| Erich R Brocker at SWISS CAPS AG examines the humidity balance in soft capsules and their potential future technological advances
Water is a key factor influencing the chemical and microbial stability of packaged nutritional and pharmaceutical products. Product development and design often goes along with the manufacturing process, from active pharmaceutical ingredients (APIs) to formulation and from bulk manufacturing to packaging.
Soft capsules (SC) are a solid dosage form, invented about 70 years ago, widely used in the pharmaceutical, nutritional and cosmetic industries. The term ‘soft’ refers to plasticisers in the capsule shell, which make it flexible and less brittle. As the capsule is filled with liquid or pasty fill formulations, it is sometimes also called a semi-solid dosage form. SCs are well established in consumer perception, largely due to the following advantages:
- Elegant appearance
- Easy to swallow
- Very good consumer confidence
- Rapid action (dispersing capsule contents)
- Improved bioavailability
- Good tolerance to intestinal mucosa
- Masks odours
Some years ago the purely vegetable-based soft capsule was manufactured by a revolutionary combination of extrusion technology and the reliable rotary-die process. This allowed for low-water shells. This breakthrough opened enormous opportunities for new formulations of existing and future products, ideally leading to an increased popularity of soft capsules, whilst addressing new and large consumer target groups.
In the past, only gelatin-water solutions could be used in the casting (or dropping) process to form a uniform shell around the fill. Throughout the shelf live period water is a major factor influencing the chemical stability of APIs, including vitamins, minerals and plant extracts. However, few publications exist which address the mechanisms of water migration between environment, soft capsule shell and its fill, influencing the stability of APIs. Special attention must be paid to an interaction of water with APIs if soft capsules with a ‘wet shell’ are used as a dosage form. After the encapsulation of fill, the soft gelatin capsules undergo a drying process to lose approximately 35 per cent of the water out of the shell. The final moisture content of a gelatin shell coming from production stays at around six to 10 per cent (aw=0.3) when delivered for packaging. |
