near a flame.
Gelatin test: A 0.5-1% solution of tannin precipitates a 1% solution of gelatin containing 10% sodium chloride.
Phenazone test: Tannins are precipitated by adding a 2% solution of phenazone to a filtrate solution.
Gold beater's skin test: A black or brown color appears on Gold beater's skin when soaked in a 2% hydrochloric acid solution, washed, and transferred to a 1% solution of ferrous sulphate, indicating the presence of tannins.

Examples of Tannin-Containing Plants

Hamamelis (Botanical origin: Hamamelis virginiana, Family: Hamamelidaceae, Part used: Dried leaves)
Cinchona
Cinnamon
Tea
Quercus
Castanea

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Test your knowledge on tannin classification based on properties, examples, and classification criteria such as self condensation, hydrolysable tannins, and tanning tests.