Oils and Fats Definition and Classification | Biology Ideas

What are Oils and Fats?

1) Like other necessities of man, oils are also used as one of the main necessities as they are required in the daily life of man.

2) They are obtained from different parts of the plant like root, rhizome, leaf, bark, flower parts, fruits, and seeds. 

3) The oils are the by-products of metabolism rather than foods.

4) The oils play a major role as hydrogen donors in oxidation-reduction reactions as potential sources of energy.

5) They also affect transpiration and other physiological processes.

6) They are obtained by expression or extraction methods.

7) Their basic function is the storage of energy.

8) Oils are combustible substances that are liquid or liquifiable on warming and soluble in ether but not in water and form greasy stains on paper, cloth, etc.


As per origin, oils are classified as follows –

i) Vegetable oils

ii) Animal oils

ii) Mineral oils

Read Also: Classification of Vegetable oil | Biology Ideas | Examples and Types


According to behavior on heating vegetable oils are known as…

i) Fixed or fatty oils

ii) Volatile or (essential) oils.

We are mainly concerned here with vegetable oils-fatty.

The properties of oil and Fats 

  1. The properties of oil and fats vary along with the degree of unsaturation, average molecular weight, and acidity from hydrolysis.
  2. Several parameters are used for their analysis which is included under physical constants and chemical constants.
  3. Physical constants include viscosity, specific gravity, refractive index, solidification point, etc.
  4. Under the group of chemical constants, conventionally the parameters like iodine value, acid value, peroxide value, saponification value saponifiable matter are noted.
  5. In recent times the gas chromatographic determination of any profile has been introduced for the identification of fats and oils.
  6. Following is a brief idea about some of the analytical parameters grouped under chemical constants.


1. Iodine value –

It is defined as the weight of iodine absorbed by 100 parts by weight of the sample of fat or oil. Iodine value is a measure of the extent of unsaturation. Susceptibility to ancestry increases for the oil or fat having higher iodine values.

2. Saponification value –

It is defined as the number of milligrams of potassium hydroxide required to neutralise the fatty acids resulting from complete hydrolysis of 1g of the sample of oil or fat. Saponification value occurs in an inverse proportion to the average molecular weight of fatty acid present in the oil. This value s normally applied for butterfat, coconut oil in which lower fatty acids glycerides occur in high content.

3. Hydroxyl value –

It is defined as a number of milligrams of potassium hydroxide required neutral acetic acid capable of combining by acetylation with 1 g sample of fat or oil.

4. Acetyl value –

It is the number of milligrams of potassium hydroxide required to neutralize acetic acid obtained when 1g of sample acetylated oil is saponified. Except castor oil (acetyl value 150) most of the oil and fat have low acetyl value (3 – 15).

5. Unsaponifiable matter –

It is the matter present in fats and oil, which after saponification by caustic alkali and subsequent extraction with an organic solvent, remains non-volatile on drying 80°C. It includes sterols (phytosterol and cholesterol), oil-soluble vitamins, hydrocarbons, and height alcohols. Paraffin hydrocarbons can be detected by this method as adulterants.

6. Acid value –

It is defined as the number of milligrams of potassium hydroxide required. to neutralize the free acids, present in 1g sample of fat or oil. Generally, rancidity causes free fatty acids liberation, hence acid value is used as an indication of rancid state.


Extractions of Oils

Vegetable oils and fats are located in the form of insoluble droplets within the plant cells. They occur mainly in seeds. mostly commonly in endosperm and cotyledons. Olive and palm oils occur in the fleshy pericarp of the fruit.

The seed coat is removed by machines like the decorticator. The seed kernel is reduced to a paste.

Read Also: Plant Resources of Alkaloids | Biology Ideas | Serial wise


The oil is extracted by following two methods –

a) Mechanical expression

b) Solvent extraction 


a) Mechanical expression –

Oil is extracted by applying pressure to the oil-bearing tissues to squeeze out the fat.

It is usually done by hydraulic pressing or screw pressing. The oil is filtered.


b) Solvent extraction –

This method oil extraction process employs a solvent to leach out the oil. It is the only practical method for recovering oils from tissues having a relatively low proportion of oil.

This method is quite effective but expensive Oils are extracted with solvents like gasoline, benzene, carbon disulfide, petroleum ether, and chlorinated hydrocarbons.

The fatty oils are freed from the extracting solvents by distillation. Such oil is then subjected to a refining process.