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CAPSULES II


I) Physicochemical properties of the gelatin.
The two most important physicochemical properties of the gelatin  a) bloom strength & b) viscosity are considered while preparing capsule shells.

a) Bloom strength:
It is an empirical gel strength measure.
It is a molecular weight of gelatin which gives an indication of firmness of the gel. i.e. internal cross linking or cohesive strength among the molecules.
It is measured in bloom gelometer.
It determines the weight in grams required to depress a standard plunger (diameter 0.5 inches) at a fixed distance (4mm deep) into 6.66% w/w gel held at 10°C for 17 hrs.
The bloom strengths in the range of 150-280 gram are considered suitable for manufacturing of capsule shells.

b) Viscosity:
Viscosity of the gelatin solution is a critical factor in order to maintain the proper thickness of gelatin shells.
It is usually a measure of chain length of gelatin.
It is determined using 6.66% by weight aqueous solution of gelatin at 60°C using capillary pipette method. Viscosity should be in the range of 25-45 milli poise.



  • Sealing Temperature of gelatin film: 37-40°C.
  • Method for determination of moisture content in gelatin shells: Toluene distillation method.
  • Iron content: NMT 15 ppm.
  • To prevent decomposition of gelatin: treatment with 0.15% sulfur dioxide.
  • Modification of gelatin solubility: shellac, CAP (cellulose acetate phthalate).

For encapsulation of suspension in soft gelatin capsules, it is necessary to define exact volume required.
For this purpose M/G factor is calculated.

M/G factor is defined as the volume of mixture in minims required for solid drug to produce a mixture which can be encapsulated.

To determine M/G (minim per gram) factor, base absorption value is required.

Base absorption: It is defined as the minimum amount of base/ vehicle in grams required per gram of solid drug to form a mixture which easily can be encapsulated in soft gelatin capsule.

Base absorption value depends on following factors:
  1. Particle size and distribution
  2. Density of drug
  3. State of drug i.e. amorphous, crystalline
  4. Hydrophilicity and hydrophobicity of drug

M/G factor= (BA+S)/D × 16.23 minims

BA: Base absorption value
S: Solid drug
D: Density of mixture
1 ml= 16.23 minims

II) Tests for gelatin
1. Picric acid test
Gelatin+picric acid --> Yellow precipitate
2. Tannic acid test
 Gelatin is a protein and tannic acid causes precipitation of proteins.
Gelatin+tannic acid--> white precipitate


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