Case study: Measuring the hardness of almonds

PRINCIPLE OF THE TEST

Assessment of the hardness of the almonds using a cutter blade.

CONTEXT

The quality of a product and its appearance are important factors for a consumer. Quality and appearance can be described by color, flavor and taste in addition to physical attributes such as size, shape and texture.

Using the CT3 texture analyzer, the hardness of the kernel and the work done to shear / bite the kernel, as well as its brittleness, can be determined. The test is performed using a replaceable cutter blade attached to the instrument and used to shear the kernel at a given speed. The sharpness of the blade means that hard samples can be sheared with great precision without compressing the sample. The hardness of the almond is determined by the maximum force on the graph. This value correlates with the force required to shear the almond between the molars. The area below the graph is a measure of the work done which correlates with the energy required to overcome the strength of the internal bonds within the almonds. The brittleness of the kernels can also be determined from the fracturing values. The crunchiness of the almonds is determined from the measurement of the amount of breaks generated during the test. Using these texture measurements, the quality of the almonds can be assessed to meet customer satisfaction.

METHOD

Equipment : CT3 with 4.5 kg load cell

Luminaire base table (TA-BT-KIT)

Craft Knife Blade (TA-CKB)

TexturePro CT software

Settings :

Type of test: Compression

Pre-test speed: 1.5 mm / s

Test speed: 2.0 mm / s

Post-test speed: 10.0 mm / s

Target type: Distance

Target value: 5 millimeters

Trigger force: 5 grams

PROCEDURE

Attach the cutter blade to the instrument.

Attach the fixture base table to the instrument base and lightly tighten the thumbscrews to allow some degree of mobility.

Insert the base plate into the fixture base table and tighten in position using the side screws.

Position the fixture base table under the probe, then tighten the thumbscrews to prevent further movement.

Remove the sample from storage and place it on the fixture baseplate.

Lower the instrument arm so that the probe is a few millimeters above the sample.

Place the sample in the center under the cutter. To allow reliable and reproducible results, the orientation of the sample when presenting the sample to the instrument must be maintained consistent throughout all tests performed.

Once the alignment is complete, start the test

Note: Each sample only needs to be sheared once. Razor blades are easily replaced if dulling is an issue between tests. The harder sample is best tested first in order to predict the maximum test range for subsequent samples to be tested.

RESULTS

The graphics show the hardness of the almonds using a utility knife blade.

Figure I shows the hardness of two samples of almonds from the same batch tested at a similar orientation and at room temperature. The maximum force value is a measure of the hardness of the sample. The area under the graph from the start of the test to the maximum force is a measure of the work done.

Figure II

Figure II shows the force versus distance for hardness of two samples of almonds tested at room temperature. This is an alternate option to view the results. The maximum force value is a measure of the hardness of the sample. The area under the graph from the start of the test to the target distance point (5mm) is a measure of the work done. The zero load distance values are the points where the knife blade retracts and separates from the sample. Negative distance values are the points where the knife blade returns to its starting position (a few millimeters from the surface of the sample).

OBSERVATIONS

When a trigger load of 5g has been detected on the surface of the sample, the probe (homemade blade) shears the sample at a test speed of 2mm / s over a specified distance of 5mm . An increase in force is observed when the craft knife cuts the outer layer of the almond. As the slide penetrates inside the sample, the force decreases due to the fact that the outside of the sample is firmer than the inside. The value of the maximum force over the specified distance is a measure of the hardness of the sample, simulating the maximum force that will be required to crush the sample between the molars; the higher the value, the harder the sample. The hardness work performed is the area under the graph from the start of the test to the maximum force (Figure I) or the target distance point (Figure II). The higher the value, the more labor required to decompose the sample. This simulates the shear energy required by the molars to pierce the almond on the first bite. The fracture value is an indication of the fragility of the sample; the higher the value, the less fragile the sample. The measured amount of fractures generated during the shearing process gives an indication of the crunchiness of the sample.

The table below summarizes the results of tests carried out on a total of 7 samples from the same lot. The hardness and fracturing values show a high level of repeatability.