Evaluation of the hardness of almonds using a craft knife blade.
The quality of a product and its appearance are important factors to a consumer. Quality and appearance can be described by colour, flavor, and taste in addition to physical attributes such as size, shape and texture.
Using the CT3 Texture Analyser, almond hardness and work done to shear/bite the almond, as well as brittleness, can be determined. The test is carried out using a replaceable craft knife blade attached to the instrument and used to shear the almond at a given speed. The sharpness of the blade means that hard samples can be sheared with great precision without compressing the sample. Almond hardness 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 under the graph is a measure of work done that correlates with the energy required to overcome the strength of the internal bonds within the almonds. The brittleness of the almonds can also be determined from the fracturability values. Almond crunchiness is determined from the measurement of the quantity of fractures generated during the test. Using these textural measurements, the quality of almonds can be assessed to meet customer satisfaction.
Note: Each sample should only be sheared once.
The razor blades are easily replaceable if blunting is a problem between tests.
The hardest sample is best tested first in order to predict the maximum testing range for subsequent samples to be tested.
The graphs show the hardness of almonds using a craft knife blade
Figure 1 shows the hardness of two almond samples from the same batch tested at a similar orientation and at room temperature. The maximum force value is a measure of sample hardness. The area under the graph from the start of the test to the maximum force is a measure of work done.
Figure 2 shows force vs. distance for the hardness of two almond samples tested at room temperature. This is an alternative option for displaying the results. The maximum force value is a measure of sample hardness. The area under the graph from the start of the test to the target distance point (5 mm) is a measure of work done. The distance values at zero load are the points when the knife blade withdraws and separates from the sample. The negative distance values are the points when the knife blade is returning to its starting position (a few millimetres from the sample surface).
When a trigger load of 5 g has been detected at the sample surface, the probe (craft blade) proceeds to shear the sample at a test speed of 2 mm/s over a specified distance of 5 mm. A rise in force is seen as the craft knife shears though the exterior layer of the almond. As the blade penetrates inside the sample, the force decreases due to the exterior of the sample being firmer than its interior. The maximum force value over the specified distance is a measure of sample hardness, 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 done is the area under the graph from the start of the test to the maximum force (Figure 1) or target distance point (Figure 2). The larger the value, the more work required to break down the sample. This simulates the shearing energy required by the molars to break through the almond on the first bite. The fracturability value is an indication of sample brittleness; the higher the value, the less brittle the sample. The measured quantity of fractures generated during the shearing process gives an indication of the crunchiness of the sample.
The table below summarizes the results for tests run on 7 samples altogether from the same batch. The hardness and fracturability values show a high level of repeatability.