Texture Analysis in Sports Nutrition – Capsules offer an innovative dosage form

At one time, “sports nutrition” might have conjured up images of body-builders and professional athletes, but today’s market has spread way beyond the weightlifting gyms and sports leagues and into urban area and shopping centres worldwide. 

This opens up nearly unlimited opportunities that manufacturers and marketers can exploit. 

While sports nutrition continues to be dominated by bulkier products such as powders, functional food and beverages (e.g. sports drinks/RTD), companies should keep in mind the strong consumer preference for capsules when considering the dosage form for a new or existing sports nutrition product.

Manufacturers of new products are attempting to transition away from the earlier image of sports nutrition products, and the introduction of encapsulated products offers a simple way to distinguish the product and create unique selling points. 

Fish oil capsules, for example, have long been popular as health and performance supplements. Unlike many other forms, capsules mask taste and odour and allow for quick speed-to-market, yet they require less excipient. Their versatility allows for a multiplicity of branding options in terms of colour, size and printing/graphics. And, of course, they are smooth, easy-to-swallow and are suitable for almost any dosage strength.

Sports nutrition is very innovation driven. “Look and feel” is critical, and packaging, as a result, is often transparent. 

Creatine (a nitrogenous organic acid used to help facilitate muscle-mass gain and to increase physical performance) is instable in water and stomach acid. The development of acid-resistant capsules allow superior shelf life of this ingredient. Many new entrants in the sports nutrition market are liquid-based, particularly the so called fat burners. Liquid formulas release rapidly into the digestive system allowing the active ingredients to provide the best possible benefits. This may require an adaptation to the capsule make-up, especially for lipid-based formulations.  

The modification of capsule construction to accommodate its content with optimum shelf life and consumer mouthfeel properties will require an assessment of its physical performance. The brittleness, hardness and flexibility of gel capsules and their resilience to variable storage and handling conditions should be considered, along with any potential effect the contents may have on the mechanical properties of the capsule itself.

Filled to bursting point?
While the comfort factor of soft gel capsules is not to be underestimated, such media are primarily used to contain water- or oil-based formulations where a failure in the encapsulation could be catastrophic. The robustness of a soft gel capsule can be determined via a particular compression test known as the bursting test. This measures the maximum force that a capsule can be subjected to and establishes whether there is a weak point in the gel film or capsule seal. 

It is important to use a rig that will prevent the capsule from rolling and shifting when pressure is first applied; frequently a plate with a small indentation is all that is needed. Some choose to have the seal of the capsule run around the capsule so that it neither is in contact with the holding plate nor the probe and the probe starts the compression of the capsule 90° to the seal. In this case a small Cylinder Probe (right) (e.g. 2-3mm diameter) would be used to puncture the capsule. 

Some say the seal is the strongest point and they want to test the bursting point of the film; in this case, the capsule seal is placed in a vertical orientation so that the probe applies the force directly against the seal line, and a cylinder probe larger than the capsule is used to compress the sample. For safety purposes, a Shatter Screen (as also shown in the photo above) is recommended for a “dramatic” test such as this.

Capsules can be tested under different conditions to assess the effects of temperature, humidity, storage and handling, but the integrity of the capsule may also be affected by its contents. Simple compression tests on gel capsules do not always adequately predict which formulations may result in failures related to brittleness, and hence those drugs which are suitable for hard or soft gel encapsulation.

Measuring Brittleness/ Flexibility
The simplified manufacture process of hard gelatine capsules and their ability to withstand higher filling temperatures is attractive to many manufacturers. Yet the introduction of certain types of liquid, such as hydrophilic solvents, to hard capsules can often affect the mechanical properties of the shell, causing them to become brittle or to soften. If the texture of a capsule is compromised, it may not be able to withstand handling and storage, resulting in fillings leaking from the capsule.

As effects are likely to be progressive, and only displaying very small changes initially, compressive tests may not be able adequately to distinguish such anomalies. The Capsule Tensile Rig (left) is designed to help identify subtle degradation, providing valuable information which can be used to avoid subsequent capsule failure. For example, manufacturers can identify the effect of liquid filling on the strength and stability of capsules and reformulate liquid type or capsule accordingly.

Prior to testing, the filling of the capsule is removed and one half of the empty shell is mounted to a separating rod fixture on the TA.XTplus texture analyser. 

Comparison of tensile strength of gelatine
capsules using the Capsule Tensile Rig

Vertical movement of the upper rod is then applied until the capsule is split apart, while Exponent software records the force required to do so. This test highlights three important parameters: elastic stiffness (if a linear region on the graph is present); tensile force; and elongation at break point (see graph). 

A reduction in elastic stiffness and tensile strength occurs when capsules become softer and therefore show a tendency to fail. The test allows manufacturers to investigate the effects of fillings on the mechanical strength of the capsule shell and identify changes that may impact their stability and long-term performance.

Request our article Texture Analysis in Sports Nutrition which looks at developments in testing for this growing product sector.

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We can design and manufacture probes or fixtures for the TA.XTplus texture analyser that are bespoke to your sample and its specific measurement.

Once your measurement is performed, our expertise in its graphical interpretation is unparalleled. Not only can we develop the most suitable and accurate method for the testing of your sample, but we can also prepare analysis procedures that obtain the desired parameters from your curve and drop them into a spreadsheet or report designed around your requirements.

For more information on how to measure texture, please visit the Texture Analysis Properties section on our website.

The TA.XTplus texture analyser is part of a family of texture analysis instruments and equipment from Stable Micro Systems. An extensive portfolio of specialist attachments is available to measure and analyse the textural properties of a huge range of food products. Our technical experts can also custom design instrument fixtures according to individual specifications.

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