Soft capsules have the excellent physical characteristic thanks to the main ingredient-gelatin. In addition, various additives are added to enhance the capsule performance.
In general, here are the main components for soft capsule:
Gelatin, glycerin, water, paraben complex, titanium dioxide, ferric oxide, ethyl vanillin, fumaric acid, phosphate.
Gelatin is a colorless, translucent (possibly slightly pale yellow), odorless and tough substance. Generally insoluble in organic solution, strong water absorption and high viscosity. Because of its excellent physical characteristic, the gelatin is widely used in the pharmaceutical industry. Gelatin for soft capsules can be broadly classified into two categories, A and B. Type A gelatin is made from pig skin with an isoelectric point between pH 7-9. Type B gelatin is made from animal bone and cowhide with an isoelectric point between pH 4.7 and 5.2. These two types of gelatin can be used singly or in combination.
Viscosity and strength determine the quality of gelatin. Low viscosity will cause "saponified" easily after being made into soft capsules while high viscosity will cause the soft capsules surface over rough. Good news is the viscosity can be adjusted by adjusting the water proportion in the gelatin to meet the relevant requirements.
Then the strength requirement for gelatin is between 150-250 Bloom. The under low-strength gelatin requires a lower conventional sealing temperature with longer drying time which causing the capsule physical problem such as lack of hardness, sticky and dull surface. The over-high strength gelatin requires a higher than conventional sealing temperature and a short drying time, making the capsule fragile and stiff. However, sometimes the characteristic can be adjusted according to the filling drugs. For example, low-viscosity and high-strength gelatin could apply to highly hygroscopic drug solution, meanwhile, the proportion of water in the formula should be lowered to make the drug solution more stable.
The plasticizer is usually glycerin, sorbitol, etc. Generally, glycerin is first choice, but a plurality of plasticizers is added depend on situation. The plasticizer can adjust the hardness of the soft capsule shell to make up for the deficiency of a part of the gelatin itself.
Water can change the overall characteristic of gelatin, high water proportion will speed up the dissolution when the soft capsule enters your stomach and intestine.
Titanium dioxide is widely used as an opacifier to reduce the transparency of the soft capsule.
Soft capsule can turn into a variety of color by different combinations of pigment and opacifier.
Preservatives primarily aim at inhibit bacterial growth. Common preservatives are Paraben, Sodium benzoate, etc., the dosage is relatively low from 0.01% to 0.5%.