NTA Level 5 • Semester 2 • PST05210

Collection, Processing and Storage of Medicinal Plants

Basic Pharmacognosy • Source Session/Topic 13

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Session 13: Collection, Processing and Storage of Medicinal Plants

Total Session Time: 120 minutes

Prerequisites

• None

Learning Tasks

By the end of this session students are expected to be able to:

• List methods for collection of medicinal drugs

• Explain the importance of processing medicinal plants

• Explain methods of drying of crude drugs

• Explain storage of medicinal plants

Resources Needed:

• Flip charts, marker pens, and masking tape

• Black/white board and chalk/whiteboard markers

• Computer and LCD Projector

SESSION OVERVIEW

SESSION CONTENTS

STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)

READ or ASK students to read the learning objectives and clarify

ASK students if they have any questions before continuing.

STEP 2: Collection of Medicinal Plants (30 minutes)

• Collection refers to harvesting or obtaining drugs from medicinal plants

• Drugs may be collected from wild or cultivated plants

• Collection may be done by skilled or unskilled labour

• Collection from cultivated plants is more advantageous and ensures

sustainability of medicinal plants

• In some cases, pharmacopoeias specify collection of certain drugs from

cultivated species such as Fennel, ginger, cinnamon and opium

• Some drugs e.g. senna, tragacanth and others may be collected from wild

or cultivated species.

• Active constituents in plants vary in amount and nature throughout the

year, so collection should be done at the right time when active

constituents are at the highest levels. For instance,

o Time (season) of the year

▪ Rhubarb contains high levels of anthranols in winter and high

levels of anthraquinones in summer. Anthranol are oxidized to

anthraquinones in summer

o Time of the day

▪ Digitalis is collected in the afternoon contains more cardiac

glycosides

▪ Solanaceous leaves collected in the morning have more

alkaloids

o Stage of maturity

▪ In Eugenia caryophyllus, buds contain high oil but mother “blown”

cloves contain very little oil

▪ Vanilla has highest levels of vanillin 8 months after flowers

open

• General factors to consider when harvesting/collecting drugs from

medicinal plants;

o Underground organs are collected when aerial parts die down

o Leaves are collected when flowers are beginning to open

o Flowers are collected in dry weather and just before they fully

expand e.g. cloves

o Fruits and seeds are collected when fully mature but unripe

o Barks are collected in damp weather

o Unorganized drugs are collected in dry weather

o Leaves, flowers and fruits should not be collected when covered with

dew or rain

o Discoloured or parts attacked by insects should not be collected

o Large organs should be sliced soon after collection to facilitate

drying

o Limits of unwanted parts in desired parts must be considered when

collecting medicinal plants e.g. aerial stems in rhizomes

STEP 3: Processing of Crude Drugs (45 minutes)

• After collection, drugs should be processed to meet various requirements

such as market requirements

• Processing of crude drugs is important in order prevent deterioration

• Processing of drugs from natural sources depends on morphological nature,

constituents, geographical source and other related factors

• Drying is an important aspect of processing crude drugs

o There various reasons for drying drugs obtained from medicinal

plants

▪ To decrease size and weight i.e. to facilitate packing,

transport and storage

▪ To facilitate powdering

▪ To prevent enzyme action

▪ To prevent microbial growth

▪ To prevent degradation of active constituents

o Enzyme action may be desired or undesirable after collection

▪ When enzyme action is desired after collection e.g. in vanilla

pods, gentian roots and cocoa seeds, the collected drug is dried

slowly at moderate temperature

▪ Drying is done as soon as possible after harvesting when enzyme

reaction is not desired e.g. digitalis leaves

o Methods of Drying

o There are various methods that are used in drying crude drugs

o The choice of a drying method depends on physical characteristics of

the plant and chemical characteristics of the active constituents

▪ Air Drying

• Sun Drying

o Is done when drugs are not adversely affected by excessive

sunlight.

