The shell of a soft gelatin capsule may be made more flexible by adding ______.

• A. Sorbitol (plasticizer)
• B. Glycerin
• C. Propylene glycol
• D. Water

Answer: (A)

Plasticization of gelatin shells is used to make them flexible by increasing chain mobility. A plasticizer inserts between gelatin chains, reducing intermolecular forces and lowering the glass transition temperature, so the film can stretch instead of cracking. Sorbitol acts as this plasticizer effectively because it is a sugar alcohol with multiple hydroxyl groups that can interact with gelatin, disrupting hydrogen bonding between chains and easing their movement. It also helps retain moisture, keeping the shell pliable during storage. While water, glycerin, and propylene glycol can influence flexibility, sorbitol is commonly used in soft gelatin capsules for its compatibility with gelatin and its strong plasticizing effect.