2.8.1.1 Dioscorea
Synonyms Rheumatism root; Yam.
Biological Source It essentially comprises of the dried tubers of Dioscorea delitoidea Wall., Dioscorea tokora Makino, and Dioscorea composita and other species of Dioscorea belonging to the family Dioscoreaceae.
Geographiacal Source D. delitoidea is grown in United States and Mexico. It is cultivated from Nepal to China at an altitude ranging from 3,000 to 10,000 feet. It is also found growing abundantly in North Western Himalayas from Kashmir to Panjab in India.
Preparation Generally, the saponins do have high molecular weight and hence their isolation in the purest form poses some practical difficulties. The tubers are washed, sliced and extracted with hot water or ethanol (95% v/v) for several hours. The resulting extract is filtered, concentrated under vacuo and the desired glycosides is precipitated with ether. However, there are various ways and means to obtain the respective steroidal saponins from the aqueous/ alcoholic extracts as stated below:
For Acid Saponins : Lead Acetate is employed to precipitate the steroidal saponins from
aqueous extract.
For Neutral Saponin : Basic lead acetate is used to precipitate the neutral steroidal saponins from aqueus extract. Nevertheless, a few saponins are also precipitated from their aqueous solutions either by the addition of Ba(OH)2 solution or by the addition of (NH4)2SO4 solution.
Note The Barayata-Saponin Complex is sometimes employed for the estimation of Saponins.
Description
Colour : Slightly brown
Odour : Odourless
Taste : Bitter and acrid
Size : Varies dependig on the actual age of the rhizomes (tubers)
Chemical Constituents The major active constituent of dioscorea is diosgenin usually present in the range of 4-6%. Diosgenin is the aglycone of saponoin dioscin
Besides, the rhizomes contain starch to the extent of 75% but it has no edible utility because of its bitter taste. They also contain phenolic compounds and an enzyme sapogenase.
Uses
1. Dioscorea is mostly employed in the treatment of rheumatic arthritis.
2. Dioscorea has a tremendous potential as a commercial product because of its high content of diosgenin, which in turn is invariably employed as a starting material for the synthesis of a host of important therapeutic drugs, for instance: sex-hormones, oral contraceptives and several corticosteroids.
