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Brookfield AMETEK

Gel Capsules

Test Principle

The test objective is to evaluate the rapture force and elasticity of soft gel capsules by penetration.


Soft gels are widely used in medicines, vitamin and mineral supplements, fragrances and cosmetics. The active ingredients are packaged inside a capsule or microcapsule protecting it from its surrounding environment until an appropriate time when the ingredients escape from the capsule wall by rapture, dissolution, melting or diffusion. The rate at which theses processes occur largely depends on the strength of the capsule.

The strength of the capsule can be quantified using the CT3 Texture Analyser by a penetration test using a 2 mm cylinder probe to determine the film strength (rapture point) of soft gel capsules. This is a common method also used to measure points of weakness in a gelatine film or seal during manufacturing simulating circumstances whereby a capsule may burst during packaging and transport.

The CT3 Texture Analyser can also quantify the elasticity of the gel capsule shell by measuring the deformation at peak load. The seal strength of the capsule can also be determined using a compression probe with a larger diameter to the capsule. The seal is positioned perpendicular to the probe and the force to break the seal measured.



  • CT3 with 4.5kg load cell
  • 2 mm Cylinder Probe (TA-39)

Note: A 2 mm cylinder probe is used in this test for testing film strength. For determining seal strength, a 36 mm Cylinder Probe will be required.


  • Test Type: Compression
  • Pre-Test Speed: 1.0 mm/s
  • Test Speed: 1.0 mm/s
  • Post-Test Speed: 4.5 mm/s
  • Target Type: Distance
  • Target Value: 8 mm
  • Trigger Force: 10 g

Note: It is recommended that the pre-test speed be the same as or less than the test speed for accurate trigger detection; for example,°.5 mm/s test speed will require =°.5 mm/s pre-test speed.


  1. Attach the 2 mm cylindrical probe onto the load cell
  2. Put the sample into the confectionary jig
  3. Place the confectionary jig onto the fixture base table and loosely tighten the screws to enable some degree of mobility.
  4. Lower the probe to about 5 mm above the sample
  5. Position the sample in the confectionary jig centrally under the probe with its seal 90° away from the probe and then tighten the screws of the base table
  6. Start the compression test

Note: When optimizing test settings the hardest sample is best tested first in order to predict the maximum testing range for subsequent samples.

For comparison purposes, the capsule in the confectionary jig must be place centrally under the probe with the capsule seal 90° from the probe.


The following is a typical CT3 Texture Pro Graph, which shows the rapture force and elasticity of a gel capsule.

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The graph in Figure 1 shows the gel capsule strength as measured by the Texture Pro CT Software. A 2 mm cylinder probe (TA39) has been used to determine the film strength.

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The graph in Figure 2 shows the load verses deformation for the gel capsule strength.


The test commences as soon as the trigger point is detected (10 g) the probe penetrates the sample to a deformation distance of 8 mm from this point. The peak load gives us an indication of the hardness of the capsules. Harder samples will give a higher peak load and a higher hardness work done (energy required to deform sample to the defined deformation distance). The elasticity of the shell can be quantified by measuring the deformation at hardness. Elastic samples will have a higher deformation distance at hardness compared to brittle samples.

Tests obtained from 10 gel capsules of the same batch give the following mean Hardness and work done values below:

Click to enlarge