Food Texture Analysis and Packaging Seal Integrity:
Evaluating Peel Strength of Packaging Seals

TEST PRINCIPLE

Assessment of the peel strength of foil on a yoghurt container using a general peeling jig (TA-GPJ).

BACKGROUND

Peel tests are vital in food texture analysis as they evaluate the adhesive or bond strength between two materials. Typical applications include packaging materials, laminated surface coatings, films, and backings, among others. A peel test is performed by applying a tensile load or force to the materials under investigation in one of three specific ways:

• 180° Peel: A flexible material is pulled away from a non-flexible material, both held vertically.
• 90° Peel: A flexible material is pulled vertically away from a non-flexible material positioned horizontally.
• T Peel Test: Two flexible materials are pulled axially apart from each other.

Although various fixtures and test grips may be required for these peel test techniques, the data analysis remains consistent, necessitating the averaging of load values during the peeling process over a defined period.

This particular example is a 90° peel test using a general peeling jig (TA-GPJ). In preparation, the flexible material (backing, film, etc.) is partially peeled and inserted into the upper grip. The product (the non-flexible material, such as a container, from which the seal strength will be measured) is secured to the fixture using a rubber holder and supported at its base by adjustable screws. As the instrument arm drives the upper grip in a tensile direction, the seal is peeled away from the product. The force required to peel the flexible material from the product is a direct measurement of bond strength.

In quality control, performing a peel test is essential for assessing packaging seal integrity and ensuring product safety. The tests also confirm that the adhesive seal functions correctly - ensuring it is sufficiently tight to keep the product sterile or protected, yet easy enough to peel without causing spillages or inconsistencies in peel strength.

METHOD

Equipment:

• Instrument: CTX Texture Analyser with 5Kg Loadcell Instrument
• Accessory: TA-GPJ - General Peeling Jig
• Software: Texture Pro Software

Settings:

• Test Type: Tension
• Pre-Test Speed: 1 mm/s
• Test Speed: 1 mm/s
• Post-Test Speed: 1 mm/s
• Target Type: Distance
• Target Value: 32 mm
• Trigger Load: 5 g

SAMPLE PREPARATION

Condition the samples to the appropriate temperature for testing, ensuring consistency in texture analysis.

PROCEDURE

1. Attach the probe shaft connector to the instrument.
2. Slide the fixture nut and spring into the slot at the base of the instrument, moving them towards the centre of the base.
3. Similarly, slide the universal peel rig into the slot at the base of the instrument, positioning it centrally.
   Note: The position of the general peeling jig fixture nut and spring will depend on the inclination angle of the platform. For a 0-degree angle, the fixture should be centred on the instrument base, while a 45° or 90° peel test requires positioning further down the base. This ensures the string connecting the grips (clamping the sample) to the probe shaft connector is parallel, not slanted.
4. Raise the support plate of the fixture using the screws at the back. This will provide adequate room to secure the fixture in position.
5. Align the orifice of the general peeling fixture with the fixture nut and spring.
6. Use the screw and Allen key provided to lock the general peeling fixture into position.
7. Place the sample on the support plate and secure it with the small screws at the front of the fixture, ensuring firm clamping for accurate packaging seal integrity testing.
8. Partially peel the protective cover and insert the loose end into the grip, tightening it securely with the screws. Ensure the protective cover is fully inserted to achieve a tight grip.
9. Lower the instrument arm so that the grip can be connected via the thread to the probe shaft connector.
10. Wind the thread of the grip around the screw on the probe shaft connector, tightening it with the screw.
11. Raise the instrument arm in 1 mm increments until the protective cover, grips, and thread are upright and perpendicular to the rim of the container, with no slack in the thread.
12. Begin the test to assess the packaging seal integrity through texture analysis.

RESULT

The peel strength of a seal from a yoghurt container was assessed using a general peeling jig (TA-GPJ). The two peak values on the graph represent the force required to break the contact between the rim and the seal, both at the beginning and at the end of the peeling process. The plateau on the graph indicates the force needed to maintain the peeling action, calculated as the average load over a period of 4 to 26 seconds. Significant fluctuations on the graph would suggest inconsistencies in the peel strength, which could impact the overall integrity of the packaging seal, a crucial factor in food texture analysis.

Figure 2. The load versus distance for the peel strength of a seal from a yoghurt container. This graph illustrates both the peak load and the final load, alongside the distance covered during the peeling process.

OBSERVATIONS

When a force of 5 g is applied in the tensile direction, the grips begin to pull the container’s protective cover, and the force quickly increases as the bond strength of the seal between the rim of the container and the cover resists the applied tension. Once the tensile load surpasses the bond strength of the seal, the peeling process begins. This is reflected by the first peak on the graph and the subsequent sharp drop in load values. As the peeling progresses, the graph plateaus, indicating the force required to maintain the peeling. When the final section of the seal is removed, the tensile load rises to form a second peak, followed by a drop in load values as the cover is completely detached from the container. This second peak represents the force necessary to separate the cover from the rim of the container.

A peel test is essential in food texture analysis as it helps identify potential issues with the packaging seal integrity. For instance, a high peak force at the start, followed by a sharp decline, may suggest the risk of spillages in low-viscosity products as the seal is peeled from the lid. Additionally, significant fluctuations in the force required to continue peeling indicate poor seal quality, with inconsistencies in peel strength likely leading to spillages. The advantage of this peel test is its applicability to various shapes of containers, including rectangular, oval, and circular, and its efficiency in providing quick results.

The table below summarises the results:

Sample	Peak Load (g)	Average Load (g)	Work Done (mJ)
Container Cover	561	35.7	14.43

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