Step 1: Understanding the Concept:
Gelatin is the main film-forming material in soft gelatin capsule shells. Trace metals such as iron in the raw gelatin can act as catalysts for oxidative reactions inside the finished capsule, so raw-material specifications place a tight cap on how much iron the gelatin can contain.
Step 2: Key Formula or Approach:
Iron catalyzes oxidation of susceptible fill ingredients and can also discolor the shell itself over the product's shelf life, so the accepted specification keeps the iron content as low as practically achievable during gelatin processing.
Step 3: Detailed Explanation:
Manufacturers source and process gelatin under controlled conditions specifically to hold iron content at or below 15 parts per million. Exceeding this figure raises the risk of catalytic oxidative degradation of oxygen-sensitive actives inside the capsule and can lead to visible discoloration or brittleness of the shell over time, both of which threaten the product's shelf life and appearance. This is why the accepted upper limit is set at the lowest of the values given, rather than at 20, 25 or 50 PPM.
Step 4: Final Answer:
The maximum permissible iron content in gelatin for soft gelatin capsule shells is 15 PPM.