Which component is commonly used as a plasticizer to increase flexibility of soft gelatin capsule shells?

• A. Sorbitol
• B. Glycerin
• C. Water
• D. Ethanol

Answer: (A)

Plasticizers are added to gelatin shells to reduce intermolecular forces between gelatin molecules, increasing chain mobility and lowering the temperature at which the shell remains flexible. Sorbitol fits this role well for soft gelatin capsules because it is a compatible, multi- hydroxyl compound that inserts between gelatin chains, disrupting strong gelatin–gelatin interactions and helping the shell stay soft and pliable at storage temperatures. It also helps maintain proper moisture interaction without making the surface overly tacky, which is important for handling and capsule integrity.

While glycerin can also act as a plasticizer, sorbitol is commonly chosen in many softgel formulations due to its good compatibility with gelatin and favorable mechanical properties. Water contributes to plasticization by hydration of gelatin, but it is a tightly controlled moisture content factor rather than a deliberate additive in the same sense. Ethanol is a solvent, not a plasticizer selected to impart long-term flexibility.