Microbiological Testing of Gelatin Capsules

Introduction

Two-piece capsules have been used for almost a century in the pharmaceutical field, and gelatin has been adopted as the main material of these capsules due to its excellent characteristic as a gelling agent. The gelatin dissolves under high concentration into water of a high temperature and quickly gels in room temperature. The thickness of the film made by the gelatin becomes uniform.

The gelatin capsules consist of gelatin, plasticizers and water. Modern day shells may, in addition, consist of preservatives, colors, opacifying agents, flavors, sugars, acids, enteric materials etc. A mixture derived from pork skin and bones is used in capsules.  Pork skin gelatin contributes plasticity while bone gelatin gives firmness.

One important reason for the exclusive use of gelatin for making hard and soft capsules is its solubility characteristics in stomach fluids. It absorbs cold water readily, though the rate of absorption depends upon moisture content of gelatin. Bloom Strength is an empirical gel strength measure which gives an indication of the firmness of gel. The plasticizers used are glycerin, sorbitol etc.  Preservatives, if included, are generally a mixture of methylparaben (4 parts) and propylparaben (1 part) to the extent of 0.2%. Flavors, if added, should not exceed 2% and are generally ethyl vanillin or essential oils. Sugar, if included, may be up to 5% to give the gelatin shell desirable chewable characteristics.

Microbiology Testing

Each incoming lot of capsules needs to be tested using USP <61> and USP<62>. The total aerobic bacterial count should not exceed 3,000 cfu per gram, the combined yeast and mold counts along with Bile-Tolerant Gram-Negative Bacteria should not exceed 300 cfu per gram.  Material must also meet the requirements of the tests for absence in 10 grams of Salmonella species, Escherichia coli, and Staphylococcus aureus.

Challenges of Current Methodology

Testing gelatin capsules for microbiology might result in several challenges.  The 1:10 dilution of the product has high viscosity and is sometimes difficult to pipette. Many capsules have vivid colors that interfere the reading of the plates. 

The current methods used in microbiology originated over 100 years ago.  There have been limited improvements in methods used for microbiological testing in the last decade. The current USP methodology is slow, requiring up to 5-7 days for product release, is manual, and in many cases is inaccurate.  Paper-based QC laboratory processes can be expensive, error-prone, time and labor-intensive.  

Rapid microbiological methods (RMM) offer a cost effective alternative to USP methodology.  With an RMM’s high degree of automation, significant reduction in time to results, faster product release, and improved process control, while providing enhanced accuracy, better repeatability, and total automation

BioLumix Alternative

The BioLumix System simplifies testing, expedites time to results, reduces the testing cost and accelerates product release while providing better control of microbial contamination.  The system can be used to automate microbial testing with a more cost effective and streamline manner. The system reduces the error rates produced by paper-based activity recording and batch data entry.  The BioLumix system also helps automate microbiological quality control processes.

The BioLumix technology is based on continuous monitoring of changes in color or fluorescence as a result of microbial metabolism in ready to use test vials. The results are presented as soon as detection occurs without any involvement of the operator. The fully automated system offers a paperless operation with increase efficiencies.

The key to the technology is the two-zone ready to use vials which eliminates any product interference.  Many types of gelatin capsules were tested in the BioLumix system for total aerobic bacterial count, combined yeast and mold counts, Bile-Tolerant Gram-Negative Bacteria, and for absence in 10 grams of Salmonella species, Escherichia coli, and Staphylococcus aureus.  As can be seen in the figure, there is no product interference even with capsules containing the most vibrant colors.  All assays yielded clear results that correlated well with the USP methodology.

Key: Dark Blue-clear capsule;Green- Brilliant Red Capsule; Light Blue-Brown capsule;Red- Teal capsule; Purple-Inoculated Brilliant Red Capsule.

The BioLumix system is validated against the USP methodology.  All assay results are complete in 48 hours with an automated Certificate of Analysis; resulting in faster product release.