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Tablets & Capsules April 2017 39 lower rod is then anchored to the instrument base, while the upper rod is attached to the drive mechanism of the analyzer. The drive lifts the upper rod at a steady rate, typically between 0.1 and 1.0 millimeter per second, stretching the capsule shell a defined distance. In some cases, the test causes the shell to rupture. Figure 1 shows that Sample A resisted stretching bet- ter than Sample B. That result is also reflected under the heading "Work done" in Table 1, which indicates Sample A was twice as resilient as Sample B. Compression test A texture analyzer can also measure the compressive strength of a soft gelatin capsule (softgel) using two test methods. In the first, a probe 36 millimeters in diameter is used to quantify the seal strength (Figure 2) and in the second—a penetration test—a 2-millimeter cylindrical probe determines the softgel's rupture point. The two tests not only identify weaknesses in the softgel's strength, they simulate the circumstances under which the softgel could burst during packaging or transport. When measuring the seal strength of any capsule—hard or soft—use a compression probe whose diameter is larger than the capsule and orient the seal perpendicular to both the probe and the applied force. See the photo below. Table 2 lists the results of softgel hardness tests. Gel strength test Gelatin is used in many industries and in many differ- ent applications, and in nearly all cases, both the gelatin manufacturer and the end-user measure gel strength, which indicates its effectiveness. Gel strength depends largely on bloom strength. The photo on the next page shows a bloom jar with a gelatin sample ready to be tested. Using a texture analyzer equipped with a standard bloom probe, bloom bottles, and a gelatin bath, you can perform simple tests and quickly and accurately deter- mine gel strength, which is measured as the force required to deform the gel over a specified distance. A texture analyzer can be used to quantify the gel strength of gelatin according to the British Standard Method, "Sampling and testing gelatin" (BS757: 1975) or by using standards from the Gelatin Manufacturers Institute of America (GMIA) or the Gelatine Manufacturers of Europe, which in 1998 adopted the GMIA standard. As a result, all current methods specify the use of a flat-faced Figure 2 Compressive strength (hardness) of softgels 0 5 10 15 20 25 Time (s) Load (g) 1200 1000 800 600 400 200 0 Table 1 Tensile load versus distance of two hard capsule shells Note: Mean values. N = 10 Sample Peak load (g) Deformation at peak load (mm) Work done (mJ) Gelatin capsule A 16,585 ±163 5.13 ±0.44 218.8 ±91.2 Gelatin capsule B 12,813 ±239 4.06 ±0.38 114.8 ±37.9 Texture analyzer set up to measure compressive strength of softgels Table 2 Compressive strength (hardness) of softgels Mean peak load, or hardness (g) Deformation at hardness (g) Mean work done (mJ) 1,344 ±16.0 4.67 ±0.3 26.8 ±2.3 Figure 1 Tensile load versus distance of two hard capsule shells 0 2 4 6 8 10 12 14 Distance (mm) Load (g) 16000 14000 12000 10000 8000 6000 4000 2000 0 Blue = Sample A Green = Sample B