Extraction of individual compounds

Not all the chemical compounds elaborated by plants have therapeutic properties. The major active compounds are alkaloids, glycosides and these, therefore, deserve special attention. Other groups such as carbohydrates, fats and proteins are of dietetic importance, and many such as starches and gums are used in pharmacy but lack any marked pharmacological action. Other substances, such as calcium oxalate, silica and coloring matters, may be of assistance in the identification of herbs and the detection of adulteration.

(i) ALKALOIDS: - Basic nitrogenous substances are having marked physiological action if taken internally. They occur in plant as salts. They are found in seeds, barks, leaves, roots etc.
     The extraction of the alkaloids is based on their basic character and solubility pattern. The normal procedure followed are to treat the moistened herb with alkali so as to set free the base as it exists in the salt form and then separate the free base with organic solvent. The basisty of alkaloid depends upon number of nitrogen items in the molecule, structure of the molecule and presence of other functional group.

(ii) GLYCOSIDES: - These are condensation products of sugar and aglycon. These are soluble in water as well as alcohol.
       Glycoside is finely powdered and the powder is extracted by continuous hot percolation using soxhlet apparatus with alcohol as solvent. The extract is treated with lead acetate to eliminate non glycosidal impurities. The excess of lead acetate is precipitate as lead sulphide by passing hydrogen sulphide gas through solution. The extract is filtered, concentrated to get crude glycoside.

(iii) TANNINS: - Tannins are present in cell sap soluble in water and alcohol. They have several medicinal properties and hence are used as herbs. They are distributed is different parts of plants depending upon the source of the tannins.
         Various modified methods are used for extraction. Methyl alcohol, hot water, acetone and ethyl acetate are the common solvent used for extraction, the extract is filtered and dried under vaccum.

(iv) RESINS: - Resins are found in abundance in the trunk of the trees in the resin ducts or in rhizomes (ginger), fruits (capsicum) and other parts of the plants. They are insoluble in water, but soluble in alcohol and may be semi-solid or solid.
       Resins are extracted with alcohol and precipitation with water. By distillation for the separation of the oil.

(v) VOLATILE OILS (Essential Oils): - These are the fragrant liquids found in plants. They are volatile and aromatic and are present in roots, leaves, barks and fruits etc. They are insoluble in water and are soluble in alcohol. Volatile oils are carminative stimulants and antiseptic.
       Volatile oils are extracted by steam distillation, solvent extraction and by ecuelle, enfleurage techniques.

(vi) LATEX: - it is wide suspension in which oil globules or small particles are suspended. They contain proteins, sugars, minerals and alkaloids salts in true solution, while gums, starch, resins are in suspended form.

(vii) MINERAL CRYSTALS: - They are occurring in cell cavity. They are all in soluble in water. They are found in roots, stems, leaves and fruit etc.