Quality Control and Evaluation of Drugs of Natural Origin
Because medicinal plants are harvested in nature and traded in huge commercial volumes, fraudulent adulteration and accidental substitution are rampant. In this unit, we explore the types of adulteration, WHO standardized evaluation methods (organoleptic, microscopic qualitative & quantitative constants, physical ash and extractive values, foaming/swelling indexes), and state-of-the-art molecular DNA barcoding.
In this topic, you will learn:
1. Types and Causes of Crude Drug Adulteration
In Simple Words:
Adulteration simply means the dishonest practice of mixing fake, inferior, exhausted, or harmful substances into genuine medicines to cheat buyers and make more profit.
Official definition: It is defined as substituting an authentic crude drug wholly or partially with other similar, defective, exhausted, or toxic substances.
The 5 Primary Types of Adulteration (Explained Simply):
Replacing expensive original herbs with wild weeds that look almost the same but contain very little active medicine. Example: Mixing cheap Arabian senna with genuine Alexandrian senna.
Re-using plant material after all the active oils or flavors have already been extracted out. Example: Selling spent cloves or ginger whose oil has already been removed in a factory.
Making fake substances in a workshop and coloring them to look like herbs. Example: Yellow-colored paraffin wax sold as pure beeswax, or brick dust added to red chili powder.
Picking free weeds with identical leaf shapes. Example: Mixing common tree leaves (Ailanthus) into expensive Belladonna leaves, or dyed flower petals sold as pure Saffron.
Mixing hazardous poisons or cheap industrial oils into expensive products to cut costs. Example: Toxic mineral motor oil added to mustard/edible oils, or counterfeit seeds lacking active healing chemicals.
2. Organoleptic (Macroscopic) Evaluation
Organoleptic Evaluation is defined as the qualitative examination of crude drugs using human sensory organs (eyes, nose, tongue, and touch).
• It is also known as: Macroscopic or sensory evaluation.
• It is used for: Quick preliminary identification and detecting obvious adulteration in raw drug shipments.
• In this method, we: Inspect color, odor, taste, size, surface shape, texture, and fracture characteristic of the raw drug.
• For example: Quassia is identified by intensely bitter taste; Ginger by aromatic odor and hot pungent taste.
In Simple Words:
In this method, we test the crude drug using our 5 natural human senses—our eyes, nose, tongue, and hands. No costly instruments or laboratory chemicals are needed!
3. Qualitative & Quantitative Microscopic Evaluation
In Simple Words:
In this method, we inspect the drug under a laboratory microscope. While fake and real herbal powders might look identical to our naked eyes, their microscopic cell structures (like leaf breathing pores, plant hairs, and calcium crystals) are completely different and act like plant fingerprints.
- Types of Stomata (Leaf Breathing Pores):
• Paracytic: Guard cells flanked by 2 helper cells running parallel to the pore (e.g., Senna).
• Diacytic: 2 helper cells crossing at a 90° right angle (e.g., Peppermint).
• Anisocytic: Stoma surrounded by 3 helper cells, where 1 cell is distinctly smaller than the other two (e.g., Belladonna).
• Anomocytic: Helper cells are irregular and look just like ordinary epidermis cells (e.g., Digitalis). - Calcium Oxalate Crystals: Microscopic mineral crystals inside cells (Prisms in Senna; needle-like Raphides in Squill; star-like Rosettes in Rhubarb).
- Stomatal Number: Average count of stomata per mm² of leaf surface.
- Stomatal Index (I): The percentage proportion of stomata compared to all epidermal skin cells:
I = [ S / (E + S) ] × 100
Why is this important? Because while stomatal count changes with sunlight and rain, the Stomatal Index remains constant for a species! - Vein-Islet Number: The number of tiny vein meshes per mm² of leaf area.
- Palisade Ratio: Average number of food-making palisade cells located beneath each upper skin cell.
4. Quantitative Microscopy: The Lycopodium Spore Method
In Simple Words (How does it work?):
Lycopodium powder consists of spores from the club moss plant Lycopodium clavatum. These spores are remarkably uniform in size and weight: exactly 1 milligram of pure Lycopodium powder always contains an average of 94,000 spores.
In this method: We mix an exact weight of Lycopodium powder with our crude drug powder. Under the microscope, we count the number of spores and the number of drug particles in 25 fields. Using this simple ratio, we calculate the exact percentage of pure drug or foreign adulterant.
Official Lycopodium Formula:
• n: Number of characteristic drug particles counted in 25 fields.
• s: Number of Lycopodium spores counted in the same 25 fields.
• w: Weight of Lycopodium powder added (mg).
• m₁: Weight of powdered drug sample taken (mg).
• 94,000: Constant number of spores per 1 mg of Lycopodium powder.
5. Physicochemical Parameters: Ash Values, Extractive Values & Indices
Ash Value Determination is defined as an analytical quality control method to measure residual inorganic mineral impurities left after complete incineration of a crude drug.
• It is used for: Detecting contamination from soil, sand, earthy matter, and inorganic adulterants.
• Total Ash is defined as: The total non-volatile inorganic matter left after incinerating the drug at 450–500°C. In this method, we: Ignite the drug in a silica crucible until carbon-free, cool in a desiccator, and weigh.
• Acid-Insoluble Ash is defined as: The siliceous portion of total ash insoluble in dilute hydrochloric acid (HCl). It is used for: Specifically measuring silica and sand contamination adhering to roots and rhizomes.
In Simple Words (What is Ash Value?):
In this method, we burn 2 to 3 grams of the drug in a furnace dish at 450°C. All organic plant parts burn away as carbon smoke, leaving behind only the non-burnable mineral ash. Why do we do this? Because if someone mixed roadside dirt, clay, or sand into the herbal medicine to make it heavier, the ash value will shoot up abnormally high!
The total weight of inorganic minerals (calcium, potassium, silica) remaining after burning the crude drug at 450°C.
Ash that does not dissolve in dilute Hydrochloric acid (HCl). Crucial test: Directly measures contamination with earthy sand, silica, and roadside dirt!
Ash that dissolves in water. Detects if the plant was previously boiled in water by a cheat to steal its extract before selling it.
| Physicochemical Test | How We Perform This Test | Why We Do This Test (Examples) |
|---|---|---|
| Alcohol / Water Extractive Value | Soaking 5 g powdered drug in alcohol or water for 24 hours, filtering, and drying 25 mL to weigh active solids. | Tells us how much active medicine will dissolve in liquid; immediately detects exhausted or spent drugs. |
| Moisture Content (Loss on Drying) | Drying the drug in an oven at 105°C until constant weight is reached. | Must be under 10%–12%. Excess moisture causes mold, fungus, and enzymatic breakdown. |
| Swelling Index | Measuring how many mL of space 1 gram of herbal seed or husk occupies after soaking in water for 24 hours. | Ispaghula husk (Psyllium) must have a swelling index ≥ 40 to relieve constipation effectively. |
| Foaming Index | Shaking 10 mL of boiled herbal decoction in a test tube and measuring 1 cm persistent foam height. | Detects soapy Saponin glycosides present in medicinal plants like Senega and Quillaja. |
6. DNA Barcoding in Herbal Drug Authentication
In Simple Words (The Supermarket Analogy):
DNA Barcoding works just like a supermarket barcode scanner. When you buy a packet of biscuits in a store, the black-and-white stripes contain a unique code that tells the computer the exact brand and price. In the same way, every medicinal plant has a short, unique sequence in its DNA genes.
Even if an herb is crushed into fine powder or mixed with other weeds, its DNA code never changes. A simple gene test confirms with 100% certainty whether the medicine is genuine or fake!