WHO Guidelines on Good Agricultural and Collection Practices (GACP) for Medicinal Plants
(2003; 80 pages) [French] [Spanish] View the PDF document
Table of Contents
View the documentAcknowledgements
View the documentForeword
Open this folder and view contents1. General introduction
Open this folder and view contents2. Good agricultural practices for medicinal plants
Open this folder and view contents3. Good collection practices for medicinal plants
Close this folder4. Common technical aspects of good agricultural practices for medicinal plants and good collection practices for medicinal plants
Close this folder4.1. Post-harvest processing
View the document4.1.1. Inspection and sorting
View the document4.1.2. Primary processing
View the document4.1.3. Drying
View the document4.1.4. Specific processing
View the document4.1.5. Processing facilities
View the document4.2. Bulk packaging and labelling
View the document4.3. Storage and transportation
Open this folder and view contents4.4. Equipment
View the document4.5. Quality assurance
View the document4.6. Documentation
Open this folder and view contents4.7. Personnel (growers, collectors, producers, handlers, processors)
Open this folder and view contents5. Other relevant issues
View the documentBibliography
View the documentAnnex 1. Good Agricultural Practice for Traditional Chinese Medicinal Materials, People's Republic of China
Open this folder and view contentsAnnex 2. Points to Consider on Good Agricultural and Collection Practice for Starting Materials of Herbal Origin
View the documentAnnex 3. Good Agricultural and Collection Practices for Medicinal Plants (GACP), Japan
View the documentAnnex 4. A model structure for monographs on good agricultural practices for specific medicinal plants
View the documentAnnex 5. Sample record for cultivated medicinal plants
View the documentAnnex 6. Participants in the WHO Consultation on Good Agricultural and Field Collection Practices for Medicinal Plants
 

4.1.3. Drying

When medicinal plant materials are prepared for use in dry form, the moisture content of the material should be kept as low as possible in order to reduce damage from mould and other microbial infestation. Information on the appropriate moisture content for particular medicinal plant materials may be available from pharmacopoeias or other authoritative monographs.

Medicinal plants can be dried in a number of ways: in the open air (shaded from direct sunlight); placed in thin layers on drying frames, wire-screened rooms or buildings; by direct sunlight, if appropriate; in drying ovens/rooms and solar dryers; by indirect fire; baking; lyophilization; microwave; or infrared devices. When possible, temperature and humidity should be controlled to avoid damage to the active chemical constituents. The method and temperature used for drying may have a considerable impact on the quality of the resulting medicinal plant materials. For example, shade drying is preferred to maintain or minimize loss of colour of leaves and flowers; and lower temperatures should be employed in the case of medicinal plant materials containing volatile substances. The drying conditions should be recorded.

In the case of natural drying in the open air, medicinal plant materials should be spread out in thin layers on drying frames and stirred or turned frequently. In order to secure adequate air circulation, the drying frames should be located at a sufficient height above the ground. Efforts should be made to achieve uniform drying of medicinal plant materials and so avoid mould formation.

Drying medicinal plant material directly on bare ground should be avoided. If a concrete or cement surface is used, medicinal plant materials should be laid on a tarpaulin or other appropriate cloth or sheeting. Insects, rodents, birds and other pests, and livestock and domestic animals should be kept away from drying sites.

For indoor drying, the duration of drying, drying temperature, humidity and other conditions should be determined on the basis of the plant part concerned (root, leaf, stem, bark, flower, etc.) and any volatile natural constituents, such as essential oils.

If possible, the source of heat for direct drying (fire) should be limited to butane, propane or natural gas, and temperatures should be kept below 60 °C.6 If other sources of fire are used, contact between those materials, smoke and medicinal plant material should be avoided.

6 Reference: Heber W. Youngken. Textbook of Pharmacognosy, 6th ed. (16).

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