Tannins: Properties, Chemistry, and Classification

• Tannins applied by Seguin in 1796 describe plant extract substances that combine with animal hide proteins. These prevent putrefaction, to convert them into leather.
• Goldbeater's Skin Test qualitatively detects a substance quantitatively determined by absorption on standard hide powder.
• Tannins are glycosides

Properties

• Source of fruit acids (Glycolic, Lactic, Mandelic, Malic, Tartaric, Citric acid).
• Tannins are in specific plant parts (leaves, fruits, barks, or stems).
• Exist in solution in cell sap, often in distinct vacuoles.
• Tannins have sharp "puckering" taste.

Chemical Properties

• Tannins are plant polyphenols
• Non-crystallizable extracts
• Complex mixes of polyphenols and non-crystallizable compounds
• Proteins get precipitated

Classification

• Hydrolysable Tannins
• Non-Hydrolysable Tannins (Condensed Tannins)
• Pseudotannins

Hydrolysable Tannins

• Hydrolyzed by acids/enzymes like Tannase.
• Several phenolic acid molecules (Gallic acid, Hexahydroxy-diphenic acid), attached by ester linkages to a central glucose molecule constitute the molecule.
• Gallic acid converts to Pyrogallol through dry distillation.
• Classified to Polyhedric phenol from which they derived.

Types of Hydrolysable Tannins

• Gallitannins contain Gallic acid.
• Ellagitannins are Hexahydroxy-diphenic acid units.

Reactions of Hydrolysable Tannins

• Ferric chloride (FeCl3) reagent turns blue
• Bromides do not precipitate

Non-Hydrolysable Tannins (Condensed Tannins)

• Proanthocyanidins, Polyflavonoid, Catechol-type, Pyrocatecollic-type
• Not readily hydrolyzed to simpler molecules
• Lacking a sugar moiety
• Molecules are related to Flavonoid pigments and have polymeric Flavan-3-ol structures
• Flavan and Catechins exist with tannins during the biosynthesis of molecules

Reactions of Non-Hydrolysable Tannins

• Ferric chloride (FeCl3) reagent turns Greenish color.
• Bromides form a precipitate.
• Converts into red insoluble compounds (Phlobaphenes) with acids/enzymes
• Catechol results from dry distillation

Reactions with Process/Reagent of Non-Hydrolysable Tannins

• Heating produces Catechol
• Boiling with HCI forms insoluble red Phlobaphenes
• Ferric chloride (FeCl3) turns Green
• Bromine T.S. forms a precipitate
• Examples are: Kino, Gambir.

Process/Reagent of Pyrogallol Tannins

• When heated produces Pyrogallol
• Boiling with HCI forms Gallic acid/Ellagic acid
• Ferric chloride (FeCl3) turns blue
• Bromine T.S. does not precipitate
• Examples: Nut gall, Oak bark, Pomegranate bark.

Uses of Tannins

• Antiseptic
• Astringent
• Alkaloidal Poisoning Antidote
• Leather Preservative
• Laboratory Reagent - for protein and alkaloid identification
• Ink Industries

Cautions

• Carcinogenic potential

Other Therapeutic Activities

• Antioxidants
• Improves Peripheral Circulation, Capillary Fragility, Retinopathies, Inflammatory Collagen Disease
• Sources include: Grape Seeds (Vitis vinifera), Needles & Barks of Pine Trees (Pinus pinaster)

Tests

• Solubility
• Ferric Salts Reaction

Plants Rich Sources of Tannins

• Some drugs like Tea, Hamamelis leaves and barks contain both Hydrolysable and Non-hydrolysable tannins,

Plant Parts and Examples

• Lime and Hawthorn Flowers
• Cranberry, Grapes, Hawthorn Fruits
• Areca, Cacao, Guarana, Kola Seeds
• Hamamelis, Hawthorn Leaves
• Acacia, Cinnamon, Hamamelis, Oak, Willow, Wild Cherry Barks
• Krameria, Male Fern Roots & Rhizomes
• Acacia Catechu, Mangrove, East Indian Kino, Eucalyptus Kino, Butea Gum Extracts & Dried Juices

Plant Family Examples

• Combretaceae - Quisqualis
• Geraniaceae - Geraniums
• Leguminosae - Acacia, Tamarind
• Myrtaceae - Eucalyptus, Guava
• Polygonaceae - Buckwheat
• Rosaceae - Red rose
• Rubiaceae - Gambir
• Theaceae - Tea

Safety considerations

• Habitual chewing of Betel Nut Linked to high rates of oral & esophageal cancer in India and South Africa

Lipids

• Lipids include Fixed Oils, Fats, Waxes and Fatty Acids.
• Esters of long-chain fatty acids and alcohols or closely related derivatives.
• Soluble in non-polar organic solvents and generally insoluble in water.