o Drugs are dried in thin layers and tuned over occasionally

o Drugs dried in this way include clove and cardamom

• Shade Drying

o Done when sunlight causes discoloration and warping/shrivelling

of the drugs e.g. cinnamon

▪ Artificial Drying

• Artificial source of heat is used in the drying process

• Drying in the oven (oven drying) is the commonest methods used in

artificial drying

• Artificial drying is more accepted and more rapid than air-drying

• Artificial drying is more suitable for use in the wet weather

• Drying temperature is governed by constituents

o Generally, leaves, herbs and flowers are dried between 20-40oC,

barks and roots: 40-65oC

• When done rapidly, the drugs retain colour and aroma

▪ Vacuum Drying

• It is also done in oven, but at low temperature

• Low pressure ensures rapid and complete drying

• It is an expensive method and thus reserved for expensive drugs or

drugs which cannot be sufficiently dried by other methods

▪ Lyophilisation

• Involves freezing of the drug and then evaporation under low

pressure

• Very suitable method for drugs that are very sensitive to heat

• The resulting product is a fine powder

• This method is used for drying biological fluids, enzymes,

proteins and royal jelly

• Some general conditions and techniques when drying medicinal plants:

o For Leaves/Herbs:

▪ Temperature should be between 40-50º C to maintain good colour

▪ Leaves or herbs should normally be destalked first

▪ They are best dried for short periods of time only to prevent

shrivelling and discoloration

▪ They may be bleached through the drying process

o For Roots/Rhizomes:

▪ They should be washed

▪ They should be sliced

▪ They should be dried between at temperatures between 30-65ºC

▪ Too high temperature may prevent further drying in deeper parts

of the drug

▪ Thick organs may require long periods of drying (10days-3weeks)

to avoid mould growth

o For Flowers;

▪ Flowers are normally destalked before drying

▪ Flowers may also be bleached when dried

o Volatile oil-containing drugs;

▪ Are air-dried at very low temperature to avoid volatilization of

oil contents

▪ They should be dried separately from other herbs

o Fruits and Seeds;

▪ They are normally partially dry before harvesting

▪ They may be air-dried afterwards

▪ Seeds are normally separated from the fruits before drying

▪ Fruits are normally left whole

▪ Some fruits (cardamom) rupture due to excessive heat.

o Bark

▪ Occasionally requires the removal of the outer layers

o Factors to consider when making a choice of a drying technique

▪ Physical characteristics of the plant

▪ Chemical characteristics of the plant

• Volatile Oils: (Thyme) Dried separately, at low temperature

• Starchy herbs (oats): gelatinize if overheated

▪ Changes occurring in herbs when drying

▪ Changes due to enzyme action

▪ Oxidation

▪ Volatilisation

▪ Browning

STEP 4: Storage of Crude Drugs (30 minutes)

|Activity: Small Group Discussion (10 minutes) |

| |

|DIVIDE students into small manageable groups |

| |

|ASK students to discuss on the following question |

|How should crude drugs be stored? |

| |

|ALLOW students to discuss for 15 minutes |

| |

|ALLOW few groups to present and the rest to add points not |

|mentioned |

| |

|CLARIFY and SUMMARIZE by using the contents below |

• During storage, drugs are affected by physicochemical and biological

factors

• Physicochemical factors include light, moisture, temperature and air

oxygen while biological factors include fungi, bacteria, worms, insects

and mites

• Long storage is not recommended, due to deterioration except in cascara

bark. Active constituents decrease massively

• Drugs should be stored in sealed containers in cool dark places

• Generally, the permissible moisture content is 8% or below.

• Air dried drugs are always liable and are easily attacked by insects and

other pests, so they should be frequently examined during storage or may

require sterilization by ethylene oxide or methyl chloride before storage

STEP 5: Key Points (5 minutes)

• Drugs may be collected from wild or cultivated plants

• Collection of drugs may be done by skilled or unskilled labour

• Collection from cultivated sources ensure sustainability of medicinal

plants

• Drying is an important process in the preparation of drugs for market

STEP 6: Evaluation (5 minutes)

• What are the factors to consider when harvesting medicinal plants?

• What are the reasons for drying crude drugs?

References

Trease, G. E., Evans, W. C., & Evans, D. (2009). Trease and Evans

pharmacognosy. London: Saunders.

Joanne Barnes et al (2002), Herbal medicines 3rd Edition: Pharmaceutical

Press

Wallis, T. E. (2005). Textbook of pharmacognosy. New Delhi: CBS.

Robbers, J. E., Speedie, M. K., Tyler, V. E., & Tyler, V. E. (1996).

Pharmacognosy and pharmacobiotechnology. Baltimore: Williams &

Wilkins.

Heinrich, M., Kinghorn, A. D., Maizels, D., Gibbons, S., & Phillipson, J.

D. (2012). Fundamentals of pharmacognosy and phytotherapy. Edinburgh:

Churchill Livingstone/Elsevier.

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