What are the Polyphenols? Polyphenols rich foods – Polyphenols in olive oil – Health benefits of the Polyphenols

Polyphenols: Chemical Composition

Polyfenolit are organic compounds characterized by the presence of multiple phenol units in their chemical structure. Phenol itself is a benzene ring with a hydroxyl (-OH) group attached. Polyphenols are defined by having more than one phenol unit, and their structure determines their function, biological activity, and classification. They are synthesized through two main pathways in plants: the shikimate pathway (shikimic acid pathway) and the phenylpropanoid pathway.

General Chemical Features

Phenolic Structure: Polyphenols are based on aromatic rings bonded to hydroxyl groups.
Functional Groups: Besides hydroxyl groups, polyphenols often contain other functional groups like methoxy (-OCH₃) and carboxyl (-COOH) groups, which influence their solubility and biological activity.
Molecular Weight: Polyphenols range from small molecules like phenolic acids to large, complex polymers like tannins.

Classification of Polyphenols by Structure

Polyphenols are broadly divided into the following categories:

Flavonoids
Core Structure: C6-C3-C6 (two aromatic rings connected by a three-carbon bridge).
Subclasses: Flavonoids are further categorized based on the oxidation and substitution pattern of their central ring:
Flavonols (e.g., quercetin, kaempferol)
Flavones (e.g., luteolin, apigenin)
Isoflavones (e.g., genistein, daidzein)
Flavan-3-ols (e.g., catechins, epicatechins)
Anthocyanins (e.g., cyanidin, malvidin).
Sources: Found in fruits, vegetables, tea, and wine.

Phenolic Acids
Core Structure: Based on benzoic acid or cinnamic acid derivatives.
Examples: Gallic acid, caffeic acid, ferulic acid, and p-coumaric acid.
Sources: Present in coffee, berries, and whole grains.

Stilbenes
Core Structure: C6-C2-C6 (two aromatic rings connected by a two-carbon ethylene bridge).
Example: Resveratrol.
Sources: Grapes, wine, and peanuts.

Lignaanit
Core Structure: Derived from the dimerization of two phenylpropanoid units.
Examples: Secoisolariciresinol and matairesinol.
Sources: Seeds (especially flaxseeds), grains, and vegetables.

Tannins
Core Structure: Large polymeric molecules made up of flavonoid or phenolic acid monomers.
Types:
Hydrolyzable tannins: Based on gallic acid or ellagic acid.
Condensed tannins: Polymers of flavan-3-ols.
Sources: Found in tea, wine, and some fruits.

Key Chemical Properties

Hydroxylation: The number and position of hydroxyl groups influence antioxidant activity.
Conjugation: Polyphenols often exist as glycosides, bound to sugar molecules, which affects their solubility and bioavailability.
Polymerization: Larger polyphenols (like tannins) have enhanced ability to bind proteins and other macromolecules.

Functional Role of Chemical Composition

Antioxidant Activity: The phenolic hydroxyl groups donate hydrogen atoms to neutralize free radicals.
Chelation: Polyphenols can bind metal ions, reducing metal-catalyzed oxidation.
Interaction with Biomolecules: The ability to interact with proteins and lipids influences their roles in health and metabolism.

In summary, the chemical composition of polyphenols—marked by their phenolic structure, hydroxylation patterns, and functional group diversity—determines their biological roles and health benefits. Their wide variety and complexity make them crucial for both plant defense and human nutrition.