Testing of edible films

30 June 2011 – Stable Micro Systems has developed a portfolio of quality control tests for a booming sector of the food market. Edible film tensile strength, resistance and adhesion can be reliably monitored to support the growing need for testing these specialist products for innovative food applications.

Edible films are used for many purposes, including surface coating, prevention of moisture transfer and carrying functional ingredients to improve the stability and nutritional value of a food. Sample testing is frequently controlled under ASTM or ISO methodology, but many procedures are based on non-edible plastic packaging materials. The new tests offer standardised test procedures which accommodate varying types and dimensions of films.

Tensile strength is a useful quantitative measure in edible films, but compliance with test method ASTM D882, which recommends that the sample film is at least 50mm long, is difficult in these applications. With its automated software and range of sample supports and grips, the TA.XTplus texture analyser can generate reproducible measurements with the associated methodology.

Tensile grips are used to clamp the film, allowing the TA.XTplus Texture Analyser to generate a load extension graph to report overall strength, tensile strength, percentage elongation at break and film flexibility. For delicate films, rubber coated pneumatic grips are available, which enable precise control of the gripping pressure. By adjusting the air pressure, the sample gripping force is optimised to minimise specimen breakage at the grip faces. This avoids failed or inaccurate tests due to specimen deformation. Similarly, the film support rig can be used to clamp small amounts of a film to measure its bioextensional properties, including burst strength, resilience and relaxation. All these tests give a valuable insight into a film’s strength, flexibility, pliability, viscoelasticity and relaxation properties.

The measurement of adhesion is also useful to edible film manufacturers, who need to balance strength and integrity with sufficient separation properties and dissolution and flavour delivery. Simple adhesive tests involve the use of a 2.5 cm ball probe, which maintains a pre-determined compression force for a specified time on the film. The force required to withdraw the probe upwards indicates the product’s adhesiveness.

Jo Smewing, applications manager at Stable Micro Systems, says “Using a texture analyser allows a more investigative and comprehensive approach to testing edible films. The films are frequently fragile and are developed to perform specific functions whilst standing up to handling and environmental factors. Repeatable test measurements can indicate where adaptations to formulations or processing methods can deliver measurable improvements for these otherwise difficult to handle materials.”