Uses of Lipids

• Emollient
• Vehicle for Medications
• Therapeutic Properties
• Enteral and Parenteral Nutrition

Industrial Uses of Lipids

• Soaps
• Paints

Differences Among Lipids

• Type of Alcohol
• Sources
• Melting Point
• Constituent
• Extraction Method

Types of Alcohol

• Fixed Oils and Fats - Glycerol combined with fatty acids.
• Waxes - High molecular weight alcohol (Cetyl alcohol) combined with fatty acids.

Sources of Lipids

• Plants
• Animals

Functions of Lipids

• Primary function → Food (energy) storage
• Used in Pharmaceuticals, industry, and food production.

Vegetable Oils and Fats

• Mainly in seeds, found in various parts of plants
• Sources include Castor seed Cotton seed Sesame seed Hemp seed Linseed Almond seed Coconut

Fixed Oils Classification Based on Drying Ability

• Drying Oils
• Semi-Drying Oils
• Non-Drying Oils

Waxes

• May be of plant or animal origin

Fixed Oils and Fats

• Liquid at normal temperature

Waxes

• Semi-solid to solid at ordinary temperature

Constituents

• Fixed Oils and Fats consist of plant and animal derived constituents
• Most vegetable oils are liquid at ordinary temperatures.
• Most animal fats are solid
• Cod Liver Oil are liquid animal fat

Extraction Methods

• Fixed Oils and Fats (Vegetative Origin) are obtained by Cold Expression, Hot Expression and using organic solvents.
• Animal Fats are separated by rendering with or without steam.

Classification of Lipids

• Fixed Oils
• Fats and Related Compounds
• Waxes
• Fatty acids

Saturated Fixed Oils

• Coconut Oil
• Palm Oil
• Palm Kernel Oil

Monounsaturated Fixed Oils

• Castor Oil
• Olive Oil
• Peanut Oil

Stearic Acid

• Arachidic Acid

Unsaturated Fatty Acids

• Contains double bonds C=C
• Oxygen saturation of double bonds leads to polymerization, Important in film industry.
• Hydrogenation of double bonds forms semi-solid fats for cooking.

Classification of Fixed Oils Based on Oxygen Absorption

• Drying Oils
• Semi-Drying Oils
• Non-Drying Oils

Tests for Fatty Acids

• Ester Value → Mg of KOH required to saponify esters in 1 g. of substance.
• Saponification Value → Mg of KOH required to neutralize free acids and saponify esters in 1 g. of substance, Equal to the sum of Acid Value and Ester Value.
• Acid Value/Acid Number → Mg of KOH required to neutralize free acids in 1 g. of substance.
• lodine Number → Grams of iodine absorbed by 100 g of substance.
• USP Tests

Examples of Lipid sources

Fixed Oils:

• Linseed seed
• Cottonseed
• Candle nut
• Physic nut
• Castor seed
• Cashew nut
• Croton seed
• Coconut
• Cacao seed
• Olive seed
• Peanut
• Sesame seed
• Sweet almond seed

Fats & Waxes:

• Honey
• Entada
• Horse-radish tree
• Squash
• Lard
• Spermaceti
• White wax
• Woolfat

Volatile Oils

• Represents the essences/odoriferous constituents of the plants
• Ethereal/Essential Oils
• As a rule they are colorless
• Soluble in ether/alcohol/organic solvents
• Can be distilled from their natural sources
• Do not consist of glyceryl ester of fatty acids
• Cannot be saponified with alkalies
• Extracted by expression, steam distillation, solvents or by maceration
• Many are isomeric hydrocarbons and are designated terpenes

Methods of Obtaining Volatile Oils

• Distillation
• Ecuelle
• Enfleurage
• Extraction
• Destructive Distillation (Dry distillation)

Distillation Method

• Water: Turpentine oil
• Steam and Water: Cinnamon oil, clove oil
• Direct Steam: Peppermint oil, Spearmint Oil

The Ecuelle Method

• Removing of citrus oils

Enfleurage Method

• Flower petals and Bland fat/fixed oils and alcohol

Extraction

• Perfumery Industry
• Destructive Distillation (Dry Distillation): Empyreumatic oil

Composition of Volatile Oils

• Terpenes or Sesquiterpenes: Pinene, Camphene, Cadinene, Guaiacol
• Esters and Alcohols: Bornyl acetate, Linalyl acetate, Menthyl acetate, Borneol, Linalol, Menthol
• Alcohols: Linalol, Geraniol, Citronellol, Santalol
• Aldehydes: Cinnamaldehyde, Cinnamic aldehyde, Citronellal and Citral
• Ketones: Carvone, Thujone and Cresol
• Phenols: Eugenol, Thymol
• Ethers: Anethole
• Non-Terpenoids: Methyl salicylate, Benzaldehyde and Glucosinolates

Volatile Oils in Aromatherapy

• Aromatherapy based on the use of volatile oils, either singly or in admixture.

Volatile Oils are Administered As:

• Baths
• Compresses
• Massage
• Inhalations: Vaporizers and burners