Pharmacognosy - medicinal plants (herbs)
Pharmacognosy - medicinal plants (herbs)

Theme XVI: Plant exudates

Plant exudates

Defining plant exudates. Definition and characteristics of the resins, the oleoresins, the gum-resins and balsams.

Exudates

Exudates are considered complex mixtures of plant origin with solid or semi solid consistency such as resins, oleoresins, balsams and gums. The proportion of constituents may vary with climate, season and other factors.

 

Resins

This term should not be mistaken with the synthetic resins result of the polymerization of long chains of low molecular weight organic compounds. We refer to the exudates obtained from plants in their natural state or insects that parasitize plants.


They are characterized by their insolubility in water, soluble in alcohol and ether, often non crystallizable, soften or melt at moderate temperature and burn at smoky flame.


Usually, resins are terpenes oxidized from the volatile oils, result from their water insolubility. They taste bitter.


Its chemical composition is not varied, some are acidic and alkali combinations that give a soapy consistency as in the case of rosin.


Should be distinguished between a natural pure resin and a prepared or derivative resin. The natural resin is obtained from plant exudate. (E.g. Mastic).


A resin prepared can be made of an extraction by alcoholic percolation of a drug, in order to obtain its active resinous constituents, then treating it with excess water to precipitate the components which are washed and dried. For example the resin of Podophyllum peltatum L.


A preparation of resin can also be obtained from a natural oleoresin by drying its volatile oil with warming. E.g. Rosin.

 

Oleoresins

They are mixtures of resins with volatile oils, usually obtained by incision of the trunk of trees that contain it. The turpentine and the copaiba are natural oleoresins recognized by the USP-NF.


The same way should be distinguished between oleoresins and prepared oleoresins, as the latter are concentrated of liquid preparations by percolation of the plant that naturally contains the resin and oil together. Suitable solvents are used (acetone, ether or alcohol) then the percolation is concentrated until remove the solvent. Examples are Aspidium, Capsicum and Ginger.

 

Gum-resins

Are natural mixtures of gums and resins obtained naturally by exudates, such as Myrrh and Gamboge.


Balsams

These resinous substances contain benzoic acid or cinnamic acid or its esters, such as the Tolu Balsam and the Balsam of Peru.


Various nomenclatures are usually used in the trade name of many plant exudates. The word “gum” is often used to identify some resins and in the same way the word "balsam" applies to certain oleoresins.

see also