Tannins: Hydrolysable and Non-Hydrolysable

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Questions and Answers

What are the two principal types of hydrolysable tannins?

Catechin and proanthocyanidin

Cinnamoyl and flavonoid tannins

Gallitannins and ellagitannins (correct)

Quercetin and resveratrol

Gallitannins are primarily composed of which type of acid?

Acetic acid

Tannic acid

Hexahydroxy-diphenic acid

Gallic acid (correct)

Which acid is associated with ellagitannins?

Gallic acid

Caffeic acid

Hexahydroxy-diphenic acid (correct)

Citric acid

Which of the following statements regarding hydrolysable tannins is accurate?

Both gallitannins and ellagitannins are types of hydrolysable tannins. Signup and view all the answers

What common characteristic do gallitannins and ellagitannins share?

They are hydrolysable tannins. Signup and view all the answers

What type of linkages unite phenolic acids to a glucose molecule?

Ester linkages Signup and view all the answers

Which of the following phenolic acids is specifically mentioned as being part of the structure?

Gallic acid Signup and view all the answers

Which of these compounds is formed from phenolic acids and glucose?

Tannins Signup and view all the answers

What is the structural role of glucose in the formation of tannins?

It serves as a backbone. Signup and view all the answers

Which of the following correctly describes the composition of tannins?

Several molecules of phenolic acids united to glucose. Signup and view all the answers

What distinguishes 2-non-hydrolysable tannins from hydrolysable tannins?

They are not readily hydrolysed to simpler molecules. Signup and view all the answers

Which of the following correctly describes 2-non-hydrolysable tannins?

They do not contain a sugar moiety. Signup and view all the answers

Which term is synonymous with 2-non-hydrolysable tannins?

Proanthocyanidins Signup and view all the answers

What is a property that 2-non-hydrolysable tannins do NOT exhibit?

Presence of sugar moieties Signup and view all the answers

Which of the following statements about 2-non-hydrolysable tannins is correct?

They are primarily encountered in certain plant sources. Signup and view all the answers

What is the chemical structure of gallic acid?

3,4,5-trihydroxybenzoic acid Signup and view all the answers

In what situation is gallic acid commonly used?

In cases of alkaloidal poisoning Signup and view all the answers

What occurs when gallic acid crystallizes?

It crystallizes with one molecule of water Signup and view all the answers

Which property is NOT associated with gallic acid?

Contains only two hydroxyl groups Signup and view all the answers

What type of acid is gallic acid classified as?

Hydroxycarboxylic acid Signup and view all the answers

What role do tannin solutions play in the treatment of alkaloidal poisoning?

They inactivate the alkaloid by forming insoluble tannates. Signup and view all the answers

Which statement accurately describes the structure formed when tannin interacts with alkaloids?

They create an insoluble tannate. Signup and view all the answers

In which scenario would tannin solutions be considered valuable?

In the antidotal treatment of alkaloidal poisoning. Signup and view all the answers

What is the primary mechanism through which tannin solutions treat alkaloidal poisoning?

They bind to alkaloids to form insoluble tannates. Signup and view all the answers

What type of compounds are tannins described as in their action against alkaloids?

Insoluble agents forming complexes. Signup and view all the answers

What is true regarding the presence of tannins in plant species?

Both types of tannins can be present, but one usually predominates. Signup and view all the answers

Which statement accurately describes the distribution of tannins?

Both classes of tannins are widely distributed in nature. Signup and view all the answers

In which way is the predominance of tannin types characterized in plants?

One type generally predominates in a specific plant part. Signup and view all the answers

Why might one type of tannin predominate in a particular plant part?

Different plant parts may have varying ecological functions. Signup and view all the answers

What can be inferred about plant species concerning tannin types?

Some species may contain high concentrations of one tannin type. Signup and view all the answers

Study Notes

Tannins

Tannins are complex plant substances widely distributed in many plant families.
They are commonly found in leaves, fruits, barks, and stems.
Chemically, tannins are usually mixtures of polyphenols.
They are categorized into two classes: hydrolysable and non-hydrolysable tannins.

Hydrolysable Tannins

These tannins can be broken down (hydrolyzed) by acids or enzymes like tannase.
They are formed from multiple phenolic acids (like gallic acid and hexahydroxydiphenic acid) linked to a glucose molecule.
Two main types are gallitannins (gallic acid) and ellagitannins (hexahydroxydiphenic acid).
Examples of plants containing hydrolysable tannins include rhubarb, hamamelis, cloves, chestnut, pomegranate rind, pomegranate bark, and oak bark.

Non-hydrolysable Tannins (Condensed Tannins)

Unlike hydrolysable tannins, these don't break down easily into simpler molecules.
They lack a sugar moiety and related to flavonoid pigments.
They have polymeric flavan-3-ol structures.
Treatment with acids or enzymes convert them into red insoluble compounds called phlobaphenes.
Phlobaphenes give a characteristic red color to some drugs (e.g., red cinchona bark).

Plant Sources Rich in Tannins

Barks of cinchona, oak, and cinnamon
Roots/rhizomes of krameria
Flowers of lime and hawthorn
Seeds of cocoa and areca
Fruits of grapes
Leaves of hamamelis and hawthorn
Extracts/dried juice of catechu and acacia

Tannin Properties

Form colloidal solutions in water with an acidic reaction and a puckering/sharp taste.
Precipitate gelatin and alkaloids.
Form deep red or greenish-black soluble compounds with ferric salts.
Also react with potassium ferricyanide and ammonia, forming a deep red color.
Precipitated by copper, lead, tin, and potassium dichromate.
In alkaline solutions, many of their derivatives readily absorb oxygen.
Precipitate proteins from solution and combine with them, making them resistant to protein-digesting enzymes.

Tannin Uses

Astringent action: Applied to living tissues to reduce/stop bleeding or inflammation; basis for therapeutic applications.
Tanning leather: Vegetable tanning converts animal hides to leather by affecting pliancy and toughness, also acts as a preservative.
In inks: Deeply colored compounds with iron salts are used in ink production.
Reagent in labs: Used to detect gelatin, proteins, and alkaloids.
Treatment of Poisoning: Solutions are used to deactivate alkaloids.
Medicine: Used as astringents in the gastrointestinal tract and on skin abrasions (e.g., burns)
Other preparations: Part of products for hemorrhoids, insect bites/stings, and teething.

Nutgalls

Excrecence (growth) from twigs of specific oak trees (Quercus infectoria).
Formed due to infestation by insects (Cynips tinctoria).
Main component is tannic acid (50-70%).
Additional components include gallic acid, ellagic acid, starch, and resin.
Used in tanning, dyeing, and ink production.

Tannic Acid

Usually extracted from nutgalls.
Extraction process involves mixing powdered nutgalls with a mixture of ether, alcohol, and water.
Liquid separates into layers, with aqueous layer containing gallotannin and ethereal layer containing free gallic acid.
Gallotannin is then evaporated to purify tannic acid.
Is an astringent.
Formerly used to treat burns, now mainly for minor wounds or ulcerations.
Used as a precipitant for alkaloid poisoning.

Gallic Acid

3,4,5-trihydroxybenzoic acid.
Crystallizes with one water molecule.
Found in nutgalls.
Can be prepared from tannic acid by hydrolysis.
Used by ostomates for odor control (with bismuth subgallate).

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Description

Explore the fascinating world of tannins, complex plant substances found in various plant parts like leaves and fruits. Learn about the two main classes of tannins—hydrolysable and non-hydrolysable—along with their chemical compositions and examples of plants that contain them